高温度梯度下Al-In偏晶合金定向凝固组织的演化规律

应用高温度梯度的方法，研究了在定向凝固条件下温度梯度与凝固速率的比值G／R对Al-17．5％In(质量分数)合金凝固组织的影响．结果表明，偏晶合金的定向凝固与共晶合金定向凝固的生长规律类似．在高温度梯度下，仅在很低的生长速度时才能形成二相有序排列的共生．在偏晶合金定向凝固进入稳态生长以后，在各自的相凝固前沿富集了另一相的溶质，由于两相的层间距不大，长大过程中的横向扩散占主导地位．随着生长速度的增大或温度梯度的降低，Al-17．5％In合金定向凝固组织从纤维结构到周期性或规则排列的串状结构再到弥散分布结构转变．这种转变与固一’液界面形状的转变有密切关系．

THE EVOLUTION OF UNIDIRECTIONAL SOLIDIFI-CATION MICROSTRUCTURE OF THE Al-In MONOTECTIC ALLOYS IN HIGH TEMPERATURE GRADIENT

High temperature gradient are employed under the directional condition to examine the influence of the ratio of gradient and solidification rate, G/R, on the microstructure of Al-17.5%In (mass fraction) alloys. The experimental results show that the microstructure evolution of monotectic alloy under the directional solidification is similar to the one of eutectic alloy. When steady growth formed, there exists an In-rich zone in the front of a phase and vice versa. The diffusion process plays a dominate role in the steady growth due to the small lamella distance. Unidirectional solidification microstructure of the alloys changes from fibrous structure to regular droplet-like array and finally random dispersion of In droplets in the aluminum matrix with increasing growth rate or decreasing temperature gradient. The change suggests that the transition of monotectic solidification structure has a closed relation to the morphological transition of solid-liquid interface.