HIGH HARDNESS SUPERELASTIC SHAPE MEMORY ALLOY NiTiCe

Info

Publication number: 20260265872
Type: Application
Filed: Mar 4, 2026
Publication Date: Sep 10, 2026
Applicant: Iowa State University Research Foundation, Inc. (Ames, IA)
Inventors: Jun Cui (Ames, IA), Gaoyuan Ouyang (Ames, IA)
Application Number: 19/556,848

Abstract

Embodiments of the disclosure relate to a superelastic alloy comprising nickel, titanium, and at least one of cerium or lanthanum, in particular up to 1 wt % of the at least one of cerium or lanthanum. The alloy has a hardness of at least 60 HRC. Embodiments of the disclosure also relate to a method of preparing a superelastic alloy in which nickel and titanium are alloyed with at least one of cerium or lanthanum. The disclosed superelastic alloy and method of forming same are particularly suitable for forming ball bearings or a race for a ball bearing.

Description

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims the benefit of U.S. Provisional Patent Application No. 63/767,966, filed Mar. 6, 2025, the entire teachings and disclosure of which are incorporated herein by reference thereto.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with government support under DE-AC02-07CH11358 awarded by the Department of Energy. The government has certain rights in the invention.

FIELD OF THE INVENTION

This invention generally relates to a superelastic shape memory alloy and, in particular, to a NiTi-based shape memory alloy with additions of Ce.

BACKGROUND OF THE INVENTION

Hydrogen gas and wind turbines will play a critical role in decarbonizing the power generation industry. Wind power can produce hydrogen via water electrolysis when the electricity consumption is at its lowest. The produced hydrogen can power gas turbines, which complements the intermittent renewable energy capable of quickly ramping up output to meet peak demands. However, there are still barriers blocking this carbon-neutral power generation scheme. Bearing failure causes damage to the system, resulting in costly downtime and significant repair costs. In an extreme situation, a bearing failure in the LH2 fuel pump may cause an explosion.

One of the state-of-the-art bearing materials in wind turbines is wear-resistant case-carburized steel. Such bearings have extra hardness and engineered residual compressive stresses at the contact surface, resulting in additional resistance to rolling contact fatigue. The bearing's more elastic core allows the designer to utilize tighter fitting practices required with increasing operating speeds. Case hardening is a localized heat treatment, so the hardness is maximized at the surface and decreases radially from the surface. While this enhanced wear resistance prolongs its service life under normal operation conditions, its inability to stand excessive load under abnormal operation conditions is a major limitation. These case-hardened bearings exhibit the so-called “white etching cracks” (WECs), a network of small, white-decorated cracks below the surface of the bearing. It is a natural consequence of rolling contact fatigue, unintended higher stresses, and lower material strength.

Bearings based on nickel-titanium (NiTi) alloys were initially developed by NASA for their superb corrosion resistance. These bearings offer significant corrosion and ductility benefits compared to many other bearing types and excellent recoverability on large deformation strain due to the alloy's unique superelasticity. Early generation binary NiTi bearing alloys require water quenching to acquire a high hardness, but water quenching results in distortion when grinding to form the bearing balls. NASA successfully addressed this issue via hafnium (Hf) addition, resulting in a finer microstructure for better fatigue life (see U.S. Pat. No. 11,033,963B1, issued Jun. 15, 2021, the entire contents of which are incorporated herein by reference thereto). However, the current NiTi alloys are not as strong and as stiff as the bearing steels.

BRIEF SUMMARY OF THE INVENTION

In view of the deficiencies of current bearing technology, Applicant has identified a need to provide bearings with the requisite strength and stiffness as well as the ability to recover from large deformation strain. According to the present disclosure, Applicant has found that cerium (Ce) added to NiTi strengthens the system by promoting formation of Ce-rich precipitates. By contrast, the hardness of conventional NiTi binary alloy results from the formation of the intermetallics Ti₃Ni₄and TiNi₃when the composition is slightly shifted from equiatomic. Cerium, which is typically among the most inexpensive rare earth elements, is more reactive than Ti and Hf. As such, Ce—Ni can be more stable and more readily formed when forming compounds with Ni than Ti—Ni or Hf—Ni. Therefore, Ce can be more effective in assisting the precipitation of intermetallic compounds. In one or more embodiments, a similar effect can be achieved by substituting Ce in whole or in part by lanthanum (La).

As will be discussed more fully below, the NiTiCe alloy developed according to the present disclosure is 20% stiffer, which the Applicant attributes to the uniform precipitation of Ce—Ni intermetallic compounds (and/or La—Ni intermetallic compounds if La is substituted in whole or in part). The higher stiffness, which brings modulus closer to typical bearing and ball bearing materials, is expected to reduce microslip and shear stress that drives fatigue wear, thereby improving wear resistance and bearing life. Moreover, the phase transformation characteristics remained the same for the presently disclosed NiTi—Ce alloy, maintaining the unique superelasticity of the shape memory alloy.

As will also be discussed more fully below, the Young's modulus and hardness of the NiTi alloy are improved when a small amount of Ce is added. SEM analysis of the presently disclosed alloy compared to conventional NiTi-based alloys showed that precipitates rich in Ce content were formed in the presently disclosed alloy. A desired size reduction of the TiNi₃precipitates was observed in samples in which Ce was added, demonstrating that addition of Ce could refine the precipitates. The Young's modulus (measured by ultrasonic pulse-echo technique) and Rockwell C hardness of the presently disclosed alloy were increased by about 25% or more and 5% or more, respectively. Ni—Ti alloys are known to have Martensite transformation around room temperature capable of accommodating significant deformation strain without any plastic strain accumulation. The same phase transformation was observed in the disclosed NiTiCe alloys sample using DSC analysis. Both transition temperatures and latent heat are slightly changed due to the depletion of the Ni atom forming the precipitates, which indicates that the desired superelasticity remains in effect for the disclosed NiTiCe alloy.

According to embodiments of the present disclosure, aspect 1 relates to a superelastic alloy comprising nickel, titanium, and at least one of cerium or lanthanum in which the alloy comprises a hardness of at least 60 HRC.

Aspect 2 relates to the superelastic alloy of Aspect 1 in which the superelastic alloy comprises up to 1 wt % of the at least one of cerium or lanthanum.

Aspect 3 relates to the superelastic alloy of Aspect 1 or Aspect 2 in which the superelastic alloy comprises from 59 wt % to 60 wt % of nickel.

Aspect 4 relates to the superelastic alloy of any of Aspects 1-3 in which the superelastic alloy comprises from 39 wt % to 40 wt % of titanium.

Aspect 5 relates to the superelastic alloy of any of Aspects 1-4 in which a microstructure of the superplastic alloy comprises at least one of CeNi₅or LaNi₅precipitates.

Aspect 6 relates to the superelastic alloy of any of Aspects 1-5 in which the superelastic alloy comprises a density of 6.80 g/cm3 or less.

Aspect 7 relates to the superelastic alloy of any of Aspects 1-6 in which the superelastic alloy comprises a Young's modulus of at least 90 GPa.

Aspect 8 relates to the superelastic alloy of any of Aspects 1-7 in which the superelastic alloy consists of the nickel, the titanium, the at least one of cerium or lanthanum, and unavoidable impurities, the unavoidable impurities being 1 wt % or less.

Aspect 9 relates to a ball bearing formed from the superelastic alloy of any of Aspects 1-8.

Aspect 10 relates to a race for a ball bearing formed from the superelastic alloy of any of Aspects 1-8.

Aspect 11 relates to a method of preparing a superelastic alloy. In the method, nickel and titanium are alloyed with at least one of cerium or lanthanum. The superelastic alloy comprises a hardness of at least 60 HRC.

Aspect 12 relates to the method of Aspect 11 in which the alloying further comprises melting elemental nickel, titanium, and the at least one of cerium or lanthanum to form a melt of the superelastic alloy.

Aspect 13 relates to the method of Aspect 12 in which the method further comprises casting the melt of the superelastic alloy to form an ingot.

Aspect 14 relates to the method of Aspect 12 in which the method further comprises atomizing the melt of the superelastic alloy to form a powder of the superelastic alloy.

Aspect 15 relates to the method of Aspect 13 in which the method further comprises melting the ingot to form a melt of the superelastic alloy and atomizing the melt of the superelastic alloy to form a powder of the superelastic alloy.

Aspect 16 relates to the method of any of Aspects 11-15 in which the superelastic alloy comprises 59 wt % to 60 wt % of nickel.

Aspect 17 relates to the method of any of Aspects 11-16 in which the superelastic alloy comprises from 39 wt % to 40 wt % of titanium.

Aspect 18 relates to the method of any of Aspects 11-17 in which the superelastic alloy comprises at most 1 wt % of the at least one of cerium or lanthanum.

Aspect 19 relates to a method of preparing a ball bearing or a race for a ball bearing. In the method, a melt of a superelastic alloy is atomized to form a powder, and the powder is sintered to form the ball bearing or the race. The superelastic alloy comprises nickel, titanium, and at least one of cerium or lanthanum, and the superelastic alloy comprises a hardness of at least 60 HRC.

Aspect 20 relates to the method of Aspect 19 in which the superelastic alloy comprises 59 wt % to 60 wt % of nickel, 39 wt % to 40 wt % of titanium, and up to 1 wt % of the at least one of cerium or lanthanum.

Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:

FIGS. 1A and 1B depict SEM micrographs of Ni₅₇Ti₄₀Ce₃(FIG. 1A) and Ni₆₀Ti₄₀(FIG. 1B) alloys showing the formation of Ni—Ce precipitates leading to increased Young's modulus (E), hardness (HRC), and a reduction of density;

FIG. 1C depicts a DSC thermogram showing the transition temperature of the alloys of FIGS. 1A and 1B after aging;

FIG. 2 is a photograph of specimens of NiTiCe, NiTi, and NiTiHf samples prepared for the purposes of comparing mechanical and microstructural properties of the specimens;

FIGS. 3A-3F includes a plurality of graphs of hardness (Vickers and Rockwell C) for various NiTiCe and NiTi samples; and

FIGS. 4A-4C depict SEM images of conventional NiTi and NiTiHf samples (FIGS. 4A and 4B) and an NiTiCe sample (FIG. 4C) prepared according to embodiments of the present disclosure.

While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present disclosure relate to a NiTi-based alloy including additions of Ce (and/or La) and to bearings made from same. Advantageously, the NiTiCe alloy is expected to impart significant improvements to bearing life and resistance to harsh environments associated with wind turbines and LH2 pumps. The NiTiCe alloy's superelastic properties and reasonably high strength are expected to lead to preferential and reversible plastic energy dissipation, leveraging the shape-memory effect. NiTiCe alloy is expected to have good corrosion resistance and should be reasonably electrically and thermally conductive, unlike alloys with thick carbide and nitride layers, aiding mitigation of electrical charging-related wear that is prominent in wind turbines. Applicant expects that improving bearing performance will significantly prolong wind turbine service life and reduce maintenance costs and frequency, promoting the proliferation of offshore wind power, where wind energy is most abundant. Additionally, NiTiCe alloys exhibit a unique combination of metallurgical properties that can improve the life of LH2-lubricated pumps and hydrogen-fueled turbomachinery overall. These and other aspects and advantages of the disclosed NiTiCe alloy and bearing made from same are discussed more fully in relation to the embodiments described below and shown in the figures. These embodiments are presented by way of illustration and not limitation.

In one or more embodiments, the NiTiCe alloy comprises nickel, titanium, and at least one of cerium or lanthanum, in particular consisting only of nickel, titanium, and at least one of cerium or lanthanum. In one or more embodiments, the NiTiCe alloy comprises nickel in an amount in a range of 59 wt % to 60 wt %. In one or more embodiments, the NiTiCe alloy comprises titanium in an amount in a range of 39 wt % to 40 wt %. In one or more embodiments, the NiTiCe alloy comprises at least one of cerium or lanthanum in an amount in a range of up to 1 wt %, in particular in a range of about 0.01 wt % to 1 wt %. As mentioned, the disclosed NiTiCe alloy preferably contains cerium, but the cerium may be substituted in whole or in part by lanthanum, and while the alloy is referred to as an NiTiCe alloy, this is not meant to imply the exclusion of lanthanum. In one or more embodiments, the NiTiCe alloy comprises no other elements with the exception of traces of unavoidable impurities, such as yttrium (Y), up to 1 wt % in total.

In one or more embodiments, the NiTiCe alloy is prepared by melting the constituent metal elements in the requisite amounts. For example, the elemental metals of nickel, titanium, and cerium and/or lanthanum (e.g., in the form of powder or other granular form, wire, shots, ribbon, pieces, etc.) can be combined in an arc furnace and melted to form a melt of the NiTiCe alloy, and then the melt can be cast into ingots of the desired shape and size. In one or more embodiments, the ingots can be utilized in an atomizer to form metal powder of the NiTiCe alloy, such as gas atomization of the melted ingot. In one or more other embodiments, the NiTiCe alloy melt can be directly atomized after formation without first forming the melt into ingots.

In one or more embodiments, the NiTiCe alloy so cast comprises a microstructure of inter-waved martensite network in a TiNi austenite matrix. Further, in one or more embodiments, the microstructure includes precipitates of nickel and cerium, in particular predominantly CeNi₅precipitates (and/or LaNi₅precipitates if lanthanum is utilized). Further, in one or more embodiments, the microstructure includes few, if any, precipitates of CeNi and CezNi₃(or LaNi and La—Ni₃), which tend to form when Ce (or La) is present in excess of 1 wt %.

In one or more embodiments, the NiTiCe alloy has a Vickers hardness of at least 525 HV or a Rockwell C hardness of at least 60 HRC. In one or more embodiments, the NiTiCe alloy has a Young's modulus of at least 90 GPa, in particular at least 100 GPa. In one or more embodiments, the NiTiCe alloy has a density of 6.80 g/cm³or less.

In one or more embodiments, the NiTiCe alloy is used to form ball bearings and/or races in which ball bearings are held. In one or more embodiments, the ball bearings and/or races are formed using powder metallurgy, in particular by sintering the NiTiCe powder into the desired shape, such as a sphere for ball bearings or a track for the races. In one or more embodiments, the bearings and/or races are utilized in a windmill.

Experimental Examples

As mentioned above, Hf has previously been included in NiTi alloys to improve fatigue life. The NiTiHf alloy has a composition 57.6Ni-39.2Ti-3.2Hf (wt %), and this alloy was as a comparative basis for the NiTiCe alloy of the present disclosure. In a first comparison, a first NiTiCe alloy had the composition of 57Ni-40Ti-3Ce (wt %). FIG. 1A depicts an SEM image of the NiTiCe alloy, and FIG. 1B depicts an SEM image of the NiTiHf alloy. In examining the respective SEM images of the alloys, Applicant determined that the microstructure of the NiTiCe alloy included TiNi₃precipitates having a smaller size, demonstrating the ability of Ce additions to refine the microstructure. Further, Applicant found precipitates rich in Ce content uniformly distributed throughout the microstructure.

Additionally, Applicant measured the Young's modulus and hardness of the respective NiTiHf and NiTiCe samples. The Young's modulus was measured using an ultrasonic pulse-echo technique, and the hardness was measured according to the Rockwell C scale. The NiTiCe sample had a higher Young's modulus and Rockwell C harness. In particular, the NiTiHf alloy had a Young's modulus of 81.9 GPa and a hardness of 47.2 HRC, whereas the NiTiCe alloy had a Young's modulus of 102.1 GPa and a hardness of 49.5 HRC. Thus, adding Ce in the NiTi alloy increased the Young's modulus and hardness compared to alloying with Hf.

Additionally, Applicant subjected the 57Ni-40Ti-3Ce (wt %) alloy to differential scanning calorimetry (DSC) analysis. FIG. 1C depicts the heating and cooling thermograms for the testing NiTiCe alloy as compared to an NiTi alloy (60-40 wt %). NiTi alloys are known to have martensite transformation around room temperature, capable of accommodating significant deformation strain without any plastic strain accumulation. As can be seen in FIG. 1C, the martensite transformation of the NiTi alloy can be seen as the valley in the heating thermogram and the peak in the cool thermogram. The heating and cooling thermograms for the NiTiCe alloy also include similarly positioned valleys and peaks representing the room temperature martensite transformation. The transition temperatures are slightly displaced as a result of depletion of Ni atoms, but the NiTiCe maintains the desired superpelastic effect of the base NiTi alloy.

Additional samples of NiTiCe alloys as well as two NiTi alloys and one NiTiHf alloy were arc cast into 17 mm rods as shown in FIG. 2. The Table below provides a summary of the compositions of the prepared.

TABLE Nominal Composition of NiTi-based Alloys Studied Ti Ni Ce Hf Ni/ Sample (wt %) (wt %) (wt %) (wt %) (Ni + Ti) No. [at %] [at %] [at %] [at %] (%) 1 40.00 60.00 — — 60.00 [44.97] [55.03] 2 43.93 56.07 — — 56.07 [49.00] [51.00] 3 39.20 57.60 — 3.20 59.50 [45.04] [53.98] [0.99] 4 39.96 59.94 0.10 — 60.00 [44.96] [55.00] [0.04] 5 39.60 59.40 1.00 — 60.00 [44.80] [54.81] [0.39] 6 38.00 57.00 5.00 — 60.00 [44.08] [53.93] [1.98] 7 36.00 54.00 10.00 — 60.00 [43.13] [52.77] [4.09] 8 40.00 59.9 0.1 — 59.96 [45.00] [54.96] [0.04] 9 40.00 59.00 1.00 — 59.60 [45.22] [54.40] [0.39] 10 40.00 50.00 10.00 — 55.56 [47.51] [48.44] [4.06] 11 39.90 60.00 0.10 — 60.06 [44.90] [55.07] [0.04] 12 39.00 60.00 1.00 — 60.61 [44.18] [55.44] [0.39] 13 30.00 60.00 10.00 — 66.67 [36.43] [59.42] [4.15]

Specimens of each sample composition were cut from the cylindrical rods for hardness measurement. To ensure homogeneity, each specimen was heat treated at 950° C. for 24 hours, followed by water quenching before the specimen was mounted and polished. Both Vickers hardness (HV) and Rockwell C hardness (HRC) measurements were completed, and the results are shown in the graphs of FIGS. 3A-3F. The indent size from the Vickers hardness test is around 20 μm in length from the diagonal direction, while that of the HRC test is roughly 500 μm in diameter. Depending on the size of the precipitates, HRC test may give a more accurate measurement of the overall specimen. Both tests were completed to compare the results to those reported in literature.

As shown in FIGS. 3A-3F, the overall trend of the results was quite consistent, i.e., the hardness increased with increasing Ce between about 0.1 wt % and about 1.0 wt % but then decreased as the Ce concentration continued to increase to about 5 wt % and up to 10 wt %. As shown in FIGS. 3C and 3D, the highest hardness was achieved when 1 wt % of Ce was added as a replacement for Ni, i.e., 59Ni-40Ti-1Ce (wt. %). The hardness of this sample is 533 HV and 66.3 HRC, which is much higher than the values reported for the 57.6Ni-39.2Ti-3.2Hf (wt %) sample, which was 520HV and 59.3HRC (dashed lines on the respective HV and HRC graphs). Additionally, even minor additions of Ce resulted in increases in hardness relative to the Hf alloyed samples. Specifically, 60Ni-39.9Ti-0.1Ce (wt. %) and 60Ni-39Ti-1Ce (wt. %) had hardness of 62.8 HRC and 63 HRC, respectively, and shown in FIG. 3F.

The microstructure features of three selected samples were studied and are depicted in FIGS. 4A-4C. As shown in FIG. 4A, the 60Ni-40Ti (wt %) specimen was characterized by a TiNi matrix with scattered blocky precipitates of TiNi₃(confirmed by EDS and XRD scans). The inset image at a higher magnification shows the presence of very fine need-like martensite, with its short axis being tens of nanometers. As shown in FIG. 4B, the martensite size in 57.6Ni-39.2Ti-3.2Hf (wt %) is roughly the same as 60Ni-40Ti, but there are additional Hf-rich precipitates (bright contrast features in inset).

As shown in FIG. 4C, the specimen of 59Ni-40Ti-1Ce (wt %) showed the same inter-waved martensite network in a TiNi austenite matrix but with additional CeNi₅precipitates (confirmed by EDS). Due to the strong tendency of Ce to form CeNi₅precipitates with Ni (Ce and Ti do not react), 59Ni-40Ti-1Ce (wt %) has much less TiNi₃precipitates than 60Ni-40Ti. Additionally, the overall precipitate size in 59Ni-40Ti-1Ce (wt %) is much smaller and more uniform than 60Ni-40Ti, which likely leads to the higher hardness. As can be seen from comparing the insets of FIGS. 4B and 4C, the precipitates fraction is much higher in 59Ni-40Ti-1Ce (wt %) than 57.6Ni-39.2Ti-3.2Hf (wt %) because of the high reactivity of Ce, leading to a higher hardness.

The formation of fine and uniformly distributed CeNi₅effectively increases the hardness of the samples. The CeNi₅is expected to be highly stable based on its high melting point (Tm=1342° C.). However, the microstructure coarsens when excess Ce is added, as it has a melting point of 795° C. Reviewing the Ce—Ni phase diagram, one can see multiple eutectics with a melting point as low as 483° C. on the Ce-rich side (~20 at % Ce). Ce does not dissolve in Ni or Ti. When excess Ce is added, Ce can agglomerate and form Ce-rich CeNi (Tm=679° C.) or CezNi₃(Tm=525° C.) precipitates that significantly coarsen and are even volatile when annealed. Optical imaging of 54Ni-36Ti-10Ce (wt %) and 60Ni-30Ti-10Ce (wt %) revealed a highly coarsened (size >20 μm) and porous microstructure likely due to the copious formation of CeNi or CezNi₃precipitates. The hardness of these two samples is significantly lower, in particular 15.5 HRC for 54Ni-36Ti-10Ce (wt %).

In view of the foregoing, Applicant has determined that minor Ce addition (≤1 wt %) to Ni—Ti alloy effectively increases the hardness of Ni—Ti alloy. The HRC hardness of 59Ni-40Ti-1Ce (66.3HRC) was increased by over 26% relative to 60Ni-40Ti (52.5HRC) and 23% relative to 57.6Ni-39.2Ti-3.2Hf (59.3HRC). The increase in hardness is the result of the formation of uniform and fine CeNi₅precipitates that are stable. However, Applicant also found that excess Ce addition can result in less stable CeNi or CezNi₃precipitates formation, which deteriorates the microstructure.

All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A superelastic alloy comprising nickel, titanium, and at least one of cerium or lanthanum, wherein the alloy comprises a hardness of at least 60 HRC.

2. The superelastic alloy of claim 1, comprising up to 1 wt % of the at least one of cerium or lanthanum.

3. The superelastic alloy of claim 1, comprising from 59 wt % to 60 wt % of nickel.

4. The superelastic alloy of claim 1, comprising from 39 wt % to 40 wt % of titanium.

5. The superelastic alloy of claim 1, wherein a microstructure of the superplastic alloy comprises at least one of CeNi5 or LaNi5 precipitates.

6. The superelastic alloy of claim 1, comprising a density of 6.80 g/cm3 or less.

7. The superelastic alloy of claim 1, comprising a Young's modulus of at least 90 GPa.

8. The superelastic alloy of claim 1, consisting of the nickel, the titanium, the at least one of cerium or lanthanum, and unavoidable impurities, the unavoidable impurities being 1 wt % or less.

9. A ball bearing formed from the superelastic alloy of claim 1.

10. A race for a ball bearing formed from the superelastic alloy of claim 1.

11. A method of preparing a superelastic alloy, comprising:

alloying nickel and titanium with at least one of cerium or lanthanum;

wherein the superelastic alloy comprises a hardness of at least 60 HRC.

12. The method of claim 11, wherein the alloying further comprises melting elemental nickel, titanium, and the at least one of cerium or lanthanum to form a melt of the superelastic alloy.

13. The method of claim 12, further comprising casting the melt of the superelastic alloy to form an ingot.

14. The method of claim 12, further comprising atomizing the melt of the superelastic alloy to form a powder of the superelastic alloy.

15. The method of claim 13, further comprising melting the ingot to form a melt of the superelastic alloy and atomizing the melt of the superelastic alloy to form a powder of the superelastic alloy.

16. The method of claim 11, wherein the superelastic alloy comprises 59 wt % to 60 wt % of nickel.

17. The method of claim 11, wherein the superelastic alloy comprises from 39 wt % to 40 wt % of titanium.

18. The method of claim 11, wherein the superelastic alloy comprises at most 1 wt % of the at least one of cerium or lanthanum.

19. A method of preparing a ball bearing or a race for a ball bearing, comprising:

atomizing a melt of a superelastic alloy to form a powder;

sintering the powder to form the ball bearing or the race;

wherein the superelastic alloy comprises nickel, titanium, and at least one of cerium or lanthanum;

wherein the superelastic alloy comprises a hardness of at least 60 HRC.

20. The method of claim 19, wherein the superelastic alloy comprises 59 wt % to 60 wt % of nickel, 39 wt % to 40 wt % of titanium, and up to 1 wt % of the at least one of cerium or lanthanum.