EFFECT OF THE STRUCTURAL STATE OF GRAPHITIC MATERIALS ON THEIR PHASE TRANSFORMATIONS UNDER SHOCK COMPRESSION

Abstract

The effect of structural disordering on phase transformations of graphitic materials into dense modifications of carbon under shock compression conditions (P_shock = 30 GPa, T_shock = 3000 K) is studied. It is shown that lower degree of three-dimensional ordering of initial structure (P₃) first decreases and then increases the overall yield of dense phases, reaching the maximum at P₃ = 0. The content of lonsdaleite simultaneously decreases and that of the dense amorphous phase (C_am) increases. The results obtained are attributed to gradual change of the transformation mechanism from predominantly martensite to predominantly diffusion, and also to the fact that the metastable phases (lonsdaleite and C_am) that form at the early transformation stage have time to partly transform into a stable diamond phase.