Abstract The excellent mechanical properties of the Ni-based superalloy IN718 mainly result from coherent γ″ precipitates. Due to a strongly anisotropic lattice misfit between the matrix and the precipitate phase, the particles exhibit pronounced plate-shaped morphologies. Using a phase-field model, we investigate various influencing factors that determine the equilibrium shapes of γ″ precipitates, minimizing the sum of the total elastic and interfacial energy. Upon increasing precipitate phase fractions, the model predicts increasingly stronger particle-particle interactions, leading to shapes with significantly increased aspect ratios. Matching the a priori unknown interfacial energy density to fit experimental γ″ shapes is sensitive to the phase content imposed in the underlying model. Considering vanishing phase content leads to 30 % lower estimates of the interfacial energy density, as compared to estimates based on realistic phase fractions of 12 % . We consider the periodic arrangement of precipitates in different hexagonal and rectangular superstructures, which result from distinct choices of point-symmetric and periodic boundary conditions. Further, non-volume conserving boundary conditions are implemented to compensate for strains due to an anisotropic lattice mismatch between the γ matrix and the γ″ precipitate. As compared to conventional boundary conditions, this specifically tailored simulation configuration does not conflict with the system's periodicity and provides substantially more realistic total elastic energies at high precipitate volume fractions. The energetically most favorable superstructure is found to be a hexagonal precipitate arrangement.

中文翻译：

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高γ''体积分数Ni基高温合金γ/γ''显微组织形成的相场模拟

摘要 Ni基高温合金IN718优异的力学性能主要来源于相干的γ″相析出。由于基质和沉淀相之间存在强烈的各向异性晶格失配，颗粒表现出明显的板状形态。使用相场模型，我们研究了各种影响因素，这些因素决定了 γ" 析出物的平衡形状，最大限度地减少了总弹性和界面能的总和。随着沉淀相分数的增加，该模型预测颗粒-颗粒相互作用会越来越强，从而导致长宽比显着增加的形状。匹配先验未知的界面能量密度以适应实验 γ'' 形状对基础模型中施加的相含量很敏感。与基于 12% 的实际相分数的估计值相比，考虑到消失相含量会导致界面能量密度的估计值降低 30%。我们考虑了不同六边形和矩形超结构中沉淀物的周期性排列，这是由于点对称和周期性边界条件的不同选择造成的。此外，实施非体积守恒边界条件以补偿由于 γ 基体和 γ″ 析出物之间的各向异性晶格失配引起的应变。与传统的边界条件相比，这种专门定制的模拟配置不会与系统的周期性发生冲突，并在高沉淀体积分数下提供更真实的总弹性能。