Effect of Pulse Duty Cycle and Oxidation Time on Microstructure and Properties of Micro-arc Oxidation Coatings on Ti6Al4V Alloy

Abstract

Micro-arc oxidation (MAO) technology can in-suit generate coatings with high hardness and strong adhesion on the surface of titanium alloy, thereby greatly improve the application range of titanium alloy. The morphology and properties of coatings are controlled by changing electrical parameters such as duty cycle and oxidation time. This work mainly aims to study the influence of different duty cycles and oxidation times on MAO coatings microstructures and properties of Ti6Al4V alloy under the condition of constant voltage and pulse frequency. The scanning electron microscopy (SEM) and X-ray Diffractometer (XRD) were used to investigate into MAO coatings microstructure and phase composition. The roughness, porosity, thickness, and microhardness of MAO coatings were evaluated respectively by roughness tester, thickness gauge, and microhardness tester. The results show that surface morphology of the MAO coatings change from crater-like micropores to foam-like protrusions with the enhancement of duty cycle and oxidation time. When duty cycle is 50% and oxidation time is 30 min respectively, the ejection of the molten material made the MAO coating surface appear foam-like protrusions, and the surface morphology is seriously damaged. When the oxidation time and the duty cycle are 30 min and 10% respectively, the rutile phase intensity is the maximum, and further increasing the duty cycle will lead to a rutile phase decrease. In a limit range, the hardness rise with increase of oxidation time and duty cycle. The highest hardness is 668.85 HV.