Complementary aspects of convective effects in solidification will be treated in a series of experimental and theoretical tasks, in order to build a numerical code to be used by companies working in the field of foundry and of solidification technology.
A software tool has been built for treating convective effects in solidification. It is articulated in a numerical frame code, and in a series of modules dedicated to specific cases. It is a contribution to rapid prototyping in the industrial sectors of shape casting foundry, and of crystal solidification processing.
As an example, it was applied to a piece in form of a 3-dimensionall loop, representing a massive cast iron piece with a core. The reslts showed how the flow separates, how solidification occurs during filling, and how paricles initially suspended in the liquid are distributed during solidification.
This software is particularly orientated to 3 kind of problems:
Solidification in thin wall castings, emphasizing the problems of fluid length and of cold shut. A criterion function was implementated and tested experimentally on a series of cast iron and aluminium-silicon thin plates. The fluid length was measured in a series of casting tests on an aluminium alloy in low pressure and high pressure conditions. The results were represented by a simple 1-dimensional model enabling to presict the ability to produce thin elongated casting pieces.
Solidification in the presence of particles in suspension (inclusions, inoculants, reinforcing particles in metal-matrix-composites, equiaxed crystals). According to relative flw and solidification conditions, they can be either entrapped in the solid or pushed at the interface.
Striations and banding phenomena in massive solidification products, including massive crystals. Dedicated modules treated coupled thermo-capillary and thermo-gravity flows, either by streamline diffusion method, or by Fourier transform spectral method. They were applied to floating zone crystal growth. The example showed the transition from stready axi-symetrical to 3D-steady, then to oscillatory growth.
It is restricted to four different aspects of flow interacting with solidification :
(i) directional solidification in centrifugal conditions. Such action could extend the conditions for planar front growth of large crystals for the optical or electronics industry
(ii) floating zone crystal growth in the presence of surface tension driven flow. The numerical module will describe how it can influenced by modifications of heat input distribution
(iii) interactions between solidification and filling flow in the casting of thin parts. It can lead to the defect called "cold shut", according to the conditions of heat transfer and of solid structure formation
(iv) interactions between the solidifying front and particles in suspension, either reactive (equiaxed grains), or non-reactive (inclusions).
OX1 3PH Oxford