A Mechanism-based Approach to the Simulations of Grain-boundary Thermodynamics and Kinetics
DescriptionMost crystalline materials, such as metals and ceramics, exist in form of polycrystals, which are composed of aggregates of single-crystalline grains differing in orientation. The long-range order of atomic arrangement within the grains is broken at the interface between the contiguous grains. So, the interface is a planar defect, called grain boundary (GB). Since GBs are prevailing defects in a polycrystalline material, the material properties can be adjusted by controlling the type and population of GBs – this is an approach towards the development of materials with novel properties, e.g. strength, ductility, resistance to radiation damage, etc. Implementation of this approach relies on the understanding of GB thermodynamics and kinetics; the former aims to predicting the equilibrium GB properties while the latter predicting the response of GBs to the external forces. The current researches are limited by the available methods and tools. The classical theories usually assume capillarity-driven, overdamped GB kinetics. Accumulated experimental observations manifest the failure of this assumption; such observations include non-parabolic grain growth, stress-induced GB migration/rotation, non-thermal GB mobility/viscosity, enhanced stability of nano grains, etc. On the other hand, GB thermodynamics/kinetics can be studied by atomistic simulations with less assumptions; however, such simulations are highly limited in length and time scales. In the proposed project, we will develop an approach to simulate the GB behaviors in and out of equilibrium under complicated external conditions. The fundamental mechanism of the GB behaviors (i.e., thermal fluctuation, GB migration/sliding) is the nucleation, annihilation and motion of disconnections. The new approach is built upon the disconnection mechanism, lattice model and Monte Carlo (MC) method. It is expected that this approach can overcome the length- and time-scale limitations inherent to the atomistic simulations and, at the same time, reproduce diverse GB kinetic behaviors which cannot be captured by the classical theory. A state-of-the-art computational tool will be developed to implement this approach. The power of this approach will be instantiated by two applications. (i) Simulation of GB phase transitions – the goal is to reveal the underlying physics and the implications on anomalous GB kinetics. (ii) Simulation of GB migration/sliding in pure metals and solid solutions – the goal is to develop workflow of the GB mobility tensor computation, explore the parameter space to optimize the GB property (such as thermal stability), and, in addition, include the triple junction effect to connect the kinetics of isolated GBs to that of polycrystals.
|Effective start/end date||1/01/22 → …|