INFLUENCE OF MICROSTRUCTURE ON GRAIN REFINING PERFORMANCE OF AL-TI-B MASTER ALLOYS

The morphological characteristics of so called duplex titanium alumini de (TiAl3) particles in several Al-5Ti-1B (wt-%) master alloys in the form of rods have been investigated using a wide range of microscopica l techniques. It has been found that both rough blocky and faceted blo cky aluminides are present in such materials and that hexagonal platel ets are entrained within these blocky aluminides. Auger spectroscopy a nd transmission electron diffraction have confirmed that the platelets are diborides. In previous work, it has been suggested that duplex al uminides are particularly effective in promoting grain refinement duri ng solidification. To investigate this, a master alloy containing dupl ex blocky aluminides was briefly remelted and recast from a range of t emperatures. This resulted in the formation of significantly different aluminide types. When the original and remelted alloys were tested in commercial purity Al, using standard procedures, it was found that th e presence of duplex aluminides does not, in itself, seem to be of gre at importance in influencing grain refiner efficiency. The experimenta l findings are discussed in the context of previously published experi mental and theoretical work.