Effect of Hf/Zr Ratio on Shape Memory Properties of High Temperature Ni50.3Ti29.7(Hf,Zr)20 Alloys

Abstract

A series of Ni50.3Ti29.7(Hf,Zr)20 (Zr=0 to 20 at %) high-temperature shape memory alloys were investigated to determine the effect of varying Hf/Zr ratio on shape memory properties. Uniaxial constant-force thermal cycling (UCFTC) tests and electron microscopy were used to determine the effect of composition on microstructure, transformation temperatures, and functional material properties. In general, substitution of Zr for Hf resulted in a slight decrease in transformation temperatures, a negligible change in transformation strain, and an improvement in dimensional stability. Thus, the entire range of NiTiHfZr alloys resulted in acceptable actuation properties across the compositions studied with the additional ability to adjust composition for cost and mass savings.