Preparation And The Infrared Emission Performance Of Black Oxide Coatings On Titanium Alloy

Recently,the application of titanium alloys in optical instruments is increasing.Not only the titanium alloy surface is required to have uniform blackness,excellent corrosion resistance,but also high infrared absorption and high emissivity.Titanium alloy black micro-arc oxide film can not only improve its protection performance and extinction,improve infrared absorption and emission performance,but also have excellent performance in special service environment,such as corrosion resistance,light aging resistance,wear resistance,etc.The study of alloy black micro-arc oxide film has very important significance.This article uses an environmentally friendly alkaline electrolyte,with(Na PO₃)₆and Na₂Si O₃as the main salt,NaOH to adjust the p H value,adding NH₄VO₃as a colorant,C₁₀H₁₆N₂O₈as a complexing agent,KF as a film-forming agent,(HOCH₂CH₂)₃N,Na₃C₆H₅O₇·2H₂O and Phytic acid sodium are used as surfactants of electrolyte to micro-arc oxidation of TA2 titanium alloy.An environmental-friendly alkaline electrolyte has been optimized.The initial voltage required of micro-arc oxidation is reduced and the formation rate of the oxide coating increased.The black micro-arc oxide coatings with excellent performance and uniform color are further analyzed for its corrosion resistance,wear resistance and infrared emission performance.Firstly,the effects of the components in the alkaline solution system on the micro-morphology and mechanical properties of the titanium alloy micro-arc oxide coatings have been studied.The experimental results show that(Na PO₃)₆plays an extremely important role in the formation and growth of the micro-arc oxide coating,which can not only improve the corrosion resistance of the oxide coating,but also increase the bonding force of the layer;KF can effectively reduce the starting voltage of micro-arc oxidation,promote the growth of oxide coating and improve the bonding force of the coating;NaOH is used to adjust the p H value,which can increase the conductivity of the electrolyte and promote the growth rate of the oxide coating,but too high a concentration will cause the ablation of the surface oxide coating and affect the bonding force of the coating layer.Secondly,the effect of different electrical conditions on the micro-morphology and mechanical properties of the titanium alloy micro-arc oxide coatings has been studied.It is found out that with increasing frequency,the oxide coating on the surface of the titanium alloy is dense and uniform.The pore size of the micropores is significantly reduced.When the oxidation frequency is 1400 Hz,the average pore size is 2?4?m,which can effectively improve the corrosion resistance of the oxide coating.Frequency has little effect on the binding force of the coating;The high duty cycle can properly increase the coating formation rate of the oxide coating and increase the content of Ti O₂rutile phase and Ti O₂anatase phase in the coatings.But it will promote the surface roughness of the coating and decrease the corrosion resistance;The increase of the oxidation time can increase the thickness of the oxide coating.The hardness and bonding force of the oxide coating are also increased.However,if the oxidation time is too long,the roughness of the coating will increase with reducing the corrosion resistance and bonding force.Finally,the infrared emission performance of micro-arc black oxide ceramic coatings on the titanium alloy has been studied.The factors affecting the infrared emission performance of the oxide coating are analyzed.The results show that the average infrared emissivity is in the range of 0.79?0.83 in the wavelength range of4?12?m.The infrared emission performance will increase with the surface roughness;When the average pore size is about 6-7?m,the infrared emissivity reaches 0.83.