Influence of Gravity on Solidified Micro-structuire.

研究了微重力环境下重力对一元合金或共晶合金凝固的影响。然而，在以前的大多数实验中，例如，在自由落体系统中、在飞行器中或在空间实验室中，生长速率太高而不能实现平面固/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、Al-Si共晶合金和Ni基高温合金显微组织的影响，分别采用向下和向上定向凝固（U.D.S.）被执行。在U. D. S.通过当前的布里奇曼方法，这会在凝固过程中在固/液界面处产生收缩空腔。（1）对于Al-In合金的单向凝固，单相L_2相在两个生长方向上连续生长。然而，在向下的U.D.S.显示出形成所谓的“带状结构”的趋势。“（2）如U.D.S.在Ag-Si合金中，共晶Si相连续长大，其形貌为典型的小面/非小面共晶结构。另一方面，在U.D.S.下降的情况下，共晶Si相呈不连续生长，弥散分布在α-Ag相中，直径约为几微米。（3）Al-Si的共晶Si相无论生长方向如何都连续生长。向上和向下的U.D.S.之间没有形态上的差异。标本（4）凝固方向对雀斑组织的形成有很大影响。这意味着雀斑结构的形成是由重力对流控制的。

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.