Now showing 1 - 4 of 4
  • 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
    Identification of key liquid metal flow features in the physical conditioning of molten aluminium alloy with high shear processing
    Although treating molten alloy with high shear processing (HSP) can dramatically refine the microstructure of solidified aluminium alloys, it was also recently employed as part of an effective route to purification of contaminated aluminium alloy scrap. The key mechanisms of HSP include the dispersion of large aluminium oxide films and clusters into very fine oxide particles by the high shear rate, and the redistribution of bulk melt by the agitation. These fine oxides act as nucleation sites for iron-based intermetallic phases, the formation of which is a pre-cursor to purification of the alloy. Macroscopic flow features of HSP, such as flow rate and shear rate, influence its performance significantly. Simulation based on Computational Fluid Dynamics was used to predict key features of fluid flow during HSP in a static direct chill (DC) caster. It was found that the distribution of shear rate and mass flow rate is highly nonuniform in the caster, and only in the close vicinity of the mixing head is there a relatively high level of shear rate and effective melt agitation. Therefore, effective dispersion of oxide films and clusters, and resulting significant nucleation of the intermetallics and/or primary aluminium phase, can only occur near the mixing head, and not throughout the whole crucible. Confidence in the model validity was built, by comparison with post-solidification microstructures in a previous experiment with similar process parameters and geometry.                  
      269Scopus© Citations 9
  • Publication
    Revealing internal flow behaviour in arc welding and additive manufacturing of metals
    Internal flow behaviour during melt-pool-based metal manufacturing remains unclear and hinders progression to process optimisation. In this contribution, we present direct time-resolved imaging of melt pool flow dynamics from a high-energy synchrotron radiation experiment. We track internal flow streams during arc welding of steel and measure instantaneous flow velocities ranging from 0.1 m s-1 to 0.5 m s-1. When the temperature-dependent surface tension coefficient is negative, bulk turbulence is the main flow mechanism and the critical velocity for surface turbulence is below the limits identified in previous theoretical studies. When the alloy exhibits a positive temperature-dependent surface tension coefficient, surface turbulence occurs and derisory oxides can be entrapped within the subsequent solid as result of higher flow velocities. The widely used arc welding and the emerging arc additive manufacturing routes can be optimised by controlling internal melt flow through adjusting surface active elements.
      262Scopus© Citations 118
  • Publication
    Elimination of porosity in bulk metallic glass castings using hot isostatic pressing
    This study presents design and implementation of a systematic method to remove the pores in as-cast bulk metallic glass using hot isostatic pressing, without changing the amorphous structure of the samples. The supercooled liquid region of Zr44Cu40Al8Ag8 was characterized using differential scanning calorimetry and dynamic mechanical analysis. This enabled informed choice of the range of hot isostatic pressing process variables likely to result in successful reduction of the porosity in the glassy alloy. The operating pressure in hot isostatic press processing was relatively less influential than either the temperature or the dwell time in controlling the porosity. It was shown that the dwell time should be longer than the average relaxation time in the glass transition range. With the specific bulk amorphous alloy under study, the optimized temperature, pressure and dwell time are 475 °C, 50 MPa and 3 min, respectively. Excess dwell times will result in crystallization.                        
      289Scopus© Citations 9