Microstructure and its scales of Cu-70%Sn peritectic alloy under high-temperature gradient directional solidification

Directionally solidified microstructure of Cu-70%Sn peritectic alloy consists of primary ε, peritectic η and the eutectic phase (η + Sn), which is different from the equilibrium microstructure consisting of η phase and eutectic phase. The theoretical analysis results indicate that η phase can be directly precipitated from melt, as the growth rate is more than 22.35 mm/s. At the growth rate ranging from 1 to 5 μ/s, the size of ε phase doesn't decrease due to the change of the solid transformation coefficient between ε and η phases, which contributes to the peritectic transformation. With the increase of growth rate, the volume fraction of η phase firstly decreases and then increases. The primary dendritic arm spacing (A) of Cu-70%Sn alloy and growth rate (V) have a relation of λV^0.325 = 199.5 μm^1.325·s^-0.325 as the growth rate is less than 50 μm/s. While, at the growth rate from 50 to 500 μ/s, the value of λV^0.528 is equal to 676 μm^1.528·s^-0.528.