Transformations in a Ti-24AI-15Nb alloy: Part I. Phase equilibria and microstructure

Abstract

A variety of heat treatments have been employed to explore phase equilibria and the development of microstructure in a Ti-24Al-15Nb alloy. These include solution treatments both above and below the β-transus, followed by controlled cooling and aging at temperatures high enough to preclude ω-phase formation. The phase fields β, β o, α2 + βo, α2 +β o + O, and β o + O have been identified in the alloy, and schematic time-temperature-transformation (TTT) curves are proposed for continuous cooling transformations from the β phase. The composition of the α2 and β o phases in the α2 +β o region and of the α2, β o and O phases in the ternary phase field have been obtained by analytical electron microscopy. © 1992 The Minerals, Metals and Materials Society, and ASM International.