Core-shell structured h-BN@Ni reinforced CoCrNi-based self-lubricating composites

Abstract

h-BN solid lubricant is added for reinforcing the wear resistance and strength of CoCrNi medium entropy alloy (MEA). However, the poor wettability of h-BN with alloy substrates limits its engineering application. Herein, core-shell structured h-BN@Ni powders were prepared to improve the wettability of h-BN and CoCrNi MEA matrix. Specifically, h-BN@Ni powders were manufactured by a new electroless plating method with silver nitrate activation. The results indicate that the effect of using silver nitrate is comparable to or even superior to that of palladium or ChCl-EG ionic liquid additive, while the cost required to prepare h-BN@Ni powders is much lower than the other two. Further, CoCrNi-based self-lubricating composites were prepared by powder metallurgy. The results demonstrate that the nickel coating improves the wettability between h-BN and CoCrNi matrix, resulting the enhanced strength, plasticity and wear resistance of CoCrNi/BN@Ni. Specifically, the yield and tensile strengths of CoCrNi/BN@Ni MEA are about 15.0 % and 14.7 % higher than CoCrNi MEA, respectively. The strain of CoCrNi/BN@Ni MEA is approximately 12 % and 19 % higher than that of CoCrNi/BN MEA and CoCrNi MEA, respectively. Moreover, CoCrNi/BN@Ni MEA has a lower wear rate than the other two by about 26.4 %, and the hardness of CoCrNi composites with h-BN or h-BN@Ni is about 11.8 % higher than CoCrNi MEA.