Solidification Rate Dependence of Microstructures and Transformation Behavior of Ti–Ni–Hf Alloys
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 (M
s) 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.
Keywords: Crystallization; Melt Spinning; Phase Transformation; Superelasticity; Ti–Ni–Hf Alloys
Document Type: Research Article
Affiliations: 1: School of Materials Science and Engineering and RIGET, Gyeongsang National University, 900 Gazwadong, Jinju, Gyeongnam 660-701, Korea 2: Department of Advanced Materials Science and Engineering, Keimyung University, 1000 Shindang-dong, Dalseo-gu, Taegu 704-701, Korea
Publication date: 01 September 2018
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