Phase relationships in an Al₃ (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 δ-Al₃ (Ti,V) and interdendritic eutectic zones in which the continuous phase was δ-Al₃ (Ti,V) and the rode-like discontinuous phase was ζ-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 δ matrix and a phase transformation was detected within the dispersed particles, as the intermetallic ζ phase was replaced by b.c.c.β-(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 β-phase in a brittle Al₃(Ti,V) intermetallic matrix. The orientation relationship between the discontinuous β-(Ti,V) particles and the DO₂₂δ-Al₃(Ti,V) matrix involved parallelism of the closest-packed planes and close-packed directions in those planes, i.e. (110)_β//(112)_δ(DO22 ) and [111]_β//[110]_δ(DO22 ).