Cobalt-based alloys with {\gamma}/{\gamma}' microstructures have the potential to become the next generation of superalloys, but alloy compositions and processing steps must be optimized to improve coarsening, creep, and rafting behavior. While these behaviors are different than in nickel-based superalloys, alloy development can be accelerated by understanding the thermodynamic factors influencing microstructure evolution. In this work, we develop a phase field model informed by first-principles density functional theory and experimental data to predict the equilibrium shapes of Co-Al-W {\gamma}' precipitates. Three-dimensional simulations of single and multiple precipitates are performed to understand the effect of elastic and interfacial energy on coarsened and rafted microstructures; the elastic energy is dependent on the elastic stiffnesses, misfit strain, precipitate size, applied stress, and precipitate spatial distribution. We observe characteristic microstructures dependent on the type of applied stress that have the same {\gamma}' morphology and orientation seen in experiments, indicating that the elastic stresses arising from coherent {\gamma}/{\gamma}' interfaces are important for morphological evolution during creep. The results also indicate that the narrow {\gamma} channels between {\gamma}' precipitates are energetically favored, and provide an explanation for the experimentally observed directional coarsening that occurs without any applied stress.

中文翻译：

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预测钴基高温合金中γʹ沉淀物的形态

具有 {\gamma}/{\gamma}' 微观结构的钴基合金有可能成为下一代超级合金，但必须优化合金成分和加工步骤以改善粗化、蠕变和漂流行为。虽然这些行为与镍基高温合金不同，但可以通过了解影响微观结构演变的热力学因素来加速合金的开发。在这项工作中，我们根据第一性原理密度泛函理论和实验数据开发了一个相场模型，以预测 Co-Al-W {\gamma}' 沉淀物的平衡形状。对单个和多个析出物进行三维模拟，以了解弹性和界面能对粗化和筏状显微组织的影响；弹性能量取决于弹性刚度、失配应变、沉淀物尺寸、施加的应力和沉淀物空间分布。我们观察到依赖于施加应力类型的特征微结构，这些微结构具有在实验中看到的相同 {\gamma}' 形态和取向，表明由相干 {\gamma}/{\gamma}' 界面产生的弹性应力对于形态学很重要。蠕变过程中的进化。结果还表明，{\gamma}' 沉淀物之间的狭窄 {\gamma} 通道在能量上受到青睐，并为实验观察到的在没有任何外加应力的情况下发生的定向粗化提供了解释。我们观察到依赖于施加应力类型的特征微结构，这些微结构具有在实验中看到的相同 {\gamma}' 形态和取向，表明由相干 {\gamma}/{\gamma}' 界面产生的弹性应力对于形态学很重要。蠕变期间的进化。结果还表明，{\gamma}' 析出物之间的狭窄 {\gamma} 通道在能量上是有利的，并为实验观察到的在没有任何外加应力的情况下发生的定向粗化提供了解释。我们观察到依赖于施加应力类型的特征微结构，这些微结构具有在实验中看到的相同 {\gamma}' 形态和取向，表明由相干 {\gamma}/{\gamma}' 界面产生的弹性应力对于形态蠕变期间的进化。结果还表明，{\gamma}' 沉淀物之间的狭窄 {\gamma} 通道在能量上受到青睐，并为实验观察到的在没有任何外加应力的情况下发生的定向粗化提供了解释。