Stage I Fatigue Crack Propagation in a Single Crystal and a Directional Solidified Ni-base Superalloy
Stage I Fatigue Crack Propagation in a Single Crystal and a Directional Solidified Ni-base Superalloy
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DOI：
10.1002/9781119075646.ch68
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
M. Sakaguchi;阪口基己;Ryota Komamura;駒村僚太;Y. Hosaka;保坂雄大;H. Inoue;井上裕嗣
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文献类型：
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作者：
M. Sakaguchi;阪口基己;Ryota Komamura;駒村僚太;Y. Hosaka;保坂雄大;H. Inoue;井上裕嗣
采用小型CT试样，研究了镍基高温合金I阶段疲劳裂纹沿着晶面的扩展规律。首先，晶体取向对第一阶段疲劳裂纹扩展的影响进行了研究，使用单晶（SC）镍基高温合金，NKH-304，具有不同的组合的主要和次要方向。基于NKH-304的试验结果，采用定向凝固（DS）高温合金CM-247 LC，通过改变CT试样初始机械缺口前的晶粒取向，研究了晶粒取向和晶界对第一阶段裂纹扩展的影响。一系列的实验表明，在SC高温合金的第一阶段裂纹显着影响的主要和次要的晶体取向，和DS高温合金的晶界引起的延迟裂纹扩展取决于裂纹平面之间的角度差横跨晶界。为了数值研究弹性各向异性的影响和几何形状的第一阶段裂纹，CT试样的三维有限元模型。从断裂力学分析中发现，三维斜裂纹的几何形状，包含模式I，II和II的组件，发挥了至关重要的作用，以确定在高温合金中的第一阶段裂纹扩展的驱动力。
Stage I fatigue crack propagation along crystallographic slip planes in Ni-base superalloys were experimentally investigated at room temperature employing miniature CT specimens. At first, effects of crystallographic orientation on the Stage I fatigue crack propagation were investigated, using a single crystal (SC) Ni-base superalloy, NKH-304, with different combinations of primary and secondary orientations. Based on the test result of the NKH-304, influences of grain orientations and grain boundary on Stage I crack propagation was investigated employing a directional solidified (DS) superalloy, CM-247LC, changing the grain orientation in front of the initial mechanical notch of CT specimen. A series of experiments revealed the Stage I cracking in the SC superalloy was significantly influenced by both primary and secondary crystal orientation, and the grain boundary in the DS superalloy caused the retardation of crack propagation depending on angular difference between crack planes across the grain boundary. In order to numerically investigate the effect of elastic anisotropy and the geometry of the Stage I crack, a 3-D finite element model for the CT specimen was developed. It was found from fracture mechanics analysis that geometries of 3-D inclined crack, containing mode I, II and II components, played an essential role to determine the driving force of the Stage I crack propagation in the superalloys.