Detonation Spraying of Refractory Metals

Due to high melting temperatures and excellent corrosion resistance of refractory metals, they are used for manufacturing parts working under extreme conditions. The formation of refractory metal coatings by thermal spraying is associated with two major challenges: 1) particles of materials having high melting temperatures should be heated to reach a semi-molten or a molten state; 2) oxidation of the metals should be prevented. In this work, the CCDS2000 detonation spray system was used for obtaining molybdenum and tantalum coatings. The coatings were deposited on steel substrates at O₂/C₂H₂=1.1 and stand-off distances of 20 mm and 100 mm. The calculation of the particle temperatures and velocities were carried out to find the optimal spraying modes for Mo and Ta powders. No oxide phases were found in the coatings obtained by spraying of the Mo powder. In the Ta-based coatings, Ta₂O₅ was found as a second phase. The hardness of the Mo coatings sprayed at 20 mm and 100 mm was 500 HV₃₀₀ and 625 HV₃₀₀, respectively. The porosity of the Mo coatings was less than 0.5% for both stand-off distances. The hardness of the Ta-based coatings sprayed at 20 mm and 100 mm was 800 HV₃₀₀ and 1000 HV₃₀₀, respectively. The porosity of these coatings was less than 1% for both stand-off distances. The bond strength of the Mo coatings determined by the pin test method was 92 and 126 MPa and that of the Ta-based coatings was 43 and 77 MPa, for coatings deposited at 20 and 100 mm, respectively.