TC6 (Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si) is a martensitic a+/3 two-phase titanium alloy with good comprehensive properties. Its service temperature can reach 450°C and is widely used in important parts of the aviation industry. Structural parts, such as wing blades and aero-engine disks. Since TC6 titanium rod is a two-phase titanium alloy, if the composition of the micro-regions is uneven, it will inevitably cause abnormalities in the macrostructure and microstructure, resulting in a significant difference in hardness between the abnormal area and the normal area, making the overall performance of the material poor. Uneven, fatigue cracks will eventually originate, which will bring great hidden dangers to the safety of parts and reduce the service life of the alloy. In view of the black stripe defect problem found during low-magnification inspection of a certain TC6 titanium alloy bar processing product, in order to accurately determine the type of defect, a metallographic microscope was used to observe the microstructure and determine the abnormal area of ​​the metallographic structure; then scanning Electron microscopy analysis shows that the black stripe area is a chemical composition segregation defect that is rich in molybdenum and poor in aluminum; through microhardness testing, it is determined that the composition segregation in the black stripe area is non-brittle segregation. The test results show that the above method can effectively determine the component segregation and type of TC6 alloy; and it is determined that this type of defect does not affect use and can be delivered after removal. Such defects can be reduced or eliminated by controlling the selection of raw materials for titanium alloy ingots, the mixing and electrode preparation processes, and the voltage and current during the smelting process. The segregation of titanium alloys is classified according to the high and low difference in hardness between the segregation site and the normal area. It can be divided into hard segregation (hardness higher than the normal area, also known as brittle segregation) and soft segregation (hardness lower than the normal area, also known as brittle segregation). Non-brittle segregation) two types. If there is only non-brittle segregation in the product, and all properties meet the requirements of product standards, the product can generally still be delivered for use after removing the segregation; brittle segregation is not allowed to be delivered after removal, and the entire batch should be scrapped. The author discussed the analysis and judgment methods of non-brittle segregation encountered in TC6 alloy rod segregation, aiming to provide reference for product inspection to improve product quality.
1) For the black stripe defects found visually in the TC6 rod, a metallographic microscope was used to observe the microstructure. The defective area was not much different from the normal area, and the type of defect could not be judged; a scanning electron microscope was further used to examine the defective area of ​​the rod. Chemical composition analysis was performed and it was found that the defect area was the segregation of chemical elements rich in giant and poor in aluminum. Finally, combined with the microhardness test, it was determined that the segregation type of the TC6 rod was non-brittle segregation of rich in giant and poor in aluminum. Through microstructure observation, micro-area The method of component analysis and microhardness testing can effectively determine the component segregation and type of TC6 alloy.
2) The segregation in the TC6 alloy rod is non-brittle segregation rich in titanium and poor in aluminum, which does not affect the use and can continue to be delivered after removal; it can be eliminated by controlling the selection of raw materials, mixing and electrode preparation parameters, and the voltage and current during the smelting process. Reduce or eliminate such defects.