The rayleigh instability and the origin of rows of droplets in the monotectic microstructure of zinc-bismuth alloys
The rayleigh instability and the origin of rows of droplets in the monotectic microstructure of zinc-bismuth alloys
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DOI：
10.1007/bf02651956
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发表时间：
1996-07
期刊：
影响因子：
--
通讯作者：
B. Majumdar;K. Chattopadhyay
中科院分区：
文献类型：
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作者：
B. Majumdar;K. Chattopadhyay
在偏晶合金与呈棒状的液相协同生长的过程中，可以观察到排列良好的棒状形态。然而，在某些加工条件下，在单向凝固过程中观察到的是成排的液滴而不是棒。Y-41 已经提出了各种模型来解释这些微观结构在生长界面不稳定性方面的起源。 t5] 另一方面，Grugel 和 Hellawell t3] 使用透明模拟的实验清楚地表明，除了由于界面速度振荡而导致生长界面处的振荡不稳定性之外，瑞利型成熟不稳定性远远落后于稳定生长前沿。 Kamio 等人，t21 在对 Al-In 偏晶合金进行详细实验研究的过程中，发现了两种不同生长条件下这两种过程的证据。然而，这两个模型都没有定量评估。在本文中，我们报告了 Zn-Bi 偏晶合金的实验结果，该合金产生包含成排液滴的微观结构。我们努力根据生长前沿后面耦合生长过程中形成的棒的瑞利不稳定性来定量解释观察到的形态。 Zn-0.6 at。使用布里奇曼型装置单向凝固pct Bi偏晶合金。详细信息可在其他地方找到。 t6j 实验在大约22·103 K/m 和30·103 KJm 的两个温度梯度下以不同的生长速度进行。实际条件如表 I 所示。图 1 给出了典型的低放大倍率排列的纵向和横截面微观结构。在较高放大倍数下观察时，可以清楚地看出每个棒都是由一排液滴组成，而不是一个连续的棒（图 2）。液滴通常是多面的（图 3 (a)）。图 3 (b) 给出了它们起源于液态的证据。树枝状结构在液滴内部清晰可见。在不同生长速度下观察到的行内相间间距（AM）和液滴间间距（A）
A well-aligned rod morphology can be observed during the cooperative growth of monotectic alloys with the liquid phase taking the form of rods. However, under certain processing conditions, rows of droplets instead of rods are observed during unidirectional solidificationY-41 Various models have been proposed to explain the origin of these microstructures in terms of growth interface instabilities. t5] On the other hand, the experiments by Grugel and Hellawell t3] using transparent analog clearly suggest that in addition to oscillatory instability at the growth interface due to oscillation in the interface velocity, a Rayleigh-type ripening instability sets in well behind the stable growth front. Kamio et al., t21 in the course of a detailed experimental study on Al-In monotectic alloy, found evidence of both the processes under two different growth conditions. However, no quantitative evaluation of either of the models exists. In the present article, we report the results of experiments on Zn-Bi monotectic alloy which yield a microstructure containing rows of droplets. We endeavor to explain the observed morphology quantitatively in terms of the Rayleigh instability of the rods formed during coupled growth behind the growth front. A Zn-0.6 at. pct Bi monotectic alloy was unidirectionally solidified using a Bridgman-type apparatus. The details are available elsewhere. t6j The experiments were performed at different growth velocities at two temperature gradients of approximately 22• 103 K/m and 30• 103 KJm. The actual conditions are given in Table I. Typical low magnification aligned microstructures of the longitudinal and cross sections are given in Figure 1. Rods, when viewed at a higher magnification, clearly reveal that each is composed of row of droplets rather than a continuous rod (Figure 2). The droplets are often faceted (Figure 3 (a)). The evidence that they have originated in the liquid state is given in Figure 3 (b). The dendritic structure is clearly resolved inside the droplets. The observed interphase spacings (AM) and interdroplet spacings (A) within the row at different growth ve-