Interdiffusion and Phase Behavior in a Vanadium / Polysynthetically Twinned Tial Diffusion Couple

Abstract

Polysynthetically twinned (PST) TiAl, which has a two phase lamellar structure composed of multiply oriented lamellae of the TiAl phase (γ, with ordered tetragonal L10 structure) with a low density of interspersed layers of the Ti3Al phase (α2, with ordered D019 hexagonal structure), has attracted a large amount of interest in the past decade for its potential as a high temperature structural material. The strongly crystallographic twins and pseudo-twins between the lamellae of the PST TiAl crystal provide an ideal system to study interface diffusion. In this paper, we describe early results on the interrelationships between phase and interface structure, bulk and interface diffusion and phase equilibrium in the diffusion- bonded system PST TiAl and vanadium.A PST TiAl “single crystal” was grown in an optical floating zone furnace by zone-melting and directional solidification of a polycrystalline as-cast TiAl rod. Within the “single crystal”, all the lamellar interfaces are parallel.