Effects of thermomechanical treatment on the evolution pattern of the α phase and mechanical properties of Ti-17 alloy

Abstract

The effects of thermomechanical treatment (TMT) on the evolution pattern of the α phase and mechanical properties of Ti-17 alloy were investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electronic microscopy (TEM). For the purpose, Ti-17 alloy with initial basketweave microstructure is rolled by 40% at 860 °C and immeiate aging at different temperatures. The results indicated that the α phase was very sensitive to the aging temperature during the TMT process. Rolling led to globularization of primary α phase (αp) and destruction of Burgers orientation relationship between αp and β phases. The subsequent immediate aging yielded further globularization and coarsening of αp, precipitation and coarsening of secondary α phase (αs), and decreasing of the volume fraction of αs. When the aging temperature was increased from 540 to 630 ℃, these changes of the α phase reduced the tensile strength, and enhanced the plasticity and impact toughness. High correlation coefficients (more than 94%) implied that linear equations accurately described the effect of microstructure evolution of the α phase on mechanical properties. Immediate aging at 600 ℃ after hot rolling yielded good comprehensive mechanical properties. This revealed that the structure with suitable matching of globular and lamellar α phase could obtain the optimal combination of strength, plasticity and toughness for Ti-17 alloy.