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金属学报  2016, Vol. 52 Issue (4): 426-436    DOI: 10.11900/0412.1961.2015.00379
  论文 本期目录 | 过刊浏览 |
定向凝固的复杂形状高温合金铸件中的雀斑形成*
马德新1,2()
1 东方汽轮机有限公司材料研究中心, 德阳 618000
2 长寿命高温材料国家重点实验室, 德阳 618000
FRECKLE FORMATION DURING DIRECTIONALSOLIDIFICATION OF COMPLEX CASTINGSOF SUPERALLOYS
Dexin MA1,2()
1 Material R&D Center, Dongfang Turbine Co., LTD, Deyang 618000, China
2 State Key Laboratory of Long-Life High Temperature Materials, Deyang 618000, China
引用本文:

马德新. 定向凝固的复杂形状高温合金铸件中的雀斑形成*[J]. 金属学报, 2016, 52(4): 426-436.
Dexin MA. FRECKLE FORMATION DURING DIRECTIONALSOLIDIFICATION OF COMPLEX CASTINGSOF SUPERALLOYS[J]. Acta Metall Sin, 2016, 52(4): 426-436.

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摘要: 

通过实施工业条件下的定向凝固实验, 对复杂形状的高温合金铸件中的雀斑进行了检测和分析, 揭示了这种凝固缺陷产生的几个新特点. 结果表明, 雀斑易于产生在铸件的棱角部位而不是平滑表面上, 称之为棱角效应; 铸件外形台阶式地突然扩张和缩小会分别抑制和促进雀斑形成, 称之为台阶效应; 雀斑易于产生在向内倾斜而不是向外倾斜的铸件表面上, 称之为斜面效应; 叶片曲率为正的外凸曲面出现严重的雀斑缺陷, 而曲率为负的内凹曲面却毫无雀斑, 此现象称之为曲率效应. 实验中还发现雀斑不但出现在铸件的外表面, 插入型芯也会诱导铸件内部雀斑的产生, 这说明糊状区的液体流动具有强烈的附壁效应, 不管这种壁面是处在铸件外部还是内部. 通过分析可以确认, 正是这种附壁效应在各种具体形状特征下发挥作用, 导致了上述关于雀斑生成的各种效应.

关键词 高温合金雀斑定向凝固铸件    
Abstract

Freckles are a detrimental grain defect formed during directional and single crystal solidification of superalloy components leading to a high rejection rate. Based on the experimental and theoretical studies over the past forty years, the occurrence of freckles is generally believed to be mainly dependent on the alloy chemistry and process parameters, while the geometrical factor of castings was hardly taken into account. In the present work, a series of superalloy castings with complex geometry were directionally solidified in a production-scale Bridgman furnace. Some new features of freckle appearance have been observed, indicating new aspects of freckle formation. The freckles are preferably formed on the edges instead of on the plane surfaces of the castings. Correspondingly, freckles were found exclusively on the casting surface having positive curvature, whereas no freckles formed on the surface with negative one. The casting portions having inward sloping surfaces are very freckle prone, while those with outward sloping surfaces are absolutely freckle free. Therefore, as an independent factor the geometrical feature of the castings can more effectively affect the freckle formation than the local thermal conditions. It was also observed that freckles could occur not only on the external surfaces, but also inside the castings where a core was inserted, because both the shell and the core wall can provide very high permeability for freckling convection in the mushy zone. Based on this wall effect, all the important phenomena observed in the present work, such as the edge effect, the step effect, the sloping effect and the curvature effect on freckle formation in complex castings of superalloys, can be reasonably explained.

Key wordssuperalloy    freckle    directional solidification    casting
收稿日期: 2015-07-13     
图1  横截面为正方形和长方形的铸件棱角处表面产生的雀斑形貌
图2  定向凝固涡轮叶片及其边缘上产生的雀斑形貌
图3  单晶涡轮叶片边缘上产生的雀斑
图4  大型叶片定向凝固中暴露的凝固界面及其附近的表面组织
图5  铸件外形突然扩张对雀斑生长的阻断作用
图6  铸件外形突然收缩对雀斑产生的激发作用
图7  铸件外形接连突然扩大和缩小对雀斑产生的影响
图8  向外和向内倾斜的铸件表面及相应纵截面的形貌
图9  复合锥体铸件的表面及纵截面显示了雀斑形成的位置
图10  实心和带陶瓷芯的圆棒铸件的横截面形貌
图11  定向凝固中倾出残液后的Al-Si合金试棒[23]、试棒侧表面和内部的倾出深度和糊状区内流通性的分布示意图
图12  多边形的铸件中附壁流通层及其叠加效应示意图
图13  铸件外形的台阶式扩张和缩小对糊状区液体对流和雀斑形成影响的示意图
图14  铸件外倾式和内倾式斜面对糊状区液体对流和雀斑形成影响的示意图
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