Performance Evaluation of Laser-Deposited Functionally Graded Stellite 6-WC Tools in Friction Stir Lap Welding of CuCrZr-SS304

Tool wear is a concern in friction stir welding (FSW), which is a solid-state welding process, especially when it is applied to relatively high melting point materials beyond Al and Mg alloys, such as Cu alloys and steel. In this work, tools for friction stir lap welding (FSLW) of CuCrZr-SS304 were developed by laser-directed energy deposition (L-DED) of functionally graded Stellite 6-WC powders on H13 tool steel. While the tool shoulder was made by cobalt-based hardfacing alloy Stellite 6 powder deposition, the tool pins were fabricated using Stellite 6 mixed with 30 and 60% WC (tungsten carbide) powder. The multilayer laser deposition of Stellite 6-WC powders under ambient condition was prone to micro-cracks. This was successfully mitigated by substrate preheating. Melt pool lifetime and cooling rate monitored with an infrared (IR) pyrometer during the process were correlated with the crack mitigation, un-melted WC fraction, and hardness of the deposition. Functionally graded tool with Stellite 6-30% WC and Stellite 6-60% WC underwent pin length reduction of 16 and 6.5% after FSLW compared to that of the 17% of the pure Stellite 6 deposited tool. With an increasing percentage of WC, the better performance of the L-DED tool pin is attributed to the enhanced resistance to abrasive wear and plastic deformation.