Hot deformation mechanisms in metastable beta titanium alloy Ti-10V-2Fe-3Al

Balasubrahmanyam, VV and Prasad, YVRK (2001) Hot deformation mechanisms in metastable beta titanium alloy Ti-10V-2Fe-3Al. In: Materials Science and Technology, 17 (10). pp. 1222-1228.

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Abstract

The mechanisms of hot deformation in the \beta titanium alloy Ti–10V–2Fe–3Al have been characterised in the temperature range $650-850^o C$ and strain rate range $0.001-100 s^{-1}$ using constant true strain rate isothermal compression tests. The \beta transus for this alloy is $\sim 790^o C$, below which the alloy has a fine grained duplex $\alpha + \beta$ structure. At temperatures lower than the \beta transus and lower strain rates, the alloy exhibits steady state flow behaviour while at higher strain rates, either continuous flow softening or oscillations are observed at lower or higher temperatures, respectively. The processing maps reveal three different domains. First, in the temperature range $650-750^o C$ and at strain rates lower than $0.01 s^{-1}$, the material exhibits fine grained superplasticity marked by abnormal elongation, with a peak at $\sim 700^o C$. Under conditions within this domain, the stress–strain curves are of the steady state type. The apparent activation energy estimated in the domain of fine grained superplasticity is $\sim 225 kJ mol^{-1}$, which suggests that dynamic recovery in the \beta phase is the mechanism by which the stress concentration at the triple junctions is accommodated. Second, at temperatures higher than $800^o C$ and strain rates lower than $\sim 0.1 s^{-1}$, the alloy exhibits large grained superplasticity, with the highest elongation occurring at $850^o C$ and $0.001 s^{-1}$; the value of this is about one-half of that recorded at $700^o C$. The microstructure of the specimen deformed under conditions in this domain shows stable subgrain structures within large \beta grains. Third, at strain rates higher than $10 s^{-1}$ and temperatures lower than $700^o C$, cracking occurs in the regions of adiabatic shear bands. Also, at strain rates above $3 s^{-1}$ and temperatures above $700^o C$, the material exhibits flow localisation.

Item Type: Journal Article Copyright of this article belongs to Maney Publishing. Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy) 13 Oct 2008 11:55 19 Sep 2010 04:50 http://eprints.iisc.ernet.in/id/eprint/15964