Annealing Process For TC4 Titanium Alloy

In order to choose a reasonable annealing process, we first observe the effect of heating temperature and cooling mode on the microstructure and mechanical properties of TC4 titanium alloy.
Test material 920 ℃ hot rolled TC4 titanium alloy bar, hot rolling total deformation rate of about 80%, a + β / β phase transition point of 980 ~ 990 ℃. The specimens were heated and held at 1000℃, 950℃, 930℃ and 830℃ for 1 hour and then air-cooled, water-cooled and furnace-cooled respectively. Different annealing methods have effects on microstructure and mechanical properties.

Among them, the cooling rate has a great influence on the microstructure and mechanical properties of the above four temperatures. When water-cooled, the β-phase components in equilibrium at 1000°C, 950°C and 930°C are subjected to martensitic transformation, and the β-phase transforms into martensite a` pin. At 1000 ℃ exhibits a clear Weinsteinite organization, and its mechanical properties are comparable to the data of 1000 ℃ air cooling. On specimens at 950°C and 930°C and water-cooled, the microstructures were similar to those characterized at air-cooling, but between the equiaxial incipient a-phases was the β+ martensite a`-needle. This time corresponds to the highest comprehensive performance, and there is better creep resistance than air-cooled organization. 830 ℃ insulation of the equilibrium β-phase composition has not touched the M line, but water-cooled in the intergranular β-phase was also found in the very small needle-like transformation products, can only be distinguished with an electron microscope. But the structure of the needle-like product has not been measured. At this time, the tensile strength and section shrinkage are very low. As for the furnace cooling, due to the slow cooling rate of the specimen, stay at high temperatures for a long time, polymorphic transformation is carried out sufficiently, all the a-phase becomes coarse. 1000 ℃ furnace cooling, in the original β grains within the production of coarse a-phase photos and interlaminar β-phase, in the original β grain boundaries, there is also strip a-phase formation of a thick network, generally known as the mesh basket-like organization. 950 ℃, 930 ℃ and 830 ℃ furnace cooling, due to the a-phase tendency to In the original a phase interface nucleation, growth, microstructure are isometric a and intergranular β phase. After cooling at 1000 ℃ furnace tensile strength than air-cooled and water-cooled low, tensile plasticity is higher. In other temperatures after furnace cooling of the comprehensive performance than water-cooled and air-cooled low.
In summary, in order to make the TC4 titanium alloy to get the best strength and plasticity of the comprehensive performance, and at the same time have a good creep resistance and fracture toughness, can be used in the 950 ℃ heat preservation for 1 hour after air-cooled (or water-cooled) annealing process. In order to facilitate the subsequent processing, metallurgical plant factory, TC4 titanium alloy are used in 700 ~ 800 ℃ insulation 1 hour air cooling process. For some large-size forgings, in order to ensure the uniformity of performance, sometimes using furnace cooling process.