There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Improving high-temperature mechanical properties of cast CrFeCoNi high-entropy alloy by highly thermostable in-situ precipitated carbides

Bridging molecular dynamics and phase-field methods for grain growth prediction

An atypical grain coarsening phenomenon was reported in welding nugget zone of friction stir welding for the first time. The average grain size and the aspect ratio were determined to be 266.3 µm and 2.9, which were respectively 74.0 times and 1.9 times as those of conventional friction stir welding. A numerical model combining a macro finite model with a micro modified Wagner-Kampmann model was proposed to analyze the evolution mechanism of the atypical microstructure. The heterogeneous precipitation and the dynamic recrystallization were calculated. The unequiaxed coarse grains doped with a small amount of small grains were achieved under the extremely low heat input and the high plastic strain rate. The atypical coarsening phenomenon only occurred at certain conditions: (a) extremely high plastic strain and strain rate by friction stir welding; (b) an elevated temperature slightly above 0.5 melting point to inhibit the dynamic recrystallization refinement under higher temperature and shear induced refinement under lower temperature.

Atypical grain coarsening of friction stir welded AA6082-T6: Characterization and modeling

Macroscopic properties of structural materials are strongly dependent on their microstructure. However, the modeling of their evolution is a complex task because of the mechanisms involved such as plasticity, recrystallization, and phase transformations, which are common processes taking place in metallic alloys. This complexity led to a growing interest in atomistic simulations formulated without any auxiliary hypotheses beyond the choice of interatomic potential. In this context, we propose here a model based on an overdamped stochastic evolution of particles interacting through inter-atomic forces. The model settles to the correct thermal equilibrium distribution in canonical and grand-canonical ensembles and is used to study the grain boundary migration. Finally, a comparison of our results with those obtained by molecular dynamics shows that our approach reproduces the complex atomic-scale dynamics of grain boundary migration correctly.

/pdf/overdamped-langevin-dynamics-simulations-of-grain-boundary-1k8oliygxr.pdf

Overdamped langevin dynamics simulations of grain boundary motion

Grain rotation has been found to be an important mechanism of microstructure evolution in addition to curvature-driven grain boundary migration in nanocrystalline materials. Grains coalesce due to rotation and this provides an additional mechanism of grain growth. We show that for growth by coupled migration and rotation coalescence the average grain size grows as indicating that the coupled problem is surprisingly more stable to grain growth. We then present an appropriate rotationally invariant multiphase field model which accounts for grain rotation to corroborate the theoretical result.

Grain growth rate for coupled grain boundary migration and grain rotation in nanocrystalline materials

Simultaneous grain boundary migration and grain rotation has been found to be an important mechanism of microstructure evolution in nanocrystalline materials. During evolution, the grains in microstructure undergo rotations and at times grow by coalescing with their surrounding neighboring grains. Therefore, both grain boundary migration and grain coalescence contribute in increasing the average grain size. In the present work, a detailed study of microstructure evolution due to simultaneous grain boundary migration and grain rotation is carried out by considering misorientation dependent energy and mobility through theoretical calculations and phase field simulations. These studies consider curvature driven migration and grain rotation due to viscous sliding. Theoretical studies of bicrystal and polycrystal settings show that the average grain radius during microstructure evolution due to simultaneous grain boundary migration and grain rotation grows as R ∼ t 0.30 , for misorientation dependent grain boundary energy and mobility. Finally, we discuss various topological and statistical aspects of microstructure in the presence of both grain boundary migration and grain rotation using multiphase field simulations.

Theory and simulation of microstructure evolution due to simultaneous grain boundary migration and grain rotation with misorientation dependent energy and mobility

Essential work of fracture studies of 3D Printed PEEK (Poly-ether-ether-ketone) polymer

Study of microstructure evolution in the form of grain growth in polycrystalline materials has been an important goal for material scientists as it drastically affects physical and mechanical properties Specifically, nanocrystalline materials, which are known for their superior mechanical properties, are highly susceptible to grain growth even at low temperatures and stresses Various experiments and simulations carried out on nanocrystalline materials indicate that the microstructure evolution in these materials takes place due to grain boundary migration and grain rotation Therefore, migration of grain boundaries and grain rotation-induced grain coalescence contribute in increasing the average grain size in the microstructure In order to simulate microstructure evolution in polycrystalline materials, the multi-order parameter phase-field model is a popular approach and is widely used for studying evolution purely due to the grain boundary migration In this work, we present a multi-order parameter phase-field model capable of capturing microstructure evolution due to grain boundary migration and grain rotation-induced grain coalescence The model couples constitutive equation of viscous sliding-induced grain rotation and the classical phase-field model for curvature-driven grain boundary migration This paper covers various topological and statistical aspects of the microstructure evolved in the presence of both these growth mechanisms in great detail

Simulation of grain growth under simultaneous grain boundary migration and grain rotation using multi-order parameter phase-field model

Microstructure evolution due to coupled grain boundary migration and grain rotation in low angle grain boundaries is studied through a combination of molecular dynamics and phase field modeling. We have performed two dimensional molecular dynamics simulations on a bicrystal with a circular grain embedded in a larger grain. Both size and orientation of the embedded grain are observed to evolve with time. The shrinking embedded grain is observed to have two regimes: constant dislocation density on the grain boundary followed by constant rate of increase in dislocation density. Based on these observations from the molecular dynamics simulations, a theoretical formulation of the kinetics of coupled grain rotation is developed. The grain rotation rate is derived for the two regimes of constant dislocation density and constant rate of change of dislocation density on the grain boundary during evolution. The theoretical calculation of the grain rotation rate shows strong dependence on the grain size and ...

Amol Vuppuluri

Papers

Grain growth rate for coupled grain boundary migration and grain rotation in nanocrystalline materials

Theory and simulation of microstructure evolution due to simultaneous grain boundary migration and grain rotation with misorientation dependent energy and mobility

Essential work of fracture studies of 3D Printed PEEK (Poly-ether-ether-ketone) polymer

Simulation of grain growth under simultaneous grain boundary migration and grain rotation using multi-order parameter phase-field model

Theory and simulation of coupled grain boundary migration and grain rotation in low angle grain boundaries