ABSTRACT
Abstract. In the AI casting industry, TiB 2 grain refiner particles are added to the melt in order to promote heterogeneous nucleation of a-Al crystallites. It has been suggested that thin Al 3Ti D022 layers, adsorbed on the bolide particles, might be necessary for successful a-Al nucleation via the peritectic reaction. In order to elucidate this suggestion, the bolide/a-A! interfaces were studied in the as-received Ti-B-Al grain refiner rod, as well as after remelting and rapid quenching of the same rod. The investigation was performed using the TEM, EDS, STEM and HREM techniques. For the asreceived rod, the EDS study failed to show conclusively enrichment of the interfaces in Ti and indicated clearly only a small enrichment in Si and Fe. The HREM investigation found no indication of a possible crystalline layer coating the bolide particles. The bolides found in the re-melted rod were observed to readily nucleate a-Al on their basal faces with a well-defined low-index orientation relationship but there was again no indication of any layer on the bolide particles. Thus, the bolides themselves appeared to be potent sites for the heterogeneous nucleation of a-Al crystals during rapid quenching without a necessary presence of the aluminide layers.
