Kim Dong-Jo, Kim Yeon-Wook, Nam Tae-Hyun
School of Materials Science and Engineering and RIGET, Gyeongsang National University, 900 Gazwadong, Jinju, Gyeongnam 660-701, Korea.
Department of Advanced Materials Science and Engineering, Keimyung University, 1000 Shindang-dong, Dalseo-gu, Taegu 704-701, Korea.
J Nanosci Nanotechnol. 2018 Sep 1;18(9):6233-6238. doi: 10.1166/jnn.2018.15651.
The microstructures and transformation behavior of Ti-49Ni-20Hf, Ti-49.5Ni-20Hf and Ti-50.3Ni- 20Hf alloys, when prepared by conventional casting, were investigated and compared with the properties of the alloys prepared by melt spinning. The area fraction of (Ti,Hf)2Ni in Ti-Ni-Hf alloys decreased to 3.9% from 9.4% as Ni content rose to 50.3 at% from 49 at%. Several cracks were observed in the hot-rolled Ti-49Ni-20Hf alloy sheet but none were found in the Ti-50.3Ni-20Hf alloy sheet. The B2-B19' transformation start temperature (Ms) decreased to 476 K from 580 K as Ni content increased to 50.3 at% from 49 at%. All the as-spun ribbons were amorphous, and the activation energy for crystallization ranged from 167.8 kJ/mol to 182.7 kJ/mol based on Ni content. When annealing temperature ranged from 810 K to 873 K, crystalline Ti-Ni-Hf alloys without (Ti,Hf)2Ni particles were obtained. At annealing temperatures higher than 873 K, very fine (Ti,Hf)2Ni particles, less than 20 nm in size, were found embedded in a crystalline matrix.
