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.

Effects of Er2(SO4)3 doping on characteristics of MAO coating

“…The resulting molten material then repeatedly condensed and accumulated in the discharge holes, eventually forming ‘crater-shaped’ sinter disks. 8,21,22…”

“…The resulting molten material then repeatedly condensed and accumulated in the discharge holes, eventually forming 'crater-shaped' sinter disks. 8,21,22 Based on Figure 2(c, e, g, i), the dimension of the discharge micropores and sintered disks on the surface gradually shrank and the quantity of micropores dramatically increased with the addition of Er 2 (SO 4 ) 3 . This was due to the increasing voltage caused by the addition of Er 2 (SO 4 ) 3 provided energy for MAO process.…”

“…to increase their corrosion and wear resistance. 8–10 Electrical parameters, oxidation period, electrolyte, and additives all have an impact on the coating performance. 11,12 Related research had demonstrated that adding the rare earth element Er to titanium alloys can enhance the alloy's overall performance.…”

Effect of electric mode of micro-arc oxidation on structural and phase state of calcium-phosphate coating

“…On the X-ray spectra of the coatings, peaks associated with the HA phase appeared at an applied voltage of 430 Montazeri et al [26] developed HA/TiO 2 coatings by MAO method at applied voltages of 350, 400, 450 and 500 V. The diffraction peaks of HA appeared only at the maximum applied voltage (500 V), while the peaks of the titanium alloy substrate were not found at this voltage. Besides, several works [27][28][29] on the effect of pulse current duty cycle on the microstructure and properties of CaP coatings have been reported. Chen et al [27] studied the effects of different duty cycles (10 and 50%) and oxidation times (10 and 30 min) on coating morphology, structure and hardness.…”

“…Besides, several works [27][28][29] on the effect of pulse current duty cycle on the microstructure and properties of CaP coatings have been reported. Chen et al [27] studied the effects of different duty cycles (10 and 50%) and oxidation times (10 and 30 min) on coating morphology, structure and hardness. The results of the authors show that the surface morphology of the coatings changes from crater-like micropores to foam-like protrusions with increase in the duty cycle and oxidation time.…”