高生长速度条件下的“层片↔棒状”共晶转变机理研究

低速生长条件下, 共晶“层片?棒状”转变只由两相的体积分数控制. 高速情况下, 这种转变有时亦发生, 其转变机理不清楚. 本文应用竞争生长准则, 结合高速生长条件下层片共晶和棒状共晶生长模型研究了生长速度引起的“层片?棒状”转变机理. 结果显示: 体积分数在临界值附近很小的范围内, 生长速度和溶质配分系数的增大可引起“棒状→ 层片”共晶转变; 而当体积分数远离临界值时, 转变不发生. 生长速度名义上引起“层片?棒状”共晶转变实际上是由生长速度变化引起的体积分数的变化导致的. 关键词： “层片?棒状”共晶转变 竞争生长 生长速度 体积分数

“Lamellar↔rod” transition mechanism under high growth velocity condition

At a low velocity, the “lamellar?rod” eutectic transition can be controlled by the volume fraction of one eutectic phase only. The factors which affect this kind of transition at high growth velocities are not clear. Based on the competitive growth rule, the criterion for “lamellar?rod” transition is obtained by combining the models of lamellar and rod eutectic growth under rapid solidification conditions. It is shown that for a certain volume fraction, if its value fluctuates around the critical point predicted by the JH Jackson and Hunt model, the increase of the growth velocity or the partition coefficient will lead to the “rod→lamellar” transition. Otherwise, no transition will take place. The “lamellar?rod” eutectic transition at high growth velocity is controlled by the volume fraction variation, which is caused by the increase of the growth velocity.
Keywords： “lamellar? rod&rdquo eutectic transition competitive growth growth velocity volume fraction