Research On Forming Process And Oxygen Diffusing Process Of TA15Titanium Alloy

In recent years, a large amount of research and application have revealed that titanium alloys have an important role in aeronautics field. TA15, a kind of titanium alloys for domestic military needs, were developed on a basis of BT20which had been successfully developed by former Soviet in the1960s (the nominally chemical composition is Ti-6Al-2Zr-1Mo-1V). In this paper, as typical parts in aero engine, the TA15titanium alloy bars and sheets which meet the technical requirements specified were test, and heat treatment technology of the die forging, welding technology and oxygen diffusion technology of the alloy sheets were established to improve the engineering application of the alloy.The article referred to a great of domestic and international engineering application technology for various titanium alloys. According to actual demand for equipages and production conditions, microstructure and properties of the die forging, welding technology and oxygen diffusion technology of the alloy sheets were studied based on the works of other research groups. From a large number of experimental data can be seen:1. TA15titanium alloys have good weldability, and the strength of welded joint could increase to0.9of the base metal. The weldability of domestic TA15titanium alloys is not inferior to that of BT20titanium alloys in Russia.2. Lamellar structure was obtained in the TA15titanium alloys after deformation above the transition temperature, while duplex microstructure or equiaxed structure was obtained after deformation under the transition temperature. The content of primary equiaxed α phase was between45%and90%, and increased with decreasing of deformation temperature. The stress rupture property of the samples was high on other conditions than that deforming by20%and the temperature below the transition point50℃. The grains of primary a phase growing, but the volume fraction keeps constant during annealing process with annealing temperature increasing. During isothermal annealing process, intergranular (3phase with the characteristic of spheroid produced because of the slow cooling rate. Recovery and recrystallization occurred in the alloy during the annealing process, together with the continuously softening of the alloy. When annealing temperature increased to850℃or near the critical decomposition temperature, the strength of the alloy enhanced slightly because of the production of the secondary a phase.3. Equiaxed α and β were obtained and equally distributed in the TA15titanium alloys after oxygen diffusing, and the content of a phase increased in comparison with that in the alloy after standard heat treating. Microhardness of oxygen diffusion layer and depth of a hardening layer increased linearly with increasing the heating temperature and holding time. The strength, plasticity and fatigue properties decreased obviously after the TA15alloy diffused by oxygen. When the oxide film on the surface of oxygen diffusion layer was removed, the properties improved and the surface abrasion resistance enhanced significantly and reached to more100times than that of the substrate after standard heat treating. Parameter of oxygen diffusion technology was800℃×10h. The a hardening layer was obtained with surface microhardness of HV0.05≥500kg/mm2and depth of d=0.05-0.1mm after oxygen diffusing, which could satisfy the design requirements of oxygen diffusion parts. The a hardening layer produced by the above technology was equivalent to the sample in Russia. The final technics process was950℃×1h+800℃×10h oxygen diffusing+530℃×6h and removing the oxide film.