Effect of spraying power on oxidation resistance and mechanical properties of plasma sprayed La-Mo-Si coating

La-doped Mo-Si (LMS) ceramic coatings were deposited on SiC-coated carbon/carbon (C/C) composites using plasma spraying at different spraying powers. The effect of spraying power on the microstructures and properties of LMS coatings was investigated. The feedstock particles were sufficiently melted and LMS coatings became more and more compact with the increase of spraying power. Especially at the power of 55 kW, a denser layer of LMS coating was obtained, which has a remarkable oxidation resistance with a mass loss of only 1.18% by comparing with other powers after oxidation in air at 1773 K for 100 h. The achieved LMS coating could endure thermal shock between 1773 K and room temperature for 25 times. Meanwhile, the final mass loss rate (0.02476) was several times lower than that of other spraying powers after the thermal cycling test. Compared with the power of 45 kW, the adhesive strength and micro-hardness of sprayed LMS coating in 55 kW were increased by 33.4% and 39.3%, respectively, which are primarily ascribed to the integrity of the oxidized coating with continuous SiO₂-rich La-Si-O glass film and silicate protective scale under the appropriate power. However, the defects of surface cracks, penetrating cracks and needle-like particles were produced within the coating when the spraying power was 60 kW due to the excessive power.