PHASE-RELATIONSHIPS IN AN AL-3(TI,V) BASED IN-SITU COMPOSITE

The phases and the crystallographic relationships between phases observed in an Al70Ti10V20 alloy following chill casting and post-solidification heat treatment have been characterized using analytical transmission electron microscopy and electron diffraction. The chill-cast microstructure comprised a mixture of primary dendrites of delta-Al-3(Ti,V) and interdendritic eutectic zones in which the continuous phase was delta-Al-3(Ti,V) and the rode-like discontinuous phase was zeta-Al8V5. Following isothermal heat treatments in the temperature range 1073-1273 K, a uniform distribution of rod-like particles was observed to develop throughout the delta matrix and a phase transformation was detected within the dispersed particles, as the intermetallic zeta phase was replaced by b.c.c. beta-(Ti,V) metallic solid solution. This transformation was typically complete within 100 hr at 1073 K, leading to the formation of an in-situ composite consisting of a uniform dispersion of metallic beta-phase in a brittle Al-3(Ti,V) intermetallic matrix. The orientation relationship between the discontinuous beta-(Ti,V) particles and the DO(22)delta-Al-3(Ti,V) matrix involved parallelism of the closest-packed planes and close-packed directions in those planes, i.e. (110)(beta)//(112)(delta(DO22)) and [($) over bar 111](beta)//[($) over bar 110](delta(DO22)).