Microstructural evolution during directional annealing

Development of a columnar-grained structure and its continued propagation during directional annealing has been studied using a front-tracking, grain-growth model. The effects of the initial microstructure, hot zone velocity, and hot zone width were investigated for a single-phase system without a texture. Decreasing zone velocity and increasing zone width increase the ease of forming and propagating a columnar-grained structure. For a given zone width, grain length decreases with increasing velocity and the grain structure becomes equi-axed at high velocities. For a given zone velocity, critical zone width for propagation of a columnar grain is lower than that for its development. Critical zone velocity for propagation is independent of zone width for widths greater than about twice the initial grain size, while it increases with the width for lower zone widths. For a given initial grain size, the critical velocity for propagation increases with increasing width of the initial columnar grain.