PREPARATION OF ALLOYS BASED ON INTERMETALLIC COMPOUNDS BY VIM WITH CENTRIFUGAL CASTING

Intermetallic compounds based on Ti-Al, Ti-Ni, Fe-Al, Ni-Al and other systems require specific conditions during melting in a high-frequency vacuum induction furnace, especially material for melting crucibles and batch arrangement. The technology of casting plays an important role, too. The most common technology, very often used, is gravity casting. However, this method has certain disadvantages, namely frequent possibility of occurrence of cavities in the upper parts of the castings. Another possibility, currently often used, is technology of centrifugal casting. In this case several variants of arrangement of the device exist. With the combined vacuum-induction-centrifugal casting systems it is possible to realize the precision fine casting very economically with a compact system, also under vacuum and/or protective gas. As a melting crucible, oxide ceramic materials based are very often used, namely Al2O3, CaO, ZrO2, with addition of Cr2O3 and others. Next material, which is very often used for manufacturing of melting crucibles, is graphite of various quality. This article deals with examination of melting and centrifugal casting of Ti-Ni and Ti-Al-X alloys with use of graphite crucibles. Both types of alloys are very sensitive to carbon content. It is known, that alloys based on titanium are during melting very reactive with graphite crucible, so the carbon content determination was realized in all prepared alloys. Microstructures were evaluated by optical microscopy (OM) and SEM techniques. For fabrication of experimental material casting mould with the inner diameter of 20 mm and length of 225 mm was used.