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.