Origins of different tensile behaviors induced by cooling rate in a near alpha titanium alloy Ti65

The influence of cooling rate after solution treatment on tensile behaviors of a near α titanium alloy Ti65 at test temperature from room temperature (RT) to 650 °C was investigated. The results show that tensile elongation and area reduction for water quenched (WQ) microstructure are 55% and 89% higher than those of air cooling microstructure tested at 650 °C, while yielding/ultimate strength are 613/743 MPa, around 8% higher than those of air cooling (AC1) microstructure. With the increase of test temperature, strength and ductility were both dramatically improved in water quenched (WQ) microstructure compared with air cooling (AC1) microstructure. This phenomenon was primarily attributed to the distinction of microstructure morphologies induced by cooling rates. The origin of differences of tensile behaviors between air cooling (AC1) and water quenched (WQ) microstructures is discussed in terms of microstructure morphologies, grain orientation dependency, tensile fracture surfaces, and the role of twining. The schematics of tensile fracture modes are proposed for air cooling and water quenched microstructures tested at room temperature and 650 °C.