Effect of heat treatment on fracture toughness properties of TC4-DT alloy

Ti-6A1-4V tilanium alloy is a key structure and rotatable parts material for aerospace craft. The heat treatment of domestic Ti-6A1-4V products is generally full annealing. This article studies TC4-DT alloy sheets by solution treatment in β area, α-β area and followed ageing,considering different solution temperatures,ageing temperatures,ageing time and cooling rate on fracture toughness properties. It is found that TC4-DT alloy sheets treated by β area solution treatment and followed ageing appear superior fracture toughness properties comparing to β area solution treatment,owing to the bulky reticular widmanstatten structure at prior β grain boundaries. Correspondingly,more α-β grain boundaries form. Both Platelet α in widmanstatten structure and at grain boundaries increases the resistance of dislocation glides and crack extension. As a result, β area solution-treated sheets have better fracture toughness properties. Fracture surface observation shows that the pathway of crack growth in TC4-DT alloy sheets treated by α-β area solution treatment with bimodal structure is relatively flat,and there are only a few short secondary cracks. On the contrary, the pathway of crack growth in β area solution-treated alloy sheets is flexuous,and there are many rough and severe secondary cracks. As the secondary cracks extension, more branches forms, which absorb more energies,and fracture is resultantly postponed.