MICROSTRUCTURE IN CHILL-CAST AL3TI-BASED AL-TI-V TERNARY ALLOYS

Ternary Al-Ti-V alloys, with compositions in the range Al3Ti to TiAl, have been selected with a view to establishing the intermediate phases possible and evaluating the potential for the development of useful m ultiphase intermetallic microstructures. In the first stage of this wo rk, Al75-xTi25Vx (x = 4-9) alloys have been chill cast and the product microstructures characterized using analytical electron microscopy. T hese rapidly cooled alloys had predominantly two-phase, dendritic micr ostructures, with small fractions of a third phase along the interphas e boundaries. In Al71Ti25V4 alloy, the major phases were Al-3(Ti, V) ( DO22) and a tetragonal phase with a one-dimensional, long-period antip hase domain structure (APS) based on Ti2Al5; the minor phase was ident ified as Ti5Al11 (DO23). In the Al66Ti25V9 alloy, the dominant phases were Ti5Al11 and a series of tetragonal, one-dimensional APSs based on Ti5Al11; the minor phase was Al-3(Ti, V). With increasing V content, and thus increasing fraction of the Ti5Al11-based constituents, the bu lk hardness of the alloys decreased and the cracking resistance improv ed.