Internal convective effects on the lifetime of the metastable phase undercooled Fe–Cr–Ni alloys

Abstract

Differences have been observed between the lifetimes of the metastable phases of undercooled samples of Fe–12 wt% Cr–16 wt% Ni alloy which had been subjected to electromagnetic levitation (EML) and electrostatic levitation (ESL). Internal flow is induced within the samples by positioning forces in EML and much weaker Marangoni forces in ESL. The hypothesis being tested is that the flow within EML samples is strong enough to cause the growing metastable dendrites to deflect so that the secondary arms of adjacent dendrites collide, resulting in early nucleation of the stable phase. Simulations using a commercial computational fluid dynamics software package were performed to determine the time required for collision of the secondary arms to occur. There is quantitative agreement between the numerical time to collision and the experimental lifetime of the metastable phase. It has been determined that the induced convective flow in EML samples is strong enough to cause collision and is the most likely cause of the difference between the lifetimes of the metastable phases in ESL and EML samples.