Microstructural Analysis of Friction Welded Joints in TiNi Alloy

Abstract

A Ti-50.7 at % Ni shape memory alloy was welded by friction welding process at several upsetting pressures. The characteristics of individual phase which relates to shape memory phenomena and mechanical properties in a weld metal was investigated and discussed. Weld metal microstructures were identified using a transmission electron microscope (TEM). It turned out that as-welded microstructure consists mainly of B2 phase and is altered to B19′ phase by a heat treatment. The NiTi2 phase was a prevailing precipitate. The density of dislocations in the B2 phase tends to increase with upsetting pressure. From these results, it can be concluded that the strength and shape memory effect of friction-welded joint in Ti-Ni alloy are comparative with those of the base metal.