Kyriacos Pericleous

Numerical modelling of tilt casting process for γ-TiAl alloys

Abstract The tilt casting method is used to achieve tranquil filling of γ-TiAl turbine blades up to 400 mm long. The reactive titanium alloy is induction melted in a cold crucible, and the crucible with the attached mould is then rotated through 180° to transfer the metal into the mould. In the cold crucible, heat losses to the water cooled copper walls and base limit the superheat available, increasing the risk of premature freezing during mould filling. A compromise is required between fast and slow rotations to minimise the casting defects, such as misruns or gas entrainment. Simulations are presented using the authors’ Computational Fluid Dynamics code with several novel developments in front tracking, heat transfer algorithms and turbulence model adaptation, which accounts for an advancing solid front. The computational results are validated against prototype castings produced at the University of Birmingham, and the model is then used to optimise the tilt casting process.

Particle Separation in Silicon Ingot Casting Using AC Magnetic Field

The AC electromagnetic (EM) field effects are investigated for the possibility to extract particles (impurities, precipitates, oxides, bubbles, etc.) from molten silicon during the directional solidification of silicon ingot. The dynamics of particles are affected by the hydrodynamic drag, buoyancy, turbulent fluctuations and the EM force via the local pressure distribution. The EM force leads to high mixing rates, transitional flow structures and turbulence of the melt, contributing to the particle dispersion, transport and separation to a desired location. Application to silicon kerf loss recycling by melting and solidifying in the presence of AC EM field is presented for a variety of cases using 3D models for general flow structure and axisymmetric models for moving solidification front long time tracking. This paper demonstrates the effects of flow on the time dependent particle ‘swarm’ transport and the eventual modified distribution in the final ingot.

Sensitivity of Contactless Ultrasound Processing to Variations of the Free Surface of the Melt with Induction Heating

Contactless ultrasound treatment can be useful for high-temperature or reactive alloys in the liquid state, where contact with an immersed vibrating probe is undesirable. The alternating component of the Lorentz force can generate sound pressure levels leading to cavitation of gas bubbles in the melt, through acoustic resonance . Resonance is a function of the speed of sound in the liquid, the shape of the volume containing it and surrounding boundary conditions. Induction forces applied to a crucible lead to bulk stirring and in general deform the free surface, whose precise shape may influence the resonance conditions. This effect is investigated here by multi-physics computer modelling. Calculated results for aluminium melts are compared with experimental data and conclusions are drawn as to the sensitivity to process parameters and the reliability of this type of ultrasound metal processing.