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 σ _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 α - and the γ -iron phases. The analysis of the P2 waves of the recorded waveforms showed that irrespective of its initial, α or γ, state the high-pressure phase of iron is the ε -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 ε -phase behind the front of the overdriven P2 wave.