Microstructure and mechanical properties of dissimilar diffusion bonded joints of Haynes 230 and Haynes 188 superalloys

This study focuses on the microstructure evolution and mechanical properties of dual metal diffusion bonded joints formed between Haynes 230 Ni-based superalloy bars and Haynes 188 Co-based superalloy plates. Joints were fabricated under vacuum conditions at 1200 °C, applying bonding pressures of 2, 5, and 10 MPa for a duration of 1 h. The microstructural evolution mechanism were extensively investigated via SEM, EPMA, EBSD, and TEM technologies, and the mechanical properties and fracture behaviors were also evaluated comprehensively at both macro and micro scales. Joints with no obvious voids were obtained, and the interfacial reaction was analyzed based on the elemental distribution and lattice structure calibration. An increase in bonding pressure facilitated recrystallization, while grain boundary migration was observed at pressures of 5 and 10 MPa. Along the boundary of the grown grain, intergranular cubic Cr2O3 and orthorhombic CrO3 were detected. Additionally, W-rich carbide and silicide were found at the triple junction in close proximity to the migrated grain boundaries. The precipitation of CrO₃ and W₅Si₃ exhibited an orientation relation of [020]_BCC//[020]_BCO. Two types of lanthanides were identified, combined with O and C respectively. The maximum tensile strength of 915.47 MPa, corresponding to approximately 98 % of the base material, was achieved in the joint fabricated under 5 MPa. The joint bonded under 10 MPa demonstrated the best elongation and impact toughness. EBSD patterns illustrated significant recrystallization and grain boundary migration in the joint bonded under 10 MPa, and the fractography revealed abundant dimples and ductile shearing lips. Nanoindentation testing revealed minimal differences in the microhardness, Young's modulus, and elastic recovery among joints bonded under various pressures, indicating a reliable bonding match between Haynes 188 and 230.