A model that describes the temporal evolution of a grain size distribution (GSD) has been used to analyze the effect of initial GSD on grain growth. The model is based on the work of Hillert and Hunderi and Ryum. Initial GSDs were synthesized by superposing two steady state GSDs with different critical radii. Two parameters describe the initial deviation from steady state: u(max) is the ratio of the largest grain radius to the critical grain radius and F-o is the initial fraction of grains larger than twice the critical radius. The evolution of initial GSDs that deviate from steady state is then modeled. In the absence of a pinning force from particles, a transient period of abnormal grain growth occurs as the GSD evolves toward steady state for all initially nonsteady state GSDs with u(max) > 2. In the presence of stable particles, grain growth stagnation occurs. When the pinning force associated with particles is removed after stagnation, a transient period of abnormal grain growth occurs during the initial stage of evolution to a steady state GSD. By using a time-dependent particle pinning force, abnormal grain growth may be avoided. An index is proposed that predicts the extent of excess grain growth from characteristics of the initial GSD.

Typically, intergranular constraint relations of various sorts are introduced to improve the accuracy of prediction of texture evolution and macroscale stress-strain behavior of metallic polycrystals within the context of simple polycrystal averaging schemes. This paper examines the capability of a 3-D polycrystal plasticity theory (Kocks, U.F., Kallend, J.S., Wank, H.-R., Rollett, A.D. and Wright, S.I. (1994), popLA, Preferred Orientation Package-Los Alamos. LANL LA-CC-89-18), based on the Taylor assumption of uniform deformation among grains, to predict texture evolution and stress-strain behavior for complex finite deformation loading paths of OFHC Cu. Compression, shear and sequences of deformation path are considered. It is shown that the evolution of texture is too rapid and that the intensity of peaks is more pronounced than for experimentally measured pole figures. Comparisons of both stress-strain behavior and texture evolution are made with experiments, with and without the inclusion of latent hardening effects. It is argued that grain subdivision processes accommodate intergranular kinematical constraints, leading to the notion of a generalized Taylor constraint that considers the distribution of subgrain orientations. The subdivision process is assumed to follow the experimentally observed refinement of low energy dislocation structures associated with geometrically necessary dislocations. A modification of the kinematical structure of crystal plasticity is proposed based on generation of geometrically necessary dislocations that accommodate a fraction of the plastic stretch and rotation at the scale of a grain. Elsevier Science Ltd. All rights reserved.

The texture and anisotropy of as-rolled and rolled and annealed Ti-22Al-23Nb foil have been investigated. The texture of the b.c.c. phase was analyzed and used to calculate the anisotropy of the foil. The predicted variation in yield stress is in good agreement with the experimental results. The texture of the b.c.c, phase is similar to textures observed in conventional b.c.c. alloys. The texture of the orthorhombic and hexagonal phases has also been analyzed. Although limited data exist for the single crystal properties of the alpha phase, prediction of the anisotropy of the orthorhombic phase is hindered by the absence of such data. The results to date indicate that the texture of the cubic phase predicts the anisotropy of the intermetallic foil reasonably well. Theoretical analysis of the single crystal yield surface of the orthorhombic phase shows that a deformation mode map can be constructed for this material. Comparison of simulated with experimental textures suggest limits on the variation of critical resolved sheer stress among the four different slip systems. Elsevier Science S.A. All rights reserved.