Microstructure and Mechanical Properties of MoSi2 Coatings Prepared by High-Velocity Oxygen-Fuel Spraying

Refractory alloys, such as NbW5-1, are susceptible to catastrophic oxidation failure in high-temperature environments. The application of MoSi2 coatings on the surface is an effective approach to address this issue. MoSi2 coatings in the case were deposited via high velocity oxygen fuel (HVOF) spraying. A systematic orthogonal experimental design was used to investigate the effects of spray distance, powder feeder rotation speed and carrier gas flow rate on the microstructure, phase composition, porosity and mechanical properties of the coatings. The results showed that spray distance was the most important process parameter affecting coating performance. Nine coatings deposited in the case all primarily contained MoSi2 and a fraction of Mo5Si3. The coating deposited under the optimal process parameters (spray distance of 200 mm, propane pressure of 8 bar, powder feed r of 23 g/min, oxygen pressure of 10 bar, gun traverse speed of 180 mm·s−1 and carrier gas flow rate of 900 NL/h) exhibited a dense microstructure with a few isolated pores (porosity of 2.75%). This coating exhibited relatively optimal overall mechanical properties within the parameter range investigated in this study, with a Vickers hardness of 854 HV, an elastic modulus of 418 GPa and a fracture toughness of 4.41 MPa·m1/2. Therefore, high-melting-point MoSi2 coatings can be successfully deposited by using HVOF technology through its optimal process parameters.