Microstructure and shape recovery characteristics in a TIG-welded Fe-Mn-Si-Cr-Ni shape memory alloy

Abstract

Microstructure of an Fe-Mn-Si-Cr-Ni shape memory alloy (SMA) after being TIG (tungsten-insert gas welding) welded was investigated using scanning electron microscope (SEM) and X-ray diffractometer. The results show that dendrite crystals composed of cellular sub-structures form in the weld zone due to remelting. There is no obvious change in microstructure of the heat-affected zone (HAZ) except for some degree of growth of austenite grains. Since both the weld zone and HAZ consist of single phase of austenite (γ), pre-strain can still induce the γ→ε martensite transformation in welding joints of the alloy. Effect of TIG welding on shape recovery characteristics of the alloy was examined by bending tests and it was found that the TIG-welded Fe-Mn-Si-Cr-Ni alloy exhibits almost the same excellent SME as the base material.