Mechanism and kinetics of phase transformation in KCl under shock compression

A mechanism of the phase transition in potassium chloride under shock loading based on the high-speed dislocation multiplication is suggested. At the shock pressure higher than the equilibrium pressure of the phase transformation, the shock-induced shear stress provides generating, motion and multiplication of partial dislocations of the initial lattice B1 (rocksalt-type), resulting in the development of the intermediate B* structure with further transformation into final cesium chloride structure B2. Since unrelaxed shear stress favors easy dislocation climb, the transformation rate is very high, of about 1-3 nsec-1. It takes place at the first, B1 to B*, stage of the transformation. At B*-to-B2 stage of the transformation a low transformation rate, of about 5-25 μsec-1, takes place. The decrease of the rate is caused by decrease of dislocations ability to crossing as well as by inhibition of the dislocation motion due an overlapping of regions of the new phase.