LIQUID IMMISCIBLE ALLOYS

The microstructure formation, during casting, of alloys being immiscib le in the liquid state such as copper-lead or aluminium-lead has gaine d renewed scientific and technical interest during the last fifteen ye ars. Especially, a new experimental tool, research under reduced gravi ty conditions, was able to cast new, unexpected results and theories i nto the discussion on the nature of the complex process of microstruct ure evolution in such alloys. Prior to the first experiments performed at reduced levels of gravity acceleration, it was generally agreed th at the process of phase separation during cooling through the miscibil ity gap is dictated solely by gravity-induced effects such as natural convection and sedimentation. Fundamental and applied research in spac e and in earth laboratories could show that there are other mechanisms operating concurrently and under suitable conditions with equal stren gth. In addition applied research was able to utilize the often unexpe cted results from space experimentation to develop new casting process es which allow one to produce microstructures on earth suitable for be arings in automotive applications. Therefore this article describes th e extensive progress that has been made during the last decade and als o the fundamentals of immiscibles. In addition it will be shown that t he combination of classical laboratory research, research under reduce d gravity conditions and a newly developed computational modelling tec hnique seems to be just becoming available to solve the problems of de composition, spatial phase separation and microstructure evolution dur ing cooling of an alloy through the liquid miscibility gap.