Electrolytic ZrO2 coating on Co-Cr-Mo implant alloys of hip prosthesis

An electrolytic ZrO₂ gel has been coated on ASTM F-75 Co-Cr-Mo alloy specimens in 0.1 M ZrO(NO₃)₂ solution at pH 2.2 and a current density of 2 mA/cm². The electrolytic ZrO₂ gel coating was annealed at 623-973 K for 120 min. in air, then evaluated by electrochemical polarization in Hank´s solution, wear tests with UHMWPE (ultra-high molecular-weight polyethylene) under a load stress of 50 Mpa, scratch tests, and morphology observations. The crystal structures of cobalt oxide and ZrO ₂ were analyzed by XRD (X-ray diffraction). The ZrO₂ -coated specimen annealed at 773 K for 120 min shows a good adhesion of 610 MPa on Co-Cr-Mo substrate, a lower wear loss of UHMWPE and a higher protection potential than the uncoated specimen in Hank´s solution. A monoclinic structure with (1¯11) preferred orientation parallel to the sheet plane was observed at 623 K⩽T⩽673 K while a tetragonal structure of ZrO₂ was detected at T⩾773 K. For T⩾973 K, a more stable monoclinic structure with random orientation mixed with a tetragonal structure was observed