Investigation of microstructures, textures, mechanical properties and fracture behaviors of a newly developed near α titanium alloy

摘要

Microstructures, textures, mechanical properties and fracture behaviors of a newly developed near α titanium alloy were investigated systematically at room temperature (RT) and high temperatures (600 ℃ and 650 ℃). Microstructure observations revealed that α colonies with large size in as-casted alloy were either broken into deformed α lamellas or colonies with small size, or transformed into equiaxed a grains by recrystallization. The recrystallized equiaxed structure exhibited lower texture intensities and poor preferential crystallographic orientation comparing with macro-zones corresponding to deformed α colonies. And recrystallized structure played an important role in reducing texture intensities of overall α phase. Due to more recrystallized equiaxed α grains, the maximum texture intensity of 980F-A was slightly lower than that of 980F-B. Moreover, TEM analyses proved that silicides promoted the recrystallization of α grains by pinning dislocations during forging. Comparison between current alloys with commonly used near α titanium alloys indicated that 980F-A exhibited optimal combination of mechanical properties at RT and 600 ℃. Observations of fracture surfaces found that silicides played an important role in the formation of voids and dimples due to the production of inhomogeneous plastic deformation and stress concentration around them. Meanwhile, silicides displayed stress bearing effect during tensile process. By observations of longitudinal section, voids closing to fracture surface were mainly located in two types of areas. First type of areas was the vicinity of macro-zones. Second type mainly distributed at the edges of coarse grain areas. Boundaries of lamellar a grains in a single deformed α colony were also the preferential formation sites of voids and micro-cracks.