Evolution of thermal and mechanical properties of Nitinol wire as a function of ageing treatment conditions
As-received and cold-worked 55Ni–45Ti wt% Nitinol wire samples were subjected to various ageing treatments. Experiments show that the properties of as-received Nitinol, including microstructure, critical temperatures in thermally induced phase transformation, and critical stresses/strains in mechani...
| Main Authors: | , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
Elsevier
2019
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| Summary: | As-received and cold-worked 55Ni–45Ti wt% Nitinol wire samples were subjected to various ageing treatments. Experiments show that the properties of as-received Nitinol, including microstructure, critical temperatures in thermally induced phase transformation, and critical stresses/strains in mechanically induced phase transformation, change significantly after ageing process at 773 K for different durations ranging from 10 min to 5 h. BSE and EBSD/EDS analysis shows that the predominant microstructural evolution is a large increase in Ni4Ti3 precipitate volume fraction, while grain growth is negligible. DSC results show that as-received material exhibits little to no phase transformation during heating-cooling cycling at 5K/min, while various ageing durations lead to the emergence of phase transformation that occurs at different critical temperatures. Tensile loading experiments conducted using a test rig equipped with a heater revealed the evolution of mechanically induced phase transformation behaviour. Mathematical models are proposed to predict the dependence of critical temperatures and critical stresses/strains on the ageing treatment conditions and alloy composition. |
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