A model of grain refinement incorporating alloy constitution and potency of heterogeneous nucleant particles

A model for the determination of relative grain size is developed based on the assumption that nucleant substrates are activated by constitutional und ercooling generated by growth of an adjacent grain. The initial rate of dev elopment of constitutional undercooling is shown to be equivalent to the gr owth restriction factor and is a useful approximation for the effect of sol ute on grain size when potent nucleant substrates are present. However, whe n the nucleants are of a poor potency then a calculation of the fraction so lid necessary to develop the constitutional undercooling required for nucle ation needs to be performed. Using the model, trends in grain size observed experimentally by the addition of titanium to pure aluminium and to a typi cal casting alloy, AlSi7Mg0.3, can be predicted. II was also found that sum ming the individual growth restriction factors of each solute element in a multi-component alloy can grossly overestimate the actual value of the grow th restriction factor for the alloy. (C) 2001 Acta Materialia Inc. Publishe d by Elsevier Science Ltd. All rights reserved.