Effect of compressive stress aging on transformation strain and microstructure of Ni-rich TiNi alloy |
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Authors: | Jin-Feng Li Zi-Qiao Zheng Xi-Wu Li Shi-Chen Li |
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Affiliation: | aSchool of Materials Science and Engineering, Central South University, Changsha 410083, China;bThe Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Changsha 410083, China |
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Abstract: | The Ti–50.7%Ni (atom fraction) alloy rods were compressive stress aged at 400 °C, 450 °C and 500 °C for different time, their strain behaviors accompanied by temperature elevation were investigated, and their microstructures were observed. It is found that the compressive stress aged TiNi alloy rod displays an obvious contractive strain behavior in the stress direction as the temperature is elevated from approximately 55–75 °C. Compressive stress causes the parallel alignment of the aging precipitate Ti3Ni4 in the TiNi alloy, which controls the martensitic transformation (B19′ transformation) and its reverse transformation, leading to its contractive strain behavior accompanied by temperature elevation. The contractive strain of the TiNi alloy compressive stress aged at 400 °C for 100 h is increased with increasing compressive stress up to 140 MPa. Higher aging temperature and longer aging time lead to the coarsening of the precipitates and the enlarging of the inter-precipitate spacing, and therefore result in a decrease in the contractive strain. |
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Keywords: | TiNi alloy Compressive stress aging Transformation strain Microstructure |
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