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Effect of Nb Doping on High Temperature Oxidation Resistance of Ti-Al Alloyed Layer

Since the 1970s, aviation materials have entered the age of titanium alloy. Titanium and titanium alloys have been widely used in aviation industry because of their high specific strength, low density, good corrosion resistance, stable medium temperature performance, easy processing and good weldability. At present, the amount of titanium alloy has become one of the indicators of the advanced degree of modern aircraft, especially with the development of high thrust-to-weight ratio aero-engine, the advantages of titanium alloy gradually appear, the amount of increasing. However, the application of conventional titanium alloy in aero engine is limited by its poor oxidation resistance at high temperature. Take (α+β) type titanium alloy TC4 as an example, because the oxidation products of high temperature oxidation are mainly TiO2, the maximum service temperature of its long-term service is not more than 350℃, so it can only be used to manufacture the lower working temperature of the fan blade in the aero-engine and the first and second stage of the compressor blade.

Since the oxidation damage mainly occurs on the surface of the workpiece, surface treatment is the most effective way to give the material surface excellent high temperature oxidation resistance without damaging the overall performance. At present, the surface modification technologies to improve the high temperature oxidation resistance of titanium and titanium alloys include plasma injection, thermal diffusion, plasma spraying, micro-arc oxidation, arc ion plating, laser surface treatment, etc. Among them, laser surface alloying technology has been widely paid attention because of its high energy density, small deformation of workpiece, short processing cycle, unrestricted shape of workpiece, controllable thickness of alloying layer and typical metallurgical combination with matrix.

Nb is considered to be one of the most effective alloying elements to improve the high temperature oxidation resistance of titanium and titanium alloys. The high temperature oxidation resistance of titanium and titanium alloys with different niobium contents was studied. The results show that doping proper amount of Nb can significantly improve the high temperature oxidation resistance of titanium and titanium alloys. However, excessive Nb doping will make the oxidation resistance of titanium and titanium alloy worse, and will deteriorate the mechanical properties of the alloy, increase the density of the alloy. The addition of Nb inhibits the outward diffusion of Ti. The oxidation rate constant of Nb samples at 700-900 ℃ is reduced by one order of magnitude compared with that of the matrix, and the oxidation activation energy is increased. Although Nb infiltration can improve the high temperature oxidation resistance of titanium alloy to a certain extent, the surface oxidation film of titanium alloy is still dominated by TiO2, which makes the high temperature oxidation resistance greatly reduced. In addition, previous studies on the oxidation behavior of high-temperature oxidation resistant coatings on titanium and titanium alloys were mostly focused on 0~100h, and the short-time high-temperature oxidation behavior could not reflect the long-term high temperature stability of the coatings.

Based on this, A1 10 Nb composite alloying was used to prepare Ti-Al alloying layers with different Nb doping amounts on the surface of TC4 alloy in this work. The high temperature oxidation behavior of the alloying layer was studied at 800℃ for 1000h, and the influence mechanism of Nb doping amount and Al content on the high temperature oxidation resistance of the Ti-Al alloying layer was discussed.
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