Non-linear elastic behavior of Ni-Fe-Ga(Co) shape memory alloy and Landau-energy landscape reconstruction

Zoubková, Kristýna; Seiner, Hanuš; Sedlák, Petr; Villa, Elena; Tahara, Masaki; Hosoda, Hideki; Chernenko, V.A.

doi:10.1016/j.actamat.2021.117530

Cited by 8 publications

(2 citation statements)

References 54 publications

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“…This strong stress-dependence of the modulus confirms that the BCC crystal lattice is unstable with respect to straining along the transformation path, and suggests that the state of the material is close to the critical point where the energy barrier between BCC and martensite completely disappears. [30] A 33Cr CCAS sample was subjected to a tensile fatigue test with limits of 380 MPa and 1.65%. The sample survived the test for up to 10 7 cycles.…”

Section: Resultsmentioning

confidence: 99%

Flexible and Tough Superelastic Co–Cr Alloys for Biomedical Applications

2022

Advanced Materials

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present, the three dominant metallic alloys used as biomaterials are Co-Cr alloys, stainless steels, and Ti alloys, and Mg alloys provide a biodegradable option. [1][2][3] There are basically three qualities required of a metallic biomaterial: good biocompatibility, high corrosion resistance, and good wear resistance. Recently, the need for a low Young's modulus similar to that of human bones has been highlighted. A large difference in the Young's modulus of the implant and the bone has been shown to result in the loosening of implants and bone atrophy due to the "stress shielding effect." [2,4] At 190-240 GPa, the Young's modulus of the Co-Cr alloys and stainless steels commonly used at present is much higher than that of the 10-30 GPa of human bones. [2,5] Many kinds of β-type Ti alloys with a body-centered-cubic (BCC) structure and a relatively low Young's modulus have been developed. [1] The Young's modulus of these polycrystalline alloys is typically in the range of 50-80 GPa. [1,2] The Young's modulus of a single-crystal Ti-Nb-Ta-Zr has been reported to be 35 GPa in the <001> direction, [6] and a low apparent Young's modulus of 20 GPa has been shown for some Ti-Nb-based alloys when stress-induced martensitic transformation is involved. [7] While these alloys are appropriate for use as the stems and the acetabular cups of totalThe demand for biomaterials has been increasing along with the increase in the population of elderly people worldwide. The mechanical properties and high wear resistance of metallic biomaterials make them well-suited for use as substitutes or as support for damaged hard tissues. However, unless these biomaterials also have a low Young's modulus similar to that of human bones, bone atrophy inevitably occurs. Because a low Young's modulus is typically associated with poor wear resistance, it is difficult to realize a low Young's modulus and high wear resistance simultaneously. Also, the superelastic property of shape-memory alloys makes them suitable for biomedical applications, like vascular stents and guide wires. However, due to the low recoverable strain of conventional biocompatible shape-memory alloys, the demand for a new alloy system is high. The novel body-centered-cubic cobalt-chromium-based alloys in this work provide a solution to both of these problems. The Young's modulus of <001>-oriented single-crystal cobalt-chromium-based alloys is 10-30 GPa, which is similar to that of human bone, and they also demonstrate high wear and corrosion resistance. They also exhibit superelasticity with a huge recoverable strain up to 17.0%. For these reasons, the novel cobalt-chromium-based alloys can be promising candidates for biomedical applications.

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Section: Resultsmentioning

confidence: 99%

Flexible and Tough Superelastic Co–Cr Alloys for Biomedical Applications

2022

Advanced Materials

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“…The value of C ′ = 7.85 GPa in the present alloy is extremely small and has a direct contribution to the low <100> Young’s modulus when the bulk modulus representing the resistance to hydrostatic deformation is large (Table 1 ) 37 . This small C ′ may be associated with the lattice instability of the β phase, which implies a low energy barrier for structural change in the tetragonal path to another structure during deformation 38 – 40 . Once the premature occurrence of such a structural change, usually a first-order martensitic phase transformation, is suppressed (this is exactly what we did for our alloy by tailoring the composition), the lattice may be highly distorted to yield a huge elastic deformation as well as a significant lattice anharmonicity 38 , 39 , 41 .…”

Section: Discussionmentioning

confidence: 99%

Non-Hookean large elastic deformation in bulk crystalline metals

Odaira

Sato

et al. 2022

Nat Commun

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Crystalline metals can have large theoretical elastic strain limits. However, a macroscopic block of conventional crystalline metals practically suffers a very limited elastic deformation of <0.5% with a linear stress–strain relationship obeying Hooke’s law. Here, we report on the experimental observation of a large tensile elastic deformation with an elastic strain of >4.3% in a Cu-based single crystalline alloy at its bulk scale at room temperature. The large macroscopic elastic strain that originates from the reversible lattice strain of a single phase is demonstrated by in situ microstructure and neutron diffraction observations. Furthermore, the elastic reversible deformation, which is nonhysteretic and quasilinear, is associated with a pronounced elastic softening phenomenon. The increase in the stress gives rise to a reduced Young’s modulus, unlike the traditional Hooke’s law behaviour. The experimental discovery of a non-Hookean large elastic deformation offers the potential for the development of bulk crystalline metals as high-performance mechanical springs or for new applications via “elastic strain engineering.”

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