This project sits within the Centre for Doctoral Training (CDT) in Advanced Metallic Systems - a distinct research centre formed by a partnership between the Universities of Sheffield and Manchester and the I-Form Advanced Manufacturing Centre, Dublin. Our doctoral students undertake a different doctoral programme, which includes a compulsory intensive technical and professional skills training programme throughout the 4-year project. For more information on our training programme content, aimed at converting graduates from a non-materials topic into metallurgy, please review our website (linked below).
Austenitic stainless steels and Ni base alloys are extensively used in the primary circuit internals of pressurized water reactors (PWR) due to their high corrosion resistance properties. However, it is also well known that materials processing can have a strong impact on the susceptibility to stress corrosion cracking (SCC) of these materials when exposed in high temperature aqueous environment water coolant under active loading. Historically, components have been manufactured via conventional manufacturing routes, such as forging and welding; however, there is the desire to produce near net shape components via additive manufacturing thanks to the reduce machining costs, more agile manufacturing, and shorter lead times. However, there is currently insufficient knowledge on the impact of the metallurgical quality of the material produced by such processes on the materials performance. It is critical, therefore, to have a fundamental understanding of the relationship between manufacturing via modern near-to-net-shape manufacturing technologies, such as laser powder bed fusion, so that potential degradation caused by changes to current manufacturing practices can be judged. This, in turn, requires a scientifically-based understanding of the various underlying mechanisms influencing/controlling the environmental degradation and their linking to the end effects.
SCC is one of the most insidious forms of materials degradation and its initiation behaviour in as manufactured components are major technical challenges. Although the SCC performance of stainless steels, Ni-base alloys in light water reactors environments has been studied extensively, the SCC data are not available for components produced using near-net-shape technologies.
The overall aim of this project is to characterise the microstructure of additively manufactured (AM) stainless steels produced via laser powder bed fusion, and compare the mechanical properties (tensile strength, fracture toughness) and susceptibility to environmentally assisted cracking (EAC) of material in the three conditions of interest: forged, AM and heat treated. The secondary aim is to develop an understanding of the processing-microstructure-mechanical property relationships at work, and hence suggest process alterations to optimise material performance.
SCC is one of the most insidious forms of materials degradation when exposed in a specific environment and it is usually characterized by long incubation times. Therefore in service cracks can go undetected for many years, if not decades before leading to fast crack propagation. One of the challenges that is addressed is therefore related with the materials testing and the need to forecast the materials performance over very long periods. A combination of tapered samples and SSRT will be used to characterise the threshold stress required for SCC initiation, and to identify the optimised microstructure. In fact, it has been shown that it is possible to predict the threshold stress required for SCC initiation by SSRT of tapered samples at different strain rates, using a methodology recently developed via the collaborative research programme NUGENIA-MICRIN/ MICRIN+. Testing will also be carried out testing coupons at constant load in high purity water doped with anionic impurities and oxidant. This testing condition is relevant to both boiling water reactors (BWR) and to occluded and poorly refreshed regions in PWR where off-spec water chemistry condition might persist for prolonged times. The generation of feedback to inform manufacturing process parameters will also be addressed in this project.
The project will be carried out at the Materials Performance Centre, part of the Department of Materials and one the centres of the Nuclear Dalton Institute at the University of Manchester. The centre has extensive expertise in microstructural characterization, metallurgy, oxidation, and structural integrity of nuclear components and benefits from the access to state-of-the-art material characterization facilities and autoclaves for replicating nuclear environments via the Henry Royce Institute. The successful candidate will acquire skills in materials performance and will become proficient in the materials and microstructural characterization, which include secondary electron microscopy (SEM), focused ion beam (FIB), transmission electron microscopy (TEM), X-ray diffraction (XRD) and other advanced characterization techniques.
This project is based across both the Department of Materials and is sponsored by Rolls Royce. We are seeking a UK resident with a 2.1 or 1st class degree in a STEM discipline.
The Centre for Doctoral Training in Advanced Metallic Systems is a partnership between industry and the Universities of Sheffield, Manchester and I-Form Advanced Manufacturing Centre, Dublin. CDT students undertake a 4-year doctorate with an in-depth compulsory technical and professional skills training programme. Please review our training programme, application process and full entry requirements at (https://www.sheffield.ac.uk/metallicscdt). Please note, application is only via the University of Manchester (see website), and general enquiries can be made to the CDT ([Email Address Removed]). For more information on the research scope of the project please contact Professor Fabio Scenini (fabio.scenini@manchester.ac.uk)
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