Modeling of graphitilization kinetics during peritectic melting of tungsten carbide

摘要

A dynamic computational model developed within the context of the classical theory of phase evolution is applied to the W-C system to simulate the kinetics of graphite nucleation during non-equilibrium peritectic melting of WC. The kinetic variables used in the model are obtained directly from the free energy formulations that characterize the stable and metastable equilibria between WC, liquid, and graphite. The isothermal kinetic analysis suggests that transformation time decreases monotonically with increasing superheat such that the minimum transformation time occurs at the metastable congruent melting point of WC (～3107 K). To crystallize 1 ppm of graphite, the minimum transformation time is computed to be ～2 ns. The non-isothermal kinetic analysis suggests that under moderate to high heating rates (10~4-10~6 K/s) graphitilization is completed at superheats of 40-50 K, while under ultra-high heating rates (～10~8 K/s) graphitilization remains incomplete giving rise to metastable congruent melting of WC.