The influence of oxygen content on the α to ω phase transformation and shock hardening of titanium

Abstract

In this study the influence of alloy chemistry on the propensity of omega phase formation in two titanium alloys during shock loading is examined. The effect of peak shock stress on the phase stability and substructural evolution of high purity and A-70 (3700ppm oxygen) titanium was probed utilizing velocity interferometer system for any reflector and post shock substructural analysis. While in the high purity titanium the alpha to omega phase transformation was found to occur at 10.4GPa, no transformation was observed in the A-70 material for stresses up to 35GPa. Transmission electron microscopy analysis and neutron diffraction of shock-recovered samples confirmed these results and probed the details of twin and dislocation structures. Debye temperature data are also presented and the Debye-Waller temperatures for the alpha and omega phases in the high purity titanium are calculated. Finally, the compressive, quasistatic reload behaviors of both high purity and A-70 titanium are compared to the as-annealed counterparts at comparable strains and discussed in terms of the phase transformation and the shock-induced defect generation.