Ti-44.5Ni-5Cu 및 Ti-45.2Ni-5Cu(at%) 합금의 형상기억특성에 미치는 어닐링온도의 영향

The effect of annealing temperature on shape memory properties in the Ti-44.5Ni-5Cu and Ti- 45.2Ni-5Cu(at%) alloys was investigated by differential scanning calorimeter (DSC) and tensile testing. The martensitic transformation temperature of Ti-44.5Ni-5Cu(at%) increased from 308K to 324K with increasing annealing temperature and did not change with further increasing annealing temperature. This is because dislocations decreased with increasing annealing temperature due to recovery and recrystallization. However, the martensitic transformation temperature of Ti-45.2Ni-5Cu(at%) increased from 286K to 317K with increasing annealing temperature until reaching a maximum, and then decreased with further increasing annealing temperature. This is understood to be due to the decrease of Ni content in the matrix by the formation of Ti(Cu, Ni)2 at the lower annealing temperature, and the increase in Ni content in the matrix by the re-solution of Ti(Cu, Ni)2 at the higher annealing temperature. The critical stress for slip of Ti-45.2Ni- 5Cu(at%) was higher than that of Ti-44.5Ni-5Cu(at%) at the lower annealing temperature. This is because of precipitation hardening of the Ti(Cu, Ni)2. (Received May 27, 2019; Accepted July 3, 2019)