Hot deformation and grain refinement mechanisms of commercially pure titanium processed via three-directional cryo-compression

Commercially pure titanium specimens were processed via three-directional compression at cryogenic temperature to activate homogeneous high-density deformation twins, and subsequent hot compression at 500 degrees C was applied to induce homogeneous grain refinement. Thus, homogenous and refined grains with an average grain size of 1.6 mu m were achieved. During three-directional compression, four type of twins were activated, namely, parallel {11<(2)overbar>2} twins, parallel {10<(1)overbar>2} twins, intersectional {10<(1)overbar>2} twins and parallel {11<(2)overbar>1} twins. In the first pass, {10<(1)overbar>2}, {11<(2)overbar>1} and {11<(2)overbar>2} twins were activated; in the second pass, {10<(1)overbar>2} and {11<(2)overbar>2} twins were activated; and in the third pass, {10<(1)overbar>2} twins were activated. During hot compression, the dynamic recrystallization (DRX) process was divided into twin-active DRX stage and continuous DRX (CDRX) stage. In the first stage, the DRX mechanisms were twinning induced CDRX (TCDRX) and twinning induce DDRX (TDDRX) in parallel {11<(2)overbar>2} twins, TCDRX and TDDRX in parallel {10<(1)overbar>2} twins, TCDRX and intersectional twins induced DRX (ITDRX) in intersectional {10<(1)overbar>2} twins and TCDRX in parallel {11<(2)overbar>1} twins. Nine types of new texture components formed in this stage. In the last stage, the DM mechanism was CDRX. The < a > basal slip, < a > pyramidal slip and 1st < c + a > pyramidal slip were the major deformation mechanisms during hot deformation.