Axial load controlled high cycle fatigue experiments were conducted on the γ/α2 alloy, Ti-48A1-1V-0.2C (at%), at 23 and 815°C. Four different microstructures, produced through thermomechanical processing, were evaluated to examine the influence of grain size and α2 content on fatigue behavior. The load controlled fatigue life was significantly reduced by increasing grain size and unaffected by α2 content at both 23 and 815°C. Although, α2 content did not greatly influence high cycle fatigue life, the room temperature crack initiation and fast fracture was changed from transgranular to partially intergranular as the volume fraction of α2 was reduced in the fine grain size material. The fatigue strength at 107 cycles (FS) to ultimate tensile strength (UTS) ratio was 0.8 to 0.9 at 23°C and 0.5 to 0.6 at 815°C for all microstructures examined. Low tensile ductility, high work hardening rate and the difficulty in forming strain local-izations all aided the high FS/UTS ratio. The dislocation microstructures produced by fatigue at room temperature were examined in the fine grained high α2 (ductile) microstructure. They consisted of loop patches of all <110] regular dislocations without any <101] or <011] super dislocations because of the large difference in CRSS for these dislocation. The inability to nucleate and move superdislocations inhibited the formation of persistent slip bands as is often found in high and intermediate stacking fault FCC metals.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.