The Influence of Interstitial Oxygen on the Alpha to Omega Phase Transition in Titanium and Zirconium

The pressure for the α to ω phase transition was investigated for two grades of titanium and three grades of zirconium. A series of shock experiments were conducted from 5 to 35GPa and revealed that the pressure for the phase transition increases with increasing interstitial oxygen content and is completely suppressed in low purity materials. For the high purity Ti and Zr in this study, the pressure for the phase transition occurred at 10.4 and 7.1GPa, respectively and no reverse transformation was observed upon unloading. Increasing the oxygen content increases the number of octahedral sites occupied; this is postulated to increase the pressure for the phase transition. Neutron diffraction was utilized to quantify the volume fraction of metastable ω phase and to characterize the microstructures within the high purity, shocked, and “soft” recovered specimens.