Controlling high-temperature deformation by varying microstructure in a ti-47al-2cr-2nb alloy

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Detail(s)

Original languageEnglish
Pages (from-to)261-262
Journal / PublicationTransactions of Nonferrous Metals Society of China (English Edition)
Volume9
Issue numberSUPPL. 1
Publication statusPublished - 1999
Externally publishedYes

Abstract

A Ti-47Al-2Cr-2Nb alloy was made by powder extrusion methods. By .varying extrusion temperature, different microstructures were produced. At an extrusion temperature of 1 400°C (above a transus), a uniform, fully lamellar structure was observed. In contrast, when powders were extruded at 1150 C, an inhomogeneous microstructure consisting of 7, 02 and metastable phases was obtained. It was demonstrated that, while alloy extruded at 1400 X exhibited an excellent creep resistance, alloy with the same composition extruded at 1 1501 exhibited superplasticity. The good creep resistance was resulted from the presence of fine lamellae which restrict dislocation slip within y grains. These fine lamellae also promote the nucleation of deformation twins which impede dislocation glide along the interfaces ( γ/γ and γ/α2) and, thus, reduces creep rate. In the case of low temperature extrusion, an elongation value of over 300% was obtained at a strain rate of 2 × 10-5s-1' and at a temperature as low as 8001, which is close to the ductile-to-brittle-transition temperature. This is in contrast to the prior major observations of superplastic behaviors in TiAl in which typical temperatures of 1 000 C have usually been required for superplasticity. It was proposed that the occurrence of superplasticity at 800 C is caused by the presence of a B2 phase which, during superplastic deformation (grain boundary sliding), accommodates sliding strains to reduce the propensity for cavitation at grain triple junctions and, thus, delays the fracture process.

Research Area(s)

  • Alloy microstructures, High-temperature deformation, Ti-47al-2cr-2nb

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