CASTING PROCESS FOR HYPERMONOTECTIC ALLOYS UNDER TERRESTRIAL CONDITIONS

Bearing materials are generally heterogeneous materials, containing ha rd as well as soft, phases. Hypermonotectic AlPb and AlBi alloys, espe cially, are considered as exceptionally qualified bearing materials if they also contain additional hard phases to decrease wear. Based on t he considerable differences in the density of the decomposed fluid pha ses at high temperatures and the high velocity of separation, such all oys cannot, to date, be manufactured under terrestrial conditions. The results of microgravity experiments for the manufacturing of suitable sample material with a fine phase dispersion of the monotectic phases were rather disappointing. The cause of the rapid phase separation an d local enrichment under microgravity conditions was found to be the M arangoni convection, the effects of which, to date, have been underest imated. The results of these space experiments are now utilized in a t errestrial casting process, whereby a comparatively high Marangoni con vection is superposed in the opposite direction to the sedimentation a ction of gravity, thereby partially compensating the effects of gravit y. Thus, cast strips of AlSiPb and AlSiBi alloys could be manufactured , the lead and bismuth phases being present in a characteristic fined ispersion over the length of the cast strips. The first tribological l aboratory tests give an indication of the excellent suitability of-suc h advanced bearing material for the future.