Microstructure and mechanical property of CoCrFeNiAlxMn(1-x) dual-phase gradient high-entropy alloy coatings prepared by laser cladding

High-entropy alloy (HEAs), known for their balanced strength and ductility, are promising candidates for impact wear-resistant applications. In this study, CoCrFeNiAlxMn(1-x)(x = 0, 0.2, 0.8, 1.0) dual-phase gradient coatings with a layered structure were prepared using laser cladding technology to explore the microstructure evolution, tensile properties and fracture mechanism of gradient coating. As the Al content increased, the single-phase face-centered cubic (FCC) HEA coatings transitioned to dual-phase of FCC+ body-centered cubic (BCC) solid-solution, and finally to a single BCC phase. The remarkable improvement of microhardness is attributed to the dominance of the BCC phase and the impeding effect of the second phase particles on dislocation movement. The gradient coating exhibited a gradual change in internal element composition, microhardness, and structure along the depth direction, with the highest hardness value reaching 530 HV. Compared with the minimum tensile strength (69.03 MPa) and the minimum elongation (0.14 %) of single-layer coating, the gradient coatings exhibited a balance of high tensile strength and good plastic toughness, with a tensile strength of 597 MPa and an elongation of 4.08 %. Fracture analysis indicated a transition from ductile to brittle fracture in single-layer coatings as x values increased. The double-layer and four-layer gradient coatings displayed a mixed mode of brittle and plastic fracture. The study provides valuable insights into the design and fabrication of HEA gradient coatings, offering a novel approach to enhance the durability and performance of laser-clad coatings for various applications. [Display omitted]