A.K. Gogia

Structure, tensile deformation, and fracture of a Ti3Al-Nb alloy

The development of Ti3Al-Nb alloys is an excellent example of the recent resurgence of interest in the use of intermetallics for high-temperature applications. We examine, in this contribution, the structure of a typical alloy Ti-24A1-11Nb and show it to consist primarily of the ordered α2 phase (based on Ti3Al, DO19) and βo, (based on Ti2NbAl, B2) phases, with small amounts of a third phase, which is distorted slightly to an orthorhombic symmetry from the D019 (hexagonal) structure. Tensile properties have been examined on samples heat-treated to vary the size, shape, and volume fraction of α2 phase and the deformation and fracture behavior of the ordered, two-phase mixture established. The tensile ductility is seen to maximize at intermediate volume fractions of the α2 and βo phases (∼30 pct) at values of 6 to 10 pct elongation to fracture, depending on the grain size of the βo phase. A rationale incorporating the failure modes of the two phases—cleavage of α2 and slipband decohesion of βo—has been evolved to explain the trends in ductility with heat treatment.

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

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 fieldsβ, βo, α2 + βo, α2 +βo + O, andβo + O have been identified in the alloy, and schematic time-temperature-transformation (TTT) curves are proposed for continuous cooling transformations from theβ phase. The composition of the α2 andβo phases in the α2 +βo region and of the α2,βo and O phases in the ternary phase field have been obtained by analytical electron microscopy.

Deformation structure in a Ti-24Al-11Nb alloy

AbstractA Ti-24Al-11Nb alloy has been heat-treated so as to obtain a microstructure of coarse α2 particles (D019 structure based on Ti3Al) in a matrix of the ordered βo phase (B2 structure based on Ti2AlNb). Dislocation structures generated by tensile strains of ∼2 pct at room temperature have been analyzed by transmission electron microscopy The βo phase is shown to deform inhomogeneously on {110}, {112}, and {123} planes by α/〈211〉 slip. The slipband structure is complex, consisting of segments of heavily pinned edge dislocations with periodic cross slip of screw components on to secondary slip planes. Incompatibility stresses at α2/βo interfaces can generate fine α[100] slip as well. The α2 phase deforms independently by α dislocation slip. Slipbands in the βo phase can shear the α2 phase by activatingc +a/2 slip on

Microstructure and texture of rolled and annealed β titanium alloy Ti-10V-4.5Fe-1.5Al

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Site occupation in the ordered beta phase of ternary TiAlz.sbnd;Nb alloys

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Effect of Al and Nb on the trigger stress for stress-induced martensitic transformation during tensile loading in Ti–Al–Nb alloys

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