Carbon alloy formation during graphite pulse laser melting in a medium with pressure of $\sim10$ MPa

The growth of metastable carbon (MC) from the melt formed by melting of high oriented pyrolitic graphite (HOPG) with a laser pulse in helium is discussed. It has been found that in the melt of the HOPG the basal face grows in the form of stepped hillocks nucleating on screw dislocations, which does not necessitate substantial overcooling of the liquid. On the contrary, the carbon alloy from MCs with different phase compositions (diamond included) is formed from the melt of the HOPG prism face. The only explanation of this fact is homogeneous nucleation in a high supercooled melt. The numerical simulation of the heating process showed that homogeneous nucleation is related to the second solidification front directed from the melt-helium interface toward the principle solidification front moving from the bottom of a liquid bath toward its surface. Correlation between the formation of the second front with laser-induced electromagnetic waves on the melt surface (SEWs) manifesting themselves as periodic surface structures in the solidified melt is demonstrated.