Effect of Boron Coating on Rockwell-C Adhesion and Corrosion Resistance of High Entropy Alloys

CrMnFeCoNi high entropy alloy was produced in a shielding gas atmosphere using TIG melting using reverse vacuum system. The produced HEAs were covered with the pack boriding method at 1173 K and 1223 K temperatures and for 2 h, 4 h, 6 h. Boride layer microstructure, XRD and hardness measurements of these samples were examined and Rockwell-C adhesion and corrosion tests were applied. The boride layer has a flat and continuous structure and its thickness ranged from 38 to 115 µm. The sawtooth appearance increased in the coating/matrix transition region depending on the increase in temperature and time. While the uncoated HEA has a face-centered cubic lattice parameter, the surface of the coated HEAs depends on the alloy elements and boron; FeB, Fe2B, NiB, CrB, Co3B, FeNi, FeCo and Fe4Mn phases were detected. By coating the HEAs with boron, the surface hardness was increased by 10 times. According to the Rockwell-C test, the adhesion weakened due to the increase in the coating layer and the hard and brittle boride phases. In the corrosion test, the corrosion rates of boron-coated HEAs decreased compared to the uncoated samples, while the corrosion resistance increased.