High Temperature Strain accommodation in MAX phase materials for advanced nuclear energy

MAX相是二维层状六方碳化物或氮化物，在高温下可以表现出非常高的机械损伤容限。与陶瓷一样，它们在快中子照射下的活性明显低于金属。因此，它们在先进核裂变的结构应用中具有潜在的应用。然而，需要更好地了解MAX阶段的结构/性能关系和损伤累积机制，以基于微观结构的建模来支持材料和工程部件的设计和开发。最大相材料的独特性能归因于晶体的扭结变形倾向。这是一个鲜为人知的现象，但与在石墨中观察到的现象相似。温度和辐照对扭结形成的影响尚不清楚，但理论研究表明，MAX相的化学成分与解理应力之间存在很强的联系，这可能会影响脆性-韧性转变。更好地理解这一基本机制将导致设计具有更好性能的MAX相材料。该项目的目标是使用高分辨率的电子背散射衍射来绘制颗粒取向图，并研究在高温下测试的TiAlC、ZrAlC和CrAlC系统的纯MAX相合金中的应变局部化。还将研究离子辐照对变形机制的影响。特别是，将在选定取向的颗粒中进行新颖的高温纳米压痕研究，以研究塑性应变如何作为温度的函数在晶体结构中调节。将使用聚焦离子束球磨对纳米压痕下的变形区进行切片，以实现高分辨率的透射镜和透射菊池衍射分析。这些研究的目的尤其是了解辐射如何影响变形机制，因为这将影响宏观尺度上延性行为和脆性行为之间的转变。该项目与同时启动的一个平行项目密切配合，即利用X射线和中子散射和成像对用于先进核能的大块MAX相材料的应变调节进行现场研究。该项目与SCK-CEN(比利时)合作，后者正在与欧洲能源研究联盟核材料联合方案一起开发核应用的最大阶段，该方案旨在为下一代可持续核能开发材料。该项目还与用于先进事故容错能源系统的创新覆层材料的H2020 Il Trovatore方案相联系，在该方案中，SCK-CEN正在进行机械测试(包括辐照材料的研究)，以及由曼彻斯特大学(P.Frankel教授)和哈德斯菲尔德大学(K.Lambrinou教授)进行的电子显微镜微结构表征、透射电子显微镜和MAX相材料的离子辐照。本项目属于EPSRC能源研究主题(核电)

MAX phases are 2D-layered hexagonal carbides or nitrides that can exhibit very high mechanical damage tolerance at high temperatures. In common with ceramics, they are significantly less activated than metals by fast neutron irradiation. Hence they have potential applications in structural applications for advanced nuclear fission. However, the structure/property relationships and mechanisms of damage accumulation in MAX phases need to be better understood for microstructure-based modelling to support the design and development of materials and engineering components. MAX phase materials owe their unique properties to the tendency for crystal deformation by kink formation. This is a little understood phenomenon, but is similar to that observed in graphite. The influence of temperature and irradiation on kink formation is not understood, but theoretical studies have shown a strong link between the chemistry of the Max phase and the cleavage stress, which may affect the brittle/ductile transition. Better understanding of this fundamnetal mechanism would lead to the design of MAX phase materials with improved properties. The objectives of the project are to use high resolution electron backscatter diffraction to map grain orientations and to study the localisation of strain in phase pure MAX phase alloys from the TiAlC, ZrAlC and CrAlC systems, tested at elevated temperature. The effects of ion-irradiation on the deformation mechanisms will also be investigated. In particular, novel high temperature nano-indentation investigations will be performed, in grains of selected orientations, to study how plastic strain is accommodated within the crystal structure as a function of temperature. Sectioning of the deformation zone beneath nano-indentation will be done using focussed ion-beam milling, to enable high resolution transmission microscopy and transmission Kikuchi diffraction analysis. The studies aim, in particular, to understand how irradiation affects the mechanisms of deformation, as this will have impact on the transition between ductile and brittle behaviour at the macroscale. This project interacts closely with a parallel project, starting at the same time, that is conducting in situ studies of strain accommodation in bulk MAX phase materials for advanced nuclear energy using X-ray and neutron scattering and imaging. This project collaborates with SCK-CEN (Belgium) who are developing MAX phases for nuclear applications in conjunction with the European Energy Research Alliance Joint Programme in Nuclear Materials that aims to develop materials for next generation sustainable nuclear energy. The project also connects with the H2020 Il Trovatore programme on Innovative cladding materials for advanced accident-tolerant energy systems, in whicb mechanical testing (including studies of irradiated materials) is being conducted by SCK-CEN, together with electron-microscopy microstructure characterisation by EBSD, Transmission electron microscopy and ion-irradiation of MAX phase materials by Manchester University (Prof. P. Frankel) and Huddersfield University (Prof. K. Lambrinou). This project falls within the EPSRC Energy Research Theme (Nuclear Power)