Solidification process and characterisation of a mass-gravity foundry ingot

The first step in the processing of metals is often a liquid moulding opera tion. Numerous defects can appear, which depend on the material, the proces s conditions and the thermal parameters and it is very important to know ho w they can evolve in order to obtain finally more homogeneous and defect-fr ee ingot. In this study, the authors have looked at a special alloy of uran ium, containing 6% of niobium. The casting operation is made up of differen t steps: melting of the metals; homogenisation of the liquid through stirri ng; and finally pouring into a graphite mould in order to obtain an ingot. In this case, the authors want to be able to validate a model that will be created after this study with the aim at minimising both the segregation th at can occur in this kind of alloy, the porosities which are very common in the foundry process. To be presented are: (i) the conditions, the material and the parameters used in this case; (ii) some parameters concerning the alloy (phase diagram, inclusions and their morphologies, thermal properties ); (iii) the location of the thermocouples in the ingot and in the mould wh ich were used in order to see how the solidification evolves; (iv) the temp erature recordings; and (v) the results of the characterisation of this ing ot, through metallography and chemistry analysis; so that it is possible to obtain a full chart of the niobium content in this ingot. This set of expe rimental measurements constitutes a complete collection of data that can be used on one hand as input for the numerical model and on the other hand as results for comparison with the numerical simulations. (C) 1999 Elsevier S cience S.A. All rights reserved.