Preparation and properties of B-modified MoSi2 powders for laser cladding

Due to the formation of protective borosilicate scale during high-temperature oxidation, Mo-62Si-5B (at.%) alloy is deemed to be the promising candidate of high-temperature oxidation resistant coatings. Nevertheless, it faces the challenges on the application on surface engineering due to the difficulty of powder fabrication. In the present study, the pre-alloyed powder was obtained by mechanical crushing from Mo-62Si-5B bulk alloy fabricated by vacuum induction levitation melting. Subsequently, the original powder was further sieved by 60 mech sifter for the compatibility of laser cladding. The size distribution, morphology, oxygen content and phase composition of the powder were characterized. The results show that the D(50) of the powder is 130.55 μm and the average particle size is 124.65 μm. There are MoSi2 and MoB2 phases distributed in the powder with irregular morphologies, which is accord with the bulk Mo-62Si-5B alloy. The oxygen content of the powder is lower than 0.11%, meeting the requirements of the powder for laser cladding. A laser cladded layer was prepared on Nb-Si based alloy substrate by using the powders, which exhibits dense structure free of voids and cracks. The study proves the feasibility of pre-alloyed Mo-62Si-5B powder, which may give guidance for producing Mo-Si-B system oxidation-resistant coating by laser cladding or thermal spraying.