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Crystallographic Fracture Mechanics Study on Creep-Fatigue Small Crack Propagation in Ni-base Superalloyas at High Temperatures

镍基高温合金高温蠕变疲劳小裂纹扩展的晶体断裂力学研究

基本信息

批准号：
04650080
负责人：
OKAZAKI Masakazu
金额：
$ 1.34万
依托单位：
Nagaoka University of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

项目摘要

Small fatigue crack growth behavior was investigated in three kinds of Ni-base superalloys at high temperatues ; a single crystal alloy, a directionally-solidified alloy and a pollycrystalline alloy. The effects of temperature and microstructures were also studies base on the muasurement of the crack openig and closing behavior.The main conclusions obtained are summarized as follows :(1) The small fatigue crack growth behavior in Ni-base superalloys are sensitive to the microstructures, such as grain boundaries, crystallographic slip plane and slip direction, and the size of gamma'precipitates. The intrinsic small fatigue crack growth resistance, in which the temperature dependence of elastic compliance and that of crack closure level are taken into account, decreases with temperature. The dissolution of gamma'precipitates by environmental effect closely contributes to the above temperature dependence.(2) The information on the long crack growth are not always applied to thesmall crack. The small cracks propagate even at lower stress intensity factor than the long crack threshold level. The similar phenomena are often found in other kinds of materials, such as the metal-matrix composites materials. These experimental evidences indicate the importance of the investigation of small crack growth behavior.(3) The diffecence between the long and small crack growth rates in the single crystal alloy are compensated by the crack closure phenomenon, but not in the polycrystalline alloy. The inhomogenity of strength properties as well as the difference of the fracture mode are closely related to the above difference between the long and small cracks.

研究了单晶、定向凝固和多晶三种镍基高温合金的高温疲劳小裂纹扩展行为。在测量裂纹张开和闭合行为的基础上，研究了温度和显微组织的影响，得到的主要结论如下：（1）镍基高温合金的疲劳小裂纹扩展行为对显微组织（如晶界、结晶滑移面和滑移方向以及γ '沉淀物的尺寸）敏感。考虑了弹性柔度和裂纹闭合度的温度依赖性，本征小裂纹疲劳扩展阻力随温度的升高而减小。γ ′相的溶解与环境效应密切相关。(2)关于长裂纹扩展的信息并不总是适用于小裂纹。小裂纹甚至在比长裂纹门槛值低的应力强度因子下扩展。类似的现象在其他材料中也经常出现，如金属基复合材料。这些实验证据表明了研究小裂纹扩展行为的重要性。(3)在单晶合金中，长裂纹和小裂纹扩展速率之间的差异被裂纹闭合现象所补偿，而在多晶合金中则不然。强度性能的不均匀性以及断裂模式的差异与长裂纹和小裂纹的上述差异密切相关。