Microstructure and Thermomechanical Properties of Shape Memory Alloys TI50-NI50 Elaborated by Arc Melting and by Powder Metallurgy

Abstract

This study was focussed on the elaboration and transformation of Ti 50 Ni 50 shape memory alloys in relation to structural and thermomechanical properties. An original method for producing TiNi alloys by powder metallurgy (PM), though combustion synthesis, was developed. After hot extrusion, intemetallic rods without porosity were obtained. Microstructural and termomechanical properties of products obtained by this method were systematically compared to those of some alloys elaborated by the more conventionnal method of arc melting (AM). For comparison, cast products were hot rolled at different temperatures; for all the transformation conditions used, the grain size remained coarser and more heterogeneous compared to PM products. Investigation of the thermomechanical behaviour was conducted by tensile and flexion tests. It was found that: - The ultimate tensile strength and the recovery stress were in the same range for PM and Am products but the ductibility of PM products was enhanced. - The better one way shape memory recovery is obtained for a PM product with an oxygen content of about 1200ppm. Also, too low content of oxygen (<600ppm) seems to decrease the stress and strain recovery during thermomechanical cycling