Computational Design of Complex Microstructures for Advanced Engineering Alloys

高性能钢和先进的钛合金是交通、能源和建筑领域实现轻量化的重要材料。例如，车辆和飞机重量分别减少10%，温室气体排放量减少6-8%，这对实现替代燃料车辆也至关重要。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，在固态下发生相变，即在加工期间随着温度升高或降低而在不同晶体结构之间转变。 通过这些相变设计微观结构是针对特定应用定制机械性能的关键冶金工具。 相场模型是描述和可视化钢和钛合金中常见的具有复杂形貌的微观结构演化的有力工具。此外，相场模型也是一种合适的方法来模拟各种材料的断裂行为。一个物理上一致的相场的方法尚未被开发来预测钢和钛合金的代表性的多相微观结构与复杂的形态和由此产生的断裂行为。根据加工路径的不同，产品可能会形成多边形、板状和不规则形状的转变，从而为优化性能提供了巨大的潜力。 拟议计划的目标是开发一个贯穿过程的相场模型的钢和钛合金的相变与多种转换产品，并预测由此产生的微观结构的断裂行为。此外，潜在的非均匀分布的合金元素的作用将探索与相场模拟设计微结构使用化学图案化的概念作为一种新的途径，以改善材料的性能，例如断裂韧性。 该计划将为两名博士生和五名本科暑期学生提供培训，他们将获得计算机工程领域备受追捧的最先进技能。该研究的新奇和意义在于将相场法发展为一种用于复相钢和钛合金的显微组织设计工具。所提出的计划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的预测相结合，这将构成该领域的一个重要的新奇。所提出的建模方法，预计将提供一个有吸引力的计算工具，为下一代工业过程模型，指导微观结构设计，以优化先进金属合金的加工和性能，作为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.