Preshock-induced phase transition in spalled U-0.75 wt% Ti

Uranium-0.75 wt% Ti samples were spalled in the range of 5-24 GPa shock pre ssure. One sample was preshocked to a pressure of 24 GPa, 'soft' recovered, and then reloaded and spalled at 10 GPa. The spall strength of U-3/4 wt% T i was found to range from -4.1 to -2.9 GPa when the Romanchenko correction is used in the spall strength calculation. The spall morphology of the samp le that was preshocked and then spalled showed a significant change in micr ostructure from a parent alpha' martensite to a 2-phase eutectoid. The ther modynamically calculated temperature rise resulting from the preshock at 15 -24 GPa in these samples is -555 degrees C. This temperature is not suffici ent to induce such a phase change. However, the preshock conditions additio nally increase the flow stress of the U-34 wt% Ti, and it is postulated tha t this additional hardening is sufficient to increase the temperature above 885 degrees C due to the increased amount of plastic work required during spall, thereby triggering the phase change. (C) 1999 Elsevier Science B.V. All rights re served.