Rebuilding of stationary shoulder friction stir welding MP 159 probes by laser metal deposition using stellite 6 powder

Laser Metal Deposition with Powder (LMDp) is an established additive manufacturing (AM) technique with great potential for repairing and remanufacturing high-value tools. This study demonstrates, for the first time, the successful remanufacturing of worn MP159 stationary shoulder friction stir welding (SS-FSW) probes using LMDp and Stellite 6 alloy. Two deposition strategies were investigated: continuous deposition and deposition with a 10-second interlayer cooling interval. The effects on microstructural evolution, bonding integrity, and mechanical performance were evaluated. The cooling-assisted process enabled the deposition of six homogeneous and geometrically precise layers, compared to four in the continuous build, while significantly reducing thermal accumulation. Microstructural characterization revealed dense, crack-free deposits with strong metallurgical bonding between Stellite 6 and the MP159 substrate. The heat-affected zone (HAZ) exhibited recrystallization and grain coarsening accompanied by a BCC→FCC phase transformation in the substrate, forming a ductile buffer that enhances durability. Interlayer cooling refined the dendritic morphology, minimized remelting, and reduced HAZ thickness from 80 µm to 30 µm, indicating improved thermal control. Microhardness profiles showed consistent values (500–550 HV) across deposited layers, with localized softening (300 HV) in the HAZ due to tempering. These results confirm that LMDp with controlled cooling provides a sustainable, high-integrity, and cost-effective approach for restoring cobalt-based FSW tools.