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Properties of the Deformation Microstructure in Al-Rich γ-TiAl Deformed by Ordinary Dislocations

  • Fabienne Grjégori (a1) and Patrick VeyssiÈRe (a2)

Abstract

In the near vicinity of the [021] load orientation, γ-TiAl deforms via ordinary dislocations (Burgers vector b = 1/2<110]). As for deformation by <110] dislocations, the flow stress shows a peak at about 600°C. Results of an extensive microstructural investigation aimed at identifying the origin of this mechanical anomaly are presented. The analysis was conducted on single crystals oriented for single slip. It confirmed that ordinary dislocations tend to align themselves along the screw direction. This preferential line direction becomes gradually accentuated as the deformation temperature is raised up to the peak temperature. This effect is accompanied by a strong tendency towards forming cusps, but there is indication that the immobilisation along the screw direction takes place prior to dislocation pinning. In the vicinity of the peak temperature, screw dislocations gather in the form of bundles. No clear correlation is found between the temperature dependence of the flow stress and that of the density of pinning points. The relationship between these microstructural findings and the occurrence of a flow stress anomaly is discussed.

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