Understanding and Modeling of Grain Boundary Pinning in Inconel 718
The microstructure stability during δ sub-solvus annealing was investigated in Inconel 718 alloy. A reference dynamically recrystallized microstructure was produced through thermomechanical processing (torsion). The reference microstructure evolution during annealing was analyzed by EBSD (grain size, intragranular misorientation) and SEM (Σ <5 phase particles). Results confirm that, in the absence of stored energy, the grain structure is controlled by the δ phase particles, as predicted by the Zener equation. If the reference microstructure is strained (å < 0.1) before annealing, then stored energy gradients between grains will induce selective grain growth leading to coarsening. The phenomenon is controlled by the balance of three forces (acting on boundaries migration) having the same order of magnitude: capillarity, stored-energy and pinning forces. All these forces could be modeled in a single framework by the level set method. The first numerical results demonstrate the capability of the method to simulate 2D Zener pinning. © 2012 The Minerals, Metals, & Materials Society. All rights reserved.