A funded 3.5-year UK PhD studentship is available in the group of Dr Sandy Knowles within the School of Metallurgy and Materials at the University of Birmingham, with a tax-free stipend of £17,668 per year.
This project is co-sponsored by UK Atomic Energy Authority (UKAEA) / Culham Centre for Fusion Energy (CCFE) and co-supervised by Dr David Bowden. The research group investigates new alloys for extreme environments from fusion/fission reactors to aerospace gas turbines and concentrated solar power. This involves the design of fundamentally new alloys by computational methods; production through arc melting, powder metallurgy or additive manufacturing; characterisation using advanced electron microscopy and x-ray diffraction techniques; mechanical testing using macro/micro-mechanical methods and failure investigation; and environmental behaviour under oxidation/corrosion and irradiation damage.
Commercial fusion power plants (FPPs) need to operate at high temperatures to allow the fusing of deuterium and tritium fuels, as well as to optimise the efficiency of the electrical output. These FPPs will require structural materials capable of operating at high temperatures, and able to maintain integrity with a high degree of radiation damage (up to 38 displacements per atom (dpa) in steel per full power year). Because of poor creep lifetimes, conventional structural steels such as Eurofer97 are constrained to a maximum operating temperature of 550°C. Conventional ferritic martensitic steels also suffer from limited radiation damage tolerance. To provide maximum economic and commercial viability, future commercial FPPs will need to increase operating temperatures beyond this conventional constraint up to, and possibly above, 650°C; as well as increasing irradiation tolerance and design life.
Steels such as castable nanostructured alloys (CNAs) and oxide dispersion strengthened (ODS) steels are proposed as next-generation structural material candidates. These steels rely on fine dispersion of phases that impart excellent strengthening, creep resistance and radiation resilience properties into the material. However, issues can arise around precipitate stability, particularly the MX carbides/nitrides within CNAs. In addition, ODS steels are challenging to manufacture at scale; and are very difficult to machine and join, as these operations can destroy the optimised oxide dispersion within their microstructures.
A unique silicide phase, identified recently [1], provides excellent strengthening of the steel it evolves within, along with a capability to fully decompose above 900°C [2], enabling machining to be carried out at elevated temperatures, without the risk of cracking or loss of optimised precipitate dispersion. Subsequent studies have shown how the silicide phase in these steels can be evolved through a range of nano to micrometre-scale precipitates. The silicide phase consists of Fe, Ni, Cr and Si, however, Ni is notably a problematic element from an activation perspective. Studies of other silicide-strengthening phases have shown the viability, notably in maraging steels, strengthened by Fe2SiTi precipitates [3]. Additionally, certain precipitates, such as B2-superlattice ordered precipitates have been shown to provide disorder reversibility during irradiation, providing an excellent degree of radiation damage resistance [4].
This project offers the translation step for fusion in exploiting our research carried out in this area previously, covering novel silicon-based intermetallic reinforcements within the body-centred cubic (bcc) steel matrix. This project will study reinforcement/matrix coherency with a focus on interface sink strengths, and in-situ evolution, alongside the engineering performance of these novel steels. Alongside the B2-aluminides, Heusler and π-silicides there is strong synergy with recently proposed G-phase reinforced steels, opening up new design space. One key area of this project is to tailor the silicide/aluminide-strengthened steel compositions for low-activation fusion environment requirements, and to perform irradiation experiments using the University of Birmingham based NNUF neutron and proton irradiation facility [5].
The aims of this project are to:
· Explore the compositional space for reduced-activation silicide strengthened steels, through modelling and alloy development.
· Assess & control coherency of the silicide phase and related precipitates and investigate routes to exploit superlattice ordering benefits into these steels, e.g. harnessing interfaces as sinks for irradiation defects.
· Undertake microstructural characterisation of the alloys produced in the project, including x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
· Investigate the performance of both maraging Fe2SiTi-strengthened steels and silicide-strengthened steels under high-temperature mechanical loads.
· Irradiation performance assessment of resultant microstructures and micromechanical properties of the novel alloys.
The candidate should have a 1st class Undergraduate or Masters degree (or equivalent) in Materials Science, or related discipline. A background in microstructural characterisation and/or mechanical testing would be advantageous.
o apply, please provide: (1) A curriculum vitae (CV), (2) A Cover Letter summarising your research interests and suitability for the position, and (3) The contact details of two Referees by email to Dr Sandy Knowles ([Email Address Removed]), www.birmingham.ac.uk/ajknowles
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