Microstructure and transformation related behaviors of a Ni45.3Ti29.7Hf20Cu5 high temperature shape memory alloy
|authors:||H.E. Karaca, E. Acar, G.S. Ded, S.M. Saghaian, B. Basaran, H. Tobe, M. Kok, H.J. Maier, R.D. Noebe, Y.I. Chumlyakov|
|publication:||Mater. Sci. Eng. A, Volume 627, 82-94|
Effects of heat treatment temperature and time on the microstructure and shape memory behaviors (e.g. transformation temperatures, load-biased shape memory effect, superelasticity, two-way shape memory effect, and related properties) were investigated in a Ni45.3Ti29.7Hf20Cu5 (at%) high temperature polycrystalline shape memory alloy. Heat treatments could be used to control the TTs and to a lesser extent recoverable and irrecoverable strains. The Ni45.3Ti29.7Hf20Cu5 alloy was capable of recovering shape memory strains of up to 2% at temperatures above 100 °C under high compressive stresses (700 MPa) and up to 0.8% TWSME strain was possible after a non-intense stress-cycling training process. However, due to high Clausius–Clapeyron slopes, large temperature hysteresis, and a strong dependence of transformation stress on temperature, fully recoverable superelastic behavior was not observed because plastic deformation occurred concurrently with the stress-induced martensitic transformation.