CRYSTALLOGRAPHY OF THE ALPHA-]OMEGA TRANSITION IN SHOCK-LOADED ZIRCONIUM

The orientation relations (ORs) between the alpha (hcp) and the omega (three-atom hexagonal) structures have been determined for Zr, in whic h alpha transformed to omega under shock loading. The ORs obtained are found to belong to the variant I OR given by Usikov and Zilbershtein in 1973 for statically compressed samples and also consist of an OR th at is the same as that reported by Song and Gray in 1995 in recent dyn amic experiments on Zr. The latter OR is shown to be a subset of the f ormer. These observations show that the same type of mechanism of tran sformation is operative under both static pressure and shock compressi on. The crystallography of the transition is discussed in terms of the required strains.