在凝固速率1－500 m/s的范围内, Cu--70%Sn包晶合金定向凝固组织由相、包晶相和共晶体组成, 相为领先相与最高界面生长温度假设的分析一致。理论计算结果显示, 当凝固速率大于22.35 mm/s时, 相可直接从液相中析出, 无需通过包晶反应进行。凝固速率越低, 向相固相转变系数越大, 造成相尺寸在1－5m/s范围内变化很小, 而包晶相的体积分数随凝固速率的增加呈现先减后增的变化趋势。
Directionally solidified microstructures of Cu-70%Sn peritectic alloy have been investigated by means of the directional solidification technique. The results show that the solidified microstructure consists of primary , peritectic and the eutectic phase (+Sn), which is different from the equilibrium microstructure consisting of phase and eutectic phase. The theoretical analysis results indicate that 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 m/s, the size of phase doesn’t decrease due to the change of the solid transformation coefficient between and phases, which contributes to the peritectic transformation. With the increase of growth rate, the volume fraction of phase firstly decreases and then increases. The primary dendritic arm spacing ( ) of Cu-70%Sn alloy and growth rate (V) have a relation of V0.325=199.5 m1.325s-0.325 as the growth rate is less than 50 m/s. While, at the growth rate from 50 to 500m/s, the value of V0.528 is equal to 676 m1.528s-0.528.
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