Ductility improvement of high-strength Ti–O material upon heteromicrostructure formation

Oxygen solid solutions are well known to impose a strong hardening effect on Ti and its alloys, but induce the undesirable embrittlement behavior. In order to improve the ductility of Ti materials with high oxygen content, Ti(O), herein, a heteromicrostructure consisting of two phases with different oxygen contents was synthesized by redistributing the oxygen solutes through heat treatment over the dual (α + β) phase temperature range, followed by water quenching. The heteromicrostructure formation and plastic deformation mechanisms were investigated by erectron backscattered diffraction (EBSD) analysis of the quenched Ti(O) material under tensile deformation coupled with SEM. It was found that the elongation at break of the sintered Ti-0.94 mass% O alloy remarkably recovered from 6% to 19% owing to the above-mentioned heat treatment and water quenching process. The quenched Ti(O) material consisted of equiaxed grains with high oxygen content, fine α' phase grains, and misorientation regions in the equiaxed grains with low oxygen content. The high and low oxygen content phases were derived from the α and β phases, respectively. The β phase was responsible for plastic deformation, which improved the tensile elongation of the Ti(O) material.