半固态处理中球晶形成与演化的直接观察
来源期刊：中国有色金属学报2000年第5期
论文作者：李涛 黄卫东 林鑫
文章页码：635 - 639
关键词：半固态处理； 凝固组织； 丁二腈 - 水；球晶
Key words：semi-solid material processing; solidification structure; succinonitrilewater; globular crystals
摘 要：采用丁二腈 - 水透明模型合金， 通过实时观察技术对半固态处理过程中的组织形成及演化机理进行了研究。结果表明， 球晶是由液相形核长大产生的， 而非由传统形成机制——断裂枝晶钝化控制； 并且半固态处理过程中剪切速率显著影响球晶的形成和分布。 随着搅动速率提高，球化率逐步降低， 当搅动速率足够高时， 无球化发生； 同时， 球化率对搅动速率的突变非常敏感， 搅动速率的突变容易造成球晶的大量形核生长。
Abstract: The microstructure formation during semisolidmaterial processing was experimentally studied through direct observation in a transparent model alloy， succinonitrile5% water(mole fraction)， whose solidification is very similar to that of metals. The results show that the globular crystals form in the direct nucleation from theliquid phase， instead of from fragments of broken dendrites, and the shearing rate during stirring has an important influence on the globular formation. With increasing stirring rate, the ratio of globular formation decreases. When the stirring rate increases to a certain value, globular formation will not happen. The ratio of globular formation is highly sensitive to the sudden change of the stirring rate which causes the numerous nucleation and growth of globularcrystals.
