On the precipitation of TiB2 in aluminum melts from the reaction with KBF4 and K2TiF6

The divergent reaction between Al and the two salts K2TiF6 and KBF4 are used in the manufacturing of Al-Ti-B master alloys for grain refinement. It is also possible to use the same reaction to make aluminum based metal matrix composites. The formation sequence of TiB2 from the reaction with K2TiF6 and KBF4 is discussed in the view of the formation of a salt/metal emulsion and agglomeration. The highly exothermic reaction with K2TiF6 will aid the formation of an emulsion and Al3Ti form that in a subsequent step transforms into TiB2. It will also support high element transfer efficiency. The reaction with KBF4 causes less heat to evolve and the tendency towards formation of an emulsion and thus lower transfer efficiency resulting in a sluggish formation of AlB2. Simultaneous additions of K2TiF6 and KBF4 increase the transfer efficiency but will cause the formation of stringer defects in a layered structure. (c) 2005 Elsevier B.V. All rights reserved.