On crystallographic aspects of the α→ω transition in shock compressed zirconium

In the present study, specimens of Zr were subjected to shock compression of 11.6 GPa. TEM examination of the recovered samples revealed that during shock compression the α phase (hexagonal close packed) has transformed into the ω (hexagonal) phase. The orientation relationships (ORs) between the α and ω phase have been determined and analysed using both the stereographic projection method and correspondence matrix method. Our ORs have been found to belong to the Variant I OR given by Usikov and Zilbershtein (UZ) for statically compressed Zr samples. These ORs also consist of an OR that is the same as that observed in later studies by Song and Gray (SG) on dynamically compressed Samples. It has been shown that the OR of SG is a subset of the OR of UZ and is not apart from it. The mechanism of α→ω transition with respect to occurrence of an intermediate β (bcc, a high temperature phase of Zr ) structure, during the transition has been explored. We have also shown in this study that the amount of the transformed ω phase decreases with increasing oxygen content in the samples that were shock loaded to the same pressure, as is revealed by both the TEM and XRD results of the recovered Zr samples. (author)