Shock response of iron between 143 and 1275 K

The shock response of polycrystalline iron of 99.995% purity was studied in a series of planar impact experiments using laser interferometer monitoring of the free surface of preheated/precooled samples. On the basis of the recorded waveforms, the dynamic yield and tensile (spall) strengths of iron were determined over the 143-1275 K temperature range. Part of the recorded waveforms had a three-wave (P-EL, P1, and P2 waves) structure reflecting a stress-induced phase transformation in the impacted samples. By estimating the stress sigma(tr) and the temperature T-tr on the top of the P1 wave, it became possible to determine the upper borders of stability with respect to the shock loading for both the alpha- and the gamma-iron phases. The analysis of the P2 waves of the recorded waveforms showed that irrespective of its initial, alpha or gamma, state the high-pressure phase of iron is the epsilon-phase. The same analysis yields the width, 5.18 GPa, of the mixed phase region, above which the three-wave structures are substituted by two-wave ones (P-EL and P2) with solely the epsilon-phase behind the front of the overdriven P2 wave. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3174442]