The Influence of Strain Rate on Dislocation Structures in γ/α₂ Titanium Aluminides Deformed at 815°C

Abstract

Elevated temperature (815°C) compression tests were performed at strain rates between 10−2 & 10−5 sec−1 on a γ/α2 alloy, Ti-48Al-1V-0.2C (at%), for two different α2 volume fractions. A large change in the flow stress was observed to occur for strain rates between 1.10−5 & 1.10−3 sec−1. The dislocations observed in the primary γ grains deformed at the high strain rates were “regular” 1/2<110]; screw dislocations. The dislocations observed at slow strain rates were also regular 1/2<110] dislocations, however their orientation was changed so that they were aligned close to [001]. Dislocation structures produced during high cycle fatigue are identical to those observed during high strain rate compression tests, while dislocation structures produced during tensile (ė- 8.10−4 sec−1 ) tests are identical to those observed in the slow strain rate compression tests. Analysis of the orientation of deformed primary γ-TiAl grains shows that the CRSS for {111}<101] slip must be at least 1.4 times the CRSS of {111}1/2<110] slip.