Abstract
Grain growth, the most fundamental mechanism forming the internal structure in metallic materials, is affected by not only grain boundary (GB) energy but also other driving forces such as internal stress fields of defects. In order to determine the explicit distinctions between the simulated evolutions and the real metallographic observations for discussing the dominant driving force, simulations of polycrystalline grain growth were performed using our proposed multi-phase-field model [T. Hirouchi, T. Tsuru and Y. Shibutani: Compt. Mater. Sci. 53 (2012) 474–482.], which was combined with pure Al and Cu < 110> tilt misorientation and inclination dependences of GB energy based on the molecular dynamics results. The real microstructures in as-annealed Al specimens exhibiting various average grain diameters and in oxygen-free Cu (OFC) specimens after several annealing treatments were characterized using scanning electron microscopy/electron backscatter diffraction (SEM/EBSD). Few low-angle GBs within misorientation angle of 2° were expected to exist in the real microstructures despite the low energies of such GBs in Al, and some Σ3 GBs migrated in the direction opposite to that which decreased their curvature in OFC. These behaviors cannot be explained by only a grain growth mechanism in which total GB energy in the system is reduced as the driving force in the simulations. Models incorporating contribution from the long-range internal stress field due to the defects of GBs and the piled-up dislocations is crucial.
