Room-temperature tensile plasticity of BT18y titanium alloy with equiaxed structure and fully lamellar structure

Tensile properties of forging Ti-6.9Al-3.6Zr-2.7Sn-0.7Mo-0.6Nb-0.21Si titanium alloy after two types of heat treatments were tested at room temperature. Optical microscope, transmission electron microscope (TEM) and scanning electron microscope (SEM) were used to investigate the relationship between microstructures and room-temperature tensile plasticity. The microstructure of the sample solutionized at 920°C for 2 h followed by cooling in air is fine equiaxed structure. Compatibility among grains is easy during deformation, so it has good tensile properties at room temperature, especially better tensile plasticity. The sample solutionized at 1020°C for 2 h followed by cooling in air possesses a coarse and lamellar structure with continuous grain boundary α phase. In the tensing process, coordinations among adjacent grains and among a colonies in grains are needed at the same time, so the plastic deformation becomes difficult. But β phase interlayer makes the material maintain some plasticity. α colony has anisotropy. The one that has small included angle to the tensile direction possesses better tensile properties. β phase interlayer in the one that has big included angle to the tensile direction is vulnerable area in the material, and cracks arise in this place firstly while tensing.