Microstructure Characterization and Robust Lubrication Performance of CoCrNi Medium Entropy Alloy with Advanced Electrochemical Boronizing Treatment

CoCrNi medium-entropy alloy (MEA) is a promising material for aviation and aerospace applications due to its excellent strength and ductility. However, its low surface hardness and poor wear resistance pose challenges for its tribological performance. To address this issue, electrochemical boronizing is explored as a potential solution, offering advantages such as a fast boronizing rate and low cost. This study demonstrates that electrochemical boronizing can significantly enhance the surface hardness and self-lubrication performance of CoCrNi MEA, as well as retain impressive mechanical performance. Results show that a boronized layer with a thickness of about 50 μm is formed on the surface in 45 min. The boronized layer is mainly composed of Co₂B, Ni₂B, CrB, CoB, and Ni₃B. After boronizing, the surface hardness of the sample increases by about 9 times, and the ultimate tensile strength and uniform elongation can reach 97% and 73% of the original sample, respectively. Compared with the original alloy, the friction coefficient and wear rate of boronized MEA are reduced by 38% and 85% under deionized water conditions, respectively. X-ray photoelectron spectroscopy analysis reveals the generation of boron-containing tribofilm on the wear scars, which significantly reduces friction and wear during the friction process.