TC11 is a kind of α + β-type heat-strength titanium alloy with good comprehensive performance. By adopting α + β zone thermal deformation and heat treatment, the maximum long-term working temperature of TC11 alloy can reach 500 ℃, which is a high-temperature titanium alloy widely used in aviation in China , It is mainly used to manufacture compressor disks, blades, drums and other parts of aeroengines, and can also be used to manufacture aircraft structural parts. The alloy also has good hot workability and can produce bars, forgings, and die forgings.
The internal quality of TC11 titanium alloy products will directly affect the reliability of aircraft engines and aircrafts. At present, when manufacturers inspect the internal quality of TC11 titanium alloy products, the conventional method used is ultrasonic flaw detection. However, ultrasonic flaw detection has certain limitations for defect detection. In actual production, no abnormality was found during ultrasonic inspection of a batch of TC11 titanium alloy forging rods, but during low magnification inspection, white bars appeared in the center of the rod. Researchers have analyzed the reasons for the formation of white bright blocks by using metallographic detection and energy spectrum analysis methods, which will have a certain guiding role in the later production of titanium alloy products.
The material used in the test is a Φ750mm ingot that has been smelted three times by vacuum consumables. After two upsetting and two drawing through the β phase area, a Φ230mm bar obtained by upsetting and multiple drawing times in the α + β phase area, The bar was double-annealed heat-treated according to standard requirements.
Car Guang’s rods were inspected using ultrasonic waves and no abnormalities were found. During the low magnification inspection of the bar samples, it was found that bright silver spots appeared on the low magnification samples. When the sample was inspected at the same position of the bar at the low magnification, there were still white bright blocks in the same part, indicating that the white bright blocks were continuous defects. In order to analyze the cause of the white bright block, a sample was prepared at the white bright block, and the metallographic microscope, scanning electron microscope and energy spectrometer were used for metallographic examination and micro area composition analysis; meanwhile, on the low magnification sample with white bright block , Take samples at and near the bright block to perform room temperature tensile test to analyze the effect of the bright block on the room temperature tensile properties of the bar. The results showed that:
(1) Through high magnification test, it is found that the content of α phase at the white bright block is significantly lower than that of the β phase, and there is no obvious boundary between the white bright block and the matrix. Therefore, it can be judged that the white bright block is caused by composition segregation. Furthermore, through energy spectrum analysis, it was found that the content of Al, Mo, Zr, and Si alloy elements at the white bright block was significantly lower than that of the matrix, while the Ti content was significantly higher than that of the matrix. Therefore, it can be determined that the white bright block is caused by the segregation of Al, Mo, Zr, and Si alloy elements, which is a titanium-rich segregation and is a metallurgical defect.
(2) Combined with the phenomenon that segregation has a certain depth, it can be determined that the segregation is caused by uneven mixing. Since the vacuum consumable smelting process is regional melting, melting and solidification are taking place at the same time, and the smelting homogenization effect is relatively poor. Therefore, if the raw materials are mixed unevenly, there may be a problem of uneven composition of the ingot after smelting, resulting in segregation.
(3) The room temperature tensile property index of the white bright block is far lower than the index of the normal part.