Effect of aqueous solution and load on the formation of DLC transfer layer against Co–Cr–Mo for joint prosthesis

•DLC coating was deposited on Co–Cr–Mo alloy by unbalanced magnetron sputtering. The coating exhibits amorphous carbon phase.•The DLC transfer layer formed on the pin under physiological saline solution.•The effect of bovine serum albumin on friction and wear is attributed to the formation of albumin tribolayer.•The tribological test showed the albumin can inhibit the formation of DLC transfer layer.

Diamond-like carbon (DLC) coating exhibits excellent mechanical properties such as high hardness, low friction and wear, which offer a promising solution for the metal-on-metal hip joint implants. In the study, the hydrogen-free DLC coating with the element Cr as the interlay addition was deposited on the surface of the Co–Cr–Mo alloy by a unbalanced magnetron sputtering method. The coating thickness was controlled as 2 µm. Nano-indentation test indicated the hardness was about 13 GPa. DLC coated Co–Cr–Mo alloy disc against un-coated Co–Cr–Mo alloy pin (spherical end SR9.5) comprised the friction pairs in the pin-on-disc tribotest under bovine serum albumin solution (BSA) and physiological saline(PS).The tribological behavior under different BSA concetrations(2–20 mg/ml), and applied load (2–15 N) was investigated.DLC transfer layer did not form under BSA solution, even though different BSA concetration and applied load changed. The coefficient of friction(COF) under 6 mg/ml BSA at 10 N was the lowest as 0.10. A higher COF of 0.13 was obtained under 20 mg/ml BSA. The boundary absorption layer of protein is the main factor for the counterparts. However, the continous DLC transfer layer was observed under PS solution, which make a lower COF of 0.08.