We present results from ramp compression experiments on high-purity Zr that show the α→ω, ω→β, as well as reverse β→ω phase transitions. Simulations with a multi-phase equation of state and phenomenological kinetic model match the experimental wave profiles well. While the dynamic α→ω transition occurs ∼9 GPa above the equilibrium phase boundary, the ω→β transition occurs within 0.9~GPa of equilibrium. We estimate that the dynamic compression path intersects the equilibrium ω−β line at P=29.2 GPa, and T=490 K. The thermodynamic path in the interior of the sample lies ∼100 K above the isentrope at the point of the ω→β transition. Approximately half of this dissipative temperature rise is due to plastic work, and half is due to the non-equilibrium α→ω transition. The inferred rate of the α→ω transition is several orders of magnitude higher than that measured in dynamic diamond anvil cell (DDAC) experiments in an overlapping pressure range. We discuss a model for the influence of shear stress on the nucleation rate. The small fractional volume change ΔV/V≈0.1 at the α→ω transition amplifies the effect of shear stress, and we estimate that for this case shear stress is equivalent to a pressure increase in the range of several GPa. Correcting our transition rate to a hydrostatic rate brings it approximately into line with the DDAC results, suggesting that shear stress plays a significant role in the transformation rate.
@article{arxiv.2112.07763,
title = {Phase Transitions in High Purity Zr Under Dynamic Compression},
author = {C. W. Greeff and J. Brown and N. Velisavljevic and P. A. Rigg},
journal= {arXiv preprint arXiv:2112.07763},
year = {2022}
}