Effect of solidification parameters on the microstructures of superalloy CMSX-6 formed during the downward directional solidification process
Effect of solidification parameters on the microstructures of superalloy CMSX-6 formed during the downward directional solidification process
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DOI：
10.1016/j.jcrysgro.2013.11.084
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发表时间：
2014-03-01
影响因子：
1.8
通讯作者：
Buehrig-Polaczek, A.
中科院分区：
文献类型：
--
作者：
Wang, F.;Ma, D.;Buehrig-Polaczek, A.
采用向下定向凝固工艺铸造了单晶镍基高温合金CMSX-6，拉速为0.0013~0.0217 cm/S，研究了拉速对铸态组织的影响。一次和二次枝晶间距lambda(1)和lambda(2)随拉伸速率的增加而减小，这与传统Bridgman工艺的实验结果相似。然而，本工作中测得的波长(1)和波长(2)的值比布里奇曼过程中测得的值小得多。此外，未考虑对流影响的一次枝晶臂间距理论模型不能合理地描述21的值。相比之下，如果假设枝晶校正因子(a(1))为13.5，Bouchard和Kirkaldy考虑对流因子的理论模型在本工作中能较好地预测Lambda(1)值。随着退火率的提高，枝晶和枝晶间区的伽马‘相尺寸也减小。在所有实验退出速率下，枝晶区域的伽马‘相的形状都是立方的。这与树枝晶核中的伽马‘相不同，在本工作中采用的最高回撤速率下，树枝晶核中的伽马’相变得更圆，由于过饱和度低，生长时间不足，回撤速率增加，样品中的伽马/伽马‘共晶岛的尺寸显著减小。同时，合金元素的微观偏析减少，伽马/伽马‘共晶体积分数先减小后增大。在低退化率和高退出率处理的样品中也发现了伽马/伽马‘共晶形状的差异。(C)2013爱思唯尔B.V.保留所有权利。
The single crystal Ni-base superalloy CMSX-6 was cast by using the downward directional solidification process (DWDS) using withdrawal rates of between 0.0013 and 0.0217 cm/s. The evolutions of as-cast microstructures were characterized as functions of the withdrawal rate. The primary and secondary dendrite arm spacings, lambda(1) and lambda(2), decreased with increasing withdrawal rate, which is similar to the experimental results obtained in the conventional Bridgman process. However, the value of lambda(1) and lambda(2) measured in the present work is much smaller than that in the Bridgman process. In addition to this, the value of 21 cannot be reasonably described by the theoretical models for the primary dendrite arm spacing in which the convection effect was not taken into account. In comparison, the theoretical model of Bouchard and Kirkaldy which considers the convection factor can predict the lambda(1) value well in the present work if the dendrite-calibrating factor (a(1)) is assumed to be 13.5. The sizes of the gamma' phase in the dendrite and interdendritic regions were also reduced with an increased withdrawal rate. The shape of the gamma' phase was cuboidal in the dendritic regions at all experimental withdrawal rates. This contrasts with the gamma' phase in the dendrite cores which became more rounded at the highest withdrawal rates employed in the present work, due to the low supersaturation and insufficient growth time With an increased withdrawal rate, significant reduction in the size of the gamma/gamma' eutectic island was observed in the samples. Meanwhile, the microsegregation of the alloying elements was reduced and the volume fraction of the gamma/gamma' eutectic initially decreased and then increased. The difference in the shape of the gamma/gamma' eutectic was also found in those samples processed at low withdrawal rates as well as at high withdrawal rates. (C) 2013 Elsevier B.V. All rights reserved.