Superplastic behavior of a powder metallurgy TiAl alloy with a metastable microstructure

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Detail(s)

Original languageEnglish
Pages (from-to)163-170
Journal / PublicationIntermetallics
Volume7
Issue number2
Publication statusPublished - 1999
Externally publishedYes

Abstract

Superplasticity in a powder metallurgy (P/M) TiAl alloy (Ti-47Al-2Cr-1Nb-1Ta) with a metastable B2 phase coexisted with a fine-grained γ+α2 duplex structure has been studied. Alloy samples were tested at temperatures ranging from 650 to 1100°C, and at strain rates ranging from 10-6 to 10-4 s-1. An elongation of over 300% was obtained at a strain rate of 2x10-5 s-1 and at a temperature of 800°C, which is close to the ductile-to-brittle transition temperature of the alloy. This is in contrast to the prior observations of superplastic behavior of TiAl alloys in which a typical temperature of 1000°C is usually required for achieving superplasticity. It is suggested that the occurrence of low-temperature (800°C) superplasticity in the present alloy is primarily due to the presence of a metastable B2 phase in addition to a fine-grained (α2+γ) duplex microstructure. The metastable B2 phase continues to decompose into fine-grained α2 and γ phases, which promotes grain boundary sliding during superplastic deformation. The retained fine B2 grains accommodate the sliding strains to reduce the propensity of cavitation at grain triple junctions and thus delay the cavitation and fracture process. © 1999 Elsevier Science Ltd. All rights reserved.

Research Area(s)

  • Cavitation, Grain boundary, Intermetallics, Phase transformations, Superplasticity

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