High-temperature phase stability and tribological properties of laser clad Mo_2Ni_3Si/NiSi metal silicide coatings

摘要

Mo_2Ni_3Si/NiSi wear-resistant metal silicide composite coatings consisting of Mo_22Ni_3Si primary dendrite and interdendritic Mo_2Ni_3Si/NiSi eutectic were fabricated on substrate of an austenitic stainless steel AISI321 by laser cladding using Ni-Mo-Si elemental powder blends. The high-temperature structural stability of the coating was evaluated by aging at 800 deg C for 1-50 h. High-temperature sliding wear resistance of the as-laser clad and aged coatings was evaluated at 600 deg C. Results indicate that the Mo_2Ni_3Si/NiSi metal silicides coating has excellent high temperature phase stability. No phase transformation except the dissolution of the eutectic Mo_2Ni_3Si and the corresponding growth of the Mo_2Ni_3Si primary dendrite and no elemental diffusion from the coating into the substrate were detected after aging the coating at 800 deg C for 50 h. Aging of the coating at 800 de C leads to gradual dissolution of the interdendritic eutectic Mo_2Ni_3Si and subsequent formation of a dual-phase structure with equiaxed Mo_2Ni_3Si primary grains distributed in the NiSi single-phase matrix. Because of the strong covalent-dominated atomic bonds and high volume fraction of the ternary metal silicide Mo_2Ni_3Si, both the original and the aged Mo_2Ni_3Si/NiSi coating has excellent wear resistance under pin-on-disc high-temperature sliding wear test conditions, although hardness of the aged coating is slightly lower than that of the as-clad coating.