Chemical composition and properties of TA15 titanium alloy
The nominal composition of TA15 titanium alloy is Ti-6.5 Al-2Zr-1Mo-1V. The main strengthening mechanism of TA15 titanium alloy is the solid solution strengthening of α-stable element Al, adding neutral element Zr and β-stable elements Mo and V to improve the process performance. The Al equivalent of the alloy is 6.58%, Mo equivalent is 2.46%, belonging to the high Al equivalent of near-α titanium alloy. Therefore, it has not only the good thermal strength and weldability of α titanium alloy, but also the process plasticity of (α + β) titanium alloy. The properties of seamless titanium tube materials are determined by their organization, and the microstructure is largely determined by how the material is processed. Therefore, it is of great significance to study the effect of thermal deformation process on the microstructure and properties of TA15 titanium alloy. In order to provide technical support for practical production and further enrich the research content, the researchers will focus on studying the microstructure and properties of TA15 titanium alloy trial-made bars under different forging conditions.
TA15 titanium alloy was smelted three times by vacuum consumable arc to obtain the finished ingot with diameter of Φ750mm. Three forging processes were used to produce the bar. Process A: Open forging is drawn at high temperature in β phase zone for 3 times, finished forging is drawn at low temperature in β phase zone for 3 times, and finally round into bars. Process B: The blank forging is the same as process A, the first forging of finished product is upset at the low temperature in the β phase zone, followed by three times of upsetting in the two-phase zone close to the phase transition temperature, and finally round into a bar. Process C: The blank forging was first carried out at the high temperature of β phase zone, and then carried out two upsetting at the same temperature; The finished product forging is drawn at a low temperature in the β phase zone for 1 time, and then at a low temperature in the two phase zone for 3 times, and finally rounded into a bar. After forging, all bars were air-cooled and annealed at 800℃ for 1h. Then transverse sampling was conducted and processed into national standard samples for microstructure and property testing. The test results are as follows:
(1) The test results of mechanical properties of bars under different forging conditions show that: from process A to process C, the plasticity index of bars is continuously improved, while the strength index increases first and then decreases. By comprehensive comparison, process C has better mechanical properties.
(2) The high forging temperature and insufficient deformation of the bar in process A result in coarse grain size and poor microstructure uniformity in the whole cross section, and the original β grain boundary is not fully broken, resulting in poor mechanical properties, especially plasticity, of the bar in process A. The mechanical properties of process B are improved compared with that of process A. The blank forging of process C carried out two upsetting of large deformation in the β zone, while the finished product forging further reduced the temperature in the two-phase zone to ensure a certain amount of deformation, so that the bar structure has been completely and fully broken and the structure is fine, which is a typical two-state structure characteristics. Therefore, the bar of process C has the best comprehensive performance.
(3) From the tensile fracture at room temperature, it can be seen that from process A to process C, the dimple of the bar fracture gradually increases and the depth also increases. The more plastic the material, the larger and deeper the dimple. It can be seen that the fracture characteristics also indicate that the bar of process C has better plasticity.
TA15 titanium alloy was smelted three times by vacuum consumable arc to obtain the finished ingot with diameter of Φ750mm. Three forging processes were used to produce the bar. Process A: Open forging is drawn at high temperature in β phase zone for 3 times, finished forging is drawn at low temperature in β phase zone for 3 times, and finally round into bars. Process B: The blank forging is the same as process A, the first forging of finished product is upset at the low temperature in the β phase zone, followed by three times of upsetting in the two-phase zone close to the phase transition temperature, and finally round into a bar. Process C: The blank forging was first carried out at the high temperature of β phase zone, and then carried out two upsetting at the same temperature; The finished product forging is drawn at a low temperature in the β phase zone for 1 time, and then at a low temperature in the two phase zone for 3 times, and finally rounded into a bar. After forging, all bars were air-cooled and annealed at 800℃ for 1h. Then transverse sampling was conducted and processed into national standard samples for microstructure and property testing. The test results are as follows:
(1) The test results of mechanical properties of bars under different forging conditions show that: from process A to process C, the plasticity index of bars is continuously improved, while the strength index increases first and then decreases. By comprehensive comparison, process C has better mechanical properties.
(2) The high forging temperature and insufficient deformation of the bar in process A result in coarse grain size and poor microstructure uniformity in the whole cross section, and the original β grain boundary is not fully broken, resulting in poor mechanical properties, especially plasticity, of the bar in process A. The mechanical properties of process B are improved compared with that of process A. The blank forging of process C carried out two upsetting of large deformation in the β zone, while the finished product forging further reduced the temperature in the two-phase zone to ensure a certain amount of deformation, so that the bar structure has been completely and fully broken and the structure is fine, which is a typical two-state structure characteristics. Therefore, the bar of process C has the best comprehensive performance.
(3) From the tensile fracture at room temperature, it can be seen that from process A to process C, the dimple of the bar fracture gradually increases and the depth also increases. The more plastic the material, the larger and deeper the dimple. It can be seen that the fracture characteristics also indicate that the bar of process C has better plasticity.