Cu-20%Co合金雾化液滴的凝固组织特征

SOLIDIFICATION MICROSTRUCTURE OF THE GAS-ATOMIZED DROP OF Cu-20%Co ALLOY

对Cu-20%Co合金进行了高压气体雾化快速凝固实验,获得了富Co相以微细球形粒子形式分布于基体的Cu- 20%Co合金粉末．富Co相粒子的尺寸随着粉末尺寸的增加而增大．在凝固过程中,富Co相液滴受固-液界面推斥;凝固后, Co相粒子主要分布于晶界．由于富Co液相的表面能较高,液-液相变时弥散相液核通常在雾化液滴内部形成,并在温度梯度的作用下向雾化液滴中心迁移,从而导致在粉末表面形成很薄的富Cu基体相层．

Rapid solidification experiments have been carried out with Cu-20%Co alloy under the high-pressure gas atomization conditions. Powders containing fine dispersions of Co-rich particles were obtained. The average radius of the Co-rich particles increases with the size of powders. The Co-rich droplets are repulsed by the solid/liquid interface during solidification and Co-rich particles distribute, therefore, mainly along the grain boundaries. Because the surface energy of the Co-rich liquid is relatively higher, the Co-rich droplets nucleate inside the atomized drop. After nucleation the Co-rich droplets move towards the center of the atomized drop under the effect of the temperature gradient. The droplets motion causes the formation of the Co-poor layer on the surface of the powder.