My research group work on understanding the behaviour of materials under extreme environments, such as radiation damage, high temperatures or high stresses. By developing an understanding of the mechanical behaviour and defects which control materials behaviour we then try and develop materials better able to operate under extreme conditions. We are now working to take technqiues we have developed for traditional engineering materials and apply them to questions in other areas such as solid state batteries for energy storage and geological materials.
Much of our work is centred on developing mechanical testing techniques at the nano and micro scale. We acces to in-situ and ex-situ high temperature nanoindentation systems which allows us to perform tests up to temperatures above 1200K. These techniques are being used to study a range of important materials for both nuclear power and aerospace applications. We also work with leading groups in Oxford and elsewhere to use understanding gained from our experiments to process new materials better suited to working under extreme conditions.
Materials systems being studied include; ceramic composites, high entropy alloys, refractory alloys, high strength steels and zirconium alloys. This is carried out with a range of partners including, UKAEA, Tokamak Energy, Rolls Royce, Karlsruhe Institute of Technology, Germany and UC Berkeley, and University of Wisconsin-Maddison, USA, as well as many collaborators within Oxford. Particular areas of current research include:
Materials for nuclear fission and fusion
Mechanical behviour of materials for energy storage
Development of micromechanical testing techniques
High entropy and nanostructured alloy development alloys
High temperature mechanical properties
Time dependent deformation
Ceramic composite materials for energy and aerospace
Microstructural and micromechanical assessment of aged ultra-fast sintered functionally graded iron/tungsten composites
Materials and Design
Functionally graded (FG) iron/tungsten (Fe/W) composites are considered for stress-relieving interlayers in tungsten-steel joints, required in future fusion reactors. The macroscopic gradation of the two materials allows relaxation of thermally-induced stresses and hence extend the lifetime of the cyclic-loaded dissimilar materials joints. While many properties, e.g. thermal expansion and strength, of the as-manufactured Fe/W composites are promising with respect to the anticipated application, the temperature-induced microstructural changes and their effect on the material properties remain largely unexplored. Given that the thermodynamic system of FeW contains two types of intermetallic phases, understanding the microstructural changes in the FG Fe/W composites are crucial for long-term operation of fusion reactors.
In the present work, the microstructure of ultra-fast sintered Fe/W composites containing 50 and 75 vol% tungsten is studied via electron microscopy (SEM) and X-ray diffraction (XRD) in as-manufactured and thermal aged conditions (300, 500, and 800 °C for up to 72 h). The hardness and modulus of selected composites are measured via nanoindentation, and the fracture toughness of the FeW interfaces is tested via notched micro-cantilever bending tests. The results from microstructural and micromechanical analyses are discussed, and the materials are evaluated for their application in fusion reactors based on the microstructure-to-property relationship.
Sodium/Na β″ Alumina Interface: Effect of Pressure on Voids.
ACS applied materials & interfaces
Three-electrode studies coupled with tomographic imaging of the Na/Na-β″-alumina interface reveal that voids form in the Na metal at the interface on stripping and they accumulate on cycling, leading to increasing interfacial current density, dendrite formation on plating, short circuit, and cell failure. The process occurs above a critical current for stripping (CCS) for a given stack pressure, which sets the upper limit on current density that avoids cell failure, in line with results for the Li/solid-electrolyte interface. The pressure required to avoid cell failure varies linearly with current density, indicating that Na creep rather than diffusion per se dominates Na transport to the interface and that significant pressures are required to prevent cell death, >9 MPa at 2.5 mA·cm-2.
Effects of neutron irradiation on the brittle to ductile transition in single crystal tungsten
JOURNAL OF NUCLEAR MATERIALS
Decoration of voids with rhenium and osmium transmutation products in neutron irradiated single crystal tungsten