Creep behavior of silica bar core during directional solidification process of single crystal superalloy
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摘要: 利用悬挂法研究不同直径石英玻璃柱型芯在单晶高温合金定向凝固过程中的蠕变变形特征。采用扫描电镜 （SEM） 观察蠕变型芯表面及径向组织，利用能谱（EDS）分析蠕变型芯表面产物成分，使用XRD方法确定其表面反应产物。结果表明：随定向凝固时间的延长，玻璃柱型芯蠕变变形量增加；随型芯直径增大，蠕变变形量降低；蠕变时间60 min、直径0.5 mm的石英柱变形最严重，平均变形量为30 mm、直径2.0 mm的石英玻璃柱最轻，平均变形量只有24 mm；高温与高真空环境下，定向炉内的C颗粒粉末及合金中挥发的Al会沉积到石英玻璃柱型芯表面，玻璃柱型芯表面与C及Al发生界面反应并形成表层疏松组织层，反应产物所占型芯体积分数导致了不同直径石英玻璃柱型芯的蠕变量不同，随反应产物体积分数的增加，玻璃柱型芯蠕变变形量线性增大。Abstract: Creep characterization of different diameter silica bar core during directional solidification of the single crystal superalloy was investigated by suspension method. The scanning electron microscope (SEM) was employed to observe the microstructure of the surface and transversal section of crept silica bar. The energy dispersive spectroscopy (EDS) and X-ray diffraction technology were used to analyse and determine the composition of the reaction product. The experimental results show that the crept deformation amount increases with prolonging of creep time and decreasing of the diameter of the silica bar. When the creep time is 60 min, the diameter 0.5 mm silica bar has the largest creep deformation, and the average deformation is 30 mm, while the 2 mm silica bar is 24 mm. The interfacial reaction of SiO2 with C and Al, which are deposited on the silica bar surface due to the elevated temperature and low vacuum, induces the formation of porous layer. The volume fraction of the porous reaction products leads to the different crept deformation amount of different diameter silica bars. The creep deformation amount of silica bars has a linear relationship with the volume fraction of surface reaction products.
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图 1 蠕变时间60 min不同直径石英玻璃柱形貌
Figure 1. Features of different diameter silica bars crept for 60 min
图 2 不同直径石英柱蠕变变形量与蠕变时间
Figure 2. Creep deformation amounts of different diameter silica bars versus creep time
图 3 蠕变60 min不同直径石英玻璃柱横截面组织 (a) ϕ 0.5 mm；(b) ϕ 1.2 mm； (c) ϕ 2 mm；（1）低倍；（2）高倍
Figure 3. Transversal section microstructures of different diameter silica bars crept for 60 min (a) ϕ 0.5 mm；(b) ϕ 1.2 mm； (c) ϕ 2 mm；（1）low magnifaction；（2）high magnifaction
图 4 蠕变60 min不同直径石英玻璃柱表面组织 (a) ϕ 0.5 mm；(b) ϕ 1.2 mm； (c) ϕ 2 mm；（1）低倍；（2）高倍
Figure 4. Surface microstructures of different diameter silica bars crept for 60 min (a) ϕ 0.5 mm；(b) ϕ 1.2 mm； (c) ϕ 2 mm；（1）low magnifaction；（2）high magnifaction
图 5 蠕变60 min不同直径石英柱变形量与表面反应层体积分数
Figure 5. Deformation of different diameter silica bar crept for 60 min versus volume fraction of surface reaction layer
图 6 0.5 mm石英柱不同蠕变时间表面组织 （a）20 min；（b）90 min；（1）低倍；（2）高倍
Figure 6. Surface microstructures of 0.5 mm diameter silica bar crept for different time （a）20 min；（b）90 min；（1）low magnifaction；（2）high magnifaction
图 7 直径2.0 mm石英玻璃柱不同状态下的表面能谱 （a）原始态SEM；（b）蠕变态SEM；（1）Si元素；（2）O元素；（3）Al元素；（4）C元素
Figure 7. EDS element maps of surface of 2.0 mm diameter silica bar （a）original state SEM；（b）crept state EM；（1）Si；（2）O；（3）Al；（4）C
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