Microstructural analysis and oxidation protection behavior of Cr–Ni surface coatings of 347 stainless steel by rapid mirror scanning of a high power CO2 laser

A surface coating technique that uses a 1 kW CO2 laser beam actuated by two high-speed raster-scanning mirrors was utilized to selectively consolidate predeposited powder coatings consisting of 50%Cr-50% Ni (wt %) over the surface of 347 austenitic stainless steel specimens. The oxidation resistance of the coated samples was evaluated by heating them in air at 750 °C for up to 300 h. The migration behavior of the coating elements was studied. Comprehensive characterization of the samples was performed using scanning electron microscopy, energy dispersive spectrochemical analysis, and optical metallography. Surface protective coatings produced by this technique demonstrated a strong metallurgical bond with homogeneous dilution, low porosity, and uniform thickness. Metallographical analysis showed migration of coating species toward the bulk preferentially by means of grain boundary diffusion as a result of high-temperature exposure. Preliminary results from this study demonstrate that the surface modification by high-speed selective raster-scanning of a high-power laser beam is a versatile and expedient technique that could be used for applications that require large surface area coverage for oxidation protection.