Processing and characterization of high aluminum multicomponent (Co,Ni)-based superalloys for friction stir welding (FSW) tools

Despite the great potential of Friction Stir Welding (FSW) process, there is a lack of technical information on Co-based alloys designed for FSW tools. Therefore, this work evaluated two multicomponent (Co-Ni)-based superalloys tools of high aluminum contents for better wear and oxidation resistance. The two alloys differed on the presence of either Nb or Ta in their chemical composition. The alloys were produced via vacuum induction melting / investment casting and then heat treated at 1000 degrees C for 16 h. The as-cast and heat-treated microstructures of both alloys presented gamma, gamma', Co7W6, CoAl, Laves and MC phases. Yield strength near 550 MPa at 900 degrees C and hardness values about 500 HV0.5 have been measured for both heat-treated alloys. Friction stir welding (FSW) tools of the two alloys were successfully used to weld (bead on plate) a plate of ASTM A1008 steel. However, superior results have been obtained from the Ta-alloy tool.