Phase transitions in high-purity zirconium under dynamic compression
Abstract
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 multiphase 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 nonequilibrium 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. We find that the shear stress sj i has the same effect on the nucleation rate as a pressure increase δ P =c εi jsj i/(Δ V /V ) , where c is a geometric constant ∼1 and εi j are the transformation shear strains. The small fractional volume change Δ V /V ≈0.1 at the α →ω transition amplifies the effect of shear stress, and we estimate that for this case δ P is 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.
- Publication:
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Physical Review B
- Pub Date:
- May 2022
- DOI:
- 10.1103/PhysRevB.105.184102
- arXiv:
- arXiv:2112.07763
- Bibcode:
- 2022PhRvB.105r4102G
- Keywords:
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- Condensed Matter - Materials Science
- E-Print:
- doi:10.1103/PhysRevB.105.184102