Computational Design of Complex Microstructures for Advanced Engineering Alloys

高性能钢和先进钛合金是交通、能源和建筑行业实现轻量化的重要材料。例如，汽车和飞机的重量分别减少10%，可以减少6-8%的温室气体排放，这对替代燃料汽车的实现也至关重要。因此，先进钢和钛合金的加工和使用性能的任何改进都有助于减少对环境影响的工程解决方案。在这两种材料中，相变都发生在固态中，即随着加工过程中温度的升高或降低，不同晶体结构之间发生转变。通过这些相变设计显微组织是为特定应用定制机械性能的关键冶金工具。相场建模是一种强大的工具，可以描述和可视化钢和钛合金中复杂形貌的微观组织的演变。此外，相场模型也是模拟各种材料断裂行为的合适方法。一种物理一致相场方法尚未被开发出来，用于预测具有复杂形貌的具有代表性的钢和钛合金多相显微组织及其断裂行为。根据加工路径，多边形、板状和不规则形状的转换产品可能形成，从而为优化性能提供了巨大的潜力。该计划的目标是开发具有多种转化产物的钢和钛合金相变的全过程相场模型，并预测由此产生的显微组织的断裂行为。此外，合金元素潜在的非均匀分布的作用将通过相场模拟来探索，利用化学图案的概念来设计微观结构，作为提高材料性能（例如断裂韧性）的新途径。该项目将为两名博士生和五名本科生暑期学生提供培训，他们将获得备受追捧的计算工程方面的最新技能。本研究的新颖性和意义在于将相场法推进到复杂相钢和钛合金的微观结构设计工具。该方案的一个特别令人兴奋的方面是，微观结构模拟将与相场模拟框架中产生的断裂行为预测相结合，这将构成该领域的一个重要创新。所提出的建模方法有望为下一代工业过程模型提供一个有吸引力的计算工具，通过指导微观结构设计来优化先进金属合金的加工和性能，这是数字化制造的一个重要方面。

High performance steels and advanced titanium alloys are essential materials for lightweighting in the transportation, energy and construction sectors. For example, 10% weight reduction in vehicles and aircrafts, respectively, decreases greenhouse gas emission by 6-8% and is also critical to enable alternative fuel vehicles. Thus, any improvement in processing and in-service performance of advanced steels and titanium alloys contributes significantly to engineering solutions with reduced environmental impact. In both materials, phase transformations occur in the solid state, i.e. transitions between different crystal structures as the temperature is increased or decreased during processing. Design of microstructures through these phase transformations is a key metallurgical tool to tailor the mechanical properties for specific applications. Phase field modelling is a powerful tool to describe and visualize the evolution of microstructures with complex morphologies as frequently found in steels and titanium alloys. In addition, phase field modelling is also an appropriate method to simulate the fracture behaviour in a wide range of materials. A physically consistent phase field approach has yet to be developed to predict for steels and titanium alloys representative multi-phase microstructures with complex morphologies and the resulting fracture behaviour. Depending on the processing path polygonal, plate-like and irregularly shaped transformations products may form thereby offering an enormous potential to optimize properties. The objectives of the proposed program are to develop a through-process phase field model for phase transformations in steels and titanium alloys with a multiplicity of transformation products and to predict the fracture behaviour of the resulting microstructures. Further, the role of potentially non-homogeneous distributions of alloying elements will be explored with phase field simulations to design microstructures using the concept of chemical patterning as a new avenue to improve material properties, e.g. fracture toughness. The program will offer training for two PhD students and five undergraduate summer students who will acquire a highly sought state-of-the-art skill set in computational engineering. The novelty and significance of the proposed research will be the advancement of the phase field method to a microstructure design tool for complex-phase steels and titanium alloys. A particularly exciting aspect of the proposed program is that microstructure simulations will be coupled with the prediction of the resulting fracture behavior in the phase field simulation framework, which will constitute an important novelty in the field. The proposed modelling method is expected to provide an attractive computational tool for next generation industrial process models by guiding microstructure design to optimize processing and properties of advanced metallic alloys as an important aspect of digital manufacturing.