Phase Transformations and Super-Elasticity of a Ni-Rich TiNi Alloy with Ultrafine-Grained Structure

Abstract:

A Ni-rich Ti-50.7.at%Ni alloy was processed by Equal Channel Angular Extrusion (ECAE) at 500°C. After 8 passes ECAE, microstructure was refined to sub-micron scale, approximately 0.2 μm～0.3 μm. TEM observation reveals that Ti3Ni4 phase precipitated in Ni-rich Ti-50.7.at%Ni alloy during the preheating treatment before each ECAE pass, but re-dissolved during sequent ECAE processes. After ECAE treatment, the B2R transformation occurred within a larger temperature range. Comparing with the solution-treated TiNi specimen, the martensitic transformations start (Ms) and peak temperatures (Mp) of TiNi specimens ECAEed were dramatically lowered. Super-elasticity characteristics of TiNi alloy were tested by tensile loading and unloading cycles. The results reveal that at a tensile strain of 4% or smaller, ultrafine-grained (UFG) TiNi alloy processed by 4 passes ECAE shows better super-elasticity than solution-treated sample. Microstructure evolution and its effect on phase transformations and super-elasticity characteristics have been discussed.

• Periodical: Materials Science Forum (Volumes 667-669)
• Pages: 1137-1142
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.667-669.1137
• Online since: December 2010
• Authors: Zhi Guo Fan, Jie Song, Xiao Ning Zhang, Chao Ying Xie
• Keywords: Equal Channel Angular Extrusion (ECAE), Martensitic Transformation (MT), R-Phase Transformation, Super Elasticity, Ti₃Ni₄ Preciptitates, TiNi Shape Memory Alloy

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