摘要:
采用类金属透明模型合金丁二腈-1.8 wt%丙酮(SCN-1.8 wt%Ace)合金,研究了平行于生长界面前沿的液相对流对定向凝固胞/枝晶生长行为及胞/枝晶间距的影响.对于胞晶生长,在液相对流作用下,其尖端将会出现分岔,使得胞晶间距减小,并且液相对流流速越大,胞晶尖端分岔越明显,胞晶组织越细小,胞晶间距越小.至于枝晶生长,其生长行为与胞晶不同.当抽拉速度较小时,液相对流作用下枝晶两侧三次臂的生长速度将会超过枝晶尖端生长速度,形成新的枝晶列,使得枝晶一次间距减小,并且液相对流流速越大枝晶一次间距越小;当抽拉速度较大时,液相对流作用下迎流侧二次臂生长发达,且会抑制上游枝晶生长,使得枝晶一次间距增大,并且液相对流越强枝晶一次间距越大.
Abstract:
The cellular and dendritic formations are two kinds of typical morphology in the solidification, and there are many theoreti-cal models and experimental researches on them. Most models and researches are based on purely diffusive transport mechanism. However, convection effects are of importance in the evolution of cellular and dendritic growth. Since the metal materials are not transparency and the researches on microstructure only after quenching, it is difficult to observe the dynamic microstructure evolution in real time. In this paper, the effect of liquid flow on the cellular and dendritic growth was investigated by the in-situ observation of SCN-1.8 wt%Ace transparent alloy during the directional solidification under the liquid flow. The cellular tip splitting is found in the presence of liquid flow and the cellular microstructure is smaller after the cellular tip splitting. The cellular spacing decreases as the flow rate becomes larger, but the spacing will become steady ultimately. At high growth rate the dendritic spacing increases with the increase of the flow rate, because the upstream side branches, which are accelerated by liquid flow, will suppress adjacent branches. But, at low growth rate the dendritic spacing decreases with the increase of the flow rate, because the lateral branches will exceed the tip of dendrite to form new dendrite by liquid flow.
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