ICROSTRUCTURE AND GRAIN REFINING EFFICIENCY OF TiC PARTICLES IN Al-Ti-C GRAIN REFINING MASTER ALLOYS

摘要

Master alloys from the Al-Ti-B ternary system are commonly used as grain refiners for cast aluminium and its alloys. However, the desire to reduce particulates in the finished product has led to the investigation of alternative master alloys based on the Al-Ti-C system. Currently little is known about the structure of the TiC particles that form in this system, or their grain refining mechanism. In the work reported, it has been found that an Al-3wt%Ti-0.15wt%C master alloy has a grain refining efficiency comparable to that of a conventional Al-5wt%Ti-1wt%B master alloy, when used at the same Ti concentration. The individual TiC particles formed during the reaction process were observed to be strongly faceted and smaller than the TiB_2 particles, typically seen in Al-Ti-B grain refiners. The TiC particles were found to grow as polycrystalline chains comprised of several particles, which are broken up on processing to rod. TEM studies of the TiC particles showed the presence of stacking faults and voids within the individual particles. In a model, metal-matrix-composite, sample α-Al grains were found to nucleate epitaxially on large artificially added TiC particles.