Effect of Solid-Liquid Co-existence Heat Treatment on the Phase Transformation of Hot Isostatic Press Diffusion Bonded NiCrBSi Hardfacing Layer

Using the hot isostatic press (HIP) diffusion bonding method, a 5 mm thick NiCrBSi hardfacing layer (69.454% Ni, 16.84% Cr, 3.45% B, 4.68% Si, 0.74% C, 4.79% Fe, 0.012% O, 0.034% Co, all in wt.%) was successfully deposited on stainless steel, resulting in a crack-free and fine-grained structure and a high averaged micro-hardness. A solid-liquid co-existence heat treatment (1000 ℃, holding 30 min, air cooling) was designed to solve micro-hardness variations and presence of pores and primary particle boundaries (PPBs). Comparing with microstructures of the as-HIP diffusion bonded and heat-treated hardfacing layers, significant homogeneity of microstructures, disappearance of pores and PPBs were observed. Meanwhile, complex phase transformation occurred, with fine-grained Ni, Ni3Si, Ni3B, CrB and Cr7C3 in the as-HIP diffusion bonded hardfacing layer and large-grained Ni, Cr3C2, CrB, Ni3Si, Ni31Si12 and Ni3B in the heat-treated hardfacing layer. The proposed in-situ high-temperature neutron experiment is to develop the scientific basis and fundamental understanding of phase transformation by means of solid-liquid co-existence heat treatment. The experiments will be carried out on the Engin-X at ISIS. Engin-X has the capability of measuring neutron diffraction at specified thermal conditions. We plan to run 9 samples of as-HIP diffusion bonded Ni-Cr-B-Si hardfacing layer to investigate the phase transformation during solid-liquid co-existence heat treatment process.