氩气雾化Ti-48Al合金液滴的快速冷却和凝固组织

Rapid Cooling and Solidification Microstructure of Argon Atomized Ti-48Al Alloy Droplets

为研究氩气雾化过程中Ti-48Al(原子分数/%)合金液滴的形核和晶粒生长形式,分析液滴冷却过程的温度变化。采用扫描电子显微镜、透射电子显微镜和电子背散射衍射观察粉末的组织形貌,并基于观察建立了初始形核数量、固/液界面速率、冷却速率和液滴直径之间的牛顿冷却模型。结果表明:随着粉末尺寸的增加,初始形核数量呈指数增加,晶核生长时固/液界面从双曲面形式转变为同心圆形式;利用模型数值计算发现,雾化液滴纯液相急剧冷却,冷却速率约为105～106 K·s-1。液滴进入再辉阶段后,温度快速上升后平缓下降,固相冷却阶段冷却速率约为105 K·s-1。

An analytical approach was developed to investigate nucleation and growth of Ti-48Al （atom fraction/%） alloy droplets during their flight in an argon atomization process. Evolution of microstructure of the solidified powders was investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electron back-scatter diffraction （EBSD）. Newton cooling model based on the initial number of nuclei, liquid/solid interface velocity, cooling rate and size of droplets was established. The results show that statistical nucleation events increase exponentially with the increase of powders size, and the growth of nuclei is transformed from a twinned spherical segment into a concentric liquid/solid interface geometry. Temperature of atomized droplets decreases rapidly with the cooling rate of 10 5-10 6K·s -1 .Then temperature increases sharply to near the liquidus temperature during recalescence. When the recalescence is completed, the droplet solidifies at a relatively slower rate. Afterwards the cooling rate of the fully solid phase decreases to about 10 5K·s -1 .