| Titanium alloy has extensive applications in numerous fields,such as aerospace,petrochemical industry,sports equipment and bio-medical et al.,which benefits from its excellent material properties including low density,high specific strength and rigidity,excellent thermal and corrosion resistance.However,some disadvantages such as large friction coefficient,stick easily,poorly wear resistance and severe oxidation under high temperature?700°C?conditions limit its potential to meet performance requirements of the aerospace engine turbine blades,piston rings,valves and other materials applications.In this paper,the composite coating was made on the surface of titanium alloy by the laser alloying technology and its properties of high temperature oxidation resistance and wear resistance was investigated.In this paper,the composite alloy powder composed of Ni60A,TiN,Al and Si in accordance with the proportion of 1:3:4:2?mass ratio?,and the composite coating was synthesized on Ti6Al4V alloy by YAG laser whose power is 500W.The effects of various laser processing parameters on the surface topography and the width and depth of the coating cross section had been investigated.And the coating by Laser alloying under the selected process parameters had been studied as follows:?1?The microstructure,phase and chemical composition analysis had been studied by means of Electron Microscope?SEM?,Energy Dispersive Spectrometer?EDS?,andX-Ray Diffraction?XRD?.And the micro-hardness of the coating cross section was measured byVickers micro-hardness tester.The experimental results indicated that the composited coating has a good metallic bonding with the TC4 titanium alloy.The coating mainly contains Ti,SiC,TiN,TiB,Ti5Si3and Al3Ti reinforcement particles,and TiN,TiB,Ti5Si3 have high strength and hardness which can improve the hardness of surface alloyed coating.The average microhardness of the coating is 685HV0.5,which is about 2times higher than that of TC4 titanium alloy.?2?The 100 hours of constant temperature oxidation experiments were carried out respectively at different temperatures of 650°C,750°C and 850°C for thecomposite coatingand Ti6Al4V alloy.Then according to the size and rate of weight change,the oxidation weight gain curve and the oxidation weight gain rate curve were plottedrespectively.In addition,the oxidation properties of the coating at 750°Chad been discussed according to the measured morphology and elemental composition as well as phase characterization of the oxide layer by SEM,EDS and XRD.And on the basis of the above work,the oxidation mechanism had been summarized.The experimental results indicated that the oxide film thickness of TC4 titanium alloy at 750°C is 150?m,while the oxide film thickness of the coating is 27?m and the former is 5.6 times thicker than the latter.The oxide layer in the coating is mainly composed of continuous dense Al2O3 oxide,accompanied by a small amount of TiO,TiO2 and SiO2.And continuous dense Al2O3oxide film can effectively prevent the oxygen atoms from entering and the outward diffusion of Ti ions.?3?The friction and wear experiments were carried out respectively at different loads?3N,6N,9N?and different temperature conditions?25°C,350°C,700°C?for thecomposite coating and Ti6Al4V alloy.And based on the analysis of obtained friction marks,the influences of load and temperature on wear resistance had been investigated.The experimental results indicated that the wear extent,wear width and depth,wear volume and wear rate of the coating were less than those of TC4 titanium alloy at room temperature.The furrows on the worn surface of the coating were shallow and debris was less,which show good wear resistance,while the wear resistance of the coating was worse than that of TC4 titanium alloyat high temperature. |
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