Microdefects and electron densities in NiTi shape memory alloys studied by positron annihilation

• 作 者: HU Yi-feng DENG Wen HAO Wen-bo YUE Li HUANG Le HUANG Yu-yang XIONG Liang-yue
• 机 构: College of Physics Science and Technology, Guangxi University, Nanning 530004, China;Department of B
• 出 处: 中国有色金属学会会刊（英文版）
• 发表日期: 2006年6期
• 关键词: NiTi alloy microdefect electron density martensite transformation

The microdefects and free electron densities in B2, R and B19’ phases of Nis0.78Ti49.22 alloy were studied by positron lifetime measurements. Comparing the lifetime parameters of the Nis0.78Ti49.22 alloy measured at 295 K and 225 K, it is found that the free electron density of the R phase is lower than that of the B2 phase; the open volume of the defects of the R phase is larger, while the concentration of these defects is lower than that of the B2 phase. The Nis0.78Ti49.22 alloy exhibits B19’ phase at 115 K. In comparison with the R phase, the free electron density of the B19’ phase increases, the open volume of the defects of the B19’ phase reduces, and the concentration of these defects increases. The microdefects and the free electron density play an important role during the multi-step transformations (B2→R→B19’ phase transformations) in Nis0.78Ti49.22 alloy with the decrease of temperature.