Effect of quenching media on the properties of TiNi shape memory alloys fabricated by powder metallurgy

Abstract

Abstract TiNi shape memory alloys (SMAs) are one of the significantly important materials group, which serve in the advanced applications requiring unique characteristics. Although their wide use is well established, further improvement of mechanical properties is still needed. The conventional TiNi SMA is usually manufactured by casting, hot forging and heat treatment processes. In this study, Ti-x at.%Ni alloys, with x equals 50, 51, and 52, were fabricated by powder metallurgy (PM) process through spark plasma sintering, followed by hot extrusion, homogenization, solution, aging and cryogenic quenching treatment. The effects of the compositions, processing conditions, and quenching media on the microstructural and mechanical properties of the alloys were evaluated by XRD, SEM, TEM analyses and tensile hysteresis test. The results showed that hot extrusion could lead to a considerable grain refinement, while the cryogenic quenching lead to a shift in the transformation temperatures and to an improvement of the tensile properties of the alloys such as the tensile strength increment and marginally improved ductility.