Defect dynamics in energy materials

先进材料构成了许多新兴技术的基石，从下一代能源生产、运输和国防，到假肢和靶向药物输送。其中的一些例如。聚变能源需要尚不存在的材料，因为工作环境非常恶劣：高温、腐蚀性环境和强烈的辐射意味着目前没有可用的材料可用。理论建模和预测性计算机模拟是新材料开发中的关键步骤，因为它们可以更深入地了解工作中的复杂过程，并减少产品开发的交货期。所有的建模和仿真技术都是基于近似的，这限制了它们的适用范围。虽然它们在过去发挥了很好的作用，但上述极端情况意味着这些简化近似中的一些不再适用，需要新的技术。该项目的目的是开发能够处理这种情况的新的建模途径和模拟方法，并将它们应用于核材料科学中尚未解决的问题。目前可用的最精确的模拟方法跟踪系统中的每个原子。尽管它们可以非常精确，但运行它们所需的计算机能力意味着它们只能在几纳秒内模拟几立方米的材料。这无法捕捉到控制材料性能的大规模、长期的过程，并最终决定，例如，一个核反应堆在需要更换之前可以安全运行多少年。在天平的另一端，计算机辅助设计程序模拟反应堆大小的部件，但这是基于材料行为的简单规则。理想情况下，这些是从微观模拟中得出的，但它们之间在长度和时间尺度上存在巨大差距。该项目将开发的中尺度模拟旨在弥合这一差距。在过去的60年里，粒子物理学家开发了强大的数学工具来理解量子涨落。可以对这些工具进行修改以处理热波动，这将形成新的模拟方法的基础。新技术不会跟踪系统中的每个原子，而是只识别在材料随着时间的演变中发挥重要作用的自由度。这些缺陷是：杂质原子、空位和自间隙(当原子在Eg的规则晶格中被击出位置时形成的)。金属)和位错(其运动控制变形的缺陷线)。虽然新方法将得到广泛应用，但本项目将侧重于3个案例研究。这将回答技术上的重要问题，以及测试新技术。第一个案例研究了W中Re原子的聚集，在聚变堆的强辐射下，高达5%的W原子将转化为Re原子。根据目前可用的模型，Re原子应该分散在W中，但实验表明形成了团簇。这些团簇会导致材料变脆，限制其使用寿命。第一个案例研究将应用新的模拟来理解这一点。第二个是关于位错在辐照下的行为。这可能与它们通常的行为非常不同，并将严重影响反应堆材料的机械性能。目前的模拟方法忽略了单原子缺陷，但这些缺陷对于理解辐射效应是至关重要的。新方法将跟踪这两种缺陷，并帮助提供减轻和控制它们所需的理解。最后的案例研究将研究碳原子与位错的相互作用。这是把铁变成钢的过程，它的重要性怎么强调都不为过。虽然几十年前就已经确定了，但重要的悬而未决的问题仍然存在，该项目旨在开发的新工具将回答这些问题。

Advanced materials form the cornerstone of many emerging technologies, from next-generation energy production, transport and defence, to prosthetics and targeted drug delivery. Some of these eg. fusion energy require materials that do not yet exist, because the operating environment is so ferocious: high temperatures, corrosive environments and intense radiation mean no currently available material can be used. Theoretical modelling and predictive computer simulations are crucial steps in the development of new materials, since they can provide deeper understanding of the complex processes at work, and reduce lead times in product development. All modelling and simulation techniques are based on approximations, which limit their range of applicability. Whilst they have served well in the past, the extreme conditions mentioned above mean that some of these simplifying approximations no longer apply, and new techniques are required. The aims of this project are to develop new modelling approaches and simulation methods that are capable of handling the conditions, and apply them to unsolved problems in nuclear materials science. The most precise simulation methods currently available track every atom in the system. Although they can be very accurate, the computer power required to run them means they can only model a few cubic nanometres of material for a few nanoseconds. This cannot capture the large-scale, long-time processes that control material performance, and eventually decide, for example, how many years a nuclear reactor can be safely run before it needs to be replaced. At the other end of the scale, computer-aided design programs simulate reactor-sized components, but base this on simple rules on how materials behave. Ideally, these would be derived from microscopic simulations, but there is a huge gap in length and time-scales between them. The mesoscale simulations that this project will develop aim to bridge that gap. Over the last 60 years, particle physicists have developed powerful mathematical tools to understand quantum fluctuations. These tools can be modified to treat thermal fluctuations instead, and this will form the foundations of the new simulation methods. Instead of following every atom in the system, the new techniques will identify only the degrees of freedom that play important roles in the evolution of the material over time. These are the defects: impurity atoms, vacancies and self-interstitials (formed when atoms are knocked out of place in the regular lattice of eg. a metal) and dislocations (defect lines whose motion controls deformation). Though the new methods will be widely applicable, this project will focus on 3 case studies. This will answer technologically important questions, as well as testing the new techniques. The first case study concerns the clustering of Re atoms in W. Under the intense radiation of a fusion reactor, up to 5% of W atoms will transmute into Re. According to currently available modelling, the Re atoms should disperse through the W, yet experiments show clusters form. These clusters cause the material to become brittle, limiting its useful lifetime. The first case study will apply the new simulations to understand this. The second concerns the behaviour of dislocations under irradiation. This can be very different from their usual behaviour, and will strongly affect the mechanical properties of reactor materials. Current simulation methods ignore the single-atom defects, but these are crucial for understanding radiation effects. The new methods will track both kinds of defect, and help provide the understanding needed to mitigate and control them. The final case study will investigate the interaction of C atoms with dislocations. This is the process that makes iron into steel, and its importance can hardly be overstated. Although identified decades ago, important unanswered questions remain, and the new tools this project aims to develop will answer them.