声悬浮条件下Ag-Cu共晶合金的无容器凝固研究

Containerless solidification of Ag-Cu eutectic alloy under acoustic levitation condition

采用声悬浮技术结合激光加热,实现了Ag-Cu共晶合金的无容器熔化与凝固,并通过CMOS图像分析与数值计算,研究了声悬浮过程中合金熔体的温度场分布特性.由于声辐射压作用,合金熔体在声悬浮条件下呈现扁球或圆饼形,表面温度沿赤道点到极点方向升高.凝固样品表面出现涟漪状波纹,统计分析发现,该表面波纹出现在大变形(a/b>2.1)的样品上.波纹中心为共晶形核点,且波纹传播方向与共晶生长方向相同.分析表明,表面形核以及形核后辐射推移的固液界面是形成表面波纹的先决条件.声场的增强能够促进悬浮样品在表面形核.

The containerless melting and solidification of Ag-Cu eutectic alloy were accomplished by acoustic levitation together with laser heating.The temperature field of levitated alloy droplet was investigated through CMOS image processing and numerical calculation.Due to the effect of acoustic radiation pressure,the alloy droplets deform from spherical to oblate or disklike shapes.Their surface temperature rises along the meridian line from the equator to the poles during cooling process.Surface ripples are observed on those samples with greater deformation（a/b2.1）.And it is found that eutectic grains nucleate at the center of these ripples,and grow in the direction parallel to the propagation of ripples.The surface nucleation and the radial advance of solid-liquid interface are revealed to be the two key factors for the formation of surface ripples.The enhancement of sound pressure can induce the surface nucleation of levitated Ag-Cu eutectic alloy.