Microstructure and wear resistance of CoCrFeNiMn coatings prepared by extreme-high-speed laser cladding

Abstract

In this study, CoCrFeNiMn high-entropy alloy coatings with remarkable formability were deposited on a 316-steel substrate using conventional laser cladding (CLC) and extreme-high-speed laser cladding (EHLA) techniques. The microstructure, phase composition, element distribution, microhardness, and wear properties of the coatings prepared at various deposition speeds were analyzed. The results illustrated that the coatings comprised a stable FCC solid solution phase. The microstructure of the CLC-HEA coating was predominantly composed of columnar grains with an average size of 60.8 μm, whereas the grain size of the EHLA-HEA coating decreased to approximately 32.9 μm and 24.5 μm at deposition speeds of 20 m/min and 40 m/min, respectively. The quick cooling and heating properties of the EHLA-HEA coating finally led to a lowered dilution rate, changed grain growth orientation, and enhanced dislocation density. Furthermore, the surface hardness of the EHLA-HEA coating (251 HV) surpasses that of the CLC-HEA coating (173 HV), particularly at higher deposition speeds. The wear test analysis demonstrates a transition in wear mechanisms from abrasive to adhesive, fatigue, and oxidative wear as the load increases. Moreover, EHLA-HEA coating exhibited superior wear resistance, especially at low loads (5 N); the wear rate of EHLA-HEA coating (1.07 × 10−6 mm3N−1 m−1) deposited at 40 m/min is nearly an order of magnitude lower than for CLC-HEA coating (9.97 × 10−6 mm3N−1 m−1), which is owing to its fine sub-grain structure and its higher dislocation density.