Abstract:In order to improve oxidation resistance of niobium alloy, an Al-Si coating was obtained on the surface of the niobium alloy by Al-Si co-deposition method and then a MoSi2 coating was prepared continuously by laser cladding technique. The growth mechanism of the Al-Si co-deposition was investigated and the high-temperature oxidation resistance was discussed by comparing the Al-Si layer to the MoSi2/Al-Si coating. The results showed that the formation process of the Al-Si coating is derived from the sequential deposition of Al and Si elements, and Al3Nb phase is preferentially formed. The thickness X and the holding time t follow the relationship: x=At1/2+7.4, here A= 11.6 at 1000 ℃ and A= 16.2 at 1050 ℃. The MoSi2/ Al-Si coating prepared by laser cladding was uniformly continuous and compact, which was tightly bound to the substrate without cracks and holes found. MoSi2, Al3Nb, NbSi2, Nb5Si3 and Mo(Si,Al)2 phases were detected in the as-deposited duplex coatings. After oxidation at 1200 ℃, a large amount of SiO2 were formed to prevent the inward diffusion of oxygen atoms on the Al-Si coating and the MoSi2/Al-Si coating, respectively. Compared with the Al-Si coating, presence of continuous oxide scales on the duplex coatings effectively avoids rapid consumption of the Al-Si layer, so that the MoSi2/Al-Si coating exhibited more excellent high temperature oxidation resistance.