The Role of Carbon in Wear Resistance of CoCrFeNiTi_0.5 High-Entropy Alloy Layer

The influence of C doping on the phase and microstructure of CoCrFeNiTi_0.5C_x high-entropy alloy layer is revealed in this study, and C doping improves the microhardness and wear resistance successfully. It is found that CoCrFeNiTi_0.5C_x high-entropy alloy layers with different C contents are composed of BCC solid solution (Fe-Cr-based), Ti-rich phase and TiC. The increase of C content makes the lattice constant and lattice distortion of BCC solid solution increase, and the stability of Ti atoms in BCC solid solution decrease so that Ti segregates and forms TiC. The microstructure of CoCrFeNiTi_0.5C_x high-entropy alloy layers all shows the characteristic of gradient change of "equiaxed crystal-dendrite-columnar crystal". The increase of C content makes the TiC stacked between grains dense and the microstructure refine, which results in an increase in microhardness accompanied by a decrease in frictional coefficient, friction track depth and wear rate. Especially, the nucleation, growth, and precipitation behavior of the second phase in CoCrFeNiTi_0.5C_x high-entropy alloy layer have been systematically studied. The strengthening behavior of CoCrFeNiTi_0.5C_x high-entropy alloy layer is researched with emphasis on precipitation and fine grain. Simultaneously, the friction behavior, damage mechanism and wear-resistant mechanism of CoCrFeNiTi_0.5C_x high-entropy alloy layers under different friction parameters are clearly revealed.