| In order to reveal the titanium alloy plas ma electrolytic oxidation(Plasma electrolyt ic oxidation, PEO) characterist ics, in this paper, Firstly, a comparative study of plasma electrolyt ic oxidation of Ti- 6Al-4V alloy and Zr-2 alloy in the N a2SiO3 and(N aPO3)6 electrolyte, and in- depth ana lys is of the two kinds of alloys exhibit different reason of film- forming process kinet ics and coatings microstructure. Secondly, study the behavior of Ti-6Al- 4V alloy plasma electrolyt ic oxidation w ith constant current and constant voltage mode in the aluminate electrolyte, evaluated the wear resistance of the coating and other properties. The fo llowing conclus ions were drawn fro m this study:(1) Under the pulsed bipolar constant current condit ions, Ti-6Al-4V alloy at the early stage of coating growth faster than Zr- 2 alloy by plasma electrolytic oxidation in the N a2SiO3 and(Na PO3)6 electrolyte, but the zirconium a lloy coatings growth rate with time to speed up, after about 800 s, zirconium alloy coating thickness are similar to titanium alloy,at 3600 s, the thickness of the oxide coating on Zr-2 alloy is far higher than the thickness of the coating on Ti- 6Al-4V alloy. The results show that, coating forming efficie ncy of Ti- 6Al- 4V alloy is lower than Zr- 2 alloy, the reason is attributed to the Ti-6Al- 4V alloy consumes more current density on the anode process of oxygen release.(2) Two kinds of alloy was studied gas evolut ion behavior on the anode, PEO coated Ti-6Al-4V alloy showed strong oxygen evo lut ion at constant posit ive potent ial in t he range 400 to 600 V, while the PEO coated Zr- 2 alloys only disp layed a small amount of oxyge n evolut ion in the voltage range. However, PEO coated Zr-2 alloys showed a strong plasma discharge at 600 V, at the same time the strong plas ma discharge caused anomalous gas evolut ion, which far exceeds estimated by Faradaic theory of oxygen evo lut io n. Ti-6Al-4V alloy was also found the anoma lous gas evolut ion, but at a higher potentia l(640V), and the gas evolut ion is less than Zr-2 allo y.(3) The “coral reef” structure are formed on the titanium alloy, while a lot of “pancake” structure were existed in zirconium alloy coatings, analysis the reason of different microstructure of the two different alloys, considered that titania and zirconia had different conductivity was the ma in factors of for ming different microstructure. Due to the high electronic resistance of zirconia, dur ing the plas ma electrolyt ic oxidation w ill shows a intense type B discharges, which result in forming coatings wit h “pancake” structure, while attributed to the semiconductor nature of the titanium alloy, whic h decided to the dominance of A or C type discharges of oxide coatings surface and shallow, for ming “coral reef” structure. A schematic diagram was proposed for based on the titanium and zirconium alloy discharge types in the plasma electrolyt ic oxidation process.(4) Under the constant vo ltage condit ions, Ti-6Al-4V alloy w ith t he extension of PEO treatment time the coatings appeared fall off phenomeno n, which was more serious when electrolyte concentration increased. PEO treatment 60 min coating thickness only ~29 ?m in 15 g/L N a AlO2+1 g/L KO H electrolyte. PEO treatment 30min(t hickness ~ 33 ?m) in t his electrolyte under the load of 2N did not wear out, while the load of 10 N was worn through about 35 s, but PEO treatment 60 min coating(~29 ?m) under the load of 5N did not worn out wit h improving the wear resistance.PEO treated 2min?30min coatings in the 32 g/L N a AlO2+1 g/L KO H electrolyte, under a load of 2N condit ions processed frict ion experiments, results of PEO treated 2min coating showed better wear resistance, but the wear resistance compared to the coating of 15g/L N a AlO2 decreased.(5) Under the condit ion of constant current, us ing emiss ion spectrum studied the plasma luminescence behavior of Ti- 6Al- 4V alloy in 8g/L Na AlO2 + 1g/ L KO H electrolyte by PEO processin g. The luminescence intensit y increased with t ime, the spectral line spectrum is mainly N a, H? spectrum line; the oxide coating mainly composed of aluminum titanate?rut ile phase. The micro- morphology of treated 30 min coating was microporous, crack and strumae. A better corrosion resistance of PEO treatment 1min coating; due to longer treatment time(30min), coating had more defects(pores cracks), which corrosion resistance decreased. But processing fr iction experiments under the load of 2N, the inlayer of coating had a very low fr iction coeffic ient(0.2), wit h potentia l applications in anti- fr iction sit uations. |
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