高温合金中的分裂不稳定性：一项相场研究
Splitting Instability in Superalloys: A Phase-Field Study
AI总结：
该研究建立含弹性与界面能各向异性的相场模型，揭示高温合金 γ′ 树枝状沉淀物分裂由弹性能密度降低驱动，并由负弹性相互作用能维持稳定。
摘要：
沉淀强化合金，例如镍基、钴基和铁基高温合金，在接近 γ′ 固溶线温度下时效时，会在固态中形成树枝状沉淀物。这些特征源于一种扩散不稳定性：由于扩散的点效应，生长中的球体或圆柱体上的形貌扰动是不稳定的。这些树枝状扰动表现出各向异性生长，这是由界面能和弹性能的各向异性导致的。此外，这些合金中的微观结构还呈现出“分裂”形貌，即树枝状沉淀物在超过临界尺寸后发生碎裂，形成由近等尺寸沉淀物组成的规则八重或四重排列图案，沉淀物之间由狭窄的基体通道分隔。此类形貌的形成机制一直是深入研究的课题，并且已有多种理论被提出以解释其出现。在此，我们建立了一个包含弹性能与界面能各向异性的相场模型，以研究树枝状 γ′ 沉淀物在生长和粗化过程中这些分裂微观结构的演化。我们的主要发现是，尽管表面能密度随之增加，但弹性能密度的降低驱动了分裂形貌的发展。我们还发现，过饱和度、弹性错配、弹性各向异性程度以及界面能等因素会显著调节这些微观结构的形成。我们结合弹性应力影响粗化的经典理论分析了模拟结果，并证明负的弹性相互作用能导致分裂沉淀物的稳定性。
英文摘要：
Precipitation-strengthened alloys, such as Ni-base, Co-base and Fe-base superalloys, show the development of dendrite-like precipitates in the solid state during aging at near-$γ^{\prime}$ solvus temperatures. These features arise out of a diffusive instability wherein, due to the point effect of diffusion, morphological perturbations over a growing sphere/cylinder are unstable. These dendrite-like perturbations exhibit anisotropic growth resulting from anisotropy in interfacial/elastic energies. Further, microstructures in these alloys also exhibit "split" morphologies wherein dendritic precipitates fragment beyond a critical size, giving rise to a regular octet or quartet pattern of near-equal-sized precipitates separated by thin matrix channels. The mechanism of formation of such morphologies has remained a subject of intense investigation, and multiple theories have been proposed to explain their occurrence. Here, we developed a phase-field model incorporating anisotropy in elastic and interfacial energies to investigate the evolution of these split microstructures during growth and coarsening of dendritic $γ^{\prime}$ precipitates. Our principal finding is that the reduction in elastic energy density drives the development of split morphology, albeit a concomitant increase in the surface energy density. We also find that factors such as supersaturation, elastic misfit, degree of elastic anisotropy and interfacial energy strongly modulate the formation of these microstructures. We analyze our simulation results in the light of classical theories of elastic stress effects on coarsening and prove that negative elastic interaction energy leads to the stability of split precipitates.
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