Study On The Process And Properties Of TA15 Titanium Alloy Solid Boronizing

Titanium alloys are widely used in aerospace, civil, military and other fields due to the advantages of their low density, high specific strength, good corrosion resistance and excellent welding performance. However, it has the defects of low hardness and poor wear resistance, which limits its further application. Boronizing on titanium alloy surface can make it to form high hardness boron titanium compounds,so as to effectively improve the surface wear resistance. In the present work, TA15 titanium alloy was selected as substrate to study the effect of single boronizing and orthogonal optimization RE-catalyzing boronizing on the microstructure and properties of boronizing layer. The main conclusions are as follows:(1) After studying the effects of without adding rare earth single boronizing process and different concentration of RE boronizing process on the microstructure of boronizing layer, it was found that the boronizing layer of RE boronizing is thicker than that of single boronizing, and it is composed of boron titanium compounds layer and transition layer. The best dosage of RE was determined as 5%, the thickness of boronizing layer obtained at this dosage is 23.54μm.(2) When the dosage of RE oxide at 5%, by studying the effects of different boronizing holding time on boronizing layer to determine the best boronizing holding time is 20 h, the thickness of permeation layer is obtained at this time is 28.93μm.Meanwhile the phase composition, element distribution, hardness and wear resistance of permeation layer were studied, the results showed that permeation boronizing layer is composed of two kinds of boron-titanium ceramic phase, that is, the outer layer of TiB2 and internal TiB. The microhardness of permeation boron layer is 1850HV0.025 ~860HV0.025, this value is 4 to 5 times higher than that of the substrate surface. The friction coefficient of permeation boron layer is stable between 0.2 and 0.25,compared with 0.45, which of the substrate, this value increased nearly two times, this shows that RE-catalyzing solid boronizing makes the wear resistance of TA15 titanium alloy substrate has been improved a great extent.(3) In single factor conditions, 3 factors and 3 levels orthogonal optimization RE-catalyzing boronizing experiment was carried out to determine the best proportion of solid boronizing agent and the best boronizing process, namely the boronizing heating temperature is 1040℃, boronizing holding time is 20 h, temperature is1080 ℃, boronizing time of heat preservation is 20 h, boronizing agent formulated asa proportion: 25%B4C+5%La2O3+70%SiC. The thickness of the co permeation layer was 50.96μm after optimization process. Analysising phase composition and mechanical property of permeation layer after the optimization process showed that permeation layer is composed of two phase, that is, TiB2 and TiB, the hardness and friction coefficient of it were 1900 HV and 0.16, respectively, which relative to the substrate is greatly improved.(4) According to the principle of thermodynamics and diffusion principle, by discussing the formation of dual phase boride(TiB and TiB2) and catalytic mechanism of RE, it was found that the higher the temperature at, the more conducive to the formation of Ti and TiB2 chemical reaction. The addition of La2O3(RE) can reduce the energy requirement for the system reaction, and adsorb on the surface of substrate to form an active center, to further promote the formation of TiB and TiB2.