Realizing excellent tribological properties of BCC/FCC gradient high -entropy alloy coating via an in-situ interface reaction

The simultaneous improvement of strength and toughness has been a long-standing problem in the pursuit of high-performance materials. Using a gradient-structure design that exploits the migration and recrystallization processes of elements in the molten pool, this study generates an FeCoCrNiAl intermediate interfacial layer from FeCoCrNi and FeCoCrAl powders in situ. Further, a strong and tough integrated composite high-entropy alloy (HEA) coating with an outer layer of high-strength body centered-cubic (BCC) HEA, an interface of BCC and face centered-cubic (FCC) dual-phase HEA, and an inner layer of high-toughness FCC HEA is innovatively designed and prepared. The Vickers hardness of the composite exhibited a stepped gradient of 594.4Hv(0.5), 311.8Hv(0.5), and 182.9Hv(0.5) from top to bottom. Subsequently, the surface and cross-sectional tribological behaviors of the gradient coating are studied in various air environments. The composite HEA coating overcomes the brittle fracture problem of single FeCoCrAl coatings and the adhesion problem of single FeCoCrNi coatings. The composite HEA coating exhibits a low friction coefficient, a small width/depth, and a low wear rate (0.374 x 10(-5) mm(3)/(N center dot m)). The cross-section wear is a dynamic friction process coupled with multiple wear mechanisms, and the wear marks are characterized by ladders, width changes, and debris accumulation. This new approach can guide the future development and design of HEA wear-resistant gradient coatings and HEA composite coatings.