Characterization of electrolytic ZrO2 coating on Co-Cr-Mo implant alloys of hip prosthesis.

An electrolytic Zr(OH)4 gel has been coated on ASTM F-75 Co-Cr-Mo alloy specimens in 0.0625 M ZrO(NO3)2 solution with pH = 2.2 at a current density of 2 mA/cm2. After annealing at 623-973 K for 120 min in air, the ZrO2-coated specimen was 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, surface morphology observations, and XRD analysis. The ZrO2-coated specimen annealed at 773 K for 120 min revealed 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 1 1) preferred orientation parallel to the sheet plane was detected at 623 K < or = T < or = 673 K and a tetragonal structure of ZrO2 was detected at T > or = 773 K. Then a monoclinic structure with random orientation and a tetragonal structure were mixed at T > or = 973 K.