Microsegregation and dendrite arm coarsening in tin bronze

Specimens of the peritectic alloy Cu - 10 wt-%Sn were subjected to various cooling rates typically observed in, industrial casting processes. Some of the specimens were quenched immediately after the end of solidification to avoid further solute homogenisation of the dendrite structure during cooling to room temperature. Characterisation of specimens was carried out by measuring the distribution of secondary arm spacings and two microsegregation indices, namely the volume fraction of non-equilibrium phase and the segregation deviation parameter, calculated from a large number of microanalyses at random points. A tendency of increasing microsegregation with an increase in cooling rate was observed. The microsegregation results were compared with those of a comprehensive microsegregation model using different equations for coarsening of secondary dendrite arms. The comparison indicated that predictions are more accurate when an empirical equation for coarsening, based on the relationship between secondary arm spacing and cooling rate, is used.