Effect of interpass temperature on in-situ alloying and additive manufacturing of titanium aluminides using gas tungsten arc welding
Through the combination of in-situ alloying and additive manufacturing with gas tungsten arc welding, a new approach to fabricating titanium aluminide alloys is proposed. This innovative and low cost process has many similarities to multipass welding. It has been a generally accepted practice to maintain a specified interpass temperature when multipass welding many different alloys to prevent defects such as cracks. Increasing the interpass temperature can facilitate phase transformation by extending the high temperature period and produce the desired weld microstructure.This study examines the influence of different interpass temperatures on in-situ alloyed and additively manufactured γ-TiAl alloy. The microstructure, chemical composition, phase constitution and microhardness of all the test components were respectively examined by using light microscopy, SEM-EDS, X-ray diffraction and a Duromain 70 Hardness Tester. No appreciable changes in microstructure and composition were found as interpass temperature was changed. However, as the interpass temperature was increased from 100°C to 400°C, a decrease of α2 phase fraction was observed due to the lower cooling rate. Consequently, the microhardness value also decreased. A further increase of interpass temperature to 500°C produced only minor reductions in the brittle α2 phase fraction and the microhardness value. In view of these results, a suitable interpass temperature was found for producing crack-free components.