| With the vigorous development of the aerospace and other fields,the application of titanium alloy is more and more widely.But its poor wear resistance and high temperature oxidation resistance limit its application range.Metal silicides can be used as a strengthening phase to improve the surface properties of materials due to their high melting point hardness and good high temperature oxidation resistance.Silicide composite coating is prepared on titanium alloy substrate by laser cladding to improve the surface properties of the matrix.In this work,pure Ni,Ti,Si powders with different compositions were used to prepare the composite coating composed of Ti5Si3,Ti Si2and Ti2Ni phases on the Ti6Al4V titanium alloy substrate by laser cladding.The microstructure evolution of the coatings were analyzed.The effects of silicide of different coatings on high temperature oxidation resistance and high temperature wear resistance were studied.The microstructure and phase composition of the coatings were analyzed by using scanning electron microscopy?SEM?,energy dispersive spectrometer?EDS?and X-ray diffraction?XRD?.The laser cladding coating mainly consists of Ti5Si3and Ti2Ni phases.When the Si content gradually increased,the Ti Si2phase appeared in the coating gradually.The wear behavior and high temperature oxidation behavior of the coatings and the matrix were investigated by friction and wear test and oxidation test at 800?.The results of EDS and XRD showed the composition of oxide film on the wear surface and the oxide surface.It is beneficial to reveal the mechanism of high temperature oxidation and wear mechanism of the coating and obtain the strengthening effect of the silicide on the coating.During the friction and wear test at room temperature,the friction coefficient of the coatings and the substrate did not change significantly with the increase of the load,but the wear volume of the substrate increased obviously.The wear volume of the coatings increased slowly,that is to say,the coatings were not sensitive to the load.Due to the higher hardness of Ti5Si3and Ti2Ni phases evenly distributed in the coatings and an abnormal temperature-hardness relationship for Ti5Si3,the coating can always maintain a higher hardness.Differernt from the substrate,which showed serious plastic deformation,adhesive wear and abrasive wear,the coatings exhibited excellent abrasive and adhesive wear resistance for the combining the Ti5Si3with Ti2Ni.In the high temperature friction and wear test,the results showed that the average friction coefficient of the substrate and the different coatings is 0.376,0.21,0.222,0.171and 0.152,respectively.Compared with the coating,the wear volume of the substrate is about 4.91 times,3.842 times,5.364 times and 5.541 times than that of the coating,and the wear rate of the coating shows a decreasing trend with the increase of Si content in the coating.According to the results of XRD and EDS,the wear surface of the substrate is mainly composed of Ti O2and the wear surface of the coating is mainly composed of Si O2,containing a small amount of Ti O2,Al2O3and Ti2Ni.In coatings,Si O2played a dominant role with good load carrying capacity and compactness.The wear rate of coatings were reduced and coatings exhibited a good anti-wear effect.The wear mechanism of titanium alloy is mainly oxidation,micro-cutting and brittle flaking and the wear mechanism of the coating is mainly combined with oxidation,slight brittle flaking.High temperature oxidation test results showed that the coatings and the substrate of the entire oxidation process can be divided into rapid oxidation stage and stable oxidation stage.In the first oxidation stage,the oxidation and weight gain of the matrix and coating all accorded with the trend of linear increase.The oxidation rates were 0.379 mg/?cm2·h?,0.349 mg/?cm2·h?,0.345 mg/?cm2·h?,0.311 mg/?cm2·h?and 0.289 mg/?cm2·h?.During the second oxidation stage,the oxidation weight gain of matrix and coating conformed to the law of parabola growth,the oxidation rates were 1.08mg/(cm2·h1/2),0.58mg/(cm2·h1/2),0.53mg/(cm2·h1/2),0.45mg/(cm2·h1/2)and 0.67mg/(cm2·h1/2).In both oxidation stages,the oxidation rate of the matrix was higher than the oxidation rate of the coating,indicating that the coating had less oxidation weight gain at the same time and the coating showed excellent high temperature oxidation resistance.According to the results of XRD and EDS,the oxidized surface of the matrix mainly contains Ti O2and a small amount of Al2O3.Due to the low content of V in titanium and V2O5volatility,it was not detected.The oxidized surface of the coating contained mainly Si O2and small amounts of Ti O2,Al2O3,Ti5Si3,Ti Si2and Ti2Ni.The content of Si in the coating increases,the proportion of Ti-Si intermetallic in the microstructure increases,the wear rate and oxidation rate of the coating decrease,which can effectively improve the high temperature oxidation resistance and high temperature friction and wear performance. |
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