Metallurgical investigation of laser welds in wrought Waspaloy

Wrought Waspaloy was autogenously welded by means of Nd-YAG pulsed and CO₂ continuous wave lasers and the microstructures of laser welds investigated using scanning and transmission electron microscopy. The fusion zones of as welded specimens contained fine γ′ and isolated MC carbides. The hardness profile of laser welds in wrought Waspaloy peaked at the fusion zone and heat affected zone (HAZ) boundaries, owing to fine γ′ precipitation and MC carbides in the fusion zone, and γ′ and M₂₃C₆ precipitates at the HAZ boundaries. After a full post-weld heat treatment, the hardness of the bead can be recovered to around 400 IIV but the hardness peaks at the HAZ boundaries became higher relative to the fusion zone and base material after aging at 450°C for 20 h. The microstructures in the fusion zone of post-weld heat treated welds consist of M₂₃C₆, MC, and γ′ which are quite uniform in size. The low cycle fatigue (LCF) strength of laser welds decreased to 400 MPa compared with 450 MPa for the base material. Fatigue cracks are initiated at the boundaries of the fusion zone and grow into the HAZ or along the boundary of the fusion zone. Fractography of LCF specimens showed ductile transgranular fracture.