Evolution of Twin-Related Variants of α Phase in a Ti-V-Cu Alloy

The precipitation of a-phase has been investigated in a concentrated b-alloy of the Ti-V-Cu system. a-precipitates in geometrically coupled forms were developed in the alloy when subject to isothermal ageing at 500°C. High-resolution transmission electron microscopy (HRTEM) revealed that a-phase embryos tend to nucleate in a symmetrical manner directly from an early-stage solute-partitioned diffusional product. The a-precipitates so developed constitute twin-related variants characterized by a twin plane lying on one of the {0111}a planes. The results are discussed with respect to the role of Cu on the formation of heterogeneous nucleation sites for a-phase.