Properties Of Ultrafine-grained Materials Research Articles

Evaluating the Flow Properties of Ultrafine-Grained Materials

Processing through the application of severe plastic deformation (SPD) provides an opportunity for achieving significant grain refinement, typically to the submicrometer or even the nanometer level. If these small grains are reasonably stable at elevated temperatures, it is possible to achieve excellent superplastic capabilities at very rapid strain rates. Recent developments on the flow properties of ultrafine-grained materials are examined and it is shown that the flow mechanisms can be readily depicted using deformation mechanism maps. Examples of maps are presented for materials processed by SPD techniques.

Modeling of grain refinement by cellular automata

Prediction of microstructure evolution and properties of ultrafine-grained materials is one of the most significant problems in materials science. Cellular automata (CA) method is able for proper simulation of the microstructure evolution and can be used for evaluation of mechanical properties. The paper presents a new original application of cellular automata for modeling of grain refinement. CA take into account deformation, evolution of dislocation density and dislocation structures; and simulate microstructure evolution as grain refinement. Deformation of grains in polycrystalline materials depends on their crystallographic orientation, which is unique for every grain. It causes anisotropy of deformation in micro-scale. Joining CA with other methods (finite element, discrete element, crystal plasticity, etc.) improves accuracy of coupled phenomena modeling in micro- and macro-scale. Finite element method and crystal plasticity theory provide information for CA calculations. Grain refinement occurs in two stages: a creation of low-angle boundaries and their evolution into high-angle boundaries. Three CA models of low-angle boundaries creation were developed. They are described and discussed in the paper. Developed models can be used for study of processes of grain refinement, as well as can be a part of the system for modeling of microstructure evolution in the processes of solidification, hot and cold deformation and phase transformation. Examples presented in the paper are model application for processes with severe plastic deformation (SPD). Results of simulations of grain refinement during the accumulative roll-bonding (ARB) process and MAXStrain® technology are presented in the paper.

Modeling of Microstructure Evolution in Process with Severe Plastic Deformation by Cellular Automata

Prediction of microstructure evolution and properties of ultrafine-grained materials is one of the most significant, current problems in materials science. Recently, an interest to apply the cellular automata (CA) to the simulation of different phenomena in materials has been rising constantly. The main asset of the CA is the ability for accurate modeling of the microstructure. Deformation in micro-scale shows anisotropy, which is related with the different crystallographic orientation of the grains in the polycrystalline material. To improve the accuracy of modeling, CA and FEM must be combined with crystal plasticity theory. In present model, deformation in macro-scale is transferred to meso-scale, where a representative element contains several, score or hundreds grains, and then is applied in micro-scale to each grain. Strain and strain rate are decomposed into the crystallographic directions. For each crystallographic direction, development of dislocation and subgrain boundaries are considered. In each grain development of dislocation structure is distinctive because their orientation is unique. Creation of low-angle boundaries and their development into high-angle boundaries are simulated by the cellular automata on the base of calculations using finite element method and crystal plasticity theory. Some algorithms implemented into CA are described in the paper, as well as simulation results.

Mechanical Behaviors of Ultrafine Grained Metallic Materials

Ultrafine grained materials fabricated by severe plastic deformation exhibit both superior and inferior mechanical properties, as the prominent structural materials, compared to coarse grained counterparts. The superior mechanical properties are ultrahigh strength and exceptional ductility at high temperatures (i.e., superplasticity). The inferior mechanical properties are lack of strain hardenability and room temperature ductility. In this study, the relationship between microstructure and mechanical properties of ultrafine grained materials fabricated by severe plastic deformation is investigated in order to provide insight broadening their future applicability.

Simulation of normal grain growth by cellular automata

Prediction of microstructure evolution and properties of ultrafine-grained materials is one of the most significant problems in materials science. Cellular automata (CA) method is able for proper simulation of the microstructure evolution and can be used for evaluation of mechanical properties. The paper presents a new original application of cellular automata for modeling of grain refinement. CA take into account deformation, evolution of dislocation density and dislocation structures; and simulate microstructure evolution as grain refinement. Deformation of grains in polycrystalline materials depends on their crystallographic orientation, which is unique for every grain. It causes anisotropy of deformation in micro-scale. Joining CA with other methods (finite element, discrete element, crystal plasticity, etc.) improves accuracy of coupled phenomena modeling in micro- and macro-scale. Finite element method and crystal plasticity theory provide information for CA calculations. Grain refinement occurs in two stages: a creation of low-angle boundaries and their evolution into high-angle boundaries. Three CA models of low-angle boundaries creation were developed. They are described and discussed in the paper. Developed models can be used for study of processes of grain refinement, as well as can be a part of the system for modeling of microstructure evolution in the processes of solidification, hot and cold deformation and phase transformation. Examples presented in the paper are model application for processes with severe plastic deformation (SPD). Results of simulations of grain refinement during the accumulative roll-bonding (ARB) process and MAXStrain® technology are presented in the paper.