METHOD FOR HEALING METALLIC GLASS AND METALLIC GLASS HEALABLE THEREBY

Abstract

The present disclosure relates to a method for healing a metallic glass and a metallic glass healable thereby, and more specifically, to a healing method which, based on a time-temperature transformation curve showing the structural relaxation and crystallization onset of a metallic glass, may standardize the structural changes resulting from process variables of the metallic glass through heat treatment for structural relaxation at a specific healing temperature, followed by quenching, and heal structural damage caused by elastic and plastic deformation of the metallic glass, thereby enabling restoration of strength as well as repeated restoration of deformation stability properties such as ductility and toughness, and a metallic glass healable by the method.

Description

BACKGROUND

1. Technical Field

The present disclosure relates to a method for healing a metallic glass and a metallic glass healable thereby, and more particularly, to methods for standardization of a metallic glass and healing of a damaged metallic glass based on a time-temperature transformation curve showing structural relaxation and crystallization onset, and a metallic glass healable thereby.

2. Related Art

In general, metallic glasses are non-crystalline solids in which the constituent atoms are not arranged periodically, and have attracted extensive attention for use as next-generation high-quality structural materials due to their high strength and elastic limit (about 2%) compared to crystalline metal materials, and due to their excellent corrosion resistance and formability.

However, when metallic glasses undergo plastic deformation near room temperature, defects called shear bands are formed in the material, and the formation of shear bands in metallic glasses not only causes a rapid deterioration in the strength, but also promotes the formation of cracks, resulting in low fracture toughness and even causing rapid fracture, which poses significant limitations to their commercialization as structural materials.

In order to restore damage caused by deformation of metallic glasses, methods have been suggested, such as restoring strength by performing either structural relaxation of the metallic glass through heat treatment or structural rejuvenation thereof through repeated heating and cooling. However, such structural relaxation has a limited effect of simply restoring strength, and is accompanied by a rapid deterioration in the ductility and toughness of the material. Thus, a clear direction for improvement has not yet been suggested.

SUMMARY

An object of the present disclosure is to provide a healing method which, based on a time-temperature transformation curve showing the structural relaxation and crystallization onset of a metallic glass, may standardize the structure of the metallic glass to a stable structure with a specific healing temperature by heat treatment and restore not only the strength of a damaged metallic glass but also the deformation stability properties such as ductility and toughness thereof, and a metallic glass healable by the method.

However, objects of the present disclosure are not limited to the object mentioned above, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

According to one aspect of the present disclosure, there is provided a method for healing a metallic glass, including steps of: determining a temperature-dependent structural relaxation time for an unused metallic glass having the same composition as the metallic glass to be healed; determining a temperature-dependent crystallization onset time for the unused metallic glass; heat-treating the metallic glass to be healed at a specific healing temperature within a healable temperature range for a time satisfying Expression 1 below; and quenching the heat-treated metallic glass to be healed at a critical cooling rate or higher:

Structural relaxation time at the specific healing temperature≤heat treatment time at the specific healing temperature≤crystallization onset time at the specific healing temperature.  [Expression 1]

According to another aspect of the present disclosure, there is provided a method for standardizing a metallic glass, including steps: determining a temperature-dependent structural relaxation time for the metallic glass; determining a temperature-dependent crystallization onset time for the metallic glass; heat-treating the metallic glass at a specific healing temperature within a healable temperature range for a time satisfying Expression 1 below; and quenching the heat-treated metallic glass from the specific healing temperature at a critical cooling rate or higher:

Structural relaxation time at the specific healing temperature≤heat treatment time at the specific healing temperature≤crystallization onset time at the specific healing temperature.  [Expression 1]

According to still another aspect of the present disclosure, there is provided a metallic glass having any one of Formulae 1 to 4 below, which is healable by the method for healing a metallic glass:

• • wherein
  • a and b each denote atomic percent (at. %), a is 15 to 65, and b is 5 to 30;
  • TM is one selected from the group consisting of Ti, Zr, Hf, and combinations thereof;
  • E is an element that undergoes a eutectic reaction with TM, and is one selected from the group consisting of Fe, Co, Ni, Cu, Zn, and combinations thereof; and
  • N is an element that increases glass-forming ability and supercooled liquid region, and is one selected from the group consisting of Al, Nb, Ta, Mo, Be, Re, V, Ir, Pd, Au, Ag, Pt, and combinations thereof;

• • wherein
  • a, b, c, and d each denotes atomic percent (at. %);
  • X is an element that increases glass-forming ability and supercooled liquid region, and is one selected from the group consisting of Al, Ti, Nb, Ta, Mo, Be, Re, V, Ir, Pd, Au, Ag, Hf, Pt, and combinations thereof; and
  • b−c is 2 to 29, c is 1 to 40, d is 2 to 29, and a is 100−(b+d);

• • wherein
  • a, b, c, d, and f each denote atomic percent (at. %);
  • X is an element that increases glass-forming ability and supercooled liquid region, and is one selected from the group consisting of Re, V, Ir, Mo, Pd, Nb, Ta, Au, Ag, Ti, Hf, Pt, and combinations thereof; and
  • b−c is 2 to 29, c is 1 to 10, d is 2 to 29, f is 4 to 18, and a is 100−(b+d+f);

• • wherein
  • a, b, c, and d each denote atomic percent (at. %);
  • X is an element that increases glass-forming ability and supercooled liquid region, and is one selected from the group consisting of Ti, Be, and combinations thereof; and
  • b−c is 5 to 15, c is 25 to 45, d is 5 to 15, and a is 100−(b+d).

Healing of metallic glasses is to fix the glass structure and associated properties in a state of cooling at a specific healing temperature within a healable temperature range, making it possible to heal changes in the atomic-level disorder structure of the entire specimen, which are caused by differences in process conditions such as cooling rate, or local structural changes resulting from shear deformation caused by stress concentration.

When the method for healing a metallic glass according to one embodiment of the present disclosure is used, even if a metallic glass has been damaged through elastic and plastic deformation, it possible to allow the metallic glass to restore to its initial microstructure, thereby restoring not only strength but also deformation stability properties such as ductility and toughness, thus increasing the life of the metallic glass.

When the method for standardizing a metallic glass according to one embodiment of the present disclosure is used, it is possible to repeatedly produce metallic glasses having a structure having a specific healing temperature within a healable temperature range regardless of the production and processing processes of a specimen, and in particular, it is possible to produce metallic glasses having the same structure with a characteristic deviation of 5% or less.

The effects of the present disclosure are not limited to the effects described above, and effects not mentioned will be clearly understood by those skilled in the art from the present specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the healable deformation range of a metallic glass according to the present disclosure and the improvement in properties by healing.

FIG. 2 is a schematic view showing a method of healing a metallic glass through heat treatment based on the concept of fictive temperature (T_f) according to the present disclosure.

FIG. 3 is a schematic view showing a customized method of healing a metallic glass through heat treatment based on the concept of fictive temperature (T_f) at various specific healing temperatures (T_h) within a healable temperature range according to the present disclosure.

FIG. 4 is a graph of the heat capacity (C_p) of a metallic glass, measured by differential scanning calorimetry (DSC), and shows a method for measuring the fictive temperature of an unused metallic glass.

FIG. 5 is a plot showing temperature-dependent changes in the viscosity of a metallic glass having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, and shows the fragility index (D) and ideal glass transition temperature (To) calculated by fitting to the Vogel-Fulcher-Tammann (VFT) equation.

FIG. 6 is a time-temperature transformation curve plotting temperature-dependent changes in the structural relaxation and crystallization onset time of a metallic glass having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, and shows a region in which the healing process of the metallic glass is possible through heat treatment at a specific temperature (T_h) within a healable temperature range.

FIG. 7 shows the results of DSC measurements on 2-mm rod-shaped specimens having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, which were heat-treated at different healing temperatures of 0.92 T_g, 1.04 T_g, and 1.08 T_g for about 1.5 times the structural relaxation time, and then quenched.

FIG. 8 shows the results of a compression test performed on 2-mm rod-shaped specimens having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, which were heat-treated at different healing temperatures of 630 K (0.98 T_g) and 690 K (1.08 T_g) for about 1.5 times the structural relaxation time, and then water-quenched.

FIG. 9 shows a schematic view (top) and DSC results (bottom) for a 2-mm rod-shaped specimen having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, a specimen obtained by plastically deforming the rod-shaped specimen by 50%, and a specimen subjected to a healing process after 50% plastic deformation.

FIG. 10 is a schematic view showing the optimal healing process temperature range in a time-temperature transformation curve showing temperature-dependent changes in the structural relaxation and crystallization onset time of the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂.

FIG. 11 shows the results of a three-point bending test for three different 1.0-mm-thick plate-shaped specimens having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which was subjected to a standardization process at 670 K (1.08 T_g) for 10 seconds.

FIG. 12 shows an SEM image of a 1.0-mm-thick plate-shaped specimen having a composition of Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which was subjected to a standardization process at 670 K (1.08 T_g) for 10 seconds and then subjected to bending deformation up to 5% (75% of total elongation).

FIG. 13 shows the results of a three-point bending test for and SEM images of a 1.0-mm-thick plate-shaped specimen having a composition of Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, which was subjected to a standardization process at 690 K (1.08 T_g) for 30 seconds. Specifically, FIG. 13(a) shows the results of the three-point bending test and the size of serration, FIG. 13(b) shows a scanning electron microscope (SEM) image of the specimen after bending deformation up to 4%, and FIG. 13(c) shows a SEM image of the specimen after fracture.

FIG. 14 is a graph showing the results of an additional three-point bending test for a 1.0-mm-thick plate-shaped specimen having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which was subjected to a standardization process at 670 K (1.08 T_g) for 10 seconds and not subjected to a healing process after bending deformation up to 5%.

FIG. 15 is a graph showing the results of a three-point bending test for a 1.0-mm-thick plate-shaped specimen having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which was subjected to a standardization process at 670 K (1.08 T_g) for 10 seconds and then subjected to a healing process under the same conditions as those in the standardization process after being subjected to bending deformation up to 5%.

FIG. 16 is a graph showing the shape and three-point bending test results of a 1.0-mm-thick plate-shaped specimen having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which was subjected to a standardization process at 670 K (1.08 T_g) for 10 seconds and then subjected to repeated healing processes under the same conditions as those the standardization process after being subjected to bending deformation up to 5%.

FIG. 17 is a graph showing the results of a three-point bending test for a 1.0-mm-thick plate-shaped specimen having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which was subjected to a standardization process at 670 K (1.08 T_g) for 10 seconds and then subjected to repeated healing processes with thermoplastic deformation after being subjected to bending deformation up to 5%.

FIG. 18 shows the shapes and vertical cross-sectional SEM images of a 1.0-mm-thick plate-shaped specimen having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which is shown in FIG. 16 and was subjected to bending deformation up to 5%, and the 1.0-mm-thick plate-shaped specimen having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which was subjected to a healing process with thermoplastic forming after being subjected to bending deformation up to 5%.

DETAILED DESCRIPTION

Throughout the present specification, it is to be understood that when any part is referred to as “including” any component, it does not exclude other components, but may further include other components, unless otherwise specified.

Throughout the present specification, “at. %” may mean the proportion of the number of atoms.

Throughout the present specification, “A and/or B” means “A and B” or “A or B”.

Hereinafter, the present disclosure will be described in more detail.

One embodiment of the present disclosure provides a method for healing a metallic glass, including steps of: determining a temperature-dependent structural relaxation time for an unused metallic glass having the same composition as the metallic glass to be healed; determining a temperature-dependent crystallization onset time for the unused metallic glass; heat-treating the metallic glass to be healed at a specific healing temperature within a healable temperature range for a time satisfying Expression 1 below; and quenching the heat-treated metallic glass to be healed from the specific healing temperature at a critical cooling rate or higher:

Structural relaxation time at the specific healing temperature≤heat treatment time at the specific healing temperature≤crystallization onset time at the specific healing temperature.  [Expression 1]

FIG. 1 is a schematic view showing the healable deformation range of a metallic glass according to the present disclosure and the improvement in properties by healing. Specifically, a free volume exists in a metallic glass, and as plastic deformation progresses due to local stress concentration, shear bands with a thickness of about 20 nm form and propagate in a shear transformation zone based on the free volume. As the plastic deformation continues, micro-cracks occur in the shear bands, and eventually lead to fracture, making the metallic glass unusable. By performing the metallic glass healing process of the present disclosure before the metallic glass reaches an irreversible critical point, the metallic glass may be restored to its initial structure, and continuous deformation is possible as shown in the bottom of FIG. 1, thereby significantly increasing the service life of the metallic glass.

FIG. 2 is a schematic view showing a method of healing a metallic glass through heat treatment based on the concept of fictive temperature (T_f) according to the present disclosure. The fictive temperature (T_f) is a fictive temperature that defines the glass structure, and is defined as the temperature at which decoupling occurs when changing from a supercooled liquid into a glassy state. Eventually, if the glass is heat-treated at a specific temperature for a time equal to or longer than the relaxation time to form a liquid structure corresponding to the fictive temperature, and then quenched within a time shorter than the structural relaxation time to maintain the supercooled liquid, it may change into a glass structure and an metallic glass having a structure with the fictive temperature may be obtained. If this concept of fictive temperature is applied to healing, when the structure of an initial metallic glass is damaged during use, the damaged glass may reach a stable liquid structure with a specific healing temperature by heat treatment at a specific healing temperature (T_h) within a healable temperature range for a time exceeding the structural relaxation time. Thereafter, when the stable liquid structure with the specific healing temperature is cooled from the specific healing temperature at a critical cooling rate or higher, the same glass structure as the stable liquid structure with the specific healing temperature may be obtained by glass transition. Using this concept, the microstructure of the initial glass may be obtained by heat-treating the damaged glass at the specific healing temperature, followed by quenching.

FIG. 3 is a schematic view showing a customized method of healing a metallic glass through heat treatment based on the concept of fictive temperature (T_f) at various specific healing temperatures (T_h) within a healable temperature range according to the present disclosure. The healable temperature range of a metallic glass is preferably between 0.7 T_g, at which the structural relaxation behavior of the metallic glass upon heating may be detected, and Tm, which is the melting point of a stable liquid, which is a reference point for a supercooled liquid. When heat treatment based on the concept of fictive temperature is performed at a specific healing temperature within this range, followed by quenching, it is possible to heal so that the metallic glass may have a structure with the specific healing temperature and properties corresponding thereto.

FIG. 4 is a graph of the heat capacity (C_p) of a metallic glass, measured by differential scanning calorimetry (DSC), and shows a method for measuring the fictive temperature of an unused metallic glass, which is shown in FIG. 2. Specifically, through DSC (differential scanning calorimetry), the metallic glass is heated to T_e at a heating rate of 20 K/min, maintained at that temperature for 1 minute, and then cooled to 80° C. at the same cooling rate of 20 K/min (first cycle). After maintaining the temperature at 80° C. for 1 minute, a second cycle is performed in the same manner as the first cycle. In FIG. 4, T_z denotes the temperature at which quenched-in energy begins to be released (onset temperature), and T_e represents the temperature after quenched-in energy is completely released (endset temperature). Therefore, the liquid after T_e reaches internal equilibrium (C_p1=C_p2). That is, the horizontally hatched portion and the vertically hatched portion in FIG. 4 have the same area, and thus the fictive temperature of the metallic glass satisfies the relationship represented by Equation 5 below:

$\begin{array}{cc}{\int }_{T_z}^{T_e}\left(C_{p1}-C_{p2}\right)\mathrm{dT}={\int }_{T_g}^{T_f}\left(C_{p,l}-C_{p,g}\right)\mathrm{dT}& \left[\mathrm{Equation}5\right]\end{array}$

In Equation 5 above, T_f is the fictive temperature, T_g is the glass transition temperature, T_z is the temperature at which quenched-in energy begins to be released, T_e is the temperature after quenched-in energy is completely released, C_p1 and C_p2 represent the heat capacity curves in the first and second cycles, respectively, C_p1 is the heat capacity of the liquid, which is equal to the heat capacity value at the T_e temperature, and C_p,g represents the heat capacity curve of the glass and may be obtained as the tangent line at the T_z temperature on the second heat capacity curve. Using this concept, it is possible to determine the structural relaxation time at a specific healing temperature (T_h) within the healable temperature range.

According to one embodiment of the present disclosure, the step of determining the temperature-dependent structural relaxation time for the metallic glass may include steps of: determining a structural relaxation time (τ_Tg) for glass transition temperature (T_g) through the time difference between T_g,onset and T_g,endset at each glass transition temperature (T_g) measured depending on the heating rate of the metallic glass; determining D and T₀ by fitting the T_g, measured depending on the heating rate of the metallic glass, to Equation 1 below; and substituting said D and T0 into Equation 2 below, and fitting Equation 2, into which said D and T₀ have been substituted, to a structural relaxation time (τ_Tg) measured at at least two T_gs obtained at varying heating rates, thereby deriving a curve of structural relaxation time (τ_Tg) versus continuous T_g, and determining a temperature-dependent structural relaxation time (τ) for the unused metallic glass:

$\begin{array}{cc}\ln \left(\beta \right)=\ln \left(A\right)-\left(\frac{{\mathrm{DT}}_0}{T_0-T}\right)& \left[\mathrm{Equation}1\right]\end{array}$

• • wherein β is the heating rate, A is a constant determined by fitting, D is the fragility index, T₀ is the ideal glass transition temperature, and T is T_g,

$\begin{array}{cc}\tau ={\tau }_0\exp \left(\frac{{\mathrm{DT}}_0}{T-T_0}\right)& \left[\mathrm{Equation}2\right]\end{array}$

• • wherein T is a specific healing temperature or a glass transition temperature (T_g) corresponding to measured structural relaxation time (τ_Tg), D is the fragility index, T₀ is the ideal glass transition temperature, and τ₀=2.5*10⁻¹³.
  • When Equation 2 into which said D and T0 have been substituted is fitted to the structural relaxation time (τ_Tg) measured at at least two T_gs obtained at varying heating rates, the pattern of changes in the τ value may be determined without measuring the τ value at all temperatures.

According to one embodiment of the present disclosure, the step of determining the crystallization time of the metallic glass includes a step of plotting a time-temperature transformation curve, and may include steps of: heating the metallic glass to a specific heat treatment temperature between 0.7 T_g and lower than T_m at a heating rate of 1,000 K/s or higher, and then measuring the time at which crystallization occurs by performing isothermal heat treatment at the heat treatment temperature; fitting the measured crystallization onset time (t) using Equation 3 below and graphing the results:

$\begin{array}{cc}t=\exp \left(\Gamma \right)\exp \left(\frac{B}{T-T_0}\right)\exp \left(\frac{C}{T\Delta G_v^2}\right)\frac{1}{T}& \left[\mathrm{Equation}3\right]\end{array}$

In Equation 3 above,

$\Gamma =\ln \left(\frac{3\pi a^{3}A}{{\rho }_s\mathrm{Vk}}\right),$

wherein ρs is available site density, V is the volume at a given temperature T, k is Boltzmann's constant, a is an atomic size, and A is a fitting coefficient; T is a specific healing temperature, T₀ is an ideal glass transition temperature, B is a fitting coefficient,

$\Delta G_v^2$

is the free energy difference between the liquid and crystal phases, and the constant C represents part of the nucleation barrier and is given by

$C=\left(\frac{16\pi }{3k}\right){\sigma }^{3}f\left(\theta \right),$

wherein 16π/3 is a geometrical factor characteristic of the formation of a spherical nucleus, σ is the interfacial energy between the liquid and the solid, and f(θ) is a catalytic factor, with a range 0≤f(θ)≤1.

In general, the onset of crystallization is defined as the point in time at which a nucleation event occurs within a volume (V) at a given temperature T after a crystallization time (t) by equation JVt=1 (a). Here, based on classical nucleation theory for heterogeneous nucleation, the steady-state nucleation rate J can be expressed as equation

$\begin{array}{cc}J=\frac{{\rho }_s{D}_L}{d^2}\exp \left(\frac{-\Delta G^{*}f\left(\theta \right)}{\mathrm{kT}}\right),& \left(b\right)\end{array}$

wherein k is Boltzmann's constant, f(θ) is a catalysis factor, with a range 0≤f(θ)≤1, ρ_s is available site density, D_L is liquid diffusivity, and d is jump distance. In this equation, the activation barrier for nucleation of a spherical nucleus, ΔG*, may be obtained from classical theory as equation

$\begin{array}{cc}\Delta G^{*}=\left(\frac{16\pi }{3}\right)\left(\frac{{\sigma }^3}{\Delta G_v^2}\right),& \left(c\right)\end{array}$

wherein 16π/3 is a geometrical factor characteristic for the formation of a spherical nucleus, o is the interfacial energy between liquid and solid, and

$\Delta G_v^2$

is the free energy difference between the liquid and crystalline phases.

The diffusion coefficient that is used to evaluate the attachment frequency for nucleation may often be obtained by the relation between the diffusivity and the viscosity through the Stokes-Einstein equation, by assuming that diffusion and viscous flow occur with the same mechanism that is based on Brownian motion: equation

$\begin{array}{cc}{D}_L=\frac{\mathrm{kT}}{3\pi a\eta },& \left(d\right)\end{array}$

wherein η is the kinematic viscosity and a is taken as an atomic size.

Inserting the above equations (a), (c) and (d) into (b), the following equation linking the onset time for nucleation to the temperature may be obtained:

$\ln \left(t\right)=\Gamma +\frac{B}{T-T_0}-\ln T+\frac{C}{T\Delta G_v^2}$

Here, the pre-factor

$\Gamma =\ln \left(\frac{3\pi a^{3}A}{{\rho }_s\mathrm{Vk}}\right)$

is assumed independent of temperature. The constant C represents part of the nucleation barrier and is given by

$C=\left(\frac{16\pi }{3k}\right){\sigma }^{3}f\left(\theta \right).$

Therefore, the crystallization onset time (t) may be expressed as Equation 3 above according to the equation derived as above. Therefore, when the crystallization onset time (t) through isothermal heat treatment at a specific healing temperature obtained experimentally is fitted through Equation 3 above, the pattern of changes in the crystallization onset time (t) may be determined without conducting experiments for all temperatures.

According to one embodiment of the present disclosure, the step of heat-treating the metallic glass at a specific healing temperature may be a step of heat-treating the metallic glass while immersing in a vacuum chamber or a heat-treating salt to prevent oxidation, or may be a step of heat-treating the metallic glass by applying current, or may be a step of heat-treating the metallic glass while applying pressure thereto. In particular, heat-treating the metallic glass by applying pressure thereto may be thermoplastic forming. By heat-treating the metallic glass by applying pressure thereto, the shape of the damaged metallic glass may be easily restored to its original shape, the shear bands in the damaged metallic glass may be healed (restored), and standardization heat treatment may be performed while forming into a desired shape. In this case, the pressure applied for shape restoration may be 0.1 kN to 10 kN. However, the pressure is not limited to the pressure range described above, and any pressure that can restore the shape of the metallic glass without damaging the metallic glass may be applied.

According to one embodiment of the present disclosure, the method includes, after the step of heat-treating the metallic glass at a specific healing temperature, a step of quenching the heat-treated metallic glass at a critical cooling rate or higher. Specifically, the critical cooling rate means the minimum cooling rate required to successfully form a stable glass structure with a specific healing temperature by glass transition after heat-treating the metallic glass at a specific healing temperature. In addition, the quenching may be water quenching. In general, if a bulk specimen with a thickness of 1 mm or more is quenched with water, a cooling rate of 500 K/s may be achieved. Thus, a glass structure at a specific fictive temperature with a critical cooling rate of 500 K/s or less may be easily maintained through water quenching.

According to one embodiment of the present disclosure, the critical cooling rate may be determined by Equation 4 below:

$\begin{array}{cc}\mathrm{Cooling}\mathrm{rate}\left(\frac{\mathrm{dT}}{d\tau }\right)=-1/\left({\tau }_0\exp \left(\frac{{\mathrm{DT}}_0}{T-T_0}\right){\mathrm{DT}}_0\frac{1}{{\left(T-T_0\right)}^2}\right)& \left[\mathrm{Equation}4\right]\end{array}$

• • wherein T is a specific fictive temperature, D is a fragility index, T₀ is an ideal glass transition temperature, and τ₀=2.5*10⁻¹³.

According to one embodiment of the present disclosure, the method may further include, after the step of quenching the heat-treated metallic glass, a step of polishing the surface of the quenched metallic glass. Specifically, by polishing the surface of the metallic glass after quenching the metallic glass, stress concentration caused by a shear step generated during shear deformation may be prevented.

According to one embodiment of the present disclosure, the relaxation enthalpy of the metallic glass may be restored by 90% or more. The relaxation enthalpy of the metallic glass is a value that quantitatively expresses each glass structural difference as a value of the amount of heat generated (H) before T_g due to the structural relaxation behavior of the free volume within the glass structure during differential scanning calorimetry of the metallic glass. When the healing process of the present disclosure is applied and healing heat treatment is performed at a specific healing temperature between 0.7 T_g and T_m (~1.7 T_g) for a time equal to or longer than the structural relaxation time and equal to or shorter than the crystallization onset time, it is possible to restore 90% or more of the relaxation enthalpy of the glass structure obtained at the glass transition at each specific healing temperature, regardless of the production, processing, and use history of the glass.

According to one embodiment of the present disclosure, the specific healing temperature may be a temperature at which the number of healable repetitions (crystallization time/structural relaxation time) of the metallic glass is 10 or more times at a specific healing temperature of 0.7 T_g to T_m. Specifically, the number of healable repetitions means the number of repetitions at which the method for healing a metallic glass according to the present disclosure may be performed, and the number of healable repetitions may be determined by Expression 2 below:

Theoretical number of healable repetitions (times)=crystallization onset time/structural relaxation time  [Expression 2]

When the number of healable repetitions of the metallic glass is within the above-described range, structural relaxation may be easily performed during the healing process, whereas if the number of healable repetitions of the metallic glass is smaller than the lower limit of the above-described range, it is difficult to improve properties through repeated healing, which is not preferable.

According to one embodiment of the present disclosure, the specific healing temperature may be between 0.95 T_g, which is a temperature at which the heat treatment time for structural relaxation of the metallic glass is within 1 hour, and 1.25 T_g, which is a temperature at which the crystallization onset time of the metallic glass is 1 second or more. The specific healing temperature may be 1.0 T_g or more, which is the boundary at which the ductile-brittle transition of the metallic glass occurs, and specifically may be between 1.18 T_g, at which the critical cooling rate is achievable by water quenching, and 1.15 T_g, at which the crystallization onset time is 5 seconds or more. Specifically, the crystallization onset time of the metallic glass may be 1 second or more, 5 seconds or more, 10 minutes or more, 30 minutes or more, 1 hour or more, or 2 hours or more. When the crystallization onset time of the metallic glass is within the above-described range, the healing process of the present disclosure may be easily performed before the metallic glass crystallizes. On the other hand, if the crystallization onset time of the metallic glass is shorter than the lower limit of the above-described range, the crystallization of the metallic glass may occur too quickly, and thus ultra-rapid heating and cooling may be required, making it difficult to perform the healing process of the present disclosure. The above-described specific fictive temperature is possible when the crystallization onset time of the metallic glass is 1 second or more, but may be more preferable when the crystallization onset time is 5 seconds or more because the degree of freedom of the process increases.

According to one embodiment of the present disclosure, the specific healing temperature may be 1.0 T_g or higher, which is a temperature at which the yield strength and elongation of the metallic glass are not reduced by 10% or more during the healing process. When the specific healing temperature is lower than 1.0 T_g, a brittle fracture tendency may be exhibited in which the ductile-brittle transition occurs and the elongation is rapidly reduced.

In summary, the healing process temperature may be primarily limited to a temperature between 0.7 T_g and T_m, but may be limited to a temperature between 1.0 T_g to avoid brittle fracture and 1.25 T_g to prevent rapid crystallization behavior, and a healing process temperature between 1.0 T_g and 1.15 T_g is more desirable because the degree of freedom of the process increases.

According to one embodiment of the present disclosure, healable damage to the metallic glass to be healed may be either damage before plastic deformation stage 3 (σ_T/ε_T<0 MPa/%, where σ_T is a compressive true stress and is given by σ_T=σ×(1−ε), and ε_T is a compressive true strain and is given by ε_T=−ln(1−ε), wherein σ is a true stress, and ε is a true strain) in which shear bands begin to overlap during compressive deformation, or 90% of the maximum bending strain. Since a metallic glass deformed beyond healable damage cannot be healed even if the method for healing a metallic glass according to the present disclosure is performed, the healable deformation range of the metallic glass may be either damage before plastic deformation stage 3 where shear bands begin to overlap during compressive deformation, or damage equal to 90% or less of the maximum bending strain.

According to one embodiment of the present disclosure, the method may further include a step of repeating the heat treatment step and the quenching step at least once, and the total elongation increasing after the repeated healing process may be 200% or more of the elongation of the initial metallic glass. In detail, since the healing process of the present disclosure may be applied repeatedly, it is possible to achieve a total elongation equal to at least twice the inherent elongation of the original metallic glass through repeated healing.

According to one embodiment of the present disclosure, a metallic glass healable by the healing method may have a composition represented by Formula 1, Formula 2, Formula 3, or Formula 4 below. This metallic glass composition has excellent glass-forming ability corresponding to 1 mm or more in diameter and a high elongation of 5% or more, and thus is suitable for the healing method of the present disclosure; however, the metallic glass healable by the healing method of the present disclosure is not limited to this composition.

In Formula 1 above, a and b each denote atomic percent (at. %); TM is one selected from the group consisting of Ti, Zr, Hf, and combinations thereof; E is an element that undergoes a eutectic reaction with TM, and is one selected from the group consisting of Fe, Co, Ni, Cu, Zn, and combinations thereof; N is an element that increases glass-forming ability and supercooled liquid region, and is one selected from the group consisting of Al, Nb, Ta, Mo, Be, Re, V, Ir, Pd, Au, Ag, Pt, and combinations thereof; and a is 15 to 65, and b is 5 to 30.

In Formula 2 above, a, b, c, and d each denotes atomic percent (at. %); X is an element that increases glass-forming ability and supercooled liquid region, and is one selected from the group consisting of Al, Ti, Nb, Ta, Mo, Be, Re, V, Ir, Pd, Au, Ag, Hf, Pt, and combinations thereof; and b−c is 2 to 29, c is 1 to 40, d is 2 to 29, and a is 100−(b+d).

In Formula 3 above, a, b, c, d, and f each denote atomic percent (at. %); X is an element that increases glass-forming ability and supercooled liquid region, and is one selected from the group consisting of Re, V, Ir, Mo, Pd, Nb, Ta, Au, Ag, Ti, Hf, Pt, and combinations thereof; and b−c is 2 to 29, c is 1 to 10, d is 2 to 29, f is 4 to 18, and a is 100−(b+d+f).

In Formula 4 above, a, b, c, and d each denote atomic percent (at. %); X is an element that increases glass-forming ability and supercooled liquid region, and is one selected from the group consisting of Ti, Be, and combinations thereof; and b−c is 5 to 15, c is 25 to 45, d is 5 to 15, and a is 100−(b+d).

Another embodiment of the present disclosure provides a method for standardizing a metallic glass, including steps: determining a temperature-dependent structural relaxation time for the metallic glass; determining a temperature-dependent crystallization onset time for the metallic glass; heat-treating the metallic glass at a specific healing temperature within a healable temperature range for a time satisfying Expression 1 below; and quenching the heat-treated metallic glass from the specific healing temperature at a critical cooling rate or higher, thereby standardizing the metallic glass to have a structure with the specific healing temperature:

Structural relaxation time at the specific healing temperature≤heat treatment time at the specific healing temperature≤crystallization onset time at the specific healing temperature.  [Expression 1]

As shown in FIG. 2 mentioned above with respect to the healing method, standardization is a process for homogenizing a glass structure and associated properties that vary depending on the cooling rate and processing process during the production of the metallic glass. Specifically, it is a process of heat-treating a metallic glass at a specific healing temperature for a time exceeding the structural relaxation time, and then cooling the metallic glass from the specific healing temperature at a critical cooling rate (=differential value of T/t at the specific healing temperature) or higher for glass formation, thereby obtaining a standardized metallic glass structure and associated properties due to the specific healing temperature.

During subsequent use, the standardized initial metallic glass is damaged, and as described above, the structure of the damaged metallic glass may reach a stable liquid structure with a specific healing temperature by performing the healing process including heat-treating the damaged metallic glass at a specific healing temperature (T_h) within a healable temperature range for a time exceeding the structural relaxation time. Thereafter, when the stable liquid structure with the specific healing temperature is cooled from the specific healing temperature at a critical cooling rate or higher, the same metallic glass structure as the stable liquid structure with the specific healing temperature may be obtained by glass transition. Using this concept, the microstructure of the initial metallic glass may be obtained by heat-treating the damaged metallic glass at the specific healing temperature, followed by quenching. Although the standardization process is not necessarily required before the healing process, even if the structure and properties of a pre-standardized metallic glass change due to deformation resulting from the production and processing or usage environment, the structure and properties of the standardized metallic glass may be restored by performing the method for healing a metallic glass according to the present disclosure.

For the method for standardizing a metallic glass according to the present disclosure, the matters mentioned above in the method for healing a metallic glass are equally applied as long as they do not contradict each other. In particular, when the method for healing is applied after standardizing a metallic glass, the standardized metallic glass structure and related properties may be used repeatedly and continuously.

Hereinafter, the present disclosure will be described in detail with reference to examples. However, the examples according to the present disclosure may be modified into various different forms, and the scope of the present disclosure is not to be interpreted as being limited to the examples described below. The examples of the present specification are provided to more completely explain the present disclosure to those skilled in the art.

Production Example 1. Production of Metallic Glass Having Composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂

An metallic glass raw material containing 65 at. % Zr, 12 at. % Ni, 13 at. % Cu, 8 at. % Al, 0.5 at. % Ti, 0.5 at. % Nb, 0.5 at. % Ta, and 0.5 at. % Mo to have the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂ was prepared, and a master metallic glass was produced therefrom through arc melting. Then, a rod-shaped bulk metallic glass with a diameter of 2 mm was prepared through suction casting.

Production Example 2. Production of Metallic Glass Having Composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅

A metallic glass having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ was produced in the same manner as in Production Example 1, except that the composition of the metallic glass was adjusted as described in Production Example 2 in Table 1 below.

TABLE 1
Composition of metallic glass
Production Example 1 Zr65Ni12Cu13Al8(TiNbTaMo)2
Production Example 2 Zr44Ti11Ni10Cu10Be25

Example 1. Measurement of T_e and Tx Depending on Heating Rate of Metallic Glass

The T_g (glass transition temperature) and Tx (crystallization onset temperature) of the metallic glasses of Production Examples 1 and 2 were measured using DSC (differential scanning calorimetry) and FDSC (flash differential scanning calorimetry) while controlling the heating rate from 0.17 K/s to 10,000 K/s, and the results are shown in Table 2 below. In the present specification, if the heating rate for the T_g and T_x of the metallic glass is not specified, T_g and T_x mean the T_g and T_x values measured at a heating rate of 0.33 K/s.

	TABLE 2
	Heating
	rate (K/s)	Tg (K)	Tx (K)
Production Example 1	0.17	632.15	700.55
Zr65Ni12Cu13Al8(TiNbTaMo)2	0.33	637.21	713.84
	0.67	641.96	728.13
	1.33	655.15	745.1
	2.66	660.13	769.14
	100	680.3	839.36
	1,000	703.28	915.34
	10,000	759.15	977.64
Production Example 2	0.33	618	734
Zr44Ti11Ni10Cu10Be25	0.67	623	745
	1.33	624	759
	2.66	630	783
	100	657	867
	1,000	685	897
	10,000	705	924

Example 2. Graph of Viscosity Change with Temperature

The heating rate and T_g value of the metallic glasses of Production Examples 1 and 2, obtained in Example 1, were fitted with the Vogel-Fulcher-Tammann (VFT) equation using Equation 1 below to obtain the D value and To, and then a graph of the predicted viscosity change with temperature was constructed using Equation 6 below. In this case, the D and T0 values of the compositions of Production Example 1 and Production Example 2 are shown in Table 3 below, and a graph of predicted temperature-dependent changes in the viscosity of the metallic glass of the composition of Production Example 1 is shown in FIG. 5.

$\begin{array}{cc}\ln \left(\beta \right)=\ln \left(A\right)-\left(\frac{{\mathrm{DT}}_0}{T_0-T}\right)& \left[\mathrm{Equation}1\right]\end{array}$

In Equation 1 above, β is the heating rate, A is a constant determined by fitting, D is the fragility parameter, T₀ is an ideal glass transition temperature, and T is T_g.

	TABLE 3
	D	T0 (K)
	Production Example 1	19.2	427.5
	Zr65Ni12Cu13Al8(TiNbTaMo)2
	Production Example 2	19.3	418.6
	Zr44Ti11Ni10Cu10Be25

$\begin{array}{cc}\eta ={\eta }_0\exp \left(\frac{{\mathrm{DT}}_0}{T-T_0}\right)& \left[\mathrm{Equation}6\right]\end{array}$

In Equation 6 above, D is the fragility parameter, T is a specific healing temperature, To is an ideal glass transition temperature, and η₀=4*10⁻⁵. In Formula 6, D, T₀, and η₀ are constants determined by the composition regardless of the temperature, and thus the viscosity (n) value at the process temperature can be determined by substituting the temperature (T) to be used in the healing process into Equation 6.

Example 3. Structural Relaxation Time Depending on Healing Temperature

In order to determine the structural relaxation time depending on the healing temperature of the metallic glass, in the present disclosure, the structural relaxation time (t) from the glass structure to the supercooled liquid at the corresponding temperature was measured through the time difference between T_g,onset and T_g,endpoint at each T_g (glass transition temperature) measured depending on the heating rate of the metallic glass. Since viscosity is generally proportional to the structural relaxation time (t), it is possible to replace η(T) of Equation 6 with τ(T) as shown in Equation 2. Therefore, using the D and T₀ values of the metallic glasses having the compositions of Production Examples 1 and 2, obtained in the above Example 2, the temperature-dependent structural relaxation time for the metallic glass was determined by fitting using Equation 2 below, and as a result, the changes in the τ value at various temperatures are shown in Table 4 below.

$\begin{array}{cc}\tau ={\tau }_0\exp \left(\frac{{\mathrm{DT}}_0}{T-T_0}\right)& \left[\mathrm{Equation}2\right]\end{array}$

In Equation 2 above, T is a specific healing temperature, D is a fragility parameter, To is an ideal glass transition temperature, and τ₀=2.5*10⁻¹³.

	TABLE 4
	Temperature	Relaxation
	(K)	time (s)
	Production Example 1	600	10,900
	Zr65Ni12Cu13Al8(TiNbTaMo)2	610	2,656
		620	714
		630	210
		640	68
		650	23
		660	8.5
		670	3.3
		680	1.3
		690	0.6
		700	0.29
		710	0.18
		720	0.1
		730	0.05
		740	0.023
		750	0.02
		760	0.005
		770	0.003
	Production Example 2	580	23,800
	Zr44Ti11Ni10Cu10Be25	590	5,950
		600	1,540
		610	440
		620	135
		630	45
		640	16
		650	6
		660	2
		670	1
		680	0.5
		690	0.2
		700	0.1
		710	0.05
		720	0.02
		730	0.01
		740	0.008
		750	0.004
		760	0.002
		770	0.001

As shown in Table 4 above, it was confirmed that the structural relaxation time of the metallic glass varied depending on the temperature. In addition, since the crystallization onset time of the metallic glass also varies significantly depending on the temperature, an appropriate heat treatment temperature and time should be set in order to prevent crystallization during heat treatment of the metallic glass and satisfy the glass structure with the desired characteristics. Specifically, it was confirmed that, for the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, the structural relaxation time at 650 K was about 23 seconds, and for the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, the structural relaxation time at 650 K was about 6 seconds or less. It can be seen that, in order to resolve such a difference depending on composition, it is necessary to control process conditions through a relative ratio normalized by the T_g value that changes depending on composition rather than simply the temperature value, when determining a specific healing temperature.

FIG. 6 is a time-temperature transformation curve plotting temperature-dependent changes in the structural relaxation and crystallization onset time of a metallic glass having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, and shows a region in which the healing process of the metallic glass is possible through heat treatment at a specific healing temperature within a healable temperature range.

In FIG. 6, the metallic glass was heated to a specific heat treatment temperature between 0.7 T_g and lower than T_m at a heating rate of 1,000 K/s or higher, and then the time at which crystallization occurs by performing isothermal heat treatment at the heat treatment temperature was measured, and the measured crystallization onset time (t) of the metallic glass was expressed as Equation 3 below:

$\begin{array}{cc}t=\exp \left(\Gamma \right)\exp \left(\frac{B}{T-T_0}\right)\exp \left(\frac{C}{T\Delta G_v^2}\right)\frac{1}{T}& \left[\mathrm{Equation}3\right]\end{array}$

In Equation 3 above,

$\Gamma =\ln \left(\frac{3\pi a^{3}A}{{\rho }_s\mathrm{Vk}}\right),$

wherein ρ_s is available site density, V is the volume at a given temperature T, k is Boltzmann's constant, a is an atomic size, and A is a fitting coefficient; T is a specific healing temperature, T₀ is an ideal glass transition temperature, B is a fitting coefficient,

$\Delta G_v^2$

is the free energy difference between the liquid and crystal phases, and the constant C represents part of the nucleation barrier and is given by

$C=\left(\frac{16\pi }{3k}\right){\sigma }^{3}f\left(\theta \right),$

wherein 16π/3 is a geometrical factor characteristic of the formation for a spherical nucleus, σ is the interfacial energy between liquid and solid, and f(θ) is a catalytic factor, with a range 0≤f(θ)≤1.

Referring to FIG. 6, the structural relaxation time and crystallization onset time at a specific healing temperature of the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂ can be found. It can be confirmed that, when the healing process is performed between the structural relaxation time and the crystallization onset time at a specific healing temperature shown in FIG. 6, the structural relaxation enthalpy value is restored by 90% or more (See FIG. 9).

Example 4. Critical Cooling Rate after Healing Heat Treatment

Equation 2 above was differentiated with respect to time to obtain Equation 4 below. In addition, the required critical cooling rate depending on the heat treatment temperature for healing was calculated through Equation 4 below, and the results are shown in Table 5 below.

$\begin{array}{cc}\frac{\mathrm{dT}}{d\tau }=-1/\left({\tau }_0\exp \left(\frac{{\mathrm{DT}}_0}{T-T_0}\right){\mathrm{DT}}_0\frac{1}{{\left(T-T_0\right)}^2}\right)& \left[\mathrm{Equation}4\right]\end{array}$

In Equation 4 above, D is a fragility parameter, T₀ is an ideal glass transition temperature, and τ₀=2.5*10⁻¹³.

	TABLE 5
			Whether healing is
	Temperature	Critical cooling	possible through
	(K)	rate (K/s)	water quenching
Production Example 1	600	−3.1E−08	◯
Zr65Ni12Cu13Al8(TiNbTaMo)2	610	−4.7E−07	◯
	620	−5.4E−06	◯
	630	−4.9E−05	◯
	640	−0.0003	◯
	650	−0.002	◯
	660	−0.01	◯
	670	−0.05	◯
	680	−0.2	◯
	690	−0.8	◯
	700	−3	◯
	710	−9	◯
	720	−27	◯
	730	−73	◯
	740	−186	◯
	750	−448	◯
	760	−1024	X
	770	−2235	X
Production Example 2	600	−7.4E−07	◯
Zr44Ti11Ni10Cu10Be25	610	−8.5E−06	◯
	620	−7.6E−05	◯
	630	−0.00056	◯
	640	−0.0034	◯
	650	−0.018	◯
	660	−0.084	◯
	670	−0.34	◯
	680	−1.27	◯
	690	−4	◯
	700	−13	◯
	710	−38	◯
	720	−102	◯
	730	−259	◯
	740	−619	X
	750	−1406	X
	760	−3047	X
	770	−6331	X

As shown in Table 5 above, the required cooling rate depending on the heat treatment temperature for healing indicates the minimum critical cooling rate required to maintain the glass structure at a specific healing temperature during cooling after heat treatment at a specific healing temperature. Specifically, the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂ may have a glass structure corresponding to a specific healing temperature (T_h) of 720 K only when it is cooled from 720 K at a rate of about 27 K/s or more, and may have a glass structure corresponding to a specific healing temperature (T_h) of 770 K only when it is cooled from 720 K at a rate of about 2,235 K/s or more. Generally, it is known that a cooling rate of 500 K/s can be achieved when a bulk specimen with a thickness of 1 mm or more is quenched with water. Therefore, it was confirmed 10 that the achievable specific healing temperature of the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂ through water quenching is about 752 K (1.18 T_g) or lower, and that the achievable specific healing temperature of the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ is about 735 K (1.19 T_g) or lower.

Referring to Table 4 about, it takes 10,900 seconds (about 3 hours) to produce the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂ having a structure with a specific healing temperature of 600 K, and it takes 23,800 seconds (about 6.6 hours) to produce the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ having a structure with a specific healing temperature structure of 590 K, indicating that these compositions are difficult to use industrially. Therefore, in order to improve the efficiency of the healing process, it is desirable to perform the healing process at a specific healing temperature of 0.95 T_g or higher under conditions where structural relaxation is possible through heat treatment within 1 hour.

Taken together, it was confirmed that the specific healing temperature range for an efficient healing process in terms of process time (heat treatment within 1 hour) and methodology (water quenching) was 610 K (0.95 T_g) to 752 K (1.18 T_g) for the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂ (Production Example 1) and 590 K (0.95 T_g) to 730 K (1.19 T_g) for the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ (Production Example 2).

Example 5. Production of Metallic Glass Having Structure with Specific Healing Temperature

The 2.0-mm-diameter rod-shaped specimens having the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂, produced in Production Example 1, were heat-treated at different specific healing temperatures of 0.92 T_g, 1.04 T_g and 1.08 T_g, respectively. In this case, the heat treatment was performed for about 1.5 times the structural relaxation time at the heat treatment temperature.

The DSC measurement results of each heat-treated specimen are shown in FIG. 7.

As shown in FIG. 7, it was confirmed that metallic glasses having structures with specific healing temperatures of 0.92 T_g, 1.04 T_g, and 1.08 T_g were successfully produced through the heat treatment. As a result of DSC measurement of the metallic glasses having structures with different specific healing temperatures, it could be seen that, as the specific healing temperature increased, the absolute value of the relaxation enthalpy increased (convex downward), suggesting, through Equation 5, that the value of the left side increased (the area increased), and thus the specific healing temperature (T_h) shifted to a temperature higher than T_g. That is, referring to FIG. 7, it can be seen that the absolute value of the structural relaxation enthalpy of the metallic glass having a structure with the highest specific healing temperature (1.08 T_g) is the largest (convex downward), and that the absolute value of the structural relaxation enthalpy of the metallic glass having a structure with the lowest specific healing temperature (0.92 T_g) is the smallest (flat). Through this method, a process of standardizing a glass structure to have a glass structure with a specific healing temperature can be performed using the healing process of the present disclosure.

Experimental Example 1. Compressive Strain Test

The 2.0-mm-diameter rod-shaped specimens having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, produced in Production Example 1, were heat-treated at different specific healing temperatures of 610 K (0.95 T_g) to 750 K (1.18 T_g). In this case, the heat treatment was performed for about 1.5 times the structural relaxation time through isothermal heat treatment at the heat treatment temperature.

The heat-treated specimens were cooled to room temperature at a rate of about 500 K/s through water quenching, and then a 50% compressive strain test was performed on the metallic glass specimens under a strain rate condition of 5×10⁴/s using a universal material tester (model: Instron 5967, manufacturer: Instron). The results are shown in Table 6 below.

	TABLE 6
			Presence or absence
	Specific healing		of superplastic
	temperature (K)	Th/Tg	behavior
Production Example 1	610	0.95	X
Zr65Ni12Cu13Al8(TiNbTaMo)2	620	0.97	X
	630	0.98	X
	640	1.00	◯
	650	1.02	◯
	660	1.03	◯
	670	1.05	◯
	680	1.06	◯
	690	1.08	◯
	700	1.09	◯
	710	1.11	◯
	720	1.13	◯
	730	1.14	◯
	740	1.16	◯
	750	1.18	◯

FIG. 8 shows the results of compressive strain tests on the metallic glasses water-quenched after 9 hours at 630 K (0.98 T_g) or after 5 seconds at 690 K (1.08 T_g), which are different specific healing temperatures. Referring to FIG. 8, it can be seen that the metallic glass specimen having the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂, heat-treated at a specific healing 5 temperature of 690 K (1.08 T_g) in the healing process, did not break even when compressed, and the pressure continuously increased due to compression, indicating that the specimen exhibited superplastic behavior with maximized mechanical stability. On the other hand, it can be seen that the metallic glass having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, heat-treated at a specific healing temperature of 630 K (0.98 T_g), exhibited an elongation of less than 9%, indicating that it did not exhibit superplastic behavior.

Thus, in the structure of the metallic glass that has undergone the healing process at a low specific healing temperature below the DBT (ductile-brittle transition) point, the amount of internal free volume decreased below the DBT point, and thus cracks occurred rather than deformation through shear band formation, resulting in deterioration of the metallic glass. Although the DBT point may vary depending on the composition, it can generally be seen that when a metallic glass is heat-treated at a specific healing temperature lower than 1.0 T_g, with 1.0 T_g as the boundary, degradation of the metallic grass occurs.

Referring to Table 6 above, it can be confirmed that the specific healing temperature range in which no deterioration (deterioration) in the properties of the metallic glass having the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂ occurs is 640 K or higher and 1.0 T_g or higher.

FIG. 9 shows a schematic view (top) and DSC results (bottom) for a 2-mm rod-shaped specimen having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂ and standardized at 1.08 T_g (690 K), a specimen obtained by plastically deforming the rod-shaped specimen by 50% in uniaxial compression mode, and a specimen subjected to a healing process at 1.08 T_g (690 K) after 50% plastic deformation. Referring to FIG. 9, it can be seen that the DSC results for relaxation enthalpy of the 505 plastically deformed specimen are different (increase or decrease; increase in the case of FIG. 8) from those for the specimen before plastic deformation due to the occurrence of multiple shear bands caused by plastic deformation, indicating that damage to the internal structure of the metallic glass has occurred. However, the DSC results for relaxation enthalpy of the specimen that underwent the healing process at 1.08 T_g (690 K) are not different from those for the specimen before plastic deformation, suggesting that damage to the internal structure of the metallic glass was healed through the healing process at 1.08 T_g (690 K). These results demonstrate that the plastically deformed region within the critical strain can also be successfully healed through the healing process of the present disclosure.

Experimental Example 2. 3-Point Bending Test

A 1.0-mm-thick plate-shaped specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ was produced in the same manner as in Production Example 2. The plate-shaped specimen was subjected to healing heat treatment (standardization) at each healing temperature from 600 K (0.97 T_g) to 730 K (1.18 T_g) to obtain a glass structure. In this case, the heat treatment was performed for about 1.5 times the structural relaxation time at the heat treatment temperature. Each of the heat-treated specimens was subjected to a three-point bending test using a universal material tester (model: Instron 5967, manufacturer: Instron) with a 2810-400 jig under the conditions of span length of 24 mm and strain rate of 1×10⁻⁴/s, and the results are shown in Table 7 below.

	TABLE 7
	Specific healing		3-point bending
	temperature (K)	Th/Tg	ductility (%)
Production Example 2	600	0.97	3
Zr44Ti11Ni10Cu10Be25	610	0.98	3
	620	1.00	6
	630	1.01	6
	640	1.03	6
	650	1.05	6
	660	1.06	6
	670	1.08	6
	680	1.10	6
	690	1.11	6
	700	1.13	6
	710	1.14	6
	720	1.16	6
	730	1.18	6

As shown in Table 7 above, it was confirmed that the metallic glass specimens having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, heat-treated (standardized) at a specific healing temperature of 620 K (1.0 T_g) or higher, had an elongation of about 6% specific to the composition.

On the other hand, it was confirmed that the metallic glass having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, heat-treated (standardized) at a specific healing temperature below 620 K (1.0 T_g), had a low elongation of 3% or less and was easily fractured (deteriorated).

As described above, the structure of the metallic glass formed through standardization heat treatment at a specific low healing temperature below the DBT point was deteriorated because the amount of free volume therein was reduced. In particular, it can be seen that the metallic glass heat-treated at a specific healing temperature below 1.0 T_g has deteriorated characteristics.

As shown in Table 7 above, it was confirmed that the specific healing temperature range for standardization heat treatment, in which the metallic glass having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ did not deteriorate, was 620 K (1.0 T_g) or higher. Summarizing the results of the evaluation of the healing-mechanical properties in Experimental Examples 1 and 2, it can be seen that the specific healing temperature at which ductile-brittle transition occurs is 1.0 T_g or higher, and the condition where a glass structure can be obtained through water quenching is 1.18 T_g or lower.

Experimental Example 3. Number of Healable Repetitions

The standardization heat treatment temperature, structural relaxation time, and crystallization time of the metallic glass having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂, produced in Production Example 1, and the metallic glass having the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, produced in Production Example 2, are shown in Table 8 below.

In addition, the number of healable repetitions at each standardization heat treatment temperature was calculated using Equation 2 below, and the results are shown in Table 8 below.

Theoretical number of healable repetitions (times)=crystallization onset time/structural relaxation time  [Expression 2]

	TABLE 8
		Structural		Theoretical number
	Temperature	relaxation	Crystallization	of healable
	(K)	temperature (s)	time (s)	repetitions
Production Example 1	620	714	2,500,000	3,501
Zr65Ni12Cu13Al8(TiNbTaMo)2	630	210	600,000	2,857
	640	68	200,000	2,941
	650	23	50,000	2,173
	660	8.5	15,000	1,764
	670	3.3	5,000	1,515
	680	1.3	1,800	1,384
	690	0.6	700	1,166
	700	0.29	280	965
	710	0.18	116	644
	720	0.1	50	500
	730	0.05	22	440
	740	0.023	10	400
	750	0.020	5	250
Production Example 2	620	135	100,000	740
Zr44Ti11Ni10Cu10Be25	630	45	30,000	666
	640	16	9,000	562
	650	6	2,800	466
	660	2	800	400
	670	1	350	350
	680	0.5	150	300
	690	0.2	50	250
	700	0.1	22	220
	710	0.05	10	200
	720	0.02	3.5	175
	730	0.01	1.5	150

As shown in Table 8 above, it can be seen that the theoretical number of healable repetitions decreased as the heat treatment temperature increased. This may be because the crystallization time decreased more significantly than the structural relaxation time decreased during isothermal heat treatment as the temperature increased. Therefore, it can be seen that, at a temperature of 1.25 T_g or lower, the theoretical number of healable repetitions was as good as 100 or more. However, it can be seen that, when healing was performed at temperatures higher than 1.15 T_g, the crystallization onset time was within 10 seconds, and when healing was performed at temperature higher than 1.18 T_g, the crystallization onset time was within 1 second, indicating that the time allowed for the process rapidly decreased as the temperature increased.

Summarizing the results of the above Examples and Experimental Examples, it was confirmed that a specific fictive temperature range suitable for the method for healing the metallic glass having the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂ is 635 K to 735 K (1.0 T_g to 1.15 T_g). It can be seen that, in the above temperature range, the metallic glass does not exhibit any deterioration in its properties, a glass structure may be formed by cooling from a specific fictive temperature at a critical cooling rate or higher using a water cooling process suitable for process convenience, the theoretical number of healable repetitions is 10 or more, and the crystallization time is 5 seconds or more.

FIG. 10 shows the number of healable repetitions and a temperature range suitable for the healing process, in a time-temperature transformation curve showing temperature-dependent changes in the structural relaxation and crystallization onset time crystallization onset time of the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂. As can be seen in the drawing, it was confirmed that a specific fictive temperature range suitable for the method for healing the metallic glass with the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂ is 635 K to 735 K (1.0 T_g to 1.15 T_g). It can be seen that, in the above temperature range, the properties of the metallic glass do not deteriorate, a specific fictive temperature can be realized by water quenching, the theoretical number of healable repetitions is 10 or more, and the crystallization time is 5 seconds or more.

Experimental Example 4. Evaluation of Deformation Limit

A 1.0-mm-thick plate-shaped specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ was produced in the same manner as in Production Example 2. The plate-shaped specimen was heat-treated for 10 seconds at the specific healing temperature of 670 K (1.08 T_g) suitable for the healing method, confirmed in Experimental Example 3. The heat-treated specimen was cooled to room temperature at a rate of about 500 K/s through water quenching, thereby preparing a standardized specimen, and then a 3-point bending test for the specimen was performed using a universal material tester (model: Instron 5967, manufacturer: Instron) with a 2810-400 jig under the conditions of span length of 24 mm and strain rate of 1×10⁻⁴/s, and the results are shown in FIG. 11. As shown in FIG. 11, it was confirmed that the 1.0-mm-thick plate specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ fractured at an elongation of about 5.5% to 6.0%. In particular, as can be seen in the figure, specimens subjected to standardization heat treatment at the same specific healing temperature exhibited similar elongations with a variation within +0.5% (a variation within 10% of the total elongation).

In addition, the metallic glass specimen was subjected to deformation of 5% (approximately 90% of fracture) through the three-point bending test, and then unloaded. The thickness direction of the specimen was imaged using a scanning electron microscope (SEM), and the results are shown in FIG. 12. Referring to FIG. 12, it can be seen that, when the 1.0-mm-thick plate specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ underwent a bending strain of 5% (approximately 90% of fracture), a number of shear bands were formed through plastic deformation in both the upper part of the specimen where tensile stress was applied and the lower part of the specimen where compressive stress was applied. In particular, it was confirmed that shear bands with a length of approximately 400 μm were formed in the part where tensile stress was applied. However, it was confirmed that no critical-size defects, such as cracks crossing the neutral zone at the center of the specimen, appeared even though a bending strain of 5% (approximately 90% of fracture) occurred. Therefore, it can be seen that the healable limit of the 1.0-mm-thick plate-shaped specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ is deformation of 5% (within 90% of the maximum strain) at which no unhealable damage such as a crack larger than the critical size appears.

Furthermore, a 1.0-mm-thick plate-shaped specimen having the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂ was heat-treated for 30 seconds at a specific healing temperature of 690 K (1.08 T_g) within a temperature range suitable for the healing method. The heat-treated specimen was cooled to room temperature at a rate of about 500 K/s through water quenching, and then a three-point bending test was performed thereon using the same method as the three-point bending test for the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, and the results are shown in FIG. 13(a). Also, SEM images after 4% deformation and fracture of the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂ are shown in FIGS. 13(b) and 13(c). As shown in FIG. 13(a), it was confirmed that the 1.0-mm-thick plate-shaped specimen with the composition Zr₆₅Ni₁₂Cu₁₃Al₈ (TiNbTaMo)₂ fractured at an elongation of about 6.2% to 6.75% (variation within 6.5+0.5%). In addition, as shown in FIG. 13(b), it was confirmed that, when 4% deformation occurred, shear bands of about 450 μm in size were formed, but no cracks occurred. On the other hand, as shown FIG. 13(c), it was confirmed that, when 6.75% deformation occurred, shear bands exceeding about 610 μm were formed, and unhealable damage such as cracks exceeding a critical size occurred, resulting in fracture. Therefore, it can be seen that the healable limit of the 1.0-mm-thick plate-shaped specimen with the composition Zr₆₅Ni₁₂Cu₁₃Al₈(TiNbTaMo)₂ is deformation of 6% (within 90% of the maximum strain) at which no unhealable damage such as cracks appears.

Experimental Example 6. Evaluation of Healing of Damage to Metallic Glass

A 1.0-mm-thick plate-shaped specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, subjected to deformation of 5% (within 90% of the maximum strain) in the same manner as in Experimental Example 5, was unloaded, and then deformed again without a healing process, and a load was applied thereto until fracture occurred. The results are shown in FIG. 14. As shown in FIG. 14, it was confirmed that the metallic glass that did not undergo a healing process after 5% deformation fractured at an elongation of 5.5% and 6.0%, which is the maximum elongation, in the bending test with single deformation.

In contrast, the 1.0-mm-thick plate-shaped specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, subjected to deformation of 5% (within 90% of the maximum strain) in the same manner as in Experimental Example 5, was unloaded, and then subjected to structural relaxation for 10 seconds at a specific healing temperature of 670 K (1.08 T_g) within a temperature range suitable for the healing method, and then cooled at a rate of about 500 K/s through water quenching, thereby healing the metallic glass. A load was applied to the 1.0-mm-thick plate-shaped specimen with the healed composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ until fracture occurred, and the results are shown in FIG. 15. As shown in FIG. 15, it was confirmed that the metallic glass subjected to the healing process after 5% deformation showed an increase in elongation of up to about 8% in the three-point bending test. Therefore, it can be seen that the elongation of the metallic glass increased as the damage was healed (restored) through the healing process.

Experimental Example 7. Evaluation of Repeated Healing of Damage to Metallic Glass

The 1.0-mm-thick plate-shaped specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, subjected to deformation of 5% (within 90% of the maximum strain) in the same manner as in Experimental Example 5, was unloaded, and then subjected to structural relaxation for 10 seconds at a specific healing temperature of 670 K (1.08 T_g) within a temperature range suitable for the healing method, and then cooled at a rate of about 500 K/s through water quenching, thereby healing the metallic glass. Thereafter, the healed metallic glass was subjected again to 5% deformation in the same manner, and then healed again in the same manner as described above, and then subjected again to 5% deformation.

FIG. 16 shows the results of 5% deformation of each of the standardized metallic glass before healing, the first-healed metallic glass, and the second-healed metallic glass, and the shapes of the unloaded specimens. As shown in FIG. 16, it was confirmed that the metallic glass with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which fractured at an elongation of 5.5% to 6.0%, was recovered from the structural change caused by plastic deformation whenever the healing process was performed, and the total maximum elongation thereof increased to 9% and the bending angle increased to 55°, through two repeated healing processes. Therefore, it can be confirmed that the method for healing a metallic glass according to the present disclosure can repeatedly heal (restore) damage caused by deformation.

Experimental Example 8. Evaluation of Healing of Damage to Metallic Glass Together with Thermoplastic Forming

A 1.0-mm-thick plate-shaped specimen with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, subjected to 5% deformation (approximately 90% of fracture) in the same manner as in Experimental Example 5, was unloaded, and then the specimen was placed between two stainless steel plates using a universal material tester (model: Instron 5967, manufacturer: Instron) and subjected to structural relaxation at 670 K (1.08 T_g) for 1 minute while a pressure of about 1 kN was applied thereto. Thereafter, the metallic glass was cooled to room temperature at a rate of about 500 K/s through water quenching, thereby performing the first thermoplastic forming and healing process. Then, the metallic glass subjected to the first thermoplastic forming and healing process was subjected again to 5% deformation using the same method, and then subjected to a second thermoplastic forming and healing process using the same method as above. Then, the metallic glass was subjected again to 5% deformation and a third thermoplastic forming and healing process, and then subjected to deformation until fracture occurred.

FIG. 17 shows the results of 5% deformation of the standardized metallic glass before healing, the metallic glass subjected to the first thermoplastic forming and healing process, and the metallic glass subjected to the second thermoplastic forming and healing process, and the results of deformation of the metallic glass subjected to the third thermoplastic forming and healing process. From the results in FIG. 17, it was confirmed that an elongation increase of 200% or more of the inherent elongation of the original material composition was possible through the repeated processes for healing damage according to the present disclosure. As shown in FIG. 17, it was confirmed that the metallic glass with the composition Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅, which fractured at an elongation of 5.5% to 6.0%, completely restored its original yield strength and elongation after the thermoplastic forming and healing process performed at a specific healing temperature within a temperature range suitable for the above-described healing method, thereby returning to its initial-state characteristics. In addition, it was confirmed that damage could be repeatedly healed (restored) as in Experimental Example 7.

FIG. 18 shows the shapes and SEM images of the standardized metallic glass before healing and the metallic glass subjected to the first thermoplastic forming and healing process. As shown in FIG. 18, it was confirmed that the metallic glass after 5% bending deformation had a shape bent at about 25°, but the metallic glass subjected to the first thermoplastic forming and healing process was healed to its original plate shape. In addition, it was confirmed that, in the metallic glass after 5% bending deformation, a number of shear bands occurred, but in the metallic glass subjected to the first thermoplastic forming and healing, shear bands were healed.

Although the present disclosure has been described above by way of limited embodiments, the present disclosure is not limited thereto. It should be understood that the present disclosure can be variously changed and modified by those skilled in the art without departing from the technical sprit of the present disclosure and the range of equivalents to the appended claims.

Claims

1. A method for healing a metallic glass, comprising steps of:

determining a temperature-dependent structural relaxation time for an unused metallic glass having the same composition as the metallic glass to be healed;

determining a temperature-dependent crystallization onset time for the unused metallic glass;

heat-treating the metallic glass to be healed at a specific healing temperature within a healable temperature range for a time satisfying Expression 1 below; and

quenching the heat-treated metallic glass to be healed from the specific healing temperature at a critical cooling rate or higher: Structural relaxation time at the specific healing temperature≤heat treatment time at the specific healing temperature≤crystallization onset time at the specific healing temperature.  [Expression 1]

2. The method of claim 1, wherein the step of determining the temperature-dependent structural relaxation time for the unused metallic glass comprises steps of: ln ⁢ ( β ) = ln ⁢ ( A ) - ( D ⁢ T 0 T 0 - T ) [ Equation ⁢ 1 ] τ = τ 0 ⁢ exp ⁢ ( DT 0 T - T 0 ) [ Equation ⁢ 2 ]

determining a structural relaxation time (τTg) for glass transition temperature (Tg) through a time difference between Tg,onset and Tg,endset at each glass transition temperature (Tg) measured depending on a heating rate of the unused metallic glass;

determining D and T0 by fitting Tg, measured depending on the heating rate of the unused metallic glass, to Equation 1 below; and

substituting said D and T0 into Equation 2 below, and fitting Equation 2, into which said D and T0 have been substituted, to a structural relaxation time (τTg) measured at at least two Tgs obtained at varying heating rates, thereby deriving a curve of structural relaxation time (τTg) versus continuous Tg, and determining a temperature-dependent structural relaxation time (t) for the unused metallic glass:

wherein β is the heating rate, A is a constant determined by fitting, D is a fragility index, T0 is an ideal glass transition temperature, and T is Tg;

wherein T is the specific healing temperature or a glass transition temperature (Tg) corresponding to the measured structural relaxation time (τTg), D is the fragility index, T0 is the ideal glass transition temperature, and τ0=2.5*10−13.

3. The method of claim 1, wherein the step of determining the temperature-dependent crystallization onset time for the unused metallic glass comprises steps of: t = exp ⁡ ( Γ ) ⁢ exp ⁡ ( B T - T 0 ) ⁢ exp ⁡ ( C T ⁢ Δ ⁢ G v 2 ) ⁢ 1 T [ Equation ⁢ 3 ] Γ = ln ⁡ ( 3 ⁢ π ⁢ a 3 ⁢ A ρ s ⁢ Vk ), wherein ρs is available site density, V is a volume at a given temperature T, k is Boltzmann's constant, a is an atomic size, and A is a fitting coefficient; T is the specific healing temperature, T0 is an ideal glass transition temperature, B is a fitting coefficient, Δ ⁢ G v 2 is a free energy difference between liquid and crystalline phases, and constant C represents part of a nucleation barrier and is given by C = ( 16 ⁢ π 3 ⁢ k ) ⁢ σ 3 ⁢ f ⁡ ( θ ), wherein 16π/3 is a geometrical factor characteristic of formation of a spherical nucleus, σ is an interfacial energy between liquid and solid, and f(θ) is a catalytic factor, with a range 0≤f(θ)≤1.

heating the unused metallic glass to a temperature between 0.7 Tg and lower than Tm (melting point) at a heating rate of 1,000 K/s or higher, and then measuring the time (t) at which crystallization occurs by performing isothermal heat treatment at the heat treatment temperature; and

fitting the measured crystallization onset time (t) using Equation 3 below and graphing the results

wherein

4. The method of claim 1, wherein the step of heat-treating the metallic glass to be healed at the specific healing temperature within the healable temperature range is performed under pressure.

5. The method of claim 1, wherein the clinical cooling rate in the step of quenching the heat-treated metallic glass to be healed from the specific healing temperature at the critical cooling rate or higher is determined by Equation below: Cooling ⁢ rate ⁢ ( dT d ⁢ τ ) = - 1 / ( τ 0 ⁢ exp ⁡ ( DT 0 T - T 0 ) ⁢ DT 0 ⁢ 1 ( T - T 0 ) 2 ) [ Equation ⁢ 4 ]

wherein T is the specific healing temperature, D is a fragility index, T0 is an ideal glass transition temperature, and τ0=2.5*10−13.

6. The method of claim 1, further comprising, after the step of quenching the heat-treated metallic glass to be healed from the specific healing temperature at a critical cooling rate or higher, a step of polishing a surface of the quenched metallic glass to be healed.

7. The method of claim 1, wherein the specific healing temperature is 0.7 Tg to Tm.

8. The method of claim 1, wherein the specific healing temperature is 0.95 Tg to 1.25 Tg.

9. The method of claim 1, wherein the specific healing temperature is 1.0 Tg to 1.18 Tg.

10. The method of claim 1, wherein the specific healing temperature is 1.0 Tg to 1.15 Tg.

11. The method of claim 1, wherein a yield strength of the metallic glass to be healed is restored by 90% or more.

12. The method of claim 1, wherein an elongation of the metallic glass to be healed is restored by 90% or more.

13. The method of claim 1, wherein the metallic glass to be healed has damage before plastic deformation stage 3 (σT/εT<0 MPa/%, where σT is a compressive true stress and is given by σT=σ×(1−ε), and εT is a compressive true strain and is given by εT=−ln(1−ε), wherein σ is a true stress, and ε is a true strain) in which shear bands begin to overlap during compressive deformation.

14. The method of claim 1, wherein the metallic glass to be healed has damage equal to 90% or less of a maximum bending strain.

15. The method of claim 1, further comprising a step of repeating the step of heat-treating and the step of quenching at least once, wherein a total elongation increasing after the step of repeating is 200% or more of an elongation of the unused metallic glass.

16. A method for standardizing a metallic glass, comprising steps:

determining a temperature-dependent structural relaxation time for the metallic glass;

determining a temperature-dependent crystallization onset time for the metallic glass;

heat-treating the metallic glass at a specific healing temperature within a healable temperature range for a time satisfying Expression 1 below; and

quenching the heat-treated metallic glass from the specific healing temperature at a critical cooling rate or higher: Structural relaxation time at the specific healing temperature≤heat treatment time at the specific healing temperature≤crystallization onset time at the specific healing temperature.  [Expression 1]