Fretting wear behavior of nano ZrO2 doped plasma electrolytic oxidation composite coatings on TC21 titanium alloy

Basic and ZrO2 doped composite plasma electrolytic oxidation coatings were prepared on the surface of TC21 titanium alloy. Subsequently, fretting wear tests of these two kinds of coated samples and the substrate alloy against GCr15 steel balls were conducted at 50 mu m and 150 mu m displacement amplitudes. The morphology, composition, valence states and topography of the fretting wear tracks were characterized and the wear mechanisms were studied. The results indicated that the porosity of the composite coatings was lower than that of the basic coatings, and the microhardness, adhesion strength and toughness were higher. When the fretting was in the partial slip regime (50 mu m displacement amplitude), the fretting damage of the three materials was slight. Meanwhile, the cracks and delamination in the microslip zone of the TC21 alloy were not observed in the coated samples. When the fretting was in the slip regime (150 mu m displacement amplitude), although the TC21 alloy and basic coatings experienced local wear, there was no significant material loss of the composite coatings, which demonstrated that the composite coatings could improve the fretting wear resistance.