| TC4 titanium alloy has been widely used in petrochemical,aerospace,automobile and ship fields due to its excellent corrosion resistance,good toughness and weldability.However,TC4 titanium alloy is also vulnerable to oxidation and corrosion in some high temperature service environments.Which severely limits the application of TC4 titanium alloy in these certain environments.Therefore,it is necessary to improve the oxidation resistance of TC4 titanium alloy by adopting appropriate surface treatment.As one of the commonly used surface treatment technology of TC4 titanium alloy in recent years,micro-arc oxidation can be used to grow ceramic coating on the surface of TC4 titanium alloy,and the high-temperature oxidation resistance and corrosion resistance of TC4 titanium alloy can be improved under the protection of ceramic coating.In this paper,TC4 titanium alloy was used as the matrix material.Then the influence of current density,oxidation time and duty ratio on the hardness and thickness of TC4 titanium alloy micro-arc oxide film were studied by orthogonal experiment.Using the optimized process parameters,through in the micro-arc oxidation electrolyte adding phytic acid and glycine,respectively,in combination with SEM,XRD,ftir and XPS detection methods are studied different phytic acid and amino acid concentration of TC4 titanium alloy micro-arc oxidation coating morphology structure,the influence of the membrane composition,membrane layer,then discusses the phytic acid and glycine on the modified mechanism of TC4 titanium alloy.The formula of electrolyte was determined by preliminary exploration experiment.Na3PO4 6g/L,Na2SiO34g/L,NaOH 0.5g/L,EDTA 0.3g/L,glycerin 3mL/L,triethanolamine 1mL/L.Process parameters were determined by orthogonal test:current density 7A/dm2,oxidation time 45min,duty cycle 80%.On the basis of the selected electrolyte and the optimal process,phytic acid of 0mL/L,3mL/L,6mL/L,9mL/L and 12mL/L and glycine of 0mL/L,2mL/L,4mL/L,6mL/L and 8mL/L were added respectively in two groups of experiments to study the effects of different organic acid additions on the characteristics and high-temperature oxidation behavior of TC4 titanium alloy micro-arc oxide coating.The results show that the addition of phytic acid or glycine has a significant effect on the performance of TC4 titanium alloy micro-arc oxide coating.Appropriate addition of phytic acid or glycine can improve the hardness,thickness,corrosion resistance,high temperature oxidation resistance and thermal shock resistance of the coating.With the increase of organic acid content,the number and size of holes on the coating surface will decrease.However,excessive phytic acid or glycine will lead to hardness,corrosion resistance and other properties.Due to a small amount of both additives,no additives were found by XRD.The XRD analysis showed that the coating was mainly composed of Ti matrix,including α-Al2O3,SiO2,Al2TiO5,rutile TiO2 and anatase TiO2.C-C-C、O-P=O、C-O-P and asymmetric deformed six-element ring structures were detected by Raman spectroscopy after the addition of phytic acid,CH3CN,NH3,N2H4 and TiN were detected by Raman spectroscopy after the addition of glycine.XPS also further verified such results.The results of high temperature cyclic oxidation indicated that the resistance of phytic acid to high temperature oxidation was best at 3mL/L.At 2mL/L,amino-acetic acid has the best oxidation resistance at high temperature.By analyzing the mechanism of the micro-arc oxidation coating of TC4 titanium alloy modified by organic acids,it can be found that most of the organic acids have groups with electron-absorbing ability.Therefore,the addition of such additives plays a certain role in improving the stability of the electrolyte and inhibiting spark discharge.For example,the phosphoric group and hydroxyl group in phytic acid and the amino group in amino acetic acid have a strong chelating ability in aqueous solution.They can chelate with metal ions in the matrix to form chelates,which improves the performance of the film layer. |
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