INDIRECT PROCESS CONDITION MONITORING
Disclosed is a method of controlling the production of a bulk-solidifying amorphous alloy by providing a set point control system, run in conjunction with a continuous smart feedback process control system that continuously monitors the processing conditions during manufacture, and continuously updates the smart feedback control system thereby enabling the control system to learn as the process is running.
All publications, patents, and patent applications cited in this specification are hereby incorporated by reference in their entirety.
BACKGROUNDNumerous ferrous alloys (e.g., high strength steels) and non-ferrous alloys have been developed for use in heavy construction and machinery. Although these alloys provide a good combination of strength and toughness, they typically do not show adequate resistance to wear, erosion, and corrosion. Thus, they are not well-suited for use in applications in which the surfaces of these alloys are subjected to aggressive environment or abrasion. One approach to remedy this problem is to use a hard-facing material deposited onto the surface of an underlying structure/substrate to act as a protective layer. The underlying structure (e.g., steel substrate) provides the strength and structural integrity needed for the layer-substrate structure, and the hard-facing alloy protects the substrate against wear and abrasion in adverse environments. The hard-facing material also can protect the substrate against corrosion as well.
A large portion of the metallic alloys in use today are processed by solidification casting, at least initially. The metallic alloy is melted and cast into a metal or ceramic mold, where it solidifies. The mold is stripped away, and the cast metallic piece is ready for use or further processing. The as-cast structure of most materials produced during solidification and cooling depends upon the cooling rate. There is no general rule for the nature of the variation, but for the most part the structure changes only gradually with changes in cooling rate. On the other hand, for the bulk-solidifying amorphous alloys the change between the amorphous state produced by relatively rapid cooling and the crystalline state produced by relatively slower cooling is one of kind rather than degree—the two states have distinct properties.
Bulk-solidifying amorphous alloys, or bulk metallic glasses (“BMG”), are a recently developed class of metallic materials. These alloys may be solidified and cooled at relatively slow rates, and they retain the amorphous, non-crystalline (i.e., glassy) state at room temperature. This amorphous state can be highly advantageous for certain applications. If the cooling rate is not sufficiently high, crystals may form inside the alloy during cooling, so that the benefits of the amorphous state are partially or completely lost. For example, one risk with the creation of bulk amorphous alloy parts is partial crystallization due to either slow cooling or impurities in the raw material.
Bulk-solidifying amorphous alloys have been made in a variety of metallic systems. They are generally prepared by quenching from above the melting temperature to the ambient temperature. Generally, high cooling rates such as one on the order of 105° C./sec, are needed to achieve an amorphous structure. The lowest rate by which a bulk solidifying alloy can be cooled to avoid crystallization, thereby achieving and maintaining the amorphous structure during cooling, is referred to as the “critical cooling rate” for the alloy. In order to achieve a cooling rate higher than the critical cooling rate, heat has to be extracted from the sample. Thus, the thickness of articles made from amorphous alloys often becomes a limiting dimension, which is generally referred to as the “critical (casting) thickness.” A critical thickness of an amorphous alloy can be obtained by heat-flow calculations, taking into account the critical cooling rate.
Bulk-solidifying amorphous alloys can be produced by vacuum die casting, and injection molding processes. Similar to die-casting, injection molding involves heating a material to a molding temperature and forcing such heated material into a mold. Though injection molding speed may be slower than die-casting, common die-casting defects such as blowhole, cold shut, flow line, and misrun still exist in injection molding. These aforementioned defects can be related to air that is trapped within the molding during injection of the material into the die cavity.
Different vacuum die-casting and injection molding processes were developed during the 1980's and 1990's to resolve issues such as these. One type of vacuum that was discussed in vacuum die-casting and injection molding processes is classified as a “low vacuum,” which is defined as having a vacuum pressure above 1 Torr, or, in some cases, above 25 Torr. At this vacuum level, die-casting and injection molding of plastic and metals that are not sensitive to oxygen and nitrogen can be molded. However, casting or molding oxygen and nitrogen sensitive alloys using these technologies, methods, and/or this vacuum generally produces a product of poor or low quality. One example of a vacuum die casting method is described in U.S. Pat. No. 6,021,840, the disclosure of which is incorporated by reference herein in its entirety.
Methods of quality control during production of bulk-solidifying amorphous alloys, e.g., measuring the degree of crystallinity, elongation, harness, yield strength, etc., typically include a bending test, x-ray radiography, and etching. These techniques are destructive to the measurement specimens, are time consuming, and if the measured specimen is determined to be of such inferior quality to require rejection, can result in the manufacture of numerous parts that must be rejected. This leads to significant waste, and considerable increase in production cost and expense, as well as down time to correct and or adjust the processing parameters that may have caused the defective part.
Thus, there is a need to overcome the aforedescribed challenges in a manner that improves the manufacture of these materials.
SUMMARYProvided in one embodiment is a method of controlling the manufacture of a bulk-solidifying amorphous alloy that includes establishing set points for at least two process conditions selected from the group consisting of vacuum level, viscosity of melt, temperature of melt, temperature of core, cooling rate, mold dwell time, and plunger rate. The method further includes modifying one or more of the above-mentioned process conditions and determining the physical characteristics of the bulk-solidifying amorphous alloy, wherein the physical characteristics are selected from one or more of the group consisting of degree of crystallinity, hardness, elongation, and yield strength. The method includes establishing criteria for determining when a product is considered a failure based on one or more of the physical characteristics, and performing a multi-variable statistical analysis to determine which process condition, or combination of process conditions indicate a product failure. The method controls the method of manufacturing a bulk-solidifying amorphous alloy by rejecting a part that was fabricated when at least one process condition is outside the set point, and at the same time continuously monitoring the at least two process conditions, and if the process conditions indicate a product failure even though within the set points, tagging the product or products made using those process conditions, measuring the physical characteristics of the product or products, and updating the process conditions that indicate a product failure depending on the results of measuring the physical characteristics of the tagged product or products.
The process control method therefore provides a conventional set point control system, run in conjunction with a continuous smart feedback process control system that continuously monitors the processing conditions during manufacture, and continuously updates the smart feedback control system thereby enabling the control system to learn as the process is running.
All publications, patents, and patent applications cited in this Specification are hereby incorporated by reference in their entirety.
The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “a polymer resin” means one polymer resin or more than one polymer resin. Any ranges cited herein are inclusive. The terms “substantially” and “about” used throughout this Specification are used to describe and account for small fluctuations. For example, they can refer to less than or equal to +5%, such as less than or equal to +2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.
Bulk-solidifying amorphous alloys, or bulk metallic glasses (“BMG”), are a recently developed class of metallic materials. These alloys may be solidified and cooled at relatively slow rates, and they retain the amorphous, non-crystalline (i.e., glassy) state at room temperature. Amorphous alloys have many superior properties than their crystalline counterparts. However, if the cooling rate is not sufficiently high, crystals may form inside the alloy during cooling, so that the benefits of the amorphous state can be lost. For example, one challenge with the fabrication of bulk amorphous alloy parts is partial crystallization of the parts due to either slow cooling or impurities in the raw alloy material. As a high degree of amorphicity (and, conversely, a low degree of crystallinity) is desirable in BMG parts, there is a need to develop methods for casting BMG parts having controlled amount of amorphicity.
Even though there is no liquid/crystallization transformation for a bulk solidifying amorphous metal, a “melting temperature” Tm may be defined as the thermodynamic liquidus temperature of the corresponding crystalline phase. Under this regime, the viscosity of bulk-solidifying amorphous alloys at the melting temperature could lie in the range of about 0.1 poise to about 10,000 poise, and even sometimes under 0.01 poise. A lower viscosity at the “melting temperature” would provide faster and complete filling of intricate portions of the shell/mold with a bulk solidifying amorphous metal for forming the BMG parts. Furthermore, the cooling rate of the molten metal to form a BMG part has to such that the time-temperature profile during cooling does not traverse through the nose-shaped region bounding the crystallized region in the TTT diagram of
The supercooled liquid region, the temperature region between Tg and Tx is a manifestation of the extraordinary stability against crystallization of bulk solidification alloys. In this temperature region the bulk solidifying alloy can exist as a high viscous liquid. The viscosity of the bulk solidifying alloy in the supercooled liquid region can vary between 1012 Pa s at the glass transition temperature down to 105 Pa s at the crystallization temperature, the high temperature limit of the supercooled liquid region. Liquids with such viscosities can undergo substantial plastic strain under an applied pressure. The embodiments herein make use of the large plastic formability in the supercooled liquid region as a forming and separating method.
One needs to clarify something about Tx. Technically, the nose-shaped curve shown in the TTT diagram describes Tx as a function of temperature and time. Thus, regardless of the trajectory that one takes while heating or cooling a metal alloy, when one hits the TTT curve, one has reached Tx. In
The schematic TTT diagram of
Typical differential scanning calorimeter (DSC) heating curves of bulk-solidifying amorphous alloys taken at a heating rate of 20 C/min describe, for the most part, a particular trajectory across the TTT data where one would likely see a Tg at a certain temperature, a Tx when the DSC heating ramp crosses the TTT crystallization onset, and eventually melting peaks when the same trajectory crosses the temperature range for melting. If one heats a bulk-solidifying amorphous alloy at a rapid heating rate as shown by the ramp up portion of trajectories (2), (3) and (4) in
The term “phase” herein can refer to one that can be found in a thermodynamic phase diagram. A phase is a region of space (e.g., a thermodynamic system) throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, chemical composition and lattice periodicity. A simple description of a phase is a region of material that is chemically uniform, physically distinct, and/or mechanically separable. For example, in a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, and the humid air over the water is a third phase. The glass of the jar is another separate phase. A phase can refer to a solid solution, which can be a binary, tertiary, quaternary, or more, solution, or a compound, such as an intermetallic compound. As another example, an amorphous phase is distinct from a crystalline phase.
Metal, Transition Metal, and Non-MetalThe term “metal” refers to an electropositive chemical element. The term “element” in this Specification refers generally to an element that can be found in a Periodic Table. Physically, a metal atom in the ground state contains a partially filled band with an empty state close to an occupied state. The term “transition metal” is any of the metallic elements within Groups 3 to 12 in the Periodic Table that have an incomplete inner electron shell and that serve as transitional links between the most and the least electropositive in a series of elements. Transition metals are characterized by multiple valences, colored compounds, and the ability to form stable complex ions. The term “nonmetal” refers to a chemical element that does not have the capacity to lose electrons and form a positive ion.
Depending on the application, any suitable nonmetal elements, or their combinations, can be used. The alloy (or “alloy composition”) can comprise multiple nonmetal elements, such as at least two, at least three, at least four, or more, nonmetal elements. A nonmetal element can be any element that is found in Groups 13-17 in the Periodic Table. For example, a nonmetal element can be any one of F, Cl, Br, I, At, O, S, Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and B. Occasionally, a nonmetal element can also refer to certain metalloids (e.g., B, Si, Ge, As, Sb, Te, and Po) in Groups 13-17. In one embodiment, the nonmetal elements can include B, Si, C, P, or combinations thereof. Accordingly, for example, the alloy can comprise a boride, a carbide, or both.
A transition metal element can be any of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, ununnilium, unununium, and ununbium. In one embodiment, a BMG containing a transition metal element can have at least one of Sc, Y, La, Ac, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, and Hg. Depending on the application, any suitable transitional metal elements, or their combinations, can be used. The alloy composition can comprise multiple transitional metal elements, such as at least two, at least three, at least four, or more, transitional metal elements.
The presently described alloy or alloy “sample” or “specimen” alloy can have any shape or size. For example, the alloy can have a shape of a particulate, which can have a shape such as spherical, ellipsoid, wire-like, rod-like, sheet-like, flake-like, or an irregular shape. The particulate can have any size. For example, it can have an average diameter of between about 1 micron and about 100 microns, such as between about 5 microns and about 80 microns, such as between about 10 microns and about 60 microns, such as between about 15 microns and about 50 microns, such as between about 15 microns and about 45 microns, such as between about 20 microns and about 40 microns, such as between about 25 microns and about 35 microns. For example, in one embodiment, the average diameter of the particulate is between about 25 microns and about 44 microns. In some embodiments, smaller particulates, such as those in the nanometer range, or larger particulates, such as those bigger than 100 microns, can be used.
The alloy sample or specimen can also be of a much larger dimension. For example, it can be a bulk structural component, such as an ingot, housing/casing of an electronic device or even a portion of a structural component that has dimensions in the millimeter, centimeter, or meter range.
Solid SolutionThe term “solid solution” refers to a solid form of a solution. The term “solution” refers to a mixture of two or more substances, which may be solids, liquids, gases, or a combination of these. The mixture can be homogeneous or heterogeneous. The term “mixture” is a composition of two or more substances that are combined with each other and are generally capable of being separated. Generally, the two or more substances are not chemically combined with each other.
AlloyIn some embodiments, the alloy composition described herein can be fully alloyed. In one embodiment, an “alloy” refers to a homogeneous mixture or solid solution of two or more metals, the atoms of one replacing or occupying interstitial positions between the atoms of the other; for example, brass is an alloy of zinc and copper. An alloy, in contrast to a composite, can refer to a partial or complete solid solution of one or more elements in a metal matrix, such as one or more compounds in a metallic matrix. The term alloy herein can refer to both a complete solid solution alloy that can give single solid phase microstructure and a partial solution that can give two or more phases. An alloy composition described herein can refer to one comprising an alloy or one comprising an alloy-containing composite.
Thus, a fully alloyed alloy can have a homogenous distribution of the constituents, be it a solid solution phase, a compound phase, or both. The term “fully alloyed” used herein can account for minor variations within the error tolerance. For example, it can refer to at least 90% alloyed, such as at least 95% alloyed, such as at least 99% alloyed, such as at least 99.5% alloyed, such as at least 99.9% alloyed. The percentage herein can refer to either volume percent or weight percentage, depending on the context. These percentages can be balanced by impurities, which can be in terms of composition or phases that are not a part of the alloy.
Amorphous or Non-Crystalline SolidAn “amorphous” or “non-crystalline solid” is a solid that lacks lattice periodicity, which is characteristic of a crystal. As used herein, an “amorphous solid” includes “glass” which is an amorphous solid that softens and transforms into a liquid-like state upon heating through the glass transition. Generally, amorphous materials lack the long-range order characteristic of a crystal, though they can possess some short-range order at the atomic length scale due to the nature of chemical bonding. The distinction between amorphous solids and crystalline solids can be made based on lattice periodicity as determined by structural characterization techniques such as x-ray diffraction and transmission electron microscopy.
The terms “order” and “disorder” designate the presence or absence of some symmetry or correlation in a many-particle system. The terms “long-range order” and “short-range order” distinguish order in materials based on length scales.
The strictest form of order in a solid is lattice periodicity: a certain pattern (the arrangement of atoms in a unit cell) is repeated again and again to form a translationally invariant tiling of space. This is the defining property of a crystal. Possible symmetries have been classified in 14 Bravais lattices and 230 space groups.
Lattice periodicity implies long-range order. If only one unit cell is known, then by virtue of the translational symmetry it is possible to accurately predict all atomic positions at arbitrary distances. The converse is generally true, except, for example, in quasi-crystals that have perfectly deterministic tilings but do not possess lattice periodicity.
Long-range order characterizes physical systems in which remote portions of the same sample exhibit correlated behavior. This can be expressed as a correlation function, namely the spin-spin correlation function:
In the above function, s is the spin quantum number and x is the distance function within the particular system. This function is equal to unity when x=x′ and decreases as the distance |x−x′| increases. Typically, it decays exponentially to zero at large distances, and the system is considered to be disordered. If, however, the correlation function decays to a constant value at large |x−x′|, then the system can be said to possess long-range order. If it decays to zero as a power of the distance, then it can be called quasi-long-range order. Note that what constitutes a large value of |x−x′| is relative.
A system can be said to present quenched disorder when some parameters defining its behavior are random variables that do not evolve with time (i.e., they are quenched or frozen)—e.g., spin glasses. It is opposite to annealed disorder, where the random variables are allowed to evolve themselves. Embodiments herein include systems comprising quenched disorder.
The alloy described herein can be crystalline, partially crystalline, amorphous, or substantially amorphous. For example, the alloy sample/specimen can include at least some crystallinity, with grains/crystals having sizes in the nanometer and/or micrometer ranges. Alternatively, the alloy can be substantially amorphous, such as fully amorphous. In one embodiment, the alloy composition is at least substantially not amorphous, such as being substantially crystalline, such as being entirely crystalline.
In one embodiment, the presence of a crystal or a plurality of crystals in an otherwise amorphous alloy can be construed as a “crystalline phase” therein. The degree of crystallinity (or “crystallinity” for short in some embodiments) of an alloy can refer to the amount of the crystalline phase present in the alloy. The degree can refer to, for example, a fraction of crystals present in the alloy. The fraction can refer to volume fraction or weight fraction, depending on the context. A measure of how “amorphous” an amorphous alloy is can be amorphicity. Amorphicity can be measured in terms of a degree of crystallinity. For example, in one embodiment, an alloy having a low degree of crystallinity can be said to have a high degree of amorphicity. In one embodiment, for example, an alloy having 60 vol % crystalline phase can have a 40 vol % amorphous phase.
Amorphous Alloy or Amorphous MetalAn “amorphous alloy” is an alloy having an amorphous content of more than 50% by volume, preferably more than 90% by volume of amorphous content, more preferably more than 95% by volume of amorphous content, and most preferably more than 99% to almost 100% by volume of amorphous content. Note that, as described above, an alloy high in amorphicity is equivalently low in degree of crystallinity. An “amorphous metal” is an amorphous metal material with a disordered atomic-scale structure. In contrast to most metals, which are crystalline and therefore have a highly ordered arrangement of atoms, amorphous alloys are non-crystalline. Materials in which such a disordered structure is produced directly from the liquid state during cooling are sometimes referred to as “glasses.” Accordingly, amorphous metals are commonly referred to as “metallic glasses” or “glassy metals.” In one embodiment, a bulk metallic glass (“BMG”) can refer to an alloy, of which the microstructure is at least partially amorphous. However, there are several ways besides extremely rapid cooling to produce amorphous metals, including physical vapor deposition, solid-state reaction, ion irradiation, melt spinning, and mechanical alloying. Amorphous alloys can be a single class of materials, regardless of how they are prepared.
Amorphous metals can be produced through a variety of quick-cooling methods. For instance, amorphous metals can be produced by sputtering molten metal onto a spinning metal disk. The rapid cooling, on the order of millions of degrees a second, can be too fast for crystals to form, and the material is thus “locked in” a glassy state. Also, amorphous metals/alloys can be produced with critical cooling rates low enough to allow formation of amorphous structures in thick layers—e.g., bulk metallic glasses.
The terms “bulk metallic glass” (“BMG”), bulk amorphous alloy (“BAA”), and bulk solidifying amorphous alloy are used interchangeably herein. They refer to amorphous alloys having the smallest dimension at least in the millimeter range. For example, the dimension can be at least about 0.5 mm, such as at least about 1 mm, such as at least about 2 mm, such as at least about 4 mm, such as at least about 5 mm, such as at least about 6 mm, such as at least about 8 mm, such as at least about 10 mm, such as at least about 12 mm. Depending on the geometry, the dimension can refer to the diameter, radius, thickness, width, length, etc. A BMG can also be a metallic glass having at least one dimension in the centimeter range, such as at least about 1.0 cm, such as at least about 2.0 cm, such as at least about 5.0 cm, such as at least about 10.0 cm. In some embodiments, a BMG can have at least one dimension at least in the meter range. A BMG can take any of the shapes or forms described above, as related to a metallic glass. Accordingly, a BMG described herein in some embodiments can be different from a thin film made by a conventional deposition technique in one important aspect—the former can be of a much larger dimension than the latter.
Amorphous metals can be an alloy rather than a pure metal. The alloys may contain atoms of significantly different sizes, leading to low free volume (and therefore having viscosity up to orders of magnitude higher than other metals and alloys) in a molten state. The viscosity prevents the atoms from moving enough to form an ordered lattice. The material structure may result in low shrinkage during cooling and resistance to plastic deformation. The absence of grain boundaries, the weak spots of crystalline materials in some cases, may, for example, lead to better resistance to wear and corrosion. In one embodiment, amorphous metals, while technically glasses, may also be much tougher and less brittle than oxide glasses and ceramics.
Thermal conductivity of amorphous materials may be lower than that of their crystalline counterparts. To achieve formation of an amorphous structure even during slower cooling, the alloy may be made of three or more components, leading to complex crystal units with higher potential energy and lower probability of formation. The formation of amorphous alloy can depend on several factors: the composition of the components of the alloy; the atomic radius of the components (preferably with a significant difference of over 12% to achieve high packing density and low free volume); and the negative heat of mixing the combination of components, inhibiting crystal nucleation and prolonging the time the molten metal stays in a supercooled state. However, as the formation of an amorphous alloy is based on many different variables, it can be difficult to make a prior determination of whether an alloy composition would form an amorphous alloy.
Amorphous alloys, for example, of boron, silicon, phosphorus, and other glass formers with magnetic metals (iron, cobalt, nickel) may be magnetic, with low coercivity and high electrical resistance. The high resistance leads to low losses by eddy currents when subjected to alternating magnetic fields, a property useful, for example, as transformer magnetic cores.
Amorphous alloys may have a variety of potentially useful properties. In particular, they tend to be stronger than crystalline alloys of similar chemical composition, and they can sustain larger reversible (“elastic”) deformations than crystalline alloys. Amorphous metals derive their strength directly from their non-crystalline structure, which can have none of the defects (such as dislocations) that limit the strength of crystalline alloys. For example, one modern amorphous metal, known as Vitreloy™, has a tensile strength that is almost twice that of high-grade titanium. In some embodiments, metallic glasses at room temperature are not ductile and tend to fail suddenly when loaded in tension, which limits the material applicability in reliability-critical applications, as the impending failure is not evident. Therefore, to overcome this challenge, metal matrix composite materials having a metallic glass matrix containing dendritic particles or fibers of a ductile crystalline metal can be used. Alternatively, a BMG low in element(s) that tend to cause embitterment (e.g., Ni) can be used. For example, a Ni-free BMG can be used to improve the ductility of the BMG.
Another useful property of bulk amorphous alloys is that they can be true glasses; in other words, they can soften and flow upon heating. This can allow for easy processing, such as by injection molding, in much the same way as polymers. As a result, amorphous alloys can be used for making sports equipment, medical devices, electronic components and equipment, and thin films. Thin films of amorphous metals can be deposited as protective coatings via a high velocity oxygen fuel technique.
A material can have an amorphous phase, a crystalline phase, or both. The amorphous and crystalline phases can have the same chemical composition and differ only in the microstructure—i.e., one amorphous and the other crystalline. Microstructure in one embodiment refers to the structure of a material as revealed by a microscope at 25× magnification or higher. Alternatively, the two phases can have different chemical compositions and microstructures. For example, a composition can be partially amorphous, substantially amorphous, or completely amorphous.
As described above, the degree of amorphicity (and conversely the degree of crystallinity) can be measured by fraction of crystals present in the alloy. The degree can refer to volume fraction of weight fraction of the crystalline phase present in the alloy. A partially amorphous composition can refer to a composition of at least about 5 vol % of which is of an amorphous phase, such as at least about 10 vol %, such as at least about 20 vol %, such as at least about 40 vol %, such as at least about 60 vol %, such as at least about 80 vol %, such as at least about 90 vol %. The terms “substantially” and “about” have been defined elsewhere in this application. Accordingly, a composition that is at least substantially amorphous can refer to one of which at least about 90 vol % is amorphous, such as at least about 95 vol %, such as at least about 98 vol %, such as at least about 99 vol %, such as at least about 99.5 vol %, such as at least about 99.8 vol %, such as at least about 99.9 vol %. In one embodiment, a substantially amorphous composition can have some incidental, insignificant amount of crystalline phase present therein.
In one embodiment, an amorphous alloy composition can be homogeneous with respect to the amorphous phase. A substance that is uniform in composition is homogeneous. This is in contrast to a substance that is heterogeneous. The term “composition” refers to the chemical composition and/or microstructure in the substance. A substance is homogeneous when a volume of the substance is divided in half and both halves have substantially the same composition. For example, a particulate suspension is homogeneous when a volume of the particulate suspension is divided in half and both halves have substantially the same volume of particles. However, it might be possible to see the individual particles under a microscope. Another example of a homogeneous substance is air where different ingredients therein are equally suspended, though the particles, gases and liquids in air can be analyzed separately or separated from air.
A composition that is homogeneous with respect to an amorphous alloy can refer to one having an amorphous phase substantially uniformly distributed throughout its microstructure. In other words, the composition macroscopically comprises a substantially uniformly distributed amorphous alloy throughout the composition. In an alternative embodiment, the composition can be of a composite, having an amorphous phase having therein a non-amorphous phase. The non-amorphous phase can be a crystal or a plurality of crystals. The crystals can be in the form of particulates of any shape, such as spherical, ellipsoid, wire-like, rod-like, sheet-like, flake-like, or an irregular shape. In one embodiment, it can have a dendritic form. For example, an at least partially amorphous composite composition can have a crystalline phase in the shape of dendrites dispersed in an amorphous phase matrix; the dispersion can be uniform or non-uniform, and the amorphous phase and the crystalline phase can have the same or a different chemical composition. In one embodiment, they have substantially the same chemical composition. In another embodiment, the crystalline phase can be more ductile than the BMG phase.
The methods described herein can be applicable to any type of amorphous alloy. Similarly, the amorphous alloy described herein as a constituent of a composition or article can be of any type. The amorphous alloy can comprise the element Zr, Hf, Ti, Cu, Ni, Pt, Pd, Fe, Mg, Au, La, Ag, Al, Mo, Nb, Be, or combinations thereof. Namely, the alloy can include any combination of these elements in its chemical formula or chemical composition. The elements can be present at different weight or volume percentages. For example, an iron “based” alloy can refer to an alloy having a non-insignificant weight percentage of iron present therein, the weight percent can be, for example, at least about 20 wt %, such as at least about 40 wt %, such as at least about 50 wt %, such as at least about 60 wt %, such as at least about 80 wt %. Alternatively, in one embodiment, the above-described percentages can be volume percentages, instead of weight percentages. Accordingly, an amorphous alloy can be zirconium-based, titanium-based, platinum-based, palladium-based, gold-based, silver-based, copper-based, iron-based, nickel-based, aluminum-based, molybdenum-based, and the like. The alloy can also be free of any of the aforementioned elements to suit a particular purpose. For example, in some embodiments, the alloy, or the composition including the alloy, can be substantially free of nickel, aluminum, titanium, beryllium, or combinations thereof. In one embodiment, the alloy or the composite is completely free of nickel, aluminum, titanium, beryllium, or combinations thereof.
For example, the amorphous alloy can have the formula (Zr, Ti)a(Ni, Cu, Fe)b(Be, Al, Si, B)c, wherein a, b, and c each represents a weight or atomic percentage. In one embodiment, a is in the range of from 30 to 75, b is in the range of from 5 to 60, and c is in the range of from 0 to 50 in atomic percentages. Alternatively, the amorphous alloy can have the formula (Zr, Ti)a(Ni, Cu)b(Be)c, wherein a, b, and c each represents a weight or atomic percentage. In one embodiment, a is in the range of from 40 to 75, b is in the range of from 5 to 50, and c is in the range of from 5 to 50 in atomic percentages. The alloy can also have the formula (Zr, Ti)a(Ni, Cu)b(Be)c, wherein a, b, and c each represents a weight or atomic percentage. In one embodiment, a is in the range of from 45 to 65, b is in the range of from 7.5 to 35, and c is in the range of from 10 to 37.5 in atomic percentages. Alternatively, the alloy can have the formula (Zr)a(Nb, Ti)b(Ni, Cu)c(Al)d, wherein a, b, c, and d each represents a weight or atomic percentage. In one embodiment, a is in the range of from 45 to 65, b is in the range of from 0 to 10, c is in the range of from 20 to 40 and d is in the range of from 7.5 to 15 in atomic percentages. One exemplary embodiment of the aforedescribed alloy system is a Zr—Ti—Ni—Cu—Be based amorphous alloy under the trade name Vitreloy™, such as Vitreloy-1 and Vitreloy-101, as fabricated by Liquidmetal Technologies, CA, USA. Some examples of amorphous alloys of the different systems are provided in Table 1 and Table 2.
Other exemplary ferrous metal-based alloys include compositions such as those disclosed in U.S. Patent Application Publication Nos. 2007/0079907 and 2008/0118387. These compositions include the Fe(Mn, Co, Ni, Cu) (C, Si, B, P, Al) system, wherein the Fe content is from 60 to 75 atomic percentage, the total of (Mn, Co, Ni, Cu) is in the range of from 5 to 25 atomic percentage, and the total of (C, Si, B, P, Al) is in the range of from 8 to 20 atomic percentage, as well as the exemplary composition Fe48Cr15Mo14Y2C15B6. They also include the alloy systems described by Fe—Cr—Mo—(Y,Ln)-C-B, Co—Cr—Mo-Ln-C-B, Fe—Mn—Cr—Mo—(Y,Ln)-C-B, (Fe, Cr, Co)-(Mo,Mn)-(C,B)-Y, Fe—(Co,Ni)-(Zr,Nb,Ta)-(Mo,W)-B, Fe—(Al,Ga)-(P,C,B,Si,Ge), Fe—(Co, Cr,Mo,Ga,Sb)-P-B-C, (Fe, Co)-B—Si—Nb alloys, and Fe—(Cr—Mo)-(C,B)—Tm, where Ln denotes a lanthanide element and Tm denotes a transition metal element. Furthermore, the amorphous alloy can also be one of the exemplary compositions Fe80P12.5C5B2.5, Fe80P11C5B2.5Si1.5, Fe74.5Mo5.5P12.5C5B2.5, Fe74.5Mo5.5P11C5B2.5Si1.5, Fe70Mo5Ni5P12.5C5B2.5, Fe70Mo5Ni5P11C5B2.5Si1.5, Fe68Mo5Ni5Cr2P12.5C5B2.5, and Fe68Mo5Ni5Cr2P11C5B2.5Si1.5, described in U.S. Patent Application Publication No. 2010/0300148.
The amorphous alloys can also be ferrous alloys, such as (Fe, Ni, Co) based alloys. Examples of such compositions are disclosed in U.S. Pat. Nos. 6,325,868; 5,288,344; 5,368,659; 5,618,359; and 5,735,975, Inoue et al., Appl. Phys. Lett., Volume 71, p 464 (1997), Shen et al., Mater. Trans., JIM, Volume 42, p 2136 (2001), and Japanese Patent Application No. 200126277 (Pub. No. 2001303218 A). One exemplary composition is Fe72A15Ga2P11C6B4. Another example is Fe72A17Zr1 0Mo5W2B15. Another iron-based alloy system that can be used in the coating herein is disclosed in U.S. Patent Application Publication No. 2010/0084052, wherein the amorphous metal contains, for example, manganese (1 to 3 atomic %), yttrium (0.1 to 10 atomic %), and silicon (0.3 to 3.1 atomic %) in the range of composition given in parentheses; and that contains the following elements in the specified range of composition given in parentheses: chromium (15 to 20 atomic %), molybdenum (2 to 15 atomic %), tungsten (1 to 3 atomic %), boron (5 to 16 atomic %), carbon (3 to 16 atomic %), and the balance iron.
The aforedescribed amorphous alloy systems can further include additional elements, such as additional transition metal elements, including Nb, Cr, V, and Co. The additional elements can be present at less than or equal to about 30 wt %, such as less than or equal to about 20 wt %, such as less than or equal to about 10 wt %, such as less than or equal to about 5 wt %. In one embodiment, the additional, optional element is at least one of cobalt, manganese, zirconium, tantalum, niobium, tungsten, yttrium, titanium, vanadium and hafnium to form carbides and further improve wear and corrosion resistance. Further optional elements may include phosphorous, germanium and arsenic, totaling up to about 2%, and preferably less than 1%, to reduce melting point. Otherwise incidental impurities should be less than about 2% and preferably 0.5%.
In some embodiments, a composition having an amorphous alloy can include a small amount of impurities. The impurity elements can be intentionally added to modify the properties of the composition, such as improving the mechanical properties (e.g., hardness, strength, fracture mechanism, etc.) and/or improving the corrosion resistance. Alternatively, the impurities can be present as inevitable, incidental impurities, such as those obtained as a byproduct of processing and manufacturing. The impurities can be less than or equal to about 10 wt %, such as about 5 wt %, such as about 2 wt %, such as about 1 wt %, such as about 0.5 wt %, such as about 0.1 wt %. In some embodiments, these percentages can be volume percentages instead of weight percentages. In one embodiment, the alloy sample/composition consists essentially of the amorphous alloy (with only a small incidental amount of impurities). In another embodiment, the composition includes the amorphous alloy (with no observable trace of impurities).
Electronic DevicesThe embodiments herein can be valuable in the fabrication of electronic devices using a BMG. An electronic device herein can refer to any electronic device known in the art. For example, it can be a telephone, such as a cell phone, and a land-line phone, or any communication device, such as a smart phone, including, for example an iPhone™, and an electronic email sending/receiving device. It can be a part of a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad™), and a computer monitor. It can also be an entertainment device, including a portable DVD player, conventional DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod™), etc. It can also be a part of a device that provides control, such as controlling the streaming of images, videos, sounds (e.g., Apple TV™), or it can be a remote control for an electronic device. It can be a part of a computer or its accessories, such as the hard drive tower housing or casing, laptop housing, laptop keyboard, laptop track pad, desktop keyboard, mouse, and speaker. The article can also be applied to a device such as a watch or a clock.
EmbodimentsProvided in one embodiment is a method of controlling the manufacture of a bulk-solidifying amorphous alloy that includes establishing set points for at least two process conditions selected from the group consisting of vacuum level, viscosity of melt, temperature of melt, temperature of core, cooling rate, mold dwell time, and plunger rate. The method further includes modifying one or more of the above-mentioned process conditions and determining the physical characteristics of the bulk-solidifying amorphous alloy, wherein the physical characteristics are selected from one or more of the group consisting of degree of crystallinity, hardness, elongation, and yield strength. The method includes establishing criteria for determining when a product is considered a failure based on one or more of the physical characteristics, and performing a multi-variable statistical analysis to determine which process condition, or combination of process conditions indicate a product failure. The method controls the method of manufacturing a bulk-solidifying amorphous alloy by rejecting a part that was fabricated when at least one process condition is outside the set point, and at the same time continuously monitoring the at least two process conditions, and if the process conditions indicate a product failure even though within the set points, tagging the product or products made using those process conditions, measuring the physical characteristics of the product or products, and updating the process conditions that indicate a product failure depending on the results of measuring the physical characteristics of the tagged product or products.
The method is particularly suitable for use in controlling the manufacture of bulk-solidifying amorphous alloys using a vacuum die casting method, or injection molding. These methods can be automated and run at relatively high manufacturing speeds to produce high quality bulk-solidifying amorphous alloy parts that find utility in a wide variety of applications. Described below are two exemplary vacuum mold die casting operations that can be controlled in accordance with the embodiments.
Vacuum Die Casting ProcessesSystems that are used to mold materials such as metals or alloys may implement a vacuum when forcing molten material into a die cavity.
The meltable material can be received in the melt zone in any number of forms. For example, the meltable material may be provided into melt zone 12 in the form of an ingot (solid state—shown in dashed lines in
Melt zone 12 includes a melting mechanism configured to receive meltable material and to hold the material as it is heated to a molten state. The melting mechanism may be in the form of a vessel 20, for example, that has a body 22 for receiving meltable material and configured to melt the material therein.
Vessel 20 may also have an inlet for inputting material (e.g., feedstock) into a receiving or melting portion 24 of its body. In the embodiment shown in
In an embodiment, body 22 and/or its melting portion 24 may comprise substantially rounded and/or smooth surfaces. For example, a surface of melting portion 24 may be formed in an arc shape. However, the shape and/or surfaces of body 22 are not meant to be limiting. Body 22 may be an integral structure, or formed from separate parts that are joined or machined together. Body 22 may be formed from any number of materials (e.g., copper, silver), include one or more coatings, and/or configurations or designs. In an embodiment, body 22 of vessel 20 is formed from a material that does not give off or transfer contaminants to the meltable/molten material. For example, one or more surfaces may have recesses or grooves therein.
The body 22 of vessel 20 may be configured to receive the plunger rod therethrough in a horizontal direction to move the molten material. That is, in an embodiment, the melting mechanism is on the same axis as the plunger rod, and the body can be configured and/or sized to receive at least part of the plunger rod. Thus, plunger rod 14 can be configured to move molten material (after heating/melting) from the vessel by moving substantially through vessel 20, and into mold 16. Referencing the illustrated embodiment of system 10 in
To heat melt zone 12 and melt the meltable material received in vessel 20, system 10 also includes a heat source that is used to heat and melt the meltable material. At least melting portion 24 of the vessel, if not substantially the entire body 22 itself, is configured to be heated such that the material received therein is melted. Heating can be accomplished using, for example, an induction source 26 positioned within melt zone 12 that is configured to melt the meltable material. In an embodiment, induction source 26 may be positioned adjacent body 22 of vessel 20. For example, as shown in
In one embodiment, the vessel 20 is a temperature regulated vessel. Such a vessel may include one or more temperature regulating lines, such as cooling line(s) 25 shown in
For example, cooling line(s) 25 may be positioned relative to melting portion 24 such that material thereon is melted and the vessel temperature is regulated (i.e., heat is absorbed, and the vessel is cooled). For example, in the illustrative embodiment shown in
Other components that may be present in the system 10 include a temperature sensor 27 that can be mounted on, in, or near vessel to sense, measure, and report the temperature of the melt (e.g., surface temperature of the melt, core temperature of the melt, or both). The system 10 also my include an optional cooling system 29 that may be used in addition to cooling line(s) 25. The system 10 also may include controller 300, which will be described in more detail below with reference to the control system used to control the process carried out by system 10.
After the material is melted in the vessel 20, plunger 14 may be used to force the molten material from the vessel 20 and into a mold 16 for molding into an object, a part or a piece. In instances wherein the meltable material is an alloy, such as an amorphous alloy, the mold 16 is configured to form a molded bulk amorphous alloy object, part, or piece. Mold 16 may have an inlet for receiving molten material therethrough. An output of the vessel 20 and an inlet of the mold 16 can be provided in-line and on a horizontal axis such that plunger rod 14 is moved in a horizontal direction through body 22 of the vessel to eject molten material and into the mold 16 via its inlet.
As previously noted, systems such as injection molding system 10 that are used to mold materials such as metals or alloys may implement a vacuum when forcing molten material into a mold or die cavity. Injection molding system 10 can further include at least one vacuum source 38 or pump that is configured to apply vacuum pressure to at least melt zone 12 and mold 16. The vacuum pressure may be applied to at least the parts of the injection molding system 10 used to melt, move or transfer, and mold the material therein. For example, the vessel 20, transfer sleeve 30, and plunger rod 14 may all be under vacuum pressure and/or enclosed in a vacuum chamber.
In an embodiment, mold 16 is a vacuum mold that is an enclosed structure configured to regulate vacuum pressure (e.g., via a valve 33) therein when molding materials.
Generally, first plate 32 may be connected to transfer sleeve 30. In accordance with an embodiment, plunger rod 14 is configured to move molten material from vessel 20, through a transfer sleeve 30, and into mold 16. Transfer sleeve 30 (sometimes referred to as a cold sleeve or injection sleeve in the art) may be provided between melt zone 12 and mold 16. Transfer sleeve 30 has an opening that is configured to receive and allow transfer of the molten material therethrough and into mold 16 (using plunger 14). Its opening may be provided in a horizontal direction along the horizontal axis (e.g., X axis). The transfer sleeve need not be a cold chamber. In an embodiment, at least plunger rod 14, vessel 20 (e.g., its receiving or melting portion), and opening of the transfer sleeve 30 are provided in-line and on a horizontal axis, such that plunger rod 14 can be moved in a horizontal direction through vessel 20 in order to move the molten material into (and subsequently through) the opening of transfer sleeve 30.
First plate 32 can include the inlet of the mold 16 such that molten material can be inserted therein. Molten material can be pushed in a horizontal direction through transfer sleeve 30 and into the mold cavity(ies) via the inlet between the first and second plates, 32 and 34. During molding of the material, the at least first and second plates 32 and 34 are configured to substantially eliminate exposure of the material (e.g., amorphous alloy) therebetween to at least oxygen and nitrogen. Specifically, a vacuum is applied such that atmospheric air is substantially eliminated from within the plates 32 and 34 and their cavities 42 and 44. A vacuum pressure is applied to an inside of vacuum mold 16 using at least one vacuum source that is connected via vacuum lines. For example, the vacuum pressure or level on the system can be held between 1×10−1 to 1×10−4 Torr during the melting and subsequent molding cycle. In another embodiment, the vacuum level is maintained between 1×10−2 to about 1×10−4 Torr during the melting and molding process. Of course, other pressure levels or ranges may be used, such as 1×10−9 Torr to about 1×10−3 Torr, and/or 1×10−3 Torr to about 0.1 Torr. Embodiments described herein are designed to suitably control the vacuum pressure levels during formation of the bulk-solidifying amorphous alloy part, and will be described in more detail below.
The vacuum ejector box 36 is positioned adjacent at least first and second plates 32 and 34. In an embodiment, the ejector box is enclosed and is configured to be vacuum sealed by vacuum pressure from vacuum source 38 (pump). In an embodiment, included in the enclosed vacuum ejector box 36 has an ejector mechanism 46 configured to eject molded (amorphous alloy) material from the mold cavity between the at least first and second plates 32 and 34. Ejector mechanism 46 can be vacuum sealed within the enclosed vacuum ejector box 36 and any adjacent plate or interface sealed with the open face of the box 36. Ejector mechanism 46 may include an ejector plate 66, in accordance with an embodiment. The ejector plate is configured to move within the enclosed ejector box to eject the molded material from the mold 16. More specifically, ejector plate 66 may have one or more (multiple) ejector pins (not shown) extending in a linear direction therefrom. Upon movement of ejector plate 66, the ejector pins are moved relatively to eject the molded material from the mold cavity of mold 16.
The ejection mechanism may be associated with or connected to an actuation mechanism (not shown) that is configured to be actuated in order to eject the molded material or part (e.g., after first and second parts 32 and 34 are moved horizontally and relatively away from each other, after vacuum pressure between the plates 32 and 34 is released). The ejector pins may be configured to push molded material away from cavity 44, for example.
The illustrated mold 16 is one example of a mold 16 that can be used with injection molding system 10. It should be understood that alternate types of molds also may be employed. For example, any number of additional plates may be provided between and/or adjacent the first and second plates to form the mold. Molds known as “A” series, “B” series, and/or “X” series molds, for example, may be implemented in injection molding system 10.
Generally, the injection molding system 10 may be operated in the following manner: The vacuum is applied to the injection molding system 10. Meltable material (e.g., amorphous alloy or BMG) is loaded into a feed mechanism (e.g., loading port 18) while held under vacuum, and a single ingot (feedstock) is loaded, inserted and received into the melt zone 12 into the vessel 20 (surrounded by the induction coil 26). The injection molding machine “nozzle” stroke or plunger 14 can be used to move the material, as needed, into the melting portion 24 of the vessel 20. The material is heated through the induction process. In an embodiment, the injection molding machine controls the temperature through a closed loop system, which will stabilize the material at a specific temperature (e.g., using a temperature sensor 27 and a controller 300).
In another embodiment, the injection molding machine controls the temperature through an open loop system. During heating/melting, a cooling system can be activated to flow a (cooling) liquid in any cooling line(s) of the vessel 20. Once the temperature is achieved and maintained to melt the meltable material, the machine will then begin the injection of the molten material from vessel 20, through transfer sleeve 30, and into vacuum mold 16 by moving in a horizontal direction (from right to left) along the horizontal axis. This may be controlled using plunger 14, which can be activated using a servo-driven drive or a hydraulic drive. The mold 16 is configured to receive molten material through an inlet and configured to mold the molten material under vacuum. That is, the molten material is injected into a cavity between the at least first and second plates to mold the part in the mold 16.
Once the mold cavity has begun to fill, vacuum pressure (via the vacuum lines and vacuum source 38) can be held at a given pressure to “pack” the molten material into the remaining void regions within the mold cavity and mold the material. After the molding process (e.g., approximately 10 to 15 seconds), the vacuum pressure applied to the mold 16 is released. For example, the pressure can be released using vacuum break valve 33 and/or the vacuum port. Mold 16 then can be opened to relieve pressure and to expose the part to the atmosphere. Ejector mechanism 46 is actuated to eject the solidified, molded object from between the at least first and second plates of mold 16 (ejector plate 66 is moved in a horizontal and linear direction (e.g., towards the right) via an actuation device and the ejector pins assist in ejecting the part from the cavity). Thereafter, the process can begin again. Mold 16 can then be closed by moving at least the at least first and second plates relative to and towards each other such that the first and second plates are adjacent each other. The melt zone 12 and mold 16 is evacuated via the vacuum source once the plunger 14 has moved back into a load position, in order to insert and melt more material and mold another part.
Another exemplary vacuum die casting method will be described with reference to
The die casting apparatus may comprise a tubular, horizontal shot sleeve 24 that communicates to a die cavity 30 defined by the dies 32, 34 disposed on the respective die platens 14, 16. One or more die cavities 30 can be formed by the dies 32, 34 to die cast one or more components. The shot sleeve 24 has a discharge end section 24a that communicates with an entrance passage or gate 36 to the one or more die cavities 30 so that molten metal or alloy can be pressure injected therein. The entrance passage or gate 36 can be machined in the stationary die 32 or the movable die 34, or both. The discharge end section 24a of the shot sleeve 24 can extend through a suitable passage 24b in the stationary platen 14 and die 32.
The shot sleeve 24 may extend through die 32 into a vacuum melting chamber 40 where the amorphous metal or alloy to be die cast is melted under relatively high vacuum conditions, such as less than 1000 microns. The vacuum chamber 40 can be defined by a vacuum housing wall 42 that extends about and encompasses or surrounds the opposite charging end section of the shot sleeve 24 receiving the plunger 27 and the plunger hydraulic actuator 25. The vacuum chamber 40 may be evacuated by a conventional vacuum pump P connected to the chamber 40 by a conduit 40a. The base 10 and the vacuum housing wall 42 rest on a concrete floor or other suitable support.
The chamber wall 42 preferably is airtight sealed with the fixed platen 14 by a peripheral airtight seal(s) 43 located therebetween so as to sealingly enclose the shot sleeve 24 and a pair of side-by-side stationary, horizontal shot sleeve/plunger support members 44 (one shown) extending through chamber wall 42. Such shot sleeve/plunger support members are provided on the aforementioned conventional die casting machine (250 ton HPM #73-086).
A plunger 27 may be positioned in the shot sleeve 24 for movement by plunger actuator 27 and plunger connector rod 27b between a start injection position located to the right of a melt entry or inlet opening 58 in shot sleeve 24 and a finish injection position proximate the die entrance or gate 36. The melt inlet opening 58 communicates to a metal (e.g. steel) melt-receiving vessel 52 mounted adjacent the fixed platen 14 on the shot sleeve 24 by clamps, such as screw clamps (not shown), or any other attachment mechanism. Melt-receiving vessel 52 need not be mounted, but rather may be free standing. The melt-receiving vessel 52 can be positioned beneath a melting crucible 54 to receive a charge of molten metal or alloy therefrom for die casting.
The melting crucible 54 may be an induction skull crucible comprising copper segments in which a charge of solid metal or alloy to be die cast is charged via vacuum port 40a and melted by energization of induction coils 56 disposed about the crucible in conventional manner in the chamber 40. Known ceramic or refractory lined crucibles also can be used in practicing the present invention. The crucible 54 can be tilted by rotation about crucible trunnions T using a conventional hydraulic, electrical or other actuator (not shown) disposed outside the vacuum chamber 40 and connected to the crucible by a suitable vacuum sealed linkage extending from the actuator to the crucible. The crucible may be tilted to pour the molten metal or alloy charge into the melt-receiving vessel 52, which is communicated to the shot sleeve 24 via opening 58 in the shot sleeve wall. The molten metal or alloy charge can be introduced through opening 58 into the shot sleeve 24 in front of the plunger tip 27a.
In practice, molten amorphous metal or alloy charge may be introduced into the shot sleeve in an amount that is less than 40 volume % of the effective internal volume of the shot sleeve defined in front of plunger tip 27a and extending to the entrance or gate 36 of the die cavity. Preferably, the amount of molten metal or alloy occupies less than 20 volume %, and even more preferably from about 8 to about 15 volume % of the effective internal volume of the shot sleeve. Such a relatively low volume of molten charge relative to shot sleeve internal volume provides a relatively low molten charge profile in the shot sleeve (i.e. the molten charge lies more along the bottom of the shot sleeve) to thereby reduce the contact area and contact time of the molten charge with the plunger tip 27a and resultant swelling of the plunger tip prior to melt injection into the mold cavity.
In die casting of amorphous zirconium-copper-nickel-berylium-containing alloys as an illustrative example, the shot sleeve 24 and forward plunger tip 27a contacting the molten metal or alloy can be made of an iron or copper based material, such as H-13 tool steel, or a refractory material such as based on Mo alloy or TZM alloy, ceramic material such as alumina, or combinations thereof that are compatible with the metal or alloy being melted and die cast. The plunger tip 27a can comprise a disposable tip that is thrown away after each molten metal or alloy charge is injected in the die cavity 30. A disposable plunger tip can comprise a copper based alloy such as a copper-beryllium alloy (e.g. #20 alloy) having an outer circumferential H-13 steel expandable piston ring type seal (for example only ½ inch ring width and ⅛ inch ring thickness) received in a complementary circumferential groove in the plunger tip for providing an improved seal with zero or near zero clearance with the inner wall of the shot sleeve 24.
In die casting amorphous zirconium-copper-nickel-berylium alloys, the dies 32, 34 can be made of steel and/or titanium pursuant to Colvin U.S. Pat. No. 5,287,910, although other die materials such as molybdenum, tungsten, etc. may be used in forming the bulk-solidifying amorphous alloy part. The first and second dies 32, 34 preferably are positioned outside the vacuum melting chamber 40 in ambient air atmosphere. That is, exterior surfaces or sides of the dies 32, 34 are exposed to ambient air atmosphere.
When the dies 32, 34 are closed, the die cavity 30 defined therebetween is communicated to the vacuum chamber 40 via the shot sleeve 24 and can be evacuated through the shot sleeve. The stationary die 32 typically includes a series of grooves on its inner face that mates with the opposing inner face of the movable die 34 when the dies are closed. The groove(s) may encircle or extend about the die cavity 30 as well as gate 36 and metal discharge opening communicated to gate 36 and defined by shot sleeve end 24a. The groove may receive a resilient, reusable high temperature O-ring vacuum seal 60 for sealing in vacuum tight manner against the mating face of the movable die 34 when the dies are closed. Alternately, the seal(s) 60 can be positioned in grooves on the mating face of the movable die 34, or they can be disposed on the mating faces of both dies 32, 34, so as to form a vacuum tight seal about and isolating the die cavity 30, gate 36, and shot sleeve end 24a from the ambient air atmosphere surrounding the exterior of the dies 32, 34 when closed. A series of several grooves and O-ring seals can be provided progressively outwardly relative to the die cavity perimeter to form a plurality of vacuum tight seals. The vacuum seals 60 may comprises Viton material that can withstand temperatures as high as 400° F. that may be present when the die cavity 30 is filled with molten metal or alloy.
By use of vacuum seals 60, the die cavity 30 can be isolated from the ambient air atmosphere when the dies 32, 34 are closed and enables the die cavity 30 to be evacuated through the shot sleeve 24 when the vacuum melting chamber 40 is evacuated to high vacuum levels of less than 1000 microns, preferably about 25 microns or less, employed for melting the solid charge in the crucible 54.
In operation of the die casting apparatus of
The molten charge (e.g. 500 to 200 grams of the amorphous alloy in crucible 54 is superheated from about 150° C. to above the alloy melting temperature (720° C.) and is poured under vacuum into the shot sleeve 24 via the vessel 52 and melt inlet opening 58 with the plunger 27 initially positioned at the start injection position of
The molten amorphous alloy can be introduced into the shot sleeve 24 in an amount that is less than 40 volume % of the effective internal volume of the shot sleeve. Preferably, the amount of molten charge occupies less than 40 volume % of the effective internal volume of the shot sleeve, and even more preferably from about 8 to about 15 volume % of the shot sleeve internal volume. An exemplary Vitreloy molten charge occupies approximately 20 volume % of the effective shot sleeve volume.
The molten metal or alloy may be poured into the shot sleeve 24 and resides therein for a pre-selected dwell time of between 0.005 seconds and 4 seconds, typically 0.1 second to 1.5 seconds, for the purpose of insuring that no molten alloy gets behind the plunger 27. The melt of amorphous alloy alternately can be poured directly from the crucible 54 via vessel 52 into the shot sleeve 24, thereby reducing time and metal cooling before injection can begin.
The plunger 27 then may be advanced in the shot sleeve 24 by actuator 25 at plunger speeds in the range of 5 inches/second to 500 inches/second to pressure inject the molten metal or alloy into the die cavity 30 via entrance passage or gate 36. The molten amorphous alloy is forced at high velocities, such as up to 150 inches per second, down the shot sleeve 24 and into the sealed, evacuated die cavity 30. An exemplary plunger speed useful for die casting the Vitreloy molten alloy charge is 75 inches/second.
After the molten amorphous alloy has been injected into the die cavity, the dies 32, 34 are opened by movement of die 34 relative to die 32 within a typical time period that can range from 5 to 25 seconds following injection to provide enough time for the molten alloy to form at least a solidified surface on the die cast component(s). The dies 32, 34 then are opened to allow ready removal of the die cast component(s) from the dies. A conventional ejector pin mechanism (not shown) provided on the aforementioned HPM die casting machine helps eject the components(s) from the dies. Removal of the die cast component(s) can be made directly from the dies 32, 34 simply by opening the dies without further cooling of the cast component(s). This is advantageous to increase production output of die cast components.
When the dies are opened, the vacuum seal(s) 60 is/are broken, and the die cast component(s) is/are exposed to ambient air atmosphere, removed from the die cavity and quenched immediately (e.g. within 15 seconds) in the quenching medium M, such as preferably water or oil, located proximate the open dies 32, 34 at a cooling rate sufficient to provide a die cast microstructure having at least 50 volume % or more, preferably approaching 100%, amorphous phase. Generally, an exemplary Vitreloy die cast component is cooled to below 600° F. in less than 2 minutes to provide a die cast microstructure having at least 50 volume % or more, or more than 95%, or more than 98% or about 100%, of anamorphous phase
Process Control SystemThe control system of the embodiments can be used to control the alloy production process depicted in
A suitable process control flowchart is shown in
Upon carrying out a series of variable perturbations and evaluating the effects on the product characteristics, a matrix can be prepared with the range of perturbations for each variable listed, together with the product characteristics calculated. A multi-variable statistical analysis using known statistical analysis techniques (known and embedded, for example, in Microsoft Excel) then can be carried out to determine a suitable range for each process variable so that products having acceptable quality will be produced.
Examples of suitable ranges for the following process variables, capable of producing products having acceptable quality can include the following. The vacuum drawn in the system can be within the range of from about 1.0×10−4 to about 0.02 psi, or from about 3.87×10−4 to about 0.01 psi, or from about 4.83×10−4 to about 2.0×10−3 psi. This range can then be used to establish the upper and lower set point limits for vacuum. The injection rate, or plunger speed, which typically is a function of the melt viscosity, can be from about 5 in/sec. to about 500 in/sec., or from about 15 in/sec. to about 250 in/sec., or from about 30 in/sec. to about 100 in/sec. These values result from a viscosity of the melt within the range of from about 0.1 poise to about 10,000 poise.
The temperature of the melt will vary depending on the chemical make-up of the particular bulk-solidifying amorphous alloy utilized. For an amorphous zirconium-copper-nickel-berylium alloy, such as Vitreloy, the melt temperature can be within the range of from about 650 to about 1300° C., or from about 700 to about 1000° C., or from about 715 to about 850° C., and the core temperature of the melt should be within the range of from about 700 to about 750° C., or from about 710 to about 740° C., or from about 715 to about 725° C. The dwell time in the mold can be within the range of from about 0.005 seconds to about 10 seconds, or from about 0.1 seconds to about 4 seconds, or from about 0.25 seconds to about 1 second.
The cooling rate also will depend on the chemical make-up of the particular bulk-solidifying amorphous alloy and the temperature of the molten alloy material. To maintain an adequate degree of amorphicity (e.g., greater than 95%, if desirable, or greater than 99%), the alloy should be cooled sufficiently quickly to avoid the crystallization nose shown in
The preferred product characteristics for the bulk-solidifying amorphous alloy part are as follows. The degree of amorphicity should be greater than 50%, or greater than 80%, or greater than 95%, or greater than 98%, or greater than 99%. The Vickers hardness should be from about 300 HV-1000 g to 1,500 HV-1000 g, 800 HV-1000 g to about 1,300 HV-1000 g, or from about 900 HV-1000 g to about 1,250 HV-1000 g, or from about 1,000 HV-1000 g to about 1,150 HV-1000 g. The elongation of the product should be greater than about 1.2%, or about 1.5%, or about 1.6% or about 1.8%. The yield strength should be within the range of from about 150 ksi to about 750 ksi, or from about 200 ksi to about 600 ksi, or from about 250 ksi to about 500 ksi. Persons having ordinary skill in the art will appreciate that these product properties will vary depending on the particular product and its attendant utility, and can determine the appropriate set points in the process to provide a product having properties within the desirable range, using the guidelines provided herein.
While conventional set point control systems may be adequate to control product quality, in multi-variable systems, it is possible that all parameters may be within their set points, but product quality may still be impaired. The embodiments provided herein therefore provide an additional layer of control that is a smart feedback control system. In accordance with an embodiment, the matrix prepared by perturbating various process variables and measuring the effect on product quality can be used to establish grey areas in which, even though one or more process variables may be within their set points, but if certain combinations of variable ranges exist, product quality may be predictably bad. For example, if the cooling rate is from about 1 C/s to about 5 C/s, and the melt temperature is within the range of from about 650° C. to about 725° C., then a bulk-solidifying amorphous alloy having less than 95% amorphicity may result from the process. These criteria then are pre-established and set in the control system at 820.
An algorithm can be created to predict the criteria predictive of product failure, even though the process conditions are within the set point ranges. The algorithm then can be updated to include additional criteria predictive of product failure if quality control reveals product failure for a product made from acceptable criteria, or to remove criteria predictive of product failure if the criteria actually result in an acceptable process. Accordingly, the system provides a smart feedback by continuously updating the algorithm so that it learns as the process is carried out.
The dual process control system now can run during the manufacture of, for example, a bulk-solidifying amorphous alloy using a vacuum die casting or injection molding system as shown in
Controller 320 is in communication with, and capable of controlling various process variables. For example, the temperature of the melt can be determined at 24 and communicated via 240 to controller 300. Controller 300 also can be in communication with fluid supply system to control the flow and/or temperature of cooling fluid through conduits 25 (
The dual process control system can operate by first determining at 830 whether any of the process variables communicated to controller 300 via 140, 240, 260, 270, 380 are outside the established set points for these variables. If not, the control system continues to 840. If so, the controller 300 will communicate via 310 to a gate 39 downstream from mold 16 to open the gate 39 to divert the product as a reject so that it can either be discarded, or most preferably, recycled. The control system can optionally document and reject the product at 835, although documentation is not required. The reject line in
As the process control system continues, the control system will determine whether any of the process variables, or combinations of variables are indicative of a poor product quality at 840. These conditions were established in 820. If no variables, or combinations of variables are indicative of poor product quality, then the control process continues to the next batch via 845. If there are variables, or combinations of variables indicative of poor product quality, then the controller 300 will communicate via 310 to a gate 39 to divert the product for either further evaluation 850, or optionally reject the product at 855.
If the control system calls for further evaluation of the product, the product is evaluated at 860 to determine whether it is of poor product quality. If so, then the variables are documented as indicative of poor product quality at 870, the product discarded or recycled, and the criteria are updated to reflect that the variables indeed resulted in a product of poor quality. The control system can be set up so that if the same criteria result in a product of poor quality a certain number of times in a row (e.g., more than 3 or more than 5), then the control system can be altered at 820 to automatically reject a product if the criteria occur again, and the product then will be rejected at 855.
If the product evaluation reveals that the product is not of poor quality, then the criteria are updated to reflect that the variables resulted in a product of acceptable quality. The control system can be set up so that if the same criteria result in a product of acceptable quality a certain number of times in a row (e.g., more than 3 or more than 5), then the control system can be updated at 820 to remove those criteria as indicative of poor product quality.
Although not shown in
The dual process control system provides a smart feedback system that continuously updates the controller 300 and allows controller 300 to learn as the process continues. Thus, some products that might have been rejected are now acceptable if the controller 300 learns that previously established criteria improperly indicated a poor product quality, and some products might be rejected that were previously thought to be acceptable as the controller 300 learns and is updated. The control system provides improved process control, enables the continuous production of quality bulk-solidifying amorphous alloy parts without having to test every product, thereby saving time and expense in the production of such parts.
While the invention has been described in detail with reference to particularly preferred embodiments, those skilled in the art will appreciate that various modifications may be made thereto without significantly departing from the spirit and scope of the invention.
Claims
1. A method of controlling the manufacture of a bulk-solidifying amorphous alloy comprising:
- modifying one or more process conditions selected from the group consisting of vacuum level, viscosity of melt, temperature of melt, temperature of core, cooling rate, mold dwell time, and plunger rate, and determining the physical characteristics of the bulk-solidifying amorphous alloy, wherein the physical characteristics are selected from one or more of the group consisting of degree of crystallinity, hardness, elongation, and yield strength;
- establishing set points for at least two process conditions selected from the group consisting of vacuum level, viscosity of melt, temperature of melt, temperature of core, cooling rate, mold dwell time, and plunger rate;
- establishing criteria for determining when a product is considered a failure based on one or more of the physical characteristics, and performing a multi-variable statistical analysis to determine which process condition, or combination of process conditions indicate a product failure;
- controlling the method of manufacturing a bulk-solidifying amorphous alloy by rejecting a part that was fabricated when at least one process condition is outside the set point, and at the same time continuously monitoring the at least two process conditions, and if the process conditions indicate a product failure even though within the set points, tagging the product or products made using those process conditions, measuring the physical characteristics of at least one of the products, and updating the process conditions that indicate a product failure depending on the results of measuring the physical characteristics of the tagged product or products.
2. The method of claim 1, wherein set points are established for at least three process conditions selected from the group consisting of vacuum level, viscosity of melt, temperature of melt, temperature of core, cooling rate, mold dwell time, and plunger rate.
3. The method of claim 1, wherein set points are established for at least four process conditions selected from the group consisting of vacuum level, viscosity of melt, temperature of melt, temperature of core, cooling rate, mold dwell time, and plunger rate.
4. The method of claim 1, wherein the vacuum is within the range of from about 1.0×10−4 to about 0.02 psi,
5. The method of claim 1, wherein the plunger rate is within the range of from about 5 in/sec. to about 500 in/sec.
6. The method of claim 1, wherein the viscosity of the melt is within the range of from about 0.1 poise to about 10,000 poise.
7. The method of claim 1, wherein the temperature of melt is within the range of from about 650 to about 1300° C.
8. The method of claim 1, wherein the cooling rate is within the range of from about 1 C/s to about 1,000 C/s.
9. The method as claimed in claim 1, wherein the bulk-solidifying amorphous alloy is described by the following molecular formula: (Zr, Ti)a(Ni, Cu, Fe)b(Be, Al, Si, B)c, wherein “a” is in the range of from 30 to 75, “b” is in the range of from 5 to 60, and “c” is in the range of from 0 to 50 in atomic percentages.
10. The method as claimed in claim 1, wherein the bulk-solidifying amorphous alloy is described by the following molecular formula: (Zr, Ti)a(Ni, Cu)b(Be)c, wherein “a” is in the range of from 40 to 75, “b” is in the range of from 5 to 50, and “c” is in the range of from 5 to 50 in atomic percentages.
11. The method of claim 1, wherein the method is controlled to produce a bulk-solidifying amorphous alloy having an amorphicity greater than 95%.
12. The method of claim 1, wherein the method is controlled to produce a bulk-solidifying amorphous alloy having a yield strength within the range of from about 150 ksi to about 750 ksi,
13. The method as claimed in claim 1, wherein the method is controlled to produce a bulk solidifying amorphous alloy that can sustain strains up to 1.5% or more without any permanent deformation or breakage.
14. The method of claim 1, wherein the method is controlled to produce a bulk-solidifying amorphous alloy having a Vickers hardness within the range of from about 300 HV-1000 g to about 1,500 HV-1000 g.
15. The method as claimed in claim 1, wherein updating comprises removing the criteria that indicate a product failure if measuring the physical characteristics of the product results in an acceptable product at least three consecutive times for the same criteria.
16. The method of claim 1, further comprising periodically measuring the physical characteristics of products indicated as acceptable by the control system due to their process conditions, and if the physical characteristics reveal the product as unacceptable, then updating the process conditions that indicate a product failure to include those process conditions that produced the failed product.
17. The method of claim 1, wherein updating comprises rejecting products made by the criteria that indicate a product failure if measuring the physical characteristics of the product results in a failed product at least three consecutive times for the same criteria.
Type: Application
Filed: Jul 3, 2012
Publication Date: Jan 9, 2014
Inventors: CHRISTOPHER D. PREST (San Francisco, CA), JOSEPH C. POOLE (San Francisco, CA), MATTHEW S. SCOTT (Campbell, CA), DERMOT J. STRATTON (San Francisco, CA)
Application Number: 13/541,565
International Classification: C21D 11/00 (20060101);
