Implementation of in situ Nanoindentation within a Scanning Electron Microscope for Nuclear Fusion Materials Research

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Poster Session One
Mr David England (4, 2), Dr David Cox (1), Dr Hannah Zhang (2), Dr Yiqiang Wang (3), Dr Mark Whiting (4), Dr Tan Sui (4, 2)
1. Advanced Technology Institute
2. National Physical Laboratory
3. United Kingdom Atomic Energy Authority
4. University of Surrey

SEM, in situ, nanoindentation, residual stress, fusion materials

Abstract text

Nuclear fusion has the potential to serve as a baseload power source for electricity. Environmental challenges posed by fossil fuels and the need for energy security make realising this potential more pressing than ever. A key area of research is the improvement of structural materials, as they are subjected to extreme environments in-service [1]. Careful selection and further development of candidate materials, along with characterisation of various physical and mechanical properties are vital to the structural integrity and commercial viability of fusion reactors.

One potentially problematic issue that requires thorough characterisation and measurement is residual stress, it is commonly recognised as consisting of three types. Type I concerns the macroscale such as an entire component, Type II is on a microscale and covers intergranular stress, Type III is at the nano-scale stress [2]. The multi-scale residual stress has recently been evaluated in a Eurofer97-Eurofer97 nuclear grade laser welded joint [3]. Without mitigation, the measured residual stresses have the potential to cause catastrophic failure [4]. The focus of this work is understanding the multi-scale residual stress within various brazed joints, this joining technique is a promising technique for fabricating plasma facing components.

One of the techniques used is nanoindentation, which is widely used for hardness and elastic modulus testing [5]. It can also be used for residual stress characterisation, provided a known stress-free reference is available [6]. There are two major forms of these nanoindentation instruments, either standalone or in situ, each offers distinct advantages. Standalone methods enable high throughput and can be used for Type I and II residual stress characterisation, whereas in situ approaches use high resolution instruments such as a synchrotron X-ray beamline or a scanning electron microscope (SEM). When used in an SEM, lower throughput results, but it can be a useful tool for selecting certain regions of interests with a higher degree of accuracy. This can be useful for determining the Type III residual stress. This implementation was recently completed using an Alemnis ASA within a Tescan MIRA II at the University of Surrey. Going forward, this instrument will be used to unveil the Type III residual stress within the proposed joints for DEMO class reactors, which will allow for a full characterisation and understanding of the residual stress.


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