Influence of Gravity on Solidified Micro-structuire.

在微重力环境下，研究了重力对偏晶或共晶合金凝固的影响。然而，在以往的大多数实验中，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，无法实现平面固/液界面。这是由于固化时间的限制。为了研究重力对定向凝固Al-In偏晶合金、Ag-Si和Al-Si共晶合金以及镍基高温合金向下和向上定向凝固组织的影响。都被执行了。在目前Bridgman法下拉深的情况下，这会在凝固过程中在固/液界面产生缩孔。(1)Al-In合金定向凝固时，偏晶L_2相在两个生长方向上都是连续生长的。(2)当合金向上生长时，共晶Si相不断长大，并呈现典型的多面/非多面共晶组织。另一方面，在向下生长的情况下，共晶Si相不连续生长，弥散分布在直径为几个微米的α-Ag相中。(3)无论生长方向如何，Al-Si中的共晶Si相都是连续生长的。向上和向下的UDS试件之间没有形态上的差异。(4)凝固方向对雀斑结构的形成有很大影响。这意味着斑点结构的形成受控于重力引起的对流。

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.