无容器条件下Cu-Pb偏晶的快速生长

Rapid growth of Cu-Pb monotectics under containerless condition

在落管无容器条件下实现了Cu 10 %Pb亚偏晶和Cu_37 4 %Pb偏晶的快速生长 .发现随着液滴过冷度的增大 ,亚偏晶中初生 (Cu)相的生长形态经历“粗大枝晶→碎断枝晶→等轴晶”的转变 .偏晶的组织形态从多个偏晶胞组织演化为单个偏晶胞组织 .理论计算表明 ,直径在 10 0 0— 6 0 μm之间的亚偏晶和偏晶合金液滴 ,最大过冷度分别为 2 6 9K (0 2TL)和 2 4 5K (0 2TM) .亚偏晶合金中初生 (Cu)枝晶的最大生长速度为 2 4m s,枝晶生长过程主要由溶质扩散控制 .偏晶合金中Marangoni对流效应比Stokes运动显著 ,并且随着液滴直径的减小Marangoni迁移速率逐渐减小 .

Rapid growth of Cu-10%Pb hypermonotectics and Cu-37.4%Pb monotectics have been achieved under containerless condition in drop tube. With the increase of droplet undercooling, the primary (Cu) phase in hypermonotectios shows a morphology transition of 'coarse dendrite -> fragmental dentrite -> equiaxed dentrite'. The momotectic microstructure transfers from multiple monotectic cell to single monotectic cell. Corresponding to the droplet diameter changing from 1000 to 100 mu m, the calculated maximum undercooling for hypermonotectics and monotectics are 269 K(O.2 T-L) and 245 K (0.2 T-M) respectively. The maximum growth velocity of (Cu) dendrite is 2.4 m/s in Cu-10%Pb hypermonotectics. The growth of primary (Cu) phase is always controlled by solute diffusion. The effect of Marangoni migration is more significant than that of Stokes motion, and the Marangoni migration velocity decreases when droplet diameter becomes small.