Novel Shape Memory Alloys: Session 3
Program Organizers: Othmane Benafan, NASA Glenn Research Center
Tuesday 4:00 PM
July 11, 2017
Room: Water Tower
Location: Hyatt Regency Chicago
Session Chair: Donald Brown, Los Alamos National Laboratory
Effect of Ta- vs -Nb Content on Structure and Mechanical Properties of Ti-Zr-(Nb,Ta) Shape Memory Alloys for Biomedical Application: Sergey Dubinskiy1; Anton Konopatsky1; Vadim Sheremetyev1; Sergey Prokoshkin1; Vladimir Brailovski2; 1NUST "MISIS"; 2École de technologie supérieure
Uncontrollable ω-phase precipitation occurring in Ti-Nb-Zr biomedical shape memory alloys (SMA) causes embrittlement and decline in fatigue resistance, thus excluding ω-phase age-hardening from the list of strengthening treatments applicable to these alloys. Such a negative effect of ω-phase-related embrittlement is even more pronounced in the case of new-generation Ti-Zr-Nb SMAs due to higher zirconium content. Since the Ti-Zr-Nb alloys possess significantly higher resource of recovery strain than Ti-Nb-Zr alloys, their strengthening via the age-hardening heat treatment represents an interesting technological option, especially when dealing with such complex structures as metallic foams. It is shown in this work that quaternary Ti-Zr-Nb-Ta alloys, with tantalum as a partial replacement of niobium, offer the possibility to precisely control the ω-phase precipitation process during age-hardening, without negative effect on their recovery strain resource and superelastic behavior.
Martensitic Transformation of beta Ti-based Alloys: Shuichi Miyazaki1; Hee Young Kim1; 1University of Tsukuba
The beta Titanium alloys exhibit shape memory effect, superelasticity, low Young’s modulus, high strength, non-linear large elastic deformation, Invar behavior, heating-induced martensitic transformation, etc. These unique properties are closely related with the martensitic transformation, microstructure and alloy elements. Substitutional atoms affect the transformation strain and the maretensitic transformation temperatures. Interstitial atoms such as oxygen and nitrogen affect the behavior of the martensitic transformation. Lattice distortion around an oxygen tends to the martensite phase structure, but is suppressed to form a nano-domain which is an intermediate state from the beta phase to the martensite phase. The interstitial atoms added alloys reveal heating-induced martensitic transformation due to difusion of interstitial atoms at high temperatures. These topics of the beta Titanium alloys will be overviewed in this presentation.
Recent Development of Ti-Zr Based Biomedical Superelastic Alloys: Hee Young Kim1; Shuichi Miyazaki1; 1University of Tsukuba
Over the last decade, Ni-free Ti-based alloys have attracted increasing attention due to their wide application potentials in biomedical fields. There has been substantial progress in understanding the nature of martensitic transformation in Ti-based alloys, and many novel superelastic alloys have been developed. However, most of the Ti-based superelastic alloys reported to date show a small recovery strain when compared with commercial Ti-Ni alloys. Recently we have applied the crystallography of martensitic transformation to develop biomedical superelastic alloys and proposed that Ti-Zr based alloy system is one of the promising candidates. Some of Ti-Zr based alloys such as (Ti-Zr)-Nb-Sn and (Ti-Zr)-Mo-Sn exhibited a larger recovery strain over 7% through the optimization of alloy composition, microstructure and recrystallization texture. In this presentation, the strategy in alloy development and microstructure control in Ti-Zr based alloy alloys will be reviewed.
Effects of Pd Addition on Precipitation and Martensitic Transformation in a Ni49.7Ti30.3Zr20 Alloy: Hirobumi Tobe1; Shunsuke Kojima1; Eiichi Sato1; 1ISAS/JAXA
High temperature shape memory alloys with their transformation temperatures (TTs) over 100°C are highly desired in the aerospace industry. NiTiZr alloys are one of the candidates because TTs can be increased by increasing Zr content. Aging on Ni-rich NiTiZr alloys produces fine precipitates named H-phase and makes the shape memory and superelastic properties of the alloys stable at high temperature. However, increasing Zr content changes the type of twinning in B19′ monoclinic martensite from <011> type II to (001) compound, and the reorientation of twinned martensite becomes difficult. On the other hand, (001) compound twinning does not exist in B19 martensite since the crystal structure is orthorhombic. It is known that Pd addition to NiTi binary alloys changes martensite from B19′ to B19. In this study, effects of Pd addition on precipitation and martensitic transformation in a Ni49.7Ti30.3Zr20 ternary alloy were investigated.