Multiscale Modelling of Micro/Nano-Scale Structure and Damage Evolution in Superplastically Deforming Materials

超塑性成形（SPF）越来越多地应用于一系列英国和国际行业，例如航空航天（钛合金燃气轮机部件），高性能汽车（铝合金和钛合金），建筑和国防。SPF由几家英国财富创造公司（如Doncasters、Aeromet、Superform）为一系列客户（包括空客、阿斯顿马丁、波音、庞巴迪、BAE系统公司、福特汽车、GKN洛克希德、Goodrich、雷神、西门子）开展。增加SPF的使用大致与具有超塑性的合适材料的可用性以及SPF工艺的成本、速度和能耗的改善有关。从过去十年的文献中可以明显看出，新一代超塑性材料正在出现（例如高应变率陶瓷，金属基复合材料）。新材料将带来新的应用，如复杂形状陶瓷装甲的超塑性成形。此外，适合超塑性成形的新型低成本结构合金（例如铝合金）的可用性将导致SPF在制造复杂形状和用单个连续部件取代多部件组件以提高结构完整性方面的使用增加。在较低温度下的可成形性大大降低了成本和能耗，使SPF适用于利润率低和环境限制的行业（例如消费汽车）。虽然模拟超塑性是这个项目的最终目标，但首先有必要模拟与许多其他工业材料加工方法相关的许多其他材料变形模式共同的现象（例如晶粒生长，晶粒形状变化和再结晶）。英国金属成形工业（如Doncasters， Corus）对开发其成形过程的精确模型越来越感兴趣。因此，拟议的工作是适当的和及时的进步，一个庞大的和多样化的部门的英国工业。尽管超塑性的实验研究已经进行了80多年，但对这一重要材料现象的物理过程尚未有全面的了解。由于没有独特的超塑性流动过程，过去的建模工作受到阻碍。相反，许多小规模（从原子到微观）机制与主要取决于晶粒尺寸、温度和应变速率的相对强度相结合，产生超塑性流动。为了进一步发展超塑性成形作为一种可行的制造方法，建立新的模型框架以更好地理解超塑性的微观结构与机理之间的关系是至关重要的。这将使材料能够以有效的微观结构进行热机械加工，以降低工艺温度并提高应变速率（从而降低成本并提高吞吐量），在利用这种现象形成连续复杂形状的金属和陶瓷（例如航空航天，汽车，装甲）的超塑性成型应用中。如果低温机制可以通过适当改变微观结构来实现，例如晶粒细化、晶界/位错钉住或空位/杂质配合物的形成，这是可能的。虽然所提出的工作的重点是模拟超塑性变形，但其影响将大得多；这一努力的成果将是一个由商业软件和定制子程序组成的新的多尺度建模有限元包。这将为进一步研究微观和纳米尺度上的变形机制如何决定材料的整体行为（例如疲劳、应变硬化和热成形、锻造、轧制、挤压、拉伸和加工等过程）奠定基础。

Superplastic forming (SPF) is being used increasingly by a range of UK and international industries, e.g. aerospace (Ti-alloy gas turbine components), high-performance automotive (Al- and Ti-alloys), architecture and defence. SPF is carried out by several UK wealth-generating companies (e.g. Doncasters, Aeromet, Superform) for a range of customers (including Airbus, Aston Martin, Boeing, Bombardier, BAE Systems, Ford Motor, GKN Lockheed, Goodrich, Raytheon, Siemens). Increasing use of SPF correlates roughly with availability of suitable materials capable of superplasticity, and with improvements in cost, speed and energy consumption of the SPF process. It is evident from literature of the last decade that a new generation of superplastic materials are emerging (e.g. high strain rate ceramics, metal matrix composites). New materials will lead to new applications, such as superplastic forming of complex-shaped ceramic armour plating. Furthermore, availability of new low cost structural alloys (e.g. Al-alloys) suitable for superplastic forming will lead to increased use of SPF in making complex shapes and replacing multi-part assemblies with single contiguous parts for increased structural integrity. Formability at lower temperatures reduces cost and energy consumption considerably, making SPF viable in industries with small profit margins and environmental restrictions (e.g. consumer automotive). Although modelling superplasticity is the end goal of this project, it is first necessary to model phenomena (e.g. grain growth, grain shape change and recrystallisation) common to a host of other material deformation modes relevant to many other industrial materials processing methods. UK metals forming industries (e.g. Doncasters, Corus) are increasingly interested in developing accurate models of their forming processes. Thus, the proposed work is apt and timely for advancement of a large and diverse sector of UK industry. Although superplasticity has been studied experimentally for over 80 years, there is not yet a comprehensive understanding of the physical processes of this important material phenomenon. Past modelling efforts have been hindered by there being no unique superplastic flow process. Rather, many small-scale (from atomic to micro) mechanisms combine with relative strengths that depend principally on grain size, temperature and strain rate to produce superplastic flow. It is essential for the further development of superplastic forming as a viable manufacturing method that a new modelling framework be developed in order to better understand the relation between the microstructure and mechanisms of superplasticity. This would enable materials to be thermomechanically processed with efficacious microstructures for lowering the process temperature and increasing the strain rate (and thereby reducing cost and increasing throughput) of superplastic forming applications in industries that exploit this phenomenon for forming metals and ceramics in contiguous complex shapes (e.g. aerospace, automotive, armour). This would be possible if low temperature mechanisms could be accessed via suitable changes to the microstructure, e.g. grain refinement, grain boundary/dislocation pinning or formation of vacancy/impurity complexes. Although the focus of the proposed work is modelling superplastic deformation, the impact will be far greater; a product of this effort will be a new multiscale modelling finite element package made of commercial software and custom subroutines. This will be the foundation of further studies into how deformation mechanisms at the micro and nano scales dictate overall material behaviour (e.g. fatigue, strain hardening and processes such as hot forming, forging, rolling, extrusion, drawing and machining).