Mechanical properties and joining mechanism of hot isostatic pressing (HIP) diffusion bonded Ni60A-0Cr18Ni10Ti heterogeneous joint

Ni-Cr-B-Si alloys, as alternative alloys for Co-based alloys, are expected to be used in pump in nuclear power plants owing to their excellent wear resistance and lower dose rate. In this work, Ni60A (Ni-Cr-B-Si) hardfacing layer with high hardness (average 898 HV0.2) and excellent bonding strength (ultimate tensile strength 549 MPa) was fabricated onto 0Cr18Ni10Ti (GB/T 1220–2007) austenite steel by hot isostatic pressing (HIP) diffusion bonding technique. The Ni60A-0Cr18Ni10Ti heterogeneous joint was divided into four regions based on the microstructural difference, namely Ni60A hardfacing layer, transition zone, deformation zone and 0Cr18Ni10Ti substrate. The Ni60A hardfacing layer was mainly composed of CrB, Cr7C3, Ni3B, Ni3Si and rarely γ-Ni phases, and the synergistic effects of hard phase contents and fine grain sizes resulted in the high hardness. The transition zone was predominantly composed of equiaxed (Ni, Fe) solid solution ((Fe, Ni)ss), which was attributed to diffusion-induced recrystallization (DIR). The deformation zone exhibited discernible deformation texture, which was induced by the plastic deformation of the substrate during the HIP process. Meanwhile, nano-twins (NTs) and Cr2B borides were observed in the deformation zone near the interface, while Cr-rich carbides were observed in the deformation zone away from the interface. Uniaxial tension results of the joint revealed that the failure initiated on the Ni60A side, approximately 70 μm away from the interface, was attributed to a greater prevalence of Cr7C3 precipitates with notable stacking faults.