Microstructure evolution, mechanical properties of FeCrNiMnAl high entropy alloy coatings fabricated by laser cladding

Abstract

In this work, FeCrNiMnAl high entropy alloy (HEA) coatings under different laser energy density (Led, 50–92 J/mm2) were fabricated on 17-4PH stainless steel by laser cladding (LC). The influence of different laser energy density on the geometric morphology, microstructure, microhardness and tribological properties of HEA coating was investigated. To obtain the specific solidification parameters (temperature gradient and solidification rate), the finite element model was established to express the transient change of molten pool temperature field. The columnar-to-equiaxed transition (CET) corresponding to different zones of HEA coating was revealed. The result showed that the geometric parameters increased with the rise of Led because of the Marangoni convection. Equiaxed crystals and columnar crystals were distributed on the top and bottom zones of HEA coatings respectively, and the CET behavior was observed. Higher temperature gradient and lower solidification rate were conducive to the growth of columnar-crystals. Furthermore, at the Led of 92 J/mm2, HEA coatings showed relatively high crack sensitivity. HEA coatings significantly improved the tribological properties owing to metal oxide particles generated by oxidation. In the mechanical properties test, the maximum microhardness of prepared HEA coating (1800 W) was 587.83 HV0.2, which was 1.63 times that of 17–4PH substrate. Metal oxide particles generated a flat wear-resistant enamel layer which protected the coating surface. The tribological properties was optimal at the Led of 64 J/mm2, the average friction coefficient and wear rate were 0.4654 and 7.026 × 10−8 mm2/N, respectively.