Development of Al-Ti-C grain refiners containing TiC
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INTRODUCTION
G R A I N refinement of aluminum and its alloy castings through additions of grain refiners has been a common industrial practice. It has been known that some of the transition metals, viz., Ti, Zr, and Nb, can grain-refine aluminum. Several authors ~2'3 have asserted that refinement by these elements, which form peritectic systems with aluminum, is due to nucleation of solid solution grains by crystals of aluminides of these elements via the peritectic reaction. As a contrast, it was also found that marked reduction in the grain size could occur at concentrations of these elements which are too small to produce their respective compounds with aluminum. Cibula 4 attributed this grain refinement obtainable through additions of transition elements in hypoperitectic concentrations, to their interstitial carbides which could possibly arise as a result of reaction of transition elements with the traces of carbon which is almost always present in the melts, since aluminum is usually melted in graphite crucibles. The so-called "carbide theory" has been generally accepted in spite of a few contradictory results. 1.5.6 Cibula4 made various trials to add carbon to aluminum melts in the form of graphite powder or rod, carbon tetrachloride, carbon monoxide, acetylene, or high carbon steel. Carbon was also added together with potassium halide flux or the same picked up by melting aluminum in carbonaceous crucibles. The work was further extended7 to synthesize hardeners by reacting potassium titanofluoride with graphite. TiC powder was also mixed with aluminum powder and pressed into pellets which were subsequently stirred into aluminum melts, or alternately carbide powder was stirred into small pellets of molten flux. But all the above trials virtually failed to introduce any appreciable amount of carbon, and Cibula finally concluded that very little success was achieved in attempts to increase carbon of aIloys containing titanium and no useful results were obtained owing to the difficulties in forming and dispersing the carbides. In the subsequent era, from time to time, though, there were some attempts directed toward introducing carbon or ABINASH BANERJI, Scientist on leave from Regional Research Laboratory (CSIR), Bhopal, is Research Associate, and WINFRIED REIF is Professor, both with the Institut fiir Metallforschung-Metallkunde, Technische Universit~it Berlin, Strasse des 17 Juni 135, D-1000 Berlin 12. Manuscript submitted January 2, 1986. METALLURGICAL TRANSACTIONS A
TiC in A1-Ti alloys, but they either did not succeed at all or could at the best generate only too little carbide to provide any scope for practical use. These included mainly the works of Mondolfo and co-workers, 1,6 Lihl et al. ,8 Nakao et al. ,5,9 and Thury. ~oThe latter reacted graphite with potassium titanofluoride salt in molten aluminum melt similar to that of Cibula and briefly outlined the possible chemical reactions, but failed to bring forward any new ideas other than what Cibula had already conveyed. Morimune et al. " reported
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