Papers by Author: L.A. Barrales-Mora

Abstract: Molecular dynamics simulations were performed to analyze the curvature-driven shrinkage of individual cylindrical grains with geometrically different boundaries in Al. Grains with <100> tilt and mixed tilt-twist boundaries with the misorientations 5.5°, 16.3°, and 22.6° were simulated. The results revealed that the shrinking grains with tilt boundaries concurrently rotate increasing the misorientation angles, whereas grains with the mixed boundaries did not rotate during their shrinkage. Apparently, the grain boundary geometry/structure has a crucial impact on the observed rotational behavior of the computed grains. The grains with tilt boundaries rotate due to the lack of effectively operating mechanisms for annihilation of edge dislocations, which compose such boundaries. In contrast, for the mixed boundaries composed of edge-screw dislocations the sufficiently fast operating mechanisms of dislocation elimination are available, which facilitates grain shrinkage without rotation.

Abstract: The effect of the triple line energy on grain growth was studied by means of computer simulations with a network model. The results showed that the driving force stemming from the triple lines can influence significantly the evolution of grain growth.

Abstract: A cellular automaton and a vertex model were used, respectively, for the simulation of recrystallization and grain growth in a Fe-0.374%C-21.64%Mn alloy. The results of the recrystallization simulations revealed that the preferential nucleation during the annealing of the rolled sheet occurs at shear bands, which is corroborated by experimental observations. Subsequently, grain growth simulations were carried out with a 2D vertex model. The model used experimental data as input for its validation in this specific steel. The simulations showed a good agreement with the experimental results.

Abstract: A 3D Vertex Model has been successfully implemented to investigate the evolution of a special grain assembly during grain growth. The model considers the mean curvature as driving force for the motion of the vertices and allows the consideration of all parameters affecting the motion of the system, i.e., grain boundary energy and line tension of the triple lines, as well as grain boundary (GB), triple line (TL) and quadruple point (QP) mobility as well. The used special configuration makes it possible to study the influence of all structural elements of a grain boundary network on the evolution of the system by allowing the steady-state motion of the boundaries of a shrinking grain. In the present work the different mobilities have been systematically varied and the evolution of the grain size with time has been studied as a function of TL and QP mobility. The results of the simulations are finally linked to the different kinetic regimes reached by the system.

Abstract: Modeling and simulation of recrystallization, grain growth, and related phenomena are important tools for the fundamental understanding of microstructural evolution and prediction of engineering properties. In particular for ultra fine grained and nanocrystalline materials proper account of microstructural evolution is essential for the optimal processing of these materials. It is shown that for modeling of softening phenomena it is important to discriminate between discontinuous primary recrystallization and discontinuous grain growth owing to their quite different underlying physics. Recent developments in recrystallization modeling and simulation of grain growth are addressed, in particular nucleation of recrystallization and junction effects in grain growth. Major progress is also expected from atomistic modeling and quantum-mechanical computations for making available specific material properties.

Abstract: In the present study the superplastic behavior of Al-6%Mg–0.5%Cu and Al–8%Mg– 0.5%Cu in a coarse grain size condition has been studied. The alloys are melted in an electrical furnace under argon atmosphere. The ingots (25 mm thick) are homogenized at 400 °C during 72 h and then rolled at 430 °C to a thickness of 5 mm. The mean grain size after rolling is 55 µm for the 6%Mg alloy and 61 µm for the 8%Mg alloy. Tensile test specimens are machined from the rolled plate in the rolling direction. Strain-rate-change tests at temperatures between 300 and 450 °C and strain rates between 1x10-4 and 1x10-1 s-1 are carried out to determine the strain rate sensitivity of the flow stress. Finally, elongation to failure tests are conducted at temperatures and strain rates where the alloys show a high strain rate sensitivity. Elongations higher than 390 % are obtained for the 8%Mg alloy. It is observed that the grip regions of the deformed samples show coarser grains than the regions near to the fracture surface. This means that grain refinement takes place during deformation, suggesting that the principal deformation mechanism is dislocation creep.