The effect of secondary arm coarsening on the level of microsegregation in binary alloys has been investigated by combining a composition dependent coarsening law with a solute balance under the assumptions of no solid-state diffusion and a constant cooling rate. The predictions are compared with the solution due to Mortensen, employing a t~(1/3) coarsening law. The analysis demonstrates that arm coarsening is particularly effective at controlling the levels of segregation of slower diffusing solute species with partition coefficients around unity. Calculations indicate that in many commercial alloys more than one solute element influences the secondary arm coarsening behaviour during solidification. Secondary arm coarsening theory for binary alloys has therefore been extended to multicomponent alloys, and incorporated into a finite difference micro-segregation program. Predictions of secondary arm spacings in Al-Cu-Mg alloys have been compared with measurements and good agreement found. The application to steels is considered briefly. The scope for controlling segregation is currently being investigated using the microsegregation model.
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