Preparation And Properties Of Ta Modification Layer On γ-TIAL By Double Glow Plasma Surface Alloying Technology

Compared with traditional high temperature alloy, g-Ti Al alloy possesses advantages of low density, relatively high specific strength and modulus. It is recognized as one of the most promising high temperature structure material. However, its poor oxidation resistance at temperatures above 700 °C needs to be improved, so does its shortage of the corrosion resistance in strong reducibility medium. These deficiencies severely limit its wider application. In this paper, a Ta modification layer was fabricated by double glow plasma surface alloying technology which can provides an effective way to improve the surface performance of metal. The addition of Tantalum can significantly improve the corrosion resistance of g-Ti Al alloy. The optimum process parameters obtained from the orthogonal experiment. The Ta modification layer had a thickness of about 25μm, and adhered to the substrate well, with the binding force of 60 N. The modification layer consisted of α-Ta, and the surface hardness was up to 415.36HV0.3. The modification layer had a relatively high nano-hardness and relatively low elasticity modulus. Therefore the modification layer 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 Ta modification layer was compound of Ta2O5、Al Ta O4. The oxidation layer was continuous and compact, and the oxidation kinetics followed Wagner parabolic law. The oxidation resistance of the g-Ti Al alloy was improved.Electrochemical corrosion experiments were carried out in HCl and H2SO4 solutions. The results indicated that the Ta2O5 film formed on the surface of modification had superior corrosion resistance. The film can effectively prevent the entry of Cl- and enhance the adhesion of Ti O2 passivation membrane. Melt corrosion experiments were carried out at 800℃ in 75%Na2SO4+25%Na Cl salt mixture. A complex and firm oxide film of β-Ta2O5 and Al Ta O4 formed on the modification layer, which had good thermal stability and corrosion resistance. The integrity and protection of the oxide film were guaranteed. The infiltration of S, Cl, and O were prevented effectively. Thus the melt corrosion resistance was improved.