Influence of Gravity on Solidified Micro-structuire.

研究了重力对微重力环境下单晶和共晶合金凝固的影响。然而，在之前的大多数实验中，例如在自由落体系统中，在飞机或空间实验室中，生长速率过高，无法实现平面固/液界面。这是由于凝固时间的限制。为了研究重力对定向凝固Al-In单晶合金、Ag-Si和Al-Si共晶合金以及Ni基高温合金组织的影响，分别进行了向下和向上定向凝固。在当前Bridgman方法下的u.s.向下的情况下，这会在凝固过程中在固/液界面处产生缩孔。(1)在Al-In合金的单向凝固过程中，单晶L_2相在两个方向上都不断生长。然而，在向下的美国形态显示出形成所谓的“带状结构”的趋势。(2) Ag-Si合金在usds向上的情况下，共晶Si相不断生长，形貌呈现典型的面/非面共晶结构。另一方面，在usds向下的情况下，共晶Si相不连续生长，分散在直径为几微米的α-Ag相中。(3) Al-Si的共晶Si相无论生长方向如何都是连续生长的。在向上和向下的美国标本之间没有形态学差异。(4)雀斑结构的形成受凝固方向的影响较大。这意味着雀斑结构的形成是由重力引起的对流控制的。

The influence of gravity on the solidification of monotectic or eutectic alloys has been investigated under microgravity environments. However, in most of the previous experiments, e.g., in free fall systems, in aircraft or in space laboratories, the growth rate was too high to realize the planar solid/liquid interface. This is due to the limitation of the time for solidification. In order to study the influence of gravity on the microstructure of directionally solidified Al-In monotectic alloy, Ag-Si and Al-Si eutectic alloys, and Ni base-super alloy both the downward and upward unidirectional solidifications(U.D.S.) were carried out. In the case of the downward U.D.S. by the current Bridgman method, This causes a shrinkage cavity at the solid/liquid interface during solidification.(1)Regarding the unidirectional solidifications of Al-In alloy, the Monotectic L_2 phase grows continuously in both growth directions. However, the morphology in the downward U.D.S. shows a tendency to form a so-called "banded structure."(2)In the case of the upward U.D.S. of the Ag-Si alloy, the eutectic Si phase grows continuously and its morphology shows the typical faceted/non-faceted eutectic structure. On the other hand, in the case of the downward U.D.S., the eutectic Si phase grows discontinuously and disperses in the α-Ag phase with a diameter of several micrometers.(3)The eutectic Si phase of the Al-Si grows continuously regardless of the growth direction. There is no morphological difference between the upward and the downward U.D.S. specimens.(4)The formation of freckle structure is greatly affected by the Solidification direction. This means that the formation of freckle structure is controlled with the convection due to the gravity.