[en] directional solidification ; microporosity ; LiMaRC - Liège Materials Research Center
[en] In this work we have developed two criteria which can characterize the susceptibility to microporosities formation of alloys. These defects are influential in determining mechanical properties of materials. The first criterion is used when the fraction eutectic is important : then the porosity formation is essentially caused by dissolved gases of formed during chemical reactions. The second is employed when the alloy possesses low fraction eutectic. In that case, because of the pressure drop, the liquid is unable to feed through interdendritic spaces to accomodate solidification shrinkage. The pressure drop is composed of two terms which influence in contrary direction : the first is due to solidification shrinkage and the second to gravity. This term is the most important except for low fraction eutectic. The fraction liquid (or the fraction eutectic) is an important factor. It depends on the alloy composition and on solidification conditions. In fact, we have showed that, depending on initial alloy concentration, the solidification conditions have opposite effects on the fraction liquid : if Co>KCe, the fraction liquid decreases if the ratio G/R decreases and if Co<KCe it increases if the ratio G/R decreases.