Surface strengthening and self-lubrication enhancement of CoCrNi medium-entropy alloy by powder-pack boronizing

The CoCrNi medium-entropy alloy (MEA) exhibits an impressive ductility, but its low hardness (-352 HV) and poor wear resistance limit its engineering applications. In this study, a significant increase of surface hardness and enhancement of self-lubrication were achieved for the CoCrNi MEA using powder-pack boronizing. Results indicate that dual reaction layers with a total thickness of about 50 mu m were formed on the surface. These two strengthened layers are mainly consisted of silicide (Ni2Si) and borides (CoB, Cr5B3). The hardness of the affected region reaches to 11-21 GPa dependence on the cross-sectional depth, being about 6 times higher than that of untreated MEA. In the deionized water condition, the friction and wear rate reductions of the boronizing treated specimen reach to about 25% and 63%, respectively. Energy Dispersive Spectrometer (EDS) and X-ray Photo-electron Spectroscopy (XPS) analysis on the wear scars showed that a silicon/boron-containing tribofilm was formed under the water environment, which reduces the friction coefficient and enhances the wear resistance. Our study demonstrates that powder-pack boronizing is a powerful way to enhance surface hardness and self-lubrication properties of CoCrNi MEA.

Automated summary

The study achieved a significant increase in surface hardness and enhancement of self-lubrication for the CoCrNi MEA using powder-pack boronizing, forming dual reaction layers and reducing friction and wear rate in deionized water condition.