Fabrication Of Plasma Sprayed Al₂O₃-13wt.%TiO₂ Coating On Titanium Alloy And Its Tribological Properties

Titanium alloys are widely used in aerospace,ship,automobile,petrochemical,biomedical,electronic and other fields because of their low density,high specific strength and excellent corrosion resistance.However,the low hardness,poor wear resistance and high temperature oxidation of titanium alloys limit its application.Ceramic materials have high hardness,good wear resistance and high temperature oxidation resistance.This problem can be effectively solved by using plasma spraying technology to prepare ceramic coating on the surface of titanium alloy.In this paper,ceramic coating was prepared by plasma spraying using nano-aggregated Al₂O₃-13wt.%TiO₂?N-AT13 for short?powders on the surface of titanium alloy.The preparation parameters of NiCrAlY bonding layer and N-AT13 ceramic coating were optimized by single factor test.Microstructure,mechanical properties,thermal shock resistance,thermal oxidation resistance and friction and wear properties of the coatings prepared by micron powders?M-AT13for short?and N-AT13 powders were systematically studied by means of scanning electron microscopy,X-ray diffractomer,microhardness tester and friction and wear tester.The results showed that the optimum spraying power of NiCrAlY bonding layer was 40 kW,the thickness of NiCrAlY coating was about 53.3 um.The optimum spraying power of N-AT13ceramic coating was 42 kW,the optimum spraying distance was 120 mm,the thickness of N-AT13 coating was 344.6 um,the porosity was only 1.3%,and the hardness was 943.4 HV.Under the same process conditions,M-AT13 coating was a typical single layered structure,mainly consisting of Al₂TiO₅ phase with a small amount of?-Al₂O₃ and Rutile-TiO₂.N-AT13ceramic coating consisted of fully melted regions and partial melted regions,consisting of?-Al₂O₃,?-Al₂O₃ and Anatse-TiO₂.The mechanical properties of N-AT13 ceramic coating were better than that of M-AT13 coating.H/E and H³/E² of M-AT13 coating were 0.04 and 0.01,respectively.H/E and H³/E² of N-AT13 coating were 0.06 and 0.04,respectively,which indicated that N-AT13 coating had good wear resistance.After 147 thermal shock cycles,cracks appeared in M-AT13 coating,and failure occurred after 720 cycles.After 268 thermal shock cycles,cracks appeared in the N-AT13 coating,and 720 cycles remained invalid,indicating that the bondingstrength of the N-AT13 coating was good.After 100 h thermal oxidation,the weight of TC4titanium alloy,M-AT13 coating and N-AT13 coating increased by 3.8%,2.4%and 1.7%respectively.N-AT13 coating exhibits good oxidation resistance.As the temperature increased,the friction coefficients and volume wear rates of the N-AT13coating increased first and then decreased.At room temperature,the loose micro-protrusion on the surface of N-AT13 coating peeled off and wear less.When the temperature is between250°C and 450°C,N-AT13 coating showed layered spalling caused by cracks propagation,and the wear was severe.At 550°C and 650°C,friction layer formed on the surface of N-AT13coating,The degree of wear was reduced.At 650°C,the friction coefficient of N-AT13 coating gradually decreased with the increasing of load,and the volume wear rate increased gradually.When the load was increased,the layered spalling of N-AT13 coating was intensified,and the debris was smaller and more round with function of filling and"microball",so the friction coefficient was lowered.