近年來混合多樣金屬元素而形成的高熵合金引發了廣泛的研究，有別於以往傳統合金以主要金屬元素為主，加入微量次要元素；高熵合金FeCoNiCrMn是以五種金屬元素等比例配置，突破現有金屬調合學限制，且具有優異的機械性質。以往開發金屬中材料機械性質需要精密量測，因此需要大量時間與成本，而近年電腦運算能力顯著提升，數位分身的概念被廣泛的應用在材料科學，航空太空，自駕車與其他各種工程領域中，其主要精神為利用數值模擬分析，相較於實驗分析可大大提升效率，同時提供材料中較難量測的微觀變化。
本論文提出一個整合型的計算架構於微觀尺度計算合金材料的力學性質，針對高熵合金FeCoNiCrMn進行模擬，設計一套導入晶體塑性有限元素法(Crystal plasticity finite element method, CPFEM)和內聚力模型(Cohesive zone model, CZM)的模擬工具以研究FeCoNiCrMn之高溫潛變效應，本研究考慮晶粒本身的差排滑動與晶界上的開裂與相對滑移，以釐清高熵合金在潛變試驗下之破壞機制與力學行為。
本研究先針對模型中的材料參數進行分析，並觀察其晶界變化和力學性質，進行模擬分析後進行討論，整理應變率、材料參數、晶界擴散參數和晶界黏度對模型之影響。本研究並發現由於晶粒間的排向不同會導致應力集中的現象發生於晶界，使晶界提早開裂。也針對有無晶界開裂之機制進行分析，有引入晶界效應的情況下，其潛變破壞由晶界效應主導，與潛變實驗相符。根據參數分析結果，設計出與實驗應力應變曲線相符的模型，能針對材料進行高溫潛變模擬，並且可以觀察模型微觀上的機械行為，應力會集中在晶界周圍，同時，與拉伸方向垂直的晶界會開裂，並符合真實材料微觀裂痕，達成與實驗材料相符的應力應變曲線和微觀上晶界變化。
本研究設計出一套模擬流程架構，以兩大機制為主的模型，可以模擬符合真實材料FeCoNiCrMn潛變的力學行為。未來可依照相同研究方法針對不同高熵合金調整模型後進行模擬，探討高溫下晶粒與晶界的力學行為。

High entropy alloys (HEAs) have attracted extensive attention due to the complex formation from more than five metal elements and their extraordinary performances, such as lightweight, high ductility in extreme working temperatures. This study studied the intergranular creep fracture of FeCoNiCrMn, by exploiting micromechanical modeling. We considered crystal plasticity and the evolution of dislocation density for grain interior and a cohesive zone model for grain boundary sliding and separation. We developed an integrated computational framework to simulate the mechanical properties of FeCoNiCrMn by implementing UMAT for grain interiors and UEL for grain boundaries in ABAQUS. We first performed a parametrical study to examine the robustness of the model. The simulation results agree well with the experimental measurements. Furthermore, we discussed the effects of strain rate, grain boundary separation, and grain boundary viscosity. We found that the stress concentration occurs at the grain boundaries with different grain orientation, making the grain boundary prone to separate from alleviating this severe strain inhomogeneous. Finally, the competition mechanisms of creep fracture for FeCoNiCrMn were studied. The simulation result suggested that the creep fracture is dominated by grain boundary separation, consistent with the experimental observation. Thus, our model can be applied to study grain interior and grain boundary mechanical behavior at high temperature for different high entropy alloys with great potential in automobile, aerospace, and high-performance alloy design.

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