Effect of compressive stress aging on transformation strain and microstructure of Ni-rich TiNi alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2009-10, Vol.523 (1), p.207-213
• Main Authors: Li, Jin-Feng, Zheng, Zi-Qiao, Li, Xi-Wu, Li, Shi-Chen
• Format: Article
• Language: English
• Subjects: Compressive stress aging; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Martensitic transformations; Materials science; Microstructure; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Solid solution, precipitation, and dispersion hardening; aging; TiNi alloy; Transformation strain; Treatment of materials and its effects on microstructure and properties
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2009.06.050

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 Ti 3Ni 4 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.