Microstructural Stability in Grain Boundary Engineered Materials

Grain boundary engineering (GBE) is a thermomechanical process in which sequential straining and annealing cycles are used to increase the fraction of special, low-energy grain boundaries (with Σ ≤ 29 according to the coincidence site lattice model). In the present work, two cubic face-centered materials, pure copper and Inconel 617, were processed by GBE. In addition, a conventionally processed sample was processed with a single strain step, equal to the total strain in the GBE sample. The thermomecanically-processed samples were subjected to elevated temperatures for varying times. The GBE samples exhibited a resistance to change in the fraction of special boundaries and grain size (as determined by Orientation Imaging Microscopy (OIM)), while the conventionally-processed samples experienced abnormal grain growth. Monte Carlo grain growth simulations on the OIM-determined microstructures confirm the increased microstructural stability of the GBE samples. Therefore, GBE processing can produce more stable and predictable microstructures than can conventional processing.