Preparation And Properties Of Zr-Y Modification Coating On γ-TiAl By Double Glow Plasma Surface Alloying Technology

As one of the most potential alloys, ?-TiAl alloy possesses many advantages such as low density, relatively high specific strength and modulus. However, its poor oxidation resistance at temperatures above 700 °C needs to be improved, so does its shortage of the friction resistance. These shortages severely limit its wider application. In this research, Zr-Y modification layer was manufactured by double glow plasma surface alloying technology.That could effectively improve the surface performance of substrate. The microstructure, composition and phase structure of the surface alloyed layers were analyzed. And then the micro-hardness of layer and binding force between layer and substrate were tested to value the quality of the alloyed layers. Study on oxidation resistance was important in this research. In high temperature air, the coating was oxidated and there processed yttria stabilized zirconia thermal barrier coatings. This issue has also analysised the tribology property of ZrY coating, in different parameters(speed, load, temperature).The most suitable process parameters obtained from orthogonal experiment. The Zr-Y coating had a thickness of 23μm, insist of deposite layer(18μm) and diffusion layer(5μm).The coating consisted of pure Zr and Y, and the surface hardness was enhanced to 857.2HV0.1. Throught the nano-indentation test, the coating has high nano-hardness(DHT115=828.01) and low elasticity modulus(137.4GPa). Hence, Zr-Y coating shows good deformation ability and good ability to resist plastic deformation.Oxidation experiments were carried out for 100 h at 750℃, 800℃and 850℃ in air. Oxidation product of Zr-Y modification layer was compound of ZrO2 and dispersive distribution Y2O3. Rare earth elements yitrium can refine grains. Therefore oxidation layer was continuous and compact. In contrast, oxidation layers of substrate were consist of Al2O3 and TiO2. The structures were loose and easy to spall. In 850℃,the oxidation surface was covered of yttria stabilized zirconia thermal barrier coatings which protected ?-TiAl substrate against oxidation.Friction resistance experiments were carried out in different load, speed and temperature. The results instructed that the friction coefficients of Zr-Y coating were lower than ?-TiAl substrate, just as the wear volume loss. Wear mechanism of ?-TiAl substrate was abrasive wear while Zr-Y coating was adhesion wear. Exist of Zr-Y coating improve the frition resistance of ?-TiAl substrate in all conditions.