Microstructure Evolution Of Directionally Solidifiied Cu-20wt.%Sn Peritectic Alloy

Directionally solidified experiments were conducted for Cu-20wt.%Sn peritectic alloy in a growth rate range from 1μm/s to 15μm/s. The solidification structure evolution was investigated from initial transient to steady-state solidication by optical metallographic and XRD. Temperature-stabilization experiments before quenching were carried out to study the kinetics of peritectic reaction and the solute conduction theory during peritectic reaction on the growth rate of 10μm/s. The variation of thickness of peritectic phase was measured and compared with theoretical value in different periods during peritectic reaction; the growth mechanism of peritectic reaction was analysised.With the increase of growth rate, the morphology of solid-liquid interface changes from coarse and shallow cells, fine and deep cells, to cellular dendrite and dendrite,and the length of initial zone became short. The morphology changed from single phase into dual phase with the increase of growth rate. Banded structure andα/βcoupled growth altenating with each other can be observed in low growth rate samples(v<2.5μm/s) and banded structure andα/βcoupled growth can alternate with each other under different growth conditions.The time that the temperature-stabilization samples need to reach the solute homogenization in the mushy zone were in good agreement with TGZM theoretical calculation results.But the theoretical calculation results of pure solute diffusion doesn't match the experimental ones,so the main way to conduct solute is drops but not diffusion.The influence of temperature-stabilization time on the thickness of peritectic phase is in agreement with the model given by St.John and Hogan。A function was got after fitting,Δx = 1.49t.Thickness of peritectic phase associated with growth rate was measured and with St.John Hogan's thickness model of peritectic phase,thickness of peritectic phase during different periods of peritectic reaction and peritectic transformation were analysed and compared with experimental data,then came to the conclusion that the main mechanism of petitectic phase growth was peritectic transformation.