Grain misorientation induced low-temperature impact toughness deterioration and its deformation mechanism of Ti6321 titanium alloy

In this study, the impact toughness and deformation mechanism of base metal (BM), heat affected zone (HAZ) and weld zone (WZ) of Ti6321 alloy joint at different temperatures (20 °C, 0 °C, −20 °C, −40 °C, −60 °C and −196 °C) are studied. The microstructure of BM consists of primary α (αp), acicular α and β phase. The HAZ is composed of αp, acicular α, acicular martensite (α′) and β phase. The WZ is composed of acicular α′, lath α′ and β phase. All the BM, HAZ and WZ obtain the highest impact toughness at 20 °C, which are 51 J, 75 J and 72 J, respectively. Under −196 °C, brittle fractures occurs in the BM, HAZ and WZ, and their impact toughness are 18 J, 22 J and 30 J, respectively. Compared with the impact test at −196 °C, the fracture surface of 20 °C by impact test has higher kernel average misorientation and geometrically necessary dislocation. The fracture impact resistance at 20 °C is greater. Grain deformation at 20 °C consumes more energy and the crack propagation path is more tortuous.