Nanocrystalline strain glass TiNiPt and its superelastic behavior
Daqiang Jiang, Jiale An, Yinong Liu, Zhiyuan Ma, Fangfeng Liu, Hong Yang, Xiaobing Ren, Kaiyuan Yu, Junsong Zhang, Xiaohua Jiang, Yang Ren, Lishan Cui
Abstract
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.