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 °C was applied to induce homogeneous grain refinement. Thus, homogenous and refined grains with an average grain size of 1.6 µm were achieved. During three-directional compression, four type of twins were activated, namely, parallel {112¯2} twins, parallel {101¯2} twins, intersectional {101¯2} twins and parallel {112¯1} twins. In the first pass, {101¯2}, {112¯1} and {112¯2} twins were activated; in the second pass, {101¯2} and {112¯2} twins were activated; and in the third pass, {101¯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 {112¯2} twins, TCDRX and TDDRX in parallel {101¯2} twins, TCDRX and intersectional twins induced DRX (ITDRX) in intersectional {101¯2} twins and TCDRX in parallel {112¯1} twins. Nine types of new texture components formed in this stage. In the last stage, the DRX mechanism was CDRX. The basal slip, pyramidal slip and 1st pyramidal slip were the major deformation mechanisms during hot deformation.