Subgrain Coalescence Simulation by Means of an Advanced Statistical Model of Inelastic Deformation

Abstract

The development of technological methods for processing and manufacturing of functional (with a priori targeted properties) polycrystalline materials and products made of these materials still remains an acute problem. A multilevel modeling approach offers researchers the opportunity to describe inelastic deformation by applying internal variables that give an effective characterization of the material structure at different structural scale levels. High temperature plastic deformation is accompanied by these processes, which leads to a significant rearrangement of the meso- and microstructure of the material. The most substantial contribution to changing the properties of polycrystals is made by the evolution of grain and defect structures at the expense of dynamic recrystallization, which significantly depends on dynamic recovery. In this paper, we consider the problem of the coalescence of subgrains undergoing rotation during inelastic hot deformation. This process is called subgrain coalescence, and it is one of the dynamic recovery mechanisms responsible for changes in the fine subgrain structure. Under applied thermomechanical loads, the coalescence process promotes the formation of recrystallization nuclei and their subsequent growth, which can greatly change the grain structure of a polycrystal. The problem was solved in terms of the advanced statistical model of inelastic deformation, modified to describe the subgrain coalescence process. The model takes into account the local interactions between contacting structural elements (subgrains). These have to be considered so that the grain coalescence caused by a decrease in subboundary energies during their progressive merging can be adequately analyzed. For this purpose, a subgrain structure quite similar to the real structure was modeled using Laguerre polyhedra. Subgrain rotations were investigated using the developed model, which relies on the consideration of the excess density edge component of the same sign dislocations on incidental subgrain boundaries. The results of modeling of a copper polycrystal are presented, and the effects of temperature and strain rate on the subgrain coalescence process is demonstrated.

A Multilevel Physically Based Model of Recrystallization: Analysis of the Influence of Subgrain Coalescence at Grain Boundaries on the Formation of Recrystallization Nuclei in Metals

“…The coalescence mechanism associated with the climb of dislocations and their annihilation in the subgrain boundary is likely to appear at small-angle boundaries with weak misorientation [ 7 , 77 , 78 ]. The multilevel model modified to take coalescence into account was described in [ 34 ].…”

“…At present, models based on the self-consistent approach [ 26 , 31 ] have gained broad recognition. Self-consistent models (the grain environment is replaced in these models by the effective medium) are less computationally expensive compared to direct models, but they cannot be used study the local interactions between adjacent structural elements [ 34 ]. In this connection, a compromising solution is to use advanced statistical models because they are computationally fast and permit analyzing contact interactions between crystallites.…”

“…Coalescence-related rotations occur due to the local interactions of a subgrain with adjacent subgrains. Therefore, the formulated problem is solved in the framework of the advanced statistical model of inelastic deformation, which permits the consideration of the interactions between adjacent structural elements (subgrains, grains) [ 27 , 34 ]. The modeling of coalescence for a representative volume of subgrains with consideration of their geometry as similar to real three-dimensional geometry is a laborious and complex task [ 35 , 36 , 37 ].…”

“…Previously, we have developed a method to consider subgrain coalescence by means of an advanced statistical model of inelastic deformation [ 34 ]. As the main driving force of coalescence, a reduction in the internal energy of the considered representative volume of subgrains, including the energy of subgrain boundaries, was taken [ 41 ].…”

“…Coalescence was modeled explicitly via use of a polyhedral subgrain structure. In the statistical model proposed by the authors [ 34 ], the high-angle boundary was not considered and its influence on the coalescence process was, accordingly, not taken into account. In this study, a high-angle grain boundary that affects the coalescence of subgrains and the formation of recrystallization nuclei is introduced explicitly into consideration.…”