Micro-electro-mechanical systems (MEMS) are tiny (sub-millimetre) machines, which have arisen from advances in semiconductor fabrication. Typical MEMS devices include air-bag accelerometers, gyroscopes in smartphones and implanted drug-delivery meters. The MEMS industry is currently worth around 10 billion dollars. Furthermore, their low cost, high tolerances, and ability to combine sensors and actuators with microprocessors, give MEMS the potential to profoundly affect our way of life. Unfortunately however, high friction and wear means that current commercial MEMS designs are confined to non-, or very low sliding devices. This precludes the possibility of rotating or reciprocating MEMS such as micro-engines. Clearly, there are huge possibilities if this can be changed. Research efforts to tackle the problem of friction in MEMS have suggested lubrication by liquids and vapours as possible solutions since these can continually replenish protective films on rubbing surfaces. Arguably the most promising has been liquid lubrication as my research on silicon micro-contacts has shown. To date, I have demonstrated the effectiveness of liquid lubrication in model, silicon MEMS-type, contacts but no validation has been carried out on a working MEMS device. The proposed project aims to carry out this validation and thus bridge the gap between lubrication research and the production of a commercial sliding MEMS device. To achieve this, I will collaborate with MEMS manufacturers to produce a micro-journal bearing and incorporate this into a MEMS turbine energy harvester. This is a very suitable application since energy harvesters are a rapidly growing area that would significantly benefit if low friction sliding contacts were possible. The project will break down the bearing production process into a series of studies, each dealing with a different aspect of lubrication and bearing design. These steps include addressing issues such as lubricant containment, evaporation and delivery, optimisation of bearing geometry and adaptation of fabrication techniques. In addition to the goal of producing a MEMS turbine that runs on hydrodynamic micro-bearings, a number of more fundamental avenues of research, involving tribology and silicon MEMS, will be explored. These include a feasibility study into the development of sliding MEMS with compliant surfaces. Finally, silicon MEMS technology will be used to enhance my tribology research by i) coupling fabricated silicon components with existing infrared microscopy equipment so that the temperature of rough surface contacts can be imaged - this is possible since silicon is transparent to infrared; ii) coating thin-film piezoelectric sensors onto silicon specimens to monitor lubricant film thickness using ultrasound.

The interaction of surfaces is fundamental to how we live our lives. How surfaces behave when they move against each other as part of engineered components in machines depends to a large extend on what they are made from and how they are made. This is important because surfaces made from the wrong material or the wrong surface finish could cause the component to fail before it was designed to do so. This leads to a cost penalty for repair and replacement but there is also the additional energy wastage incurred as the material needs to be recycled and re-made. Thus measuring surface composition and roughness is quite important but to do so accurately involves lots of different scientific techniques which can make it time consuming and expensive. It would be much better from a sustainability perspective if surfaces could be measured quickly and accurately when they were being made at a relatively low cost to give information about both their composition and roughness. This project aims to try and achieve this goal by combining two scientific techniques into one sensor measurement. Roughness is often measured by tracing a diamond tip across a surface to measure differences in height. Diamond is a good material for doing this as it is very hard and is not easily damaged when in contact with surfaces. Diamond is an insulator but this can be changed if it is doped with boron. This makes the diamond conductive and means we could potentially use a technique called electrochemical impedance spectroscopy, or EIS, to measure changes in the contact resistance at different AC frequencies (called the impedance) between the diamond and an engineered surface like a steel. The impedance is likely to change as the probe moves across different parts of the steel structure, for example, it will probably be different for the iron part of the steel compared to a part that has lots of carbon in it. This means we might be able to correlate the high and low points of the roughness to the different materials phases of a surface. It will be quite challenging to achieve this as EIS take several minutes to scan all the AC frequencies, but measuring the topography only takes a few seconds. The influence of vibrations, thermal drift and relative humidity will need to be taken account of when the measurement is performed. The data will be collected from a very sensitive nano-indentation machine that uses capacitance plates to provide very accurate data of surface positions. The amount of water in the air when the measurements are taken will be controlled with a chamber than can be filled with dry nitrogen. This is because water in the air will desorb near the probe when the measurements are made and could allow impedance of ambient surfaces to be measured. If the technique were to work it could be very useful across a number of different sectors. These include manufacturing, where it might be used as a quality control device, checking that manufactured components have been made to the correct surface roughness and that no contamination of the surface is present. When some manufacturing processes go wrong they sometimes 'burn' or oxide the surface and this new sensor might be capable of detecting that before a human notices. Other sectors that could benefit would be the chemical industry, especially the catalysis sector, where the surface area of different catalytic species could be correlated to surface height, allowing optimisation for particular applications. This approach would also be relevant to engineering components that experience sliding or rolling contacts as the technique could determine how surfaces change in response to damage accumulation. This could be from both a surface engineering design optimisation point of view or indeed as a condition monitoring approach, where the surfaces are measuring in-situ within their application environment to warn of potential problems developing during operation.

Nanoindentation is an attractive technique, allowing study of local mechanical characteristics in a versatile and cost-effective manner. The two MML indenters in the Gordon Laboratory represent the current state of the art. Hot and cold stages have been developed, allowing operation at up to ~800 C and down to -170 C. Impact indentation can be carried out so as to generate (transient) local strain rates ranging up to about 10^4 s^-1. One of the two systems can be operated in vacuum or under controlled atmosphere, greatly reducing the incidence of specimen oxidation and diamond tip erosion at high temperature, and also eliminating condensation at low temperature. Furthermore, a suite of FEM modelling routines has been developed, allowing quasi-static material constitutive relations, and residual stress levels in particular specimens, to be inferred from nanoindentation data, with good degrees of reliability and accuracy. The proposed work will involve development of these capabilities, particularly relating to impact mode indentation. This will require enhancement of the current modelling suite, and comprehensive characterisation of the dynamics of indenter motion. This should allow the extraction of strain rate sensitivity information, over ranges of strain rate for which conventional testing presents severe difficulties. These techniques will be applied to "reference" materials, such as pure copper, and also to alloys of particular interest. These include (depleted) uranium, which will be supplied by AWE. Such alloys can exhibit pronounced superelastic deformation at relatively low strains and methodology will be developed for the extraction of parameters characterising such behaviour. The effect of ageing on these alloys will also be investigated, which will be facilitated by the capacity for heat treatments to be carried out in situ on the indenter stage (inside the vacuum chamber). AWE will fund a PhD studentship, which will be oriented particularly towards these alloys and the role of superelastic deformation in their overall mechanical behaviour.

Nuclear research underpins the national energy strategy and plays a critical role in reducing the world's CO2 emissions. The currently world dominant nuclear reactor is the pressurised water-cooled reactors (PWR) which operates at high temperature and pressure using light water coolant, such as those at Sizewell B and Hinkley Point C in the UK. However, Generation IV reactors will have even higher operating temperatures and the Super-critical water-cooled reactor (SCWR) and molten salt reactor (MSR) are two of them. Both PWR and Generation IV reactors operate under extreme conditions such as high temperature, high stress and corrosive environments. Most importantly however, is the inevitable irradiation damage which the reactors must simultaneously endure. Therefore, to assess the reliability and lifetime of these reactors it is critical that the mechanical and corrosion performance of structural materials are conducted under relevant service conditions (e.g. under irradiation). Since the decommissioning of DIDO test reactors, there is no suitable neutron sources in the UK for materials irradiation and testing. The University of Birmingham has a high energy proton source (MC40 Cyclotron) and an accelerator-based intense neutron source under development. Building on the Birmingham irradiation facility, this proposal will develop a suite of world unique characterisation equipment for assessing the mechanical properties and corrosion resistance of nuclear materials under simultaneous irradiation, offering a range of important capabilities that currently do not exist. The proposed facility will enable the tackling of a range of scientific challenges. It will enable the industry and universities to study the stress corrosion cracking under both PWR, SCWR and MSR conditions, to evaluate the new nuclear (both nuclear fission and fusion) materials currently being developed in many UK universities. The novel capabilities will benefit the wide UK and international nuclear research community. The proposed facility can be operated with or without simultaneous irradiation, thus will have a high duty cycle and strengthen the UK nuclear material research capacity.