Surface modification of refractory ceramic using combined flame spraying and laser surface coating

Combined flame spraying of 20wt%Cr₂O₃-80wt%Al₂O₃ powder and simultaneous CO₂ laser surface melting has been developed as an accelerated process to improve the surface properties of an alumina-based refractory ceramic. The thicknesses, numbers and lengths of cracks, phases, microstructures and high-temperature erosion-corrosion resistances of the surface layers modified by the combined process have been investigated and compared with respect to laser irradiation intensity, powder feed rate and workpiece traverse velocity. The thickness, crack length and density values were measured with an optical microscope. The phases and microstructures were identified and observed using X-ray diffraction and scanning electron microscopy. The high-temperature erosion-corrosion resistance was evaluated in a laboratory fluidized bed facility at 550 °C. Results obtained have shown that both the laser irradiation intensity and the powder feed rate were critical factors for the treated surface layers, with relatively dense microstructures, stable phase constituents and smaller cracks leading to improved high-temperature erosion-corrosion resistance. Currently, a rate of area coverage of 20 mm²/s has been used to produce a treated surface layer, approximately 2 mm in thickness, with improved microstructural integrity and performance when compared with the as-received refractory ceramic material.