Effects of Substrate Roughness on Microstructure and Fatigue Behavior of Plasma Electrolytic Oxidation-Coated Ti-6Al-4V Alloy

Ceramic coatings were prepared by plasma electrolytic oxidation (PEO) on four different surface roughness' of Ti-6Al-4V alloys. The effects of substrate roughness on the microstructure and fatigue behavior were investigated. Microstructural characterization was carried out by scanning electron microscopy (SEM) and a laser scanning confocal microscope. In addition, an X-ray diffractometer (XRD) and a U-X360 stress meter were used to analyze the phase composition and residual stress properties of the coatings. The microstructure of coatings revealed the growth mechanism of the coatings. The larger and deeper grooves of the substrate promoted the nucleation and growth of the PEO coating, but the defects (cracks and pores) of the oxide layer became more serious. The fatigue test indicated a significant influence of substrate roughness on the fatigue life under low cyclic stress. The fatigue damage of PEO coatings decreases as the surface roughness of substrates decreases because of the synergistic effect of the coating surface defects and coating/substrate interface roughness. Substrate roughness influences the quality and fatigue performance of the oxide layer.