Quasi-static and dynamic mechanical properties of commercial-purity tungsten processed by ECAE at low temperatures
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In this work, we have processed commercial purity tungsten (W) via different routes of equal-channel angular extrusion (ECAE) at temperatures as low as 600 °C. We have systematically evaluated the quasi-static and dynamic compressive behaviors of the processed W. Quasi-static compression tests were performed using an MTS hydro-servo system at room temperature. It is observed that samples ECAE processed at 800 °C show higher yield and flow stresses than those processed at other temperatures; no obvious strain hardening is observed in the quasi-static stress–strain curves. Quasi-static strain rate jump tests show that the strain rate sensitivity of ECAE W is in the range of 0.02 to 0.03, smaller than that of coarse-grained W. Uni-axial dynamic compressive tests were performed using the Kolsky bar (or split-Hopkinson pressure bar, SHPB) system. Post-loading SEM observations revealed that under dynamic compression, the competition between cracking at pre-existing extrinsic surface defects, grain boundaries, and uniform plastic deformation of the individual grains control the overall plastic deformation of the ECAE W. The existence of flow softening under dynamic loading has been established for all of the ECAE W specimens.
KeywordsElectrical Discharge Machine Strain Rate Sensitivity High Pressure Torsion Commercial Purity Flow Softening
This work has been supported by the U.S. Army Research Laboratory under contract # W911QX-06-C-0124. The authors would like to thank Ms. Xueran Liu (University of North Carolina at Charlotte) for assistance with SEM operations.