Microstructure evolution of TA15 titanium alloy subjected to equal channel angular pressing and subsequent annealing at various temperatures

TA15 titanium alloy was successfully processed for the first time by equal channel angular pressing (ECAP) in the temperature range of 900–1000 °C and annealed in a wide temperature interval from 650 to 800 °C. The investigation was achieved by light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM) on the microstructure evolution of TA15 alloy subjected to ECAP and subsequent annealing after ECAP. In the present work, equal channel angular pressing (ECAP) was taken as the effective method to acquire severe plastic deformation (SPD). The studies we have performed show that grains have been obviously refined and well globularized after ECAP. When TA15 alloy was pressed at the temperatures of α + β phase region equiaxed microstructure was created. There was an increase in the equilibrium grain size with increasing pressing temperature, while a decrease in the volume fraction of equiaxed α phase. TEM microstructural images illustrate that an amount of deformation twins emerged while pressing TA15 below α–β transformation temperature (Tβ), which led to the continued plastic deformation through the restarting of many slip bands. Severe coarsening took place in β grains during ECAP at the temperature above Tβ. A larger number of well globularized and more homogeneous equiaxed α phase of TA15 alloy annealed after ECAP has been attained. Furthermore, with annealing at the optimum temperature, grains have not grown significantly.

► Refined, equiaxed and uniform microstructure of TA15 was produced by ECAP.
► Grain size increased and equiaxed α fraction decreased with increasing temperature.
► Many twins restarted slip bands to keep on plastic deformation.
► Severe coarsening took place in β grains during ECAP above Tβ.
► Well globularized and more uniform equiaxed α was attained by annealing after ECAP.