NSF-EC Cooperative Activity in Materials Research: Failure Mechanics of Layered Ceramics and Ceramic-Metal Coatings Due to Environmental Exposure

多层陶瓷和陶瓷金属涂层的实现由于过早失效而受到限制。迄今为止，对这些失败还没有令人满意或充分的理解。大多数失效是由复杂的热-机械载荷与一系列动态变化的材料特性的相互作用引起的。由于热暴露、氧化、电迁移和/或环境攻击等因素产生的使用化学变化，材料性能会发生变化。这些变化导致较低的内在强度，内部重新分配的应力和残余应力。目前的工作重点是确定和联系多层陶瓷和陶瓷金属涂层的性能变化与过早失效。为了了解失效的机械和物理机制，将实验和建模相结合的研究工作是必不可少的。实验方面，将采用TEM、SEM、纳米压痕等适当的方法，在适当的不同空间尺度（如纳米、微观、中观）上对微观结构的演变进行表征。在不同的温度循环下，在使用寿命的不同阶段，将对空间分布、化学成分和其他影响热机械性能的因素进行表征。从这个实验表征序列中，材料降解的演变状态将与相关的机械过程一起被确定。将开发分析和数值模型来模拟失效机制，将基本原理与实验观察联系起来，并提供对这些复杂系统的更好理解。这些模型将发表在行业期刊上，使设计工程师能够提高多层组件的性能。多层陶瓷和陶瓷/金属涂层用于一系列工程应用，以提高部件和结构的性能和功能。例如，保护燃气轮机叶片免受发动机高温燃烧气体影响的热障涂层，以及用于改善人体体内性能和生物相容性的髋关节或膝关节植入物的生物相容性涂层。不幸的是，陶瓷涂层有时过早失效，限制了它们在这些先进材料系统中的用途。本研究旨在了解故障并开发预测数学模型，以帮助设计工程师在这些重要产品的未来版本中消除此类缺陷。该项目由多学科活动办公室、材料研究部（陶瓷）和国际办公室（西欧）共同资助，是美国国家科学基金会与欧洲委员会材料研究合作项目（NSF 03-565）。该项目正在与西班牙加泰罗尼亚理工大学合作进行；西班牙陶瓷与玻璃研究所；斯洛伐克科学院，斯洛伐克；意大利陶瓷技术研究所；奥地利结构与功能陶瓷研究所；比利时鲁汶天主教大学；德国航空航天中心；以及英国谢菲尔德大学。

The implementation of multilayered ceramics and ceramic-metals coatings is limited due to premature failures. To date no satisfying or adequate understanding of these failures exists. Most failures are caused by an intricate interaction of thermo-mechanical loads with an array of dynamically evolving material properties. The material properties evolve due to in-use chemical changes generated by factors such as thermal exposure, oxidation, electro-migration, and/or environmental attack. These changes result in lower intrinsic strength, internal redistribution of stresses, and residual stresses. The present work focuses on determining and relating property changes to pre-mature failures of multilayered ceramics and ceramic-metals coatings. In order to understand the mechanical and physical mechanisms of failures, a research effort that integrates experiment and modeling is essential. Experimentally, the evolution of the microstructure will be characterized using TEM, SEM, nano-indentation and other appropriate methods at appropriately different spatial scales (e.g. nano, micro, meso). The spatial distribution, chemical composition, and other factors influencing thermo-mechanical properties will be characterized at various fractions of service life under different temperature cycles. From this experimental characterization sequence the evolving state of the material degradation will be identified along with the associated mechanical processes. Analytical and numerical models will be developed to simulate the failure mechanisms, to link fundamental principles with experimental observations, and to provide a greater understanding of these complex systems. The models will be published in industry journals to enable design engineers to enhance multilayer component performance.Multilayered ceramics and ceramic/metal coatings are used in a range of engineering application to improve the performance and functionality of components and structures. Examples ranges from thermal barrier coatings that protect gas turbine blades from the high combustion gas temperatures in the engine, to bio-compatible coatings on hip or a knee implants to improve the in-vivo performance and bio-compatibility in humans. Unfortunately, ceramic coatings sometimes fail prematurely, limiting their usefulness in these advanced material system. This research aims to understand the failures and to develop predictive mathematical models that will assist design engineers in eliminating such flaws in future versions of these important products.This NSF project is co-funded by the Office of Multidisciplinary Activities, and the Division of Materials Research (Ceramics) and the International Office (Western Europe) as a Cooperative Activity in Materials Research between the NSF and EC (NSF 03-565). This project is being carried out in collaboration with the Polytechnic University of Catalonia, Spain; Institute of Ceramic and Glass, Spain; Slovak Academy of Sciences, Slovakia; Research Institute for Ceramic Technology, Italy; Institute for Structural and Functional Ceramics, Austria; the Catholic University of Leuven, Belgium; the German Aerospace Center, Germany; and the University of Sheffield, UK.