Spontaneous grain refinement in alloy systems at low undercooling

In a previous paper [J. Appl. Phys. 82 (1997) 3783] we presented an analysi s of the stability of a dendrite against a small perturbation to the tip ve locity. This model demonstrated that dendritic growth in pure metals and al loys would become unstable above some upper critical undercooling DeltaT(2) * while in alloys above a critical concentration, dendritic growth may also become unstable below a lower critical undercooling, DeltaT(1)*. However, for DeltaT(1)* quantitative agreement between the example system studied, N i-Cu, and the available data was poor. In this paper, we present an improve d computational scheme which allows us to relax the assumption that dendrit es propagate as isothermal paraboloids of revolution. This results in much improved agreement with the experimental data. (C) 2001 Elsevier Science B. V. All rights reserved.