Microstructure, hardness and slurry erosion-wear behaviors of high-speed laser cladding Stellite 6 coatings prepared by the inside-beam powder feeding method

Abstract

Stellite 6 alloy has been considered a promising coating for hydro-turbine parts owing to excellent erosion resistance. In the present work, Stellite 6 coatings have been prepared by the high-speed laser cladding technique with the inside-beam powder feeding method. Microstructure, hardness and erosion-wear behaviors of the Stellite 6 coatings have been systematically investigated. The results indicate that, there are no visible defects in all the Stellite 6 coatings; the coating thickness gradually decreases with the cladding speed while it increases with the laser power, ranging from 429.35 to 842.19 μm. The coatings are mainly composed of γ-Co and carbides, and the microstructure of γ-Co gradually displays planar, columnar, dendrite and equiaxed crystals from the substrate interface to coating surface. The second dendrite arm spacing (SDAS) of γ-Co shows positively linear relationship with the line energy density (LED). The dilution rate of Stellite 6 coating increases with the laser power and cladding speed, while the microhardness shows the opposite variation trend. The highest hardness of 610.26 HV can be obtained when the laser power and cladding speed are 1600 W and 4000 mm/min. The erosion-wear resistance of Stellite 6 coating is approximately 2–5 times higher than that of the 45# steel substrate, and it mainly depends on the coating hardness. Microcutting and impacting from abrasive particles are the predominant damage mechanisms while the corrosion attack from 3.5% NaCl solution can be negligible. Thus, the erosion resistance of Stellite 6 laser cladding coating can be further improved by enhancing the coating's hardness.