Abstract In order to control the shape memory function of TiNi alloy weld joint, it is necessary to clarify the effect of the three different parts (weld metal, heat-affected zone (HAZ) and base metal) on the shape recovery temperatures of the whole weld joint, but few reports are available on this aspect. In this work, the microstructure in the HAZ was studied by Gleeble thermal-simulation test. Phase transformation temperatures of weld joint, weld metal, HAZ and base metal were measured by differential thermal analysis. The inverse phase transformation temperature was analyzed. The microstructure, distribution of precipitation and crystal structure were investigated by using OM, SEM and XRD. The weld joint shows the similar shape recovery ratio to the base metal, but the shape recovery temperature range is significantly different. The start recovery temperature of the weld joint is lower about 40 ℃ than that of the base metal. Both of the austenite start temperature (As) and finish temperature (Af) of the weld metal and HAZ vary much compared with the base metal. The change in the weld metal is attributed to the fusion-solidification process, in which the preferred crystal orientation is lost. The newly formed precipitation phases show a small size and an uneven distribution. The change in the HAZ refers to the drop of As and Af, which is possibly caused by the solution of minor precipitation phase in the matrix. The Asand Af of the laser weld joint are quite the same as those of the weld metal for TiNi shape memory alloy, which indicates that the key to guarantee the shape memory function lies in controlling the phase transformation temperatures of the weld metal.
