The effect of superheat on the nucleation undercooling of metallic melts

The influences of the superheating temperature (T-s) on the nucleation undercooling (Delta T) of metallic melts were investigated by using molecular dynamics simulations based on the embedded atom model (EAM) potential function. The results agree with the intuitive expectation that extremely high heating rates followed by short equilibration time lead to a superheating and partial melting of the solid phase. The fraction of the remained crystalline clusters in the superheated phase depends on the superheating temperature T-s and the equilibration time, as long as T-s is below the maximal superheating. A subsequent fast cooling facilitates a substantial undercooling of the molten phase. The achieved undercooling increment T below the steady-state melting temperature T-m depends on the size and the concentration of the crystalline clusters remained in the liquid phase, and thus on the initial superheating temperature T-s. Based on the simulated results, a model was proposed for describing the relationship of Delta T and T-s, with which simulated data are well fitted and the maximal undercooling for metals can be predicted.