In Situ Macroscopic Tensile Testing in SEM and Electron Channeling Contrast Imaging: Pencil Glide Evidenced in a Bulk β-Ti21S Polycrystal

In this paper, we report the successful combination of macroscopic uniaxial tensile testing of bulk specimen combined with In situ dislocation-scale observations of the evolution of deformation microstructures during loading at several stress states. The dislocation-scale observations were performed by Accurate Electron Channeling Contrast Imaging in order to follow the defects evolution and their interactions with grain boundaries for several regions of interest during macroscopic loading. With this novel in situ procedure, the slip systems governing the deformation in polycrystalline bulk β-Ti21S are tracked during the macroscopic uniaxial tensile test. For instance, curved slip lines that are associated with “pencil glide” phenomenon and tangled dislocation networks are evidenced.

Compressive Properties of Mg-3Al-2Zn-2Y Alloy at Different Strain Rates

The compressive properties of Mg-3Al-2Zn-2Y alloy at room temperature at strain rates in range of 0.001s-1~4800s-1were investigated. To the alloy compressed at 1300s-1, its basal and non-basal slip produce the mixed dislocation configuration including parallel, bended and tangled dislocation. There is significant twinning in the alloys compressed at 1800s-1and 4800s-1. The flow stress and ultimate trength show the strain rate hardening behavior at the range of 0.001s-1~1800s-1. There appears localized deformation zones formed with recrystal grains and twin crystals in the alloy compressed at 4800s-1, whose mechanical properties are lower than those of alloy compressed at 1800s-1.

Low Cycle Fatigue and Cyclic Deformation of TiAl Alloys

The relation between microstructural parameters, microscopic cyclic deformation mechanisms and macroscopic cyclic strain hardening is investigated in the case of a heat treated PM Ti-48Al-2Cr-2Nb alloy at 20°C and at 500°C. In particular it is shown that, for the different microstructures considered, a moderate hardening is related to the formation of highly tangled dislocation structures which is in turn controlled by the dislocation glide mean free path. At 500°C this structures evolves towards a braid like structure for the fine fully lamellar microstructure.

The Irradiated Microstructure of Ferritic-Martensitic Steel T91 and 9Cr-ODS

ABSTRACTA ferritic steel T91 and an oxide dispersion strengthened (ODS) martensitic steel 9Cr-ODS were irradiated with 5 MeV Ni ions at 500°C at a dose rate of 1.38×10-3 dpa/s to doses of 5, 50 and 150 dpa. Both alloys are iron-based with 9Cr and have been designed for use in higher temperature energy systems. However, the radiation effects on these two alloys are not well characterized. For T91, the irradiated microstructure was dominated by tangled dislocation and precipitates, similar to the unirradiated condition except the presence of large dislocation loops of type a<100>. The microstructure of alloy 9Cr-ODS for both the unirradiated and irradiated cases was dominated by dense dislocations, precipitates and yttrium oxides particles and no dislocation loops were observed. The average size of yttrium oxides particles slightly decreased with dose from 11.8 nm for the unirradiated to 9.1 nm at 150 dpa. No voids were detected for both alloys up to a dose of 150 dpa.

Dislocation Substructures Produced During Tensile, Creep, and Fatigue Deformation of Ti3Al at 700°C

Ti3Al is an ordered intermetallic compound having the DO19-type superlattice structure. The compound exhibits very limited ductility in tension below 700°C because of a pronounced planarity of slip and the absence of a sufficient number of independent slip systems. Significant differences in slip behavior in the compound as a result of differences in strain rate and mode of deformation are reported here.Figure 1 is a comparison of dislocation substructures in polycrystalline Ti3Al specimens deformed in tension, creep, and fatigue. Slip activity on both the basal and prism planes is observed for each mode of deformation. The dominant slip vector in unidirectional deformation is the a-type (b) = <1120>) (Fig. la). The dislocations are straight, occur for the most part in a screw orientation, and are arranged in planar bands. In contrast, the dislocation distribution in specimens crept at 700°C (Fig. lb) is characterized by a much reduced planarity of slip, a tangled dislocation arrangement instead of planar bands, and an increased incidence of nonbasal slip vectors.