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

超塑性成形（SPF）正越来越多地被英国和国际工业所使用，例如航空航天（钛合金燃气涡轮机部件）、高性能汽车（铝和钛合金）、建筑和国防。联合王国的几家创造财富的公司（如Doncasters、Aeromet、Superform）为一系列客户（包括空中客车、阿斯顿马丁、波音、庞巴迪、BAE系统公司、福特汽车、GKN洛克希德、古德里奇、雷神、西门子）实施了战略规划和战略规划。SPF使用的增加与能够超塑性的合适材料的可用性以及SPF过程的成本、速度和能耗的改善大致相关。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镀层的超塑成形。此外，适用于超塑性成形的新的低成本结构合金（例如Al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代替多部件组件以增加结构完整性中的增加的使用。在较低温度下的成型性大大降低了成本和能源消耗，使SPF在利润率低和环境限制的行业（例如消费汽车）中可行。虽然超塑性建模是该项目的最终目标，但首先需要对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所共有的现象（例如晶粒生长，晶粒形状变化和再结晶）进行建模。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，拟议的工作对于推动英国工业庞大而多样化的部门来说是恰当且及时的。虽然超塑性的实验研究已经超过80年，但对这一重要材料现象的物理过程还没有全面的了解。过去的建模工作一直受到阻碍，没有独特的超塑性流动过程。相反，许多小尺度（从原子到微观）机制联合收割机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，以产生超塑性流动。为了更好地理解超塑性的微观结构和机制之间的关系，开发一种新的建模框架对于超塑性成形作为一种可行的制造方法的进一步发展至关重要。这将使材料能够以有效的微结构进行热机械加工，以降低加工温度并增加超塑性成形应用的应变速率（从而降低成本并增加产量），这些超塑性成形应用在利用这种现象以形成连续复杂形状的金属和陶瓷的行业（例如航空航天、汽车、装甲）中。如果可以通过对微结构的适当改变（例如晶粒细化、晶界/位错钉扎或空位/杂质复合物的形成）来获得低温机制，则这将是可能的。虽然拟议工作的重点是建模超塑性变形，影响将远远大于，这一努力的产品将是一个新的多尺度建模有限元软件包的商业软件和自定义子程序。这将是进一步研究微米和纳米尺度的变形机制如何决定整体材料行为（例如疲劳，应变硬化和热成形，锻造，轧制，挤压，拉伸和机加工等工艺）的基础。

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).