Effect of Laser Cladding with Constant Specific Energy on the Hardness and Friction Properties of Stellite 21 Coatings on AISI 304 Stainless Steel

This study aims to investigate the coating properties of Stellite 21 powder laser-clad on 304 stainless steel substrates with different laser parameters, but under the same specific energy. The surface hardness of the coating was analyzed using a Vickers hardness tester and a nanoindenter instrument, while the microstructure and wear mechanisms were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). Under the same laser energy density conditions, the 1260 W-540 mm/min process (S3) produced a fine equiaxed structure containing dispersed chromium-rich carbides. The coating surface achieved a maximum average microhardness of 420.51 HV0.3, but its wear resistance was the worst, with a wear rate of 7.4 × 10−2 μm3·N−1·μm−1. By comparison, the 1400 W-600 mm/min sample (S2) formed a relatively stable carbide network structure, exhibited the smallest fluctuation in friction coefficient, and had a lower wear rate of 5.2 × 10−2 μm3·N−1·μm−1. The results indicate that identical laser energy density does not guarantee the same coating performance; the matching of power and scanning speed can significantly alter the thermal history and microstructural characteristics of the melt pool.