Study On Preparation And The Friction And Wear Properties Of MAO Coatings On TD3 Alloy

TD3 alloy is a kind of Ti3 Al based alloy with medium Nb content.TD3 has been attracted the attention in aerospace industry,but its poor wear properties limit its practical application.Surface technology is an effective method to improve the wear resistance of materials,and there are few reports on the friction and wear properties of TD3 alloys.In this paper,micro-arc oxidation(MAO)coatings was formed on TD3 alloy surface under constant current.The process parameters of MAO were studied by orthogonal test.The MAO layers were prepared by adding different content of Na F,KOH and Na2WO4 under optimization process parameters.The composition,phase,surface and cross-section morphology of MAO coatings under different process were analyzed by scanning electron microscopy(SEM),energy dispersive spectrometer(EDS)and X-ray diffraction(XRD).The thickness and surface roughness of MAO coatings were measured by eddy current thickness gauge and roughness gauge respectively.The effects of different electrolytes on the growth and properties of MAO coating were explored.Friction and wear properties of different MAO coatings were studied.The optimum technologic parameters were determined by orthogonal test:Na2Si O3 electrolyte concentration of 15g/L,MAO time of 60 min,current density of 12A/dm2.Other technologic parameters were frequency of 500 Hz and duty cycle of 10%.The main phases of the MAO coatings under the optimum technologic parameters are Al2O3,Si O2,Ti O2,Nb2O5,Al2 Si O5 and amorphous phase.The MAO coatings reduces the friction coefficient and wear rate of TD3 alloy.The wear mechanism is fatigue wear and slight abrasive wear.With the increases of Na Fcontent,the surface pores of MAO coatings decrease gradually,and the dense layer becomes more uniform and the thicker.Na F promotes the formation of Ti O2 and produces new phase of Ti F2.The average friction coefficient and wear rate of the MAO coatings decrease gradually.The MAO coatings prepared by adding 3g/L Na F has a minimum friction coefficient of 0.27 and the wear rate of 3.37×10-7mm3/(N·mm).Its wear mechanism of MAO is fatigue wear and slight adhesive wear.With the increases of KOH content,the thickness of the MAO coatings increases gradually,but the excessive concentration of KOH results in the MAO coatings are porous.KOH can promote the formation of the amorphous phase.The average friction coefficient and wear rate of the MAO coatings increase gradually.The MAO coatings prepared by adding 1 g/L KOH had an average friction coefficient of 0.35 and the wear rate of 3.16×10-7 mm3/(N·mm).As the increase of KOH content,the wear mechanism of the MAO coatings changes from fatigue wear and slight adhesive wear to severe fatigue wear.With the increase of Na2WO4 content,the thickness of the dense coatings increases gradually,but excessive addition of Na2WO4 results in more pores and defects of the MAO coatings.WO42-in Na2WO4 formed the WO3 phase.The average friction coefficient and wear rate of the MAO coatings showed a trend of decreasing at first and increasing then.The MAO coatings prepared by adding 4g/L Na2WO4 has the average friction coefficient of 0.33 and the minimum wear rate of 2.14×10-7 mm3/(N·mm).The wear mechanism of the MAO coatings prepared in the Na2 Si O3-Na2WO4 electrolyte is fatigue wear and slight adhesive wear.