Abstract
During severe plastic deformation (SPD), there is usually extended grain fragmentation, associated with the formation of a crystallographic texture. The effect of texture evolution is, however, coarsening in grain size, as neighbor grains might coalesce into one grain by approaching the same ideal orientation. This work investigates the texture-induced grain coarsening effect in face-centered cubic polycrystals during simple shear, in 3D topology. The 3D polycrystal aggregate was constructed using a cellular automaton model with periodic boundary conditions. The grains constituting the polycrystal were assigned to orientations, which were updated using the Taylor polycrystal plasticity approach. At the end of plastic straining, a grain detection procedure (similar to the one in electron backscatter diffraction, but in 3D) was applied to detect if the orientation difference between neighboring grains decreased below a small critical value (5°). Three types of initial textures were considered in the simulations: shear texture, random texture, and cube-type texture. The most affected case was the further shearing of an initially already shear texture: nearly 40% of the initial volume was concerned by the coalescence effect at a shear strain of 4. The coarsening was less in the initial random texture (~30%) and the smallest in the cube-type texture (~20%). The number of neighboring grains coalescing into one grain went up to 12. It is concluded that the texture-induced coarsening effect in SPD processing cannot be ignored and should be taken into account in the grain fragmentation process.
Highlights
The grain size is one of the key factors determining the performance of metals and alloys.In general, grain refinement improves the strength, which can be explained by the empirical Hall-Petch relation
To examine the effects of topology of the polycrystal orientation distribution as well as the mesh size on the texture-induced grain coarsening, the same initial texture was used for the three mesh sizes
A random texture was generated using the ATEX software containing 10,000 grains, with grain sizes varying between 4 and 14 μm, see the grain size distribution in Figure 2 for the highest voxel division case. (The grain size was calculated as the diameter of a sphere having the same volume as an irregular-shaped grain.) the grains were labeled by their grain IDs and were distributed randomly in the cubic space based on the cellular automaton (CA) nucleation algorithm
Summary
The grain size is one of the key factors determining the performance of metals and alloys.In general, grain refinement improves the strength, which can be explained by the empirical Hall-Petch relation. The grain size is one of the key factors determining the performance of metals and alloys. The most studied SPD techniques are equal-channel angular pressing (ECAP) [4,5], high-pressure torsion (HPT) [6,7], and accumulative roll bonding (ARB) [8], whereas others are emerging [9]. These SPD techniques present attractive application potentials as they can enhance the strength of conventional metallic materials dramatically [10].
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