Microstructure based fatigue life prediction framework for polycrystalline nickel-base superalloys with emphasis on the role played by twin boundaries in crack initiation
Microstructure based fatigue life prediction framework for polycrystalline nickel-base superalloys with emphasis on the role played by twin boundaries in crack initiation
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DOI：
10.1016/j.actamat.2016.01.038
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发表时间：
2016-04
期刊：
影响因子：
9.4
通讯作者：
Saikumar R. Yeratapally;M. Glavicic;M. Hardy;M. Sangid
中科院分区：
文献类型：
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作者：
Saikumar R. Yeratapally;M. Glavicic;M. Hardy;M. Sangid
多晶材料中疲劳裂纹的萌生取决于局部微观结构和变形机制，可归因于各种机械和微观结构特征的协同作用，如弹性应力各向异性、塑性应变积累、滑移系统长度和晶界特征。在镍基高温合金中，疲劳裂纹往往在孪晶边界附近萌生。引起疲劳裂纹萌生的因素取决于材料的微观结构，其变化会导致疲劳寿命的分散。在这项工作中，开发了一种基于稳健微观结构的疲劳框架，该框架考虑了i）材料微观结构的统计变异性，ii）微观结构内连续尺度复杂的异质3D应力和应变状态，以及iii）原子机制，例如滑移晶界（GB）相互作用、挤压形成以及由于滑移而导致的基体和析出物的剪切。应用晶体塑性模拟和分子动力学的定量信息来定义持久滑移带 (PSB) 的能量。临界 PSB 的能量及其相对于位错运动的相关稳定性被用作裂纹萌生的失效准则。这个统一的框架为我们提供了关于为什么孪晶边界是裂纹萌生的首选位点的见解。除此之外，计算框架还将疲劳寿命中观察到的散射与材料微观结构的变化联系起来。
Fatigue crack initiation in polycrystalline materials is dependent on the local microstructure and the deformation mechanism, and can be attributed to various mechanistic and microstructural features acting in concert like the elastic stress anisotropy, plastic strain accumulation, slip-system length, and grain boundary character. In nickel-base superalloys, fatigue cracks tend to initiate near twin boundaries. The factors causing fatigue crack initiation depend on the material's microstructure, the variability of which results in the scatter observed in the fatigue life. In this work, a robust microstructure based fatigue framework is developed, which takes into account i) the statistical variability of the material's microstructure, ii) the continuum scale complex heterogeneous 3D stress and strain states within the microstructure, and iii) the atomistic mechanisms such as slip-grain boundary (GB) interactions, extrusion formations, and shearing of the matrix and precipitates due to slip. The quantitative information from crystal plasticity simulations and molecular dynamics is applied to define the energy of persistent slip bands (PSB). The energy of a critical PSB and its associated stability with respect to the dislocation motion is used as the failure criterion for crack initiation. This unified framework provides us with insights on why twin boundaries act as preferred sites for crack initiation. In addition to that, the computational framework links scatter observed in fatigue life to variability in material's microstructure.