Nano-multilayered CrN/BCN coating for anti-wear and low friction applications

Co-deposition of chromium nitride (CrN) and boron carbo-nitride (BCN) was performed using a hybrid PVD system combining cathodic arc and unbalanced magnetron (UBM) sputtering, thereby creating a novel nano-multilayer coating. Subsequent TEM observation of the CrN/BCN coating showed that the coating had a layered structure of crystalline CrN and amorphous BCN. The CrN layer was 20–100-nm-thick and the BCN layer was 1–5-nm-thick. The BCN layer was found to interrupt the grain growth of the arc deposited CrN layer. Therefore, the grain size of the CrN layer was reduced considerably. The increased hardness of the CrN/BCN multilayer coating might have been caused by reduction in the grain size. Sliding tests were conducted using a reciprocating-type tribotester against bearing steel ball under dry condition. The CrN/BCN coatings had a low friction coefficient of about 0.2, which was one-third that of standard CrN coating. The wear rate of counter body (bearing steel) was also markedly reduced.