Boride and titanium aluminide particles from various master alloys have been studied by metallography, electron microscopy, and X-ray diffraction in order to reveal the role of these particles in the grain refinement of aluminium. It has been found that TiB2, (TiAl)B2, AlB2J and TiAl3 form during the production of the master alloy. The size and morphology of the borides is quite independent of the production of the master alloy. A superstructure in the TiB2 lattice develops with holding time, indicating a stable ternary Ti-Al-B phase. A preferred orientation relationship was found to exist between the Al3Ti crystals and the aluminium matrix. MT/668bTwo series of were used to In,'estlg;ate The first series was available Billiton in steps to O· 05 wt-% rol'i, samples were held in the of time. The CO]l1Ct~nt:ra1tlons" temperatures, and times for these Table 1. The second series was made adding salts (K2 TiFs, KBF4) to molten aluminium, of the same purity as above, at different temperatures.The concentrations and addition temperatures used in the preparation of these alloys are shown in Table 2.The master alloys used to study aluminides are listed in Table 3. The starting materials for synthesis of these master alloys were aluminium (99' 7 wt-%), and K2 TiF6 and KBF4 (technical quality). Two alloys, G and H, were synthesized by adding a mixture of the salts to an aluminium melt ina graphite crucible at 900°and 750°C, respectively. The preparations were stirred for 5 min and allowed to cool at a rate of 0·5 K S-l. The Ti and B concentrations were 2 and O'4wt-%, respectively. A third alloy, Ql, with the same total Ti and B concentrations, was prepared by adding K2 TiF6 at 11 OO°C to an alloy which already contained the boron and some of the titanium as titanium borides syntheIn the first paper in this series 8 it was shown that Al3 Ti crystals found in the master alloys can exhibit quite different morphologies, depending on the conditions under which they have formed, and that three main types of crystal can be distinguished: these with 'block-like', 'flakelike', and 'petal-like' aluminide particles. It was further demonstrated that the morphology of the aluminide crystals seems to influence the optimum contact time. The purpose of the present investigation was to examine the different types of aluminide crystal in more detail, and to investigate the formation and stability of TiB2, (Ti, AI)B2, and AIB2 by means of metallography, electron microscopy, and X-ray diffraction.Experimental have series of solutions, and, a forward by Backerud,3 there could a certain composition where the ternary phase Ti)Bz, due to the entropy of mixing, reaches maximum stability. Thermodynamic calculations 6 ,7 show, however, that this latter situation is unlikely to occur, but the existence of a full range of solid solutions of the (AI, Ti)B2-type phase was confirmed by Cornish. 4In the commercial use of AI-Ti-B master alloys for the grain refinement of aluminium, it is well known that the optimum co~tact time, i.e. the holding time n...
