Electrolytic ZrO/sub 2/ coating on Co-Cr-Mo implant alloys of hip prosthesis

An electrolytic ZrO/sub 2/ gel has been coated on ASTM F-75 Co-Cr-Mo alloy specimens in 0.1 M ZrO(NO/sub 3/)/sub 2/ solution at pH 2.2 and a current density of 2 mA/cm/sup 2/. The electrolytic ZrO/sub 2/ 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/sub 2/ were analyzed by XRD (X-ray diffraction). The ZrO/sub 2/-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/spl les/T/spl les/673 K while a tetragonal structure of ZrO/sub 2/ was detected at T/spl ges/773 K. For T/spl ges/973 K, a more stable monoclinic structure with random orientation mixed with a tetragonal structure was observed.