Microstructure of DD15/SC-4 dual-alloy hot isostatic pressure diffusion bonding joint

The hot isostatic pressing （HIP） technique is employed to create a diffusion-bonded joint between DD15 alloy and SC-4 alloy. This study systematically examines the impact of HIP temperature and nickel electrodeposited coating on the microstructure and elemental diffusion characteristics at the diffusion-bonded joint. The results reveal that HIP diffusion bonding effectively achieves a reliable bond between DD15 and SC-4. Both sides of the bonding interface exhibit distinct element diffusion zones and microstructure affected zones， accompanied by the precipitation of large γ' phases， carbides， and oxides in proximity to the interface. In the DD15 alloy， recrystallization occurs in a region approximately 10-20 μm from the surface. Carbides and large-sized γ' phases are present within this region. In the range of 20-140 μm away from the interface， the γ' phases undergo coarsening. For the SC-4 alloy， carbide redissolution occurs within 30 μm from the interface， and large γ' phases are observed in the vicinity of the interface.As the HIP temperature increases， the microstructure of DD15 within the heat-affected zone remains relatively unchanged， whereas the prominent γ' phase in SC-4 diminishes， and the size of carbides and oxides at the bonding interface augments. The influence of nickel plating is evident， with various shapes of γ' phases （long strip-shaped γ' phase， large γ' phase （>2 μm）， fine γ' phase （200-500 nm）） emerging near the connection interface， accompanied by the disappearance of carbides and oxides. Notably， the large γ' phases in SC-4 also vanish under this condition.