TC4 (Ti-6Al-4V) is a martensitic a + / 3 two-phase titanium alloy with good comprehensive performance. Its service temperature can reach 450. It is widely used in important structural parts of the aerospace industry, such as wing blades and aero engines Plate etc.
Because the TC4 titanium rod is a two-phase titanium alloy, if the composition of the micro-region is not uniform, 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 material behave as a whole with poor performance It is uniform and eventually generates a source of fatigue cracks, which brings great hidden dangers to the safety of parts and reduces the service life of the alloy.
In order to accurately determine the type of defects, a metallurgical microscope was used to observe the microstructure to determine the abnormal area of the metallographic structure of a TC4 titanium alloy bar processed product during the low magnification inspection. Scanning electron microscopy analysis showed that the black stripe region was molybdenum-rich and aluminum-deficient chemical composition segregation defects; the micro-hardness test determined that the black stripe region composition segregation was non-brittle segregation. The test results show that the TC4 titanium alloy composition segregation and its type can be effectively determined according to the above method; and that this type of defect does not affect the use, and can be delivered after removal. Such defects can be reduced or eliminated by controlling the selection of titanium alloy ingot raw materials, the mixing and electrode preparation process, and the voltage and current during the melting process.
The segregation of titanium alloys can be classified 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 the high and low difference between the segregation site and the normal area). Non-brittle segregation) two categories. If there is only non-brittle segregation in the product, and each performance meets the requirements of the product standard, the product can still be delivered after the segregation is generally removed; brittle segregation is not allowed to be delivered after rejection, and the entire batch should be scrapped. The author discusses the analysis and judgment method of non-brittle segregation encountered in the segregation of TC4 titanium alloy bar, aiming to provide reference for product inspection to improve product quality.
- a. Observe the black streak defects of TC4 titanium rod visually observed, and use a metallographic microscope to observe its microstructure. The defect area is not much different from the normal area, and the type of defect cannot be judged; The chemical composition analysis was carried out, and the defect area was the segregation of the chemical element of Ju-rich aluminum. The final segregation type of the TC4 titanium rod was determined to be the non-brittle segregation of the Ju-rich aluminum. The composition analysis and the method combined with the microhardness test can effectively determine the composition segregation and type of TC4 titanium alloy.
- b. The segregation in the TC4 titanium alloy bar is a non-brittle segregation of rich aluminum and poor aluminum, does not affect the use, and can continue to be delivered after removal; it can be controlled by the selection of raw materials, mixing and electrode preparation parameters, voltage and current during melting To reduce or eliminate such defects.