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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 16    No. 6    December 2006

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Microdefects and electron densities in NiTi shape memory alloys studied by positron annihilation
HU Yi-feng(胡益丰)1, 2, DENG Wen(邓 文)1, HAO Wen-bo(郝文博)1
YUE Li(岳 丽)1, HUANG Le(黄 乐)1, HUANG Yu-yang(黄宇阳)1, XION

1. College of Physics Science and Technology, Guangxi University, 
Nanning 530004, China; 
2. Department of Basic Science, Jiangsu Teachers University of Technology, 
Changzhou 213001, China; 
3. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

Abstract: The microdefects and free electron densities in B2, R and B19′ phases of Ni50.78Ti49.22 alloy were studied by positron lifetime measurements. Comparing the lifetime parameters of the Ni50.78Ti49.22 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 Ni50.78Ti49.22 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→RB19′ phase transformations) in Ni50.78Ti49.22 alloy with the decrease of temperature.

 

Key words: NiTi alloy; microdefect; electron density; martensite transformation

ISSN 1672-7029
CN 43-1423/U

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