温度和溶质分布对枝晶竞争生长的影响

Effects of Distribution of Temperature and Solute on the Dendritic Competitive Growth

实时观测了丁二腈-5%乙醇模型合金在定向凝固过程中枝晶的生长过程,研究了温度和溶质分布对枝晶生长形貌的影响。结果表明,两相互竞争生长的枝晶所夹击的枝晶界面上的溶质浓度由于两边枝晶生长时溶质的排泄而不断增大,溶质偏析越来越严重,最终在所夹击的枝晶上形成缩颈;多个枝晶竞争生长时,被夹在中间的枝晶,由于其他枝晶生长过程中凝固潜热的释放,夹击区域温度较高而形成一个成分过冷,使得被夹击的枝晶生长速度较小而出现缩颈。理论分析认为,提高固液界面的液体流动速度,加大温度和溶质浓度分布的不均匀,导致颈缩加剧,这与试验结果吻合。

Dendrite growth in directional solidification of succinonitrile-5% ethanol alloy was observed to examine effects of temperature and solute distribution.The results reveal that solute concentration in the dendrite interface which is in the middle area of two competitive growth can be increased with the drainage of solute in the process of dendritic growth in both sides,which results in more and more serious solute segregation in the middle dendrite so as to induce the necking effects.That dendrite in the middle area in multi-competitive growth dendrite appears in necking effects as a result of slow growth velocity is attributed to release latent heat from other dendrites growth,resulting in increasing temperature of middle area to form constitutional supercooling.Necking effects can be strengthened with increasing in liquid flow velocity at solid/liquid interface and in heterogeneity of temperature and solute distribution based on theoretical analysis,which is well in agreement with experimental ones.