TC4 (Ti-6Al-4V) is a martensitic a+/3 two-phase titanium alloy with good comprehensive properties. Its service temperature can reach 450. It is widely used in important structural parts of the aviation industry, such as wing blades and aero engines. Disk etc.
Since TC4 titanium rod is a two-phase titanium alloy, if the micro-region composition 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, causing the material to exhibit poor performance overall. Uniform, fatigue crack sources will eventually sprout, 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 TC4 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; Scanning electron microscopy analysis shows that the black stripe area is a chemical composition segregation defect 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 TC4 titanium 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 are only non-brittle segregations in the product, and all properties meet the requirements of product standards, generally the product can still be delivered for use after removing the segregations; brittle segregations are not allowed to be delivered after removal, and the entire batch should be scrapped.
