Papers by Keyword: Taylor Factor

Abstract: The subsurface fatigue crack generation processes in near α type titanium alloy were divided into four steps: (1) development of a saturated dislocation structure by cyclical micro-plastic strain accumulation, (2) generation of localized slip and/or microcracking to relax the stress concentration in the vicinity of a boundary, (3) microcrack growth and transition to main crack, and (4) crack propagation. The experimentals on transgranular facets formation in Ti-Fe-O alloy were reviewed and a subsurface fatigue crack generation model was discussed. The β platelets which were aligned between the recrystallized α grain and the recovered α grain were responsible for the microcrack generation to form (0001) tansgranular facet in the recrystallized α grains. A combination of the shear stress and tensile stress normal to the basal plane may give a trigger of the (0001) microcracking in the recrystallized α grain. The localized shear stress following slip off on the basal plane was activated at the microcrack tip in the recrystallizedαgrain, and the microcrack grew into the recrystallized α grain to form (0001) transgranular facet.

Abstract: A novel experimental method has been developed by amalgamating a pencil beam X-Ray diffraction (XRD) technique with the recently developed grain boundary tracking (GBT) technique. XRD and GBT are both non-destructive in-situ analysis techniques for characterizing bulk materials, which can be carried out close to the point of fracture. DAGT provides information about individual grain orientations and 1-micron-level grain morphologies in 3-dimensions (3D) together with high-density local strain mapping. An Al-3 mass % Cu model alloy was used to investigate its deformation behavior under tension. The morphology of the grains was determined by the X-ray microtomography (XMT) imaging and the liquid metal wetting technique, after which GBT provided an accurate description of the position and morphology of all the grains in a region of interests. Diffraction spots in the XRD experiments were related to grains, making it possible to describe crystallographic orientation of all the grains. It has been revealed that deformation is localized at both microscopic and meso-scopic levels. Inhomogeneous deformation was observed in each individual grain. In addition, a group of a few grains coordinately interacts and specific grain boundaries thereby exhibit intense strain localization. Hydrostatic tension was also observed at quadruple junction points and its mechanism was analyzed.

Abstract: A study has been made of the evolution of the microstructures and textures in three kinds of low-carbon steel sheets (MAFE, BH and IF) having well developed <111>//ND texture that were rolled by low reductions and annealed at 780 °C in Ar atmosphere. The steel sheets developed different microstructures and textures, even though their initial textures and thermomechanical treatments were similar. MAFE steel showed an unusual behavior that grains with high Taylor factors survived and grew very rapidly. This unusual behavior and the differences in microstructure and texture have been discussed.

Abstract: According to a sub-boundary enhanced solid-state wetting mechanism, abnormally-growing Goss grains in Fe-3%Si steel are expected to have exclusively sub-boundaries which would be formed during primary recrystallization. This microstructural feature is related with the stored energy of Goss grains after cold rolling. To investigate the possibility of existence of sub-boundary exclusively in Goss grains after primary recrystallization, the deformation feature focused on stored energy of Goss and other specific orientations was analyzed by crystal plasticity finite element method calculations. The calculations indicated that Goss grains stored the lowest energy among the orientations formed after plane strain deformation.

Abstract: Both EBSD and AFM methods were used to investigate the active slip systems and fatigue crack initiation behavior in face-centered cubic polycrystalline metal, austenitic stainless steel, SUS316NG, under cyclic torsional loading. Most active slip planes are the primary slip planes having the largest Schmid factor. Grains with slip band cracks or transcrystalline cracks have larger Taylor's factors. On the basis of EBSD and AFM observations, h, the depth of intrusion vertical to the surface, S, and the component of the slip displacement perpendicular to the surface trace, SB, showed a sharp increase at the onset of crack initiation. The critical value of SB at crack initiation was 170 nm.