Tribological performance of ultra-high-molecular-weight polyethylene sliding against DLC-coated and nitrogen ion implanted CoCrMo alloy measured in a hip joint simulator

The influence on the tribological properties in a modified metal‐on‐polymer (CoCrMo/UHMWPE) articulation should be tested with DLC coated or N+ ion implanted into artificial hip joint heads. For this a diamond like carbon (DLC) film was deposited on a CoCrMo artificial hip joint head by filtered cathodic vacuum arc technique (FCVA) with a thickness of approximately 600 nm. Alternatively nitrogen ions were implanted into the CoCrMo artificial hip joint head by plasma immersion ion implantation (PIII) technology. Before wear tests, the surface morphology and topography of unmodified, DLC coated and N+ implanted CoCrMo heads were investigated by optical microscopy (OM) and stylus profilometry. Then a MTS hip joint simulator was used to characterize the tribological properties of the artificial hip joint implants. The wear loss of UHMWPE cup and wear morphology of both the CoCrMo head and UHMWPE cup were investigated after hip joint simulator wear tests. The results showed that the DLC film deposited on the CoCrMo joint head by FCVA method had excellent tribological properties and didnʹt fail during two million wear cycles while the N+ implanted layer formed on the CoCrMo head was damaged during the wear test. Compared with sliding against unmodified CoCrMo head, the UHMWPE cup had a higher wear rate when sliding against DLC coated or N+ implanted CoCrMo head. In our opinion, only applying the surface modification (DLC film or N+ implantation) on the CoCrMo head could not improve the wear resistance of metal‐on‐polymer (CoCrMo/UHMWPE) articulation for artificial hip joint implant.