Laser welding and microstructural characterization of dissimilar γ-TiAl-Ti6242 joints

Abstract

Crack-free dissimilar TNM-Ti6242 joints were successfully obtained by laser welding with preheating temperatures of 400 °C, 600 °C and 800 °C, in spite of the differing thermophysical properties of the used alloys. The microstructure of the joints was investigated by optical microscopy, SEM, EDX, EBSD and the local mechanical properties were determined by microhardness measurements. The microstructure coarsens with increasing preheating temperature. Homogenous mixture of both alloys in the fusion zone was achieved, even so local microsegregations of Ti, Al and Nb occurred. The fusion zone mainly consists of α2 (Ti3Al). A transition zone, present as a β/βO seam, was revealed for preheating temperatures of 400 °C and 600 °C. For preheating to 800 °C the β/βO seam was penetrated with α2 lamellas. Since the alloying elements of the other alloy were detected in the heat-affected zone, diffusion processes occurred. The average microhardness in the fusion zone of the dissimilar TNM-Ti6242 joints is independent of the preheating temperature and is higher than the base material microhardness. Comparing the microhardness in the fusion zone of similar Ti6242 and TNM joints with dissimilar TNM-Ti6242 joints, the microhardness values of the dissimilar TNM-Ti6242 joints range between the values of the similar Ti6242 and TNM joints. However, the values in the fusion zone are closer to the microhardness values of the similar TNM joint, which is caused by the mainly α2 containing fusion zone of the dissimilar TNM-Ti6242 joints.