Phase-field modelling of abnormal grain growth

Heterogeneous grain structures may develop due to abnormal grain growth during thermo-mechanical processing of polycrystalline materials ranging from metals to ceramics. This phenomenon must be controlled in practical applications where typically homogeneous grain structures are desired. Recent advances in experimental and computational techniques have, thus, stimulated to revisit the underlying growth mechanisms. Here, phase field modelling is used to systematically evaluate conditions for abnormal grain growth. Grain boundaries are classified into two classes, i.e. high and low mobility boundaries. Three different approaches are considered for having high and low mobility boundaries: (i) Critical threshold angle of grain boundary disorientation above which boundaries are highly mobile; (ii) Two grain types A and B with either the AB or the AA boundaries being highly mobile; (iii) Three grain types A, B and C with AB boundaries being highly mobile. For these different scenarios, 2D and 3D simulations have been performed to quantify the effect of variations in the mobility ratio, threshold angle and fractions of grain types, respectively, on the potential onset of abnormal grain growth and the degree of heterogeneity in the resulting grain structures. The required mobility ratios to observe abnormal grain growth are quantified as a function of the fraction of high mobility boundaries. The microstructure evolutions during abnormal grain growth are analyzed in terms of the spatial distribution of the highly mobile boundaries.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat