Microstructure evaluation and fracture mechanism of dissimilar diffusion bonded joint of single crystal superalloy DD5 and polycrystalline superalloy GH4169

The reliable joining of DD5 single crystal superalloy and GH4169 polycrystalline superalloy was obtained by diffusion bonding method at 1120 °C for 90–180 min under 10 MPa with or without 730 °C /180 min aging process. The joint was divided into four distinct regions: GH4169 base metal zone, the diffusion zone, the structure affected zone, and DD5 base metal zone. The size, distribution and morphology of γ' phases at the whole joint were distinguishing under different bonding conditions. The morphology of γ' particles changed from nearly cubic shape into irregular sunflower shape, and nearly cubic shape growing up to cubic at the diffusion zone and DD5 base metal zone, which resulted from the operation of additional aging process at 730 °C for 180 min after bonded at 1120 °C for 180 min. Furthermore, the optimal tensile strength of the joint was 1058 MPa when the joint was bonded at 1120 °C/10 MPa/180 min and then heated at 730 °C for 180 min, of which the fracture was occurred at the base metal zone. The in-situ tensile test indicated the damage and fracture behavior of the joint resulted from the increasing slip lines and cracks in carbides.