Structure and properties of HEA-based coating reinforced with CrB particles

Introduction. Currently, a new class of materials, namely high-entropy alloys, is an active area of research. One of the areas of its application is the fabrication of protective coatings with high performance properties. The high-entropy alloy of CoCrFeNiMn composition is characterized by high ductility, which is retained both at elevated and cryogenic temperatures, as well as high thermal stability and, thus, can be considered as promising materials for protective coatings formation. At the same time, its disadvantages are low hardness and strength. It is known that the reinforcement of the CoCrFeNiMn high-entropy alloy with hardening particles is an effective way to improve the mechanical properties of coatings. It is assumed that the addition of hardening boride particles affects positively on the mechanical characteristics of the alloy. The aim of this work is to study the structural and phase states and wear resistance of coatings based on a CoCrFeNiMn high-entropy alloy reinforced with CrB particles. Coatings obtained by the method of non-vacuum electron-beam surfacing of powder mixtures with different mass ratios of CoCrNiMn metal powders to the CrB powder (100:0, 95:5, 90:10, 80:20, 70:30) are studied in this work. To investigate the structure and phase composition of the coatings, such methods as optical microscopy, scanning electron microscopy and X-ray diffraction analysis were applied. To study the elemental composition, energy-dispersive X-ray analysis was used. The mechanical properties were evaluated based on the microhardness measuring results. The wear resistance of the coatings was determined under conditions of dry sliding friction during reciprocating motion. Results and discussion. The addition of CrB powder to the surfacing mixture led to the formation of eutectic structures. When 5 wt. % CrB was added, a hypoeutectic structure is formed in the coating. An increase in the amount of CrB leads to the formation of coatings with a hypereutectic structure containing primary borides. The main phases found in the coatings are the fcc solid solution, and (Cr,Mn,Fe)2B, (Ni,Co,Mn)2B, CrB borides. All the studied coatings are characterized by an adhesive wear mechanism. The addition of 20 % and 30 % CrB to the surfacing mixture composition results in the wear resistance increase of the high-entropy alloy-based coatings by 3.6 and 6.1 times, respectively.