Grain growth in a low-loss cold-rolled motor-lamination steel

This article attempts to determine the mechanisms governing the grain growth process that occurs during lamination annealing of a cold-rolled, motor-lamination (CRML) steel. A new simulation approach linking a Monte Carlo model with electron backscatter diffraction (EBSD) scans used as input has been employed to incorporate the effects of crystallographic texture on the simulated grain growth process. The results from the texture analysis and the computer simulation of the grain growth process indicate that both stored energy driven grain growth and anisotropic grain boundary growth influence the overall grain growth occurring during lamination annealing.     

Correction to: An Updated Index Including Toughness for Hot-Cracking Susceptibility

Metallurgical and Materials Transactions A -     

An Updated Index Including Toughness for Hot-Cracking Susceptibility

Metallurgical and Materials Transactions A - Hot cracking is one of the major defects that can occur in laser-based additive manufacturing. During the terminal stage of solidification, hot cracking...     

Statistically representative three-dimensional microstructures based on orthogonal observation sections

Techniques are described that have been used to create a statistically representative three-dimensional model microstructure for input into computer simulations using the geometric and crystallographic observations from two orthogonal sections through an aluminum polycrystal. Orientation maps collected on the observation planes are used to characterize the sizes, shapes, and orientations of grains. Using a voxel-based tessellation technique, a microstructure is generated with grains whose size and shape are constructed to conform to those measured experimentally. Orientations are then overlaid on the grain structure such that distribution of grain orientations and the nearest-neighbor relationships, specified by the distribution of relative misorientations across grain boundaries, match the experimentally measured distributions. The techniques are applicable to polycrystalline materials with sufficiently compact grain shapes and can also be used to controllably generate a wide variety of hypothetical microstructures for initial states in computer simulations. This article is based on a presentation made at the symposium “Characterization and Representation of Material Microstructures in 3-D” held October 8–10, 2002, in Columbus, OH, under the auspices of ASM International’s Phase Transformations committee.     

Constitutive Relations for AA 5754 Based on Crystal Plasticity

Constitutive equations for the multiaxial stress-strain behavior of aluminum alloy 5754 sheets were developed, based on crystal plasticity. A Taylor-based polycrystal plasticity model, a tangent formulation of the self-consistent viscoplastic model (VPSC), and an N-site viscoplastic model based on the fast Fourier transform (VPFFT) were used to fit a single slip system hardening law to the available data for tension, plane strain, and biaxial stretching. The fitting procedure yields good agreement with the monotonic stress-strain data, with similar parameter values for each model. When simulating multiaxial tests using the developed hardening law, models that allow both stress and strain variations in grains give better predictions of the stress-strain curves. Furthermore, generally, the simulated texture evolution is too rapid when compared to the experiments. By incorporating a more detailed neighbor interaction effect, the VPFFT model predicts texture evolution in better agreement with experiments.     

Evolution of Microstructure and Texture During Deformation and Recrystallization of Heavily Rolled Cu-Cu Multilayer

A Cu-Cu multilayer processed by accumulative roll bonding was deformed to large strains and further annealed. The texture of the deformed Cu-Cu multilayer differs from the conventional fcc rolling textures in terms of higher fractions of Bs and RD-rotated cube components, compared with the volume fraction of Cu component. The elongated grain shape significantly affects the deformation characteristics. Characteristic microstructural features of both continuous dynamic recrystallization and discontinuous dynamic recrystallization were observed in the microtexture measurements. X-ray texture measurements of annealing of heavily deformed multilayer demonstrate constrained recrystallization and resulted in a bimodal grain size distribution in the annealed material at higher strains. The presence of cube- and BR-oriented grains in the deformed material confirms the oriented nucleation as the major influence on texture change during recrystallization. Persistence of cube component throughout the deformation is attributed to dynamic recrystallization. Evolution of RD-rotated cube is attributed to the deformation of cube components that evolve from dynamic recrystallization. The relaxation of strain components leads to Bs at larger strains. Further, the Bs component is found to recover rather than recrystallize during deformation. The presence of predominantly Cu and Bs orientations surrounding the interface layer suggests constrained annealing behavior.     

Controlling Plastic Flow across Grain Boundaries in a Continuum Model

A framework for modeling controlled plastic flow through grain boundaries using a continuum plasticity theory, phenomenological mesoscopic field dislocation mechanics (PMFDM), is presented in this article. The developed tool is used to analyze the effect of different classes of constraints to plastic flow through grain boundaries, as it relates to dislocation microstructure development and mechanical response of a bicrystal. It is found that in the case of low misorientation angle between adjacent grains, impenetrable grain boundaries cause significant work hardening as compared to penetrable grain boundaries due to the accumulation of excess dislocations along them. However, a penetrable grain boundary with a high misorientation angle effectively behaves as an impenetrable boundary, with respect to the stress-strain response.