Enhancement of Yield Strength in Zirconium Metal through High-Pressure Induced Structural Phase Transition

Y. Zhao and J. Zhang, Los Alamos National Laboratory

We conducted in-situ deformation studies on ultra-pure zirconium metal using synchrotron x-rays under high P-T conditions. With a well-known and also commonly used method of peak-profile analysis, we determined the differential strain and hence yield strength in polycrystalline zirconium samples under the applied stress. We observe a high-pressure phase-transition induced strengthening with more than 6-fold abrupt increase in yield strength at the transition pressure of Pc = 6 GPa, from 180 MPa in the low-pressure phase of a-Zr to 1180 MPa in the high-pressure phase of w-Zr (Figure 1). The high-P phase transition induced enhancement in yield strength can be interpreted by: (1) soft metallic bonding in a-Zr vs. strong covalent bonding of w-Zr; (2) relatively easy sliding over smooth close-pack sheets in a-Zr vs. bumpy corrugation in slip plane for the open structure in w-Zr atomic layers; and (3) large population of (101)hcp twins and basal stacking faults in a-Zr vs. repulsive nature of the preferred grain orientations and related microscopic defects such as vacancies and dislocation loops in the w-Zr, which would present strong resistance to plastic flow in the high-pressure phase of zirconium. Our finding unveils a new route for the materials strengthening and is expects to provide new prospects for the understanding of the mechanisms underlying the phase-transition driving plasticity and ductility.

This research was partially supported by COMPRES, EAR 10-43050

Y. Zhao and J. Zhang, (2007) Applied Physics Letters, Vol. 91, 201907-1-3.

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