Research On Microstructure And Tribological Behavior Of Microarc Oxidation Coatings On T30Z Alloy

In the paper,micro-air oxidation coatings were prepared on the surface of Ti30Zr5Al3V alloy,using bipolar pulse power supply and the electrolyte system which were composed of Na₂SiO₃,Na₄P₂O₇ and NaOH.The influence of different oxidation time,voltage and pulse frequency on the phase composition,compactness,surface morphology and thickness of micro-arc oxidation coating was studied by using X-ray diffraction,scanning electron microscope,energy spectrum analysis tester and other testing technologies.The tribological properties of coatings under different parameters were evaluated by CSM Tribometer and the wear mechanisms were revealed.The results showed that the ceramic coatings prepared under different process parameters exhibited a rough porous structure.The EDS analysis showed that the Si,P elements in the electrolyte and the Ti,Zr and V elements from the substrate were enriched in the coating,but there was no electrolyte cation.The cross section of the coating had three layers:dense layer,porous layer and transition layer.The growth rate and microstructure of the coatings were mainly dependent on discharging pulse energy in the same electrolyte,and the variety of parameters actually changed the discharge pulse energy.Increasing the oxidation time,voltage and reducing the pulse frequency made to increase the pulse energy,futher accelerate the growth rate of the coating,increase the discharge park on the anode surface and the thickness of the coating.At processing time of20 min,voltage of 450 V and frequency of 500 HZ,the surface of the ceramic coating was more uniform and the density was relatively good.The micro-air oxidation coatings formed on T30Z alloy in all parameters were composed of anatase Ti O₂ and rutile TiO₂,and a small amount of amorphous phase.The relative content of the two phases in the coatings was affected by the different parameters.With the increase of oxidation time and voltage,the relative content of rutile increased,while that of anatase decreased.However,the effect of pulse frequency on the content of two phases was opposite.The tribological properties of coatings were evaluated by CSM Tribometer.The results showed that the friction coefficient of T30Z alloy and GCr15 steel ball without micro-aro oxidation treatment fluctuated between 0.35 and 0.45.The dominant wear mechanisms were the coexistence of abrasive wear,adhesive wear and delamination wear.When the progress parameters were changed,the friction coefficient of T30Z alloy coating without failure was stable at about 0.8.The wear mechanisms were mild abrasive wear and mild adhesive wear.The wear resistance was obviously improved compared with the substrate.