Origin of high strength and good ductility of TiH2-based powder metallurgy titanium alloy with discontinuous lamellar structures

A unique discontinuous lamellar microstructure of titanium alloys consisting of lamellar colonies at prior β -Ti grain boundaries and internal interwoven α -laths is prepared by a TiH 2 -based powder metallurgy method. The α -variants get various crystallographic orientations and become discontinuous during vacuum annealing at 700 °C. Remarkably, nanoscale phase δ -TiH compound layers are generated between α -laths and β -strips, so that dislocations are piledup at the α / δ / β interfaces during tensile deformation. This leads to dislocation slips being confined to individual α -laths, with different 〈 a 〉 slips and particularly pyramidal 〈 c + a 〉 slips being activated. The efficiency of wavy slip is promoted and the work hardening rate is enhanced. Finally, the combined effect of dispersed micro-shear bands and lath distortions is considered contributive for alleviating the stress concentration at grain boundaries, resulting in a high-promising synergy of enhanced ultimate tensile strength of 1080 MPa and good elongation to fracture of 13.6%.