Phase Transformations During High‐Pressure Torsion of Pure Zr and of a Zr‐2.5%Nb Alloy

Abstract Zirconium at normal conditions (room temperature and atmospheric pressure) has an HCP structure with lattice parameters a = 3.2313 Å and c = 5.1477 Å (α‐phase). During loading under hydrostatic conditions in diamond anvil cells, a transition from the α ‐phase to an ω‐phase occurs at a pressure between 2 and 6 GPa and from ω to β (bcc) at 30 GPa. It has been recently reported that the α to ω + β transformation might be induced by HPT processing. The resulting microstructures are stable at room temperature and atmospheric pressure. This paper explores the influence of previous processing steps and of composition in the feasibility of the HPT induced α to α + β transformation. It will be shown that neither previous quenching nor high temperature HPT processing prevents the transformation from occurring during subsequent room temperature HPT. The addition of elements such as Nb also seems to favor the transformation. Understanding well the potential of HPT to stabilize high‐pressure phases at normal conditions might be critical, as it will open a whole new range of applications for already existing materials.