Now showing 1 - 10 of 34
  • Publication
    Research-informed Education in Materials Science and Engineering: a Case Study
    (The International Council on Materials Education, 2016) ; ; ;
    A course in Metals Processing, delivered to senior engineering students, in which much of the curriculum consists of summaries of selected relevant research projects, is presented. A balanced research team, under the leadership of the course co-ordinator, has designed and delivered an advanced module covering the near net shape processing of metallic alloys. The topics covered include alloy solidification and casting, plasticity and metal forming, and a practical laboratory exercise. Details of the course content, and the research on which much of it is based, are hereby presented, along with commentary on the pedagogic rationale for the approach taken.                       
  • Publication
    In Situ X-ray Studies of metal alloy solidification in microgravity conditions – The XRMON project
    The performance of structural metallic materials is associated with the solidification microstructures, which are strongly dependent on gravity effects. Experimentation in a microgravity environment is a unique way to suppress these effects and to provide benchmark data for testing current theories of grain and microstructure formation. This contribution presents a summary of results obtained for directional solidification of Al-Cu alloys within the framework of the XRMON project. It is focussing on (i) the first ever microgravity experiment on solidification with in situ monitoring of metal alloys performed on board a sounding rocket and (ii) solidification experiments performed on board parabolic flights, where the effects of varying gravity level have been studied.
  • Publication
    Effect of design on the replication of micro/nano scale features by micro injection moulding
    (Research Publishing Services, 2011) ; ;
    The replication of micro/nano scale features is of great interest for MEMS and Microsystems. However, the flow behaviour of melts into a micro/nano cavity is still not well understood. In this work, we used the micro injection moulding process to replicate micro/nano scale channels and ridges from a Bulk Metallic Glass (BMG) cavity insert. High density polyethylene (HDPE) was used as the moulding material. The influence of feature configuration, length, width, gap distance between features, location on substrate, and substrate thickness on the quality of replication was investigated. The experiments revealed that the replication of ridges, including feature edge, profile and filling distance, was sensitive to the flow direction; a critical feature length was found below which the filling of features was significantly reduced. Both the feature location and the substrate thickness had an influence on the filling of micro/nano features while the gap distance had a negligible effect on the replication of features.
  • Publication
    XRMON-SOL microgravity experiment module on Maser-13
    The XRMON-SOL microgravity experiment observed spatially isothermal equiaxed solidification of an Al–Cu alloy in microgravity on board the MASER 13 sounding rocket, launched in December 2015. It is the first time that isothermal equiaxed solidification of a metallic alloy has been observed in situ in space, providing unique benchmark experimental data. The experiment used a newly developed isothermal solidification furnace in the re-used module of the MASER 12 experiment XRMON-GF. A grain-refined Al–20 wt%Cu sample was fully melted and solidified during 360 s of microgravity and the solidification sequence was recorded using time-resolved X- radiography. Equiaxed nucleation, dendritic growth, solutal impingement, and eutectic transformation were thus observed in a gravity-free environment. This paper describes the technology development of the experiment module.
  • Publication
    Meso-scale thermal and solidification modelling for metallic additive manufacturing processes
    The emergence of additive manufacturing (AM) in recent decades signifies a paradigm shift in how we think about manufacturing. Throughout history, breakthroughs in manufacturing were focused on mass production, with a “one size fits all” mentality. Whilst for large batch size applications this has invariably decreased unit manufacturing costs, increased throughput and decreased prices for customers, it also imposes significant limitations for small batch production. Conventional manufacturing requires many highly specialised steps and equipment, requiring significant resources to establish and setting the barrier to entry unfeasibly high for fledgeling SMEs to enter the manufacturing space. Coupled with this, it inevitably forces manufacturers to be unresponsive to their customers’ needs, as changes to a product or manufacturing process are costly, and require significant machine downtime. Additive manufacturing on the other hand offers virtually limitless freedom to the manufacturer to make changes to a product, even for a one-off bespoke application, without significant machine downtime or costly modification to the manufacturing process. Perhaps even more importantly, since parts are generated additively many of the restrictions that traditional machining imposes on part design no longer apply, allowing for near-net- shape, highly optimised structures to be realised. However, these advantages do not come without a cost. Widespread adoption of AM is still hampered by less than ideal mechanical performance.
  • Publication
    Review of the Maxus 8 Sounding Rocket Experiment to Investigate Solidification in a Ti-Al-Nb Alloy
    (European Space Agency, 2009) ; ; ;
    A review of the MAXUS 8 sounding rocket microgravity experiment to investigate solidification structures in a Ti-Al-Nb intermetallic alloy is presented. The experiment was part of the Intermetallic Materials Processing in Relation to Earth and Space Solidification (IMPRESS) EU FP6 project. Key objectives were to investigate columnar and equiaxed solidification, and to achieve Columnar-to-Equiaxed Transition (CET) in the alloy. A microgravity experiment was designed to achieve this using a controlled power-down method. Two alloys were tested: one inoculated with a grain refiner and the other without grain refinement. Unrefined samples displayed axial and radial columnar growth. Boride inoculated samples displayed an equiaxed structure. No clear CET was achieved. The design, details, and results of the experiment are presented.
  • Publication
    Experimental and economic study of aluminium-gallium alloys as a fuel/catalyst for hydrogen propulsion
    An investigation was carried out into the feasibility of using Al-Ga alloys as a renewable agent to produce hydrogen from water, following positive claims from a research group in the USA. The hypothesis was that pellets of Al-Ga would oxidise in water, resulting in hydrogen evolution which could be directly used in a fuel cell to power a vehicle. This paper reports on new experiments on the reaction of a range of compositions of binary Al-Ga pellets in contact with water. It was found that the reaction does not go to completion, resulting in only a fraction of theoretical hydrogen evolution, and that – contrary to research findings of others – gallium is not a passive catalyst and is also partially oxidised in water. A new proposal on the reaction mechanism is presented. Even if theoretical H2 output was achieved, we show that the aluminium cycle is uneconomic and impractical, and that total CO2 emissions per km travelled are significantly higher than those from an equivalent petrol engine. Guidelines for improved alloy design and optimum microstructure for renewable hydrogen production from water are suggested.
  • Publication
    Comparison of crystalline and amorphous versions of a magnesium-based alloy: corrosion and cell response
    (AO Research Institute Davos, 2015-08-28) ; ;
    Mg-Ca-Zn alloys have been identified as potential materials for bioresorbable orthopaedic implants –e.g. for bone fixation. It is important, however, to tailor the resorption rate of the alloy to the healing rate of the bone and the rate at which the metal ion release can be tolerated by the human body. Recent work has shown that bulk metallic glass (or amorphous) alloys corrode more slowly than their conventional crystalline counterparts1, and the rate may be more suited to orthopaedic applications. It has also indicated a slower evolution of hydrogen gas during resorption2. This paper presents an experimental study on the casting of a Mg75-Zn22-Ca5 into bulk amorphous form, and testing of the resultant material in vitrofor corrosion and cytotoxicity.
  • Publication
    Combined analytical/numerical modelling of nucleation and growth during equiaxed solidification under the influence of thermal convection
    Equiaxed grain solidification in inoculated melts is modelled on a macroscopic scale. The grain initiation is based on grain refiners present in the alloy melt as in most industrial castings. The Avrami analytical approach is used to model equiaxed growth. The model considers natural thermal convection and grain transportation by the resultant fluid flow. Flow characteristics during solidification are incorporated into the model by considering the equiaxed grains in undercooled liquid initially as slurry and later as a porous medium when it becomes coherent. Solidification of Al–7wt.%Si is simulated for different conditions. Evolution of cooling-curve characteristics are compared with a previous model and found to be in close agreement. The model simulation results suggest that nucleation can continue even after the recalescense. The limitation of grain refinement by recalescense and the potential influence of solutal effects are discussed. Simulated equiaxed grain size distribution and temperature evolution in the presence and absence of convention are compared and contrasted.
      525Scopus© Citations 27
  • Publication
    Inverse estimate of heat flux on a plasma discharge tube to steady-state conditions using thermocouple data and a radiation boundary condition
    The heat flux incident upon the inner surface of a plasma discharge tube during a helicon plasma discharge was estimated using an inverse method. Temperature readings were taken from the outer surface of the tube using thermocouples, and the temperature data were interpolated over the tube surface. A numerical inverse procedure based on the Alifanov iterative regularisation method was used to reconstruct the heat flux on the tube inner surface as a function of space and time. In contrast to previously-used inverse models for this application, the current model implements a thermal radiation boundary condition to realistically model the energy exchange in the device. Additionally in these experiments, steady-state operation was reached, and the accurate modelling of the steady-state condition was facilitated by the thermal radiation boundary condition. The variation of heat flux with helicon discharge power, propellant flowrate, and electromagnet current was studied, and it was found that the waste heat flux increased with applied RF power and propellant flowrate, and decreased with current supplied to the electromagnets, over the range of parameter variation tested.
      328Scopus© Citations 11