Nanocrystalline strain glass TiNiPt and its superelastic behavior

TiNi-based shape-memory alloys are known to exhibit a strain glass state under certain conditions, generally in the presence of high-density defects such as excess solute atoms or alloying elements, dislocations, and nanoprecipitates. In this paper, we report a strain glass transition in a nanocrystalline ${\mathrm{Ti}}_{50}{\mathrm{Ni}}_{35}{\mathrm{Pt}}_{15}$ alloy. The nanocrystalline strain glass state is achieved by a combined effect of high-density grain boundaries and high concentration doping of Pt atoms in the B2 matrix. The nanocrystalline ${\mathrm{Ti}}_{50}{\mathrm{Ni}}_{35}{\mathrm{Pt}}_{15}$ strain glass alloy showed a large near-complete progressive superelasticity with a recovery strain of about 6% and a low apparent Young's modulus of about 30 GPa in a wide temperature range of over 200 \ifmmode^\circ\else\textdegree\fi{}C. In situ synchrotron x-ray diffraction measurement showed that the strain glass B2 [B2(SG)] phase experienced B2(SG)\ensuremath{\rightarrow}R\ensuremath{\rightarrow}B19 transformation upon loading and B19\ensuremath{\rightarrow}B2(SG) upon unloading. The findings of this study provide insight for the development of nanocrystalline strain glass shape-memory alloys.