High-temperature phase stability and tribological properties of laser clad Mo2Ni3Si/NiSi metal silicide coatings

Mo2Ni3Si/NiSi wear-resistant metal silicide composite coatings consisting Of Mo2Ni3Si primary dendrite and interdendritic Mo2Ni3Si/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 degreesC for 1-50 h. High-temperature sliding wear resistance of the as-laser clad and aged coatings was evaluated at 600 degreesC. Results indicate that the Mo2Ni3Si/NiSi metal silicides coating has excellent high temperature phase stability. No phase transformation except the dissolution of the eutectic Mo2Ni3Si and the corresponding growth of the Mo2Ni3Si primary dendrite and no elemental diffusion from the coating into the substrate were detected after aging the coating at 800 degreesC for 50 h. Aging of the coating at 800 degreesC leads to gradual dissolution of the interdendritic eutectic Mo2Ni3Si and subsequent formation of a dual-phase structure with equiaxed Mo2Ni3Si 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 Mo2Ni3Si, both the original and the aged Mo2Ni3Si/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. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.