About the banded structure in rapidly solidified dendritic and eutectic alloys

Prediction and characterization of heat-affected zone formation in tin-bismuth alloys due to nickel-aluminum multilayer foil reaction

“…At sufficiently high solidification rates, partitioning of solutes is reduced or even prevented entirely, which can result in a single phase structure. 50 This phenomenon is manifested in these alloys in the form of the more homogenous distribution of phases in the HAZ microstructures.…”

Diffusion-Induced Oscillations of Extended Defects

“…This includes a readjustment of the stability analysis by Merchant and Davis [11] who discovered an oscillatory instability, similar to that, discussed earlier by Coriell and Sekerka [12]. Also included is a clarifying analysis of the so far barely understood low-velocity sections of the cyclic trajectories, identified by Carrard et al [1], and by Karma and Sarkissian [9]. The limit-cycle behavior, describing the oscillations of the interface deep inside the unstable regime, is, finally, in remarkable agreement with the simulation results by Conti [10].…”

“…A prime example of such an effect is the oscillation of a solidification front, induced by the diffusion of the solute component in a dilute binary alloy, which is growing in the setup of directional solidification. In a large number of metallic materials this leads to the formation of banded structures [1], reflecting a periodic array of layers with high and low solute concentrations where the former ones show a dendritic microstructure. The appearance of similar banding effects has recently been discussed [2] in rapid solidification of colloids.…”

“…[7], and partly in Refs. [1] and [2], or they rely on a Fokker-Planck [6], or a diffusion equation with non-equilibrium boundary conditions [9]. In all approaches the source of oscillatory defect motions is identified as an unstable regime where a reduction of the driving force leads to an increase of the defect velocity.…”

“…[10], one concludes that the high-and low-concentration layers are connected by large-acceleration segments, explaining the sharpness of the interfaces between these layers. In order to explore the possible formation of dendritic ripples, one has to consider perturbations of the form h(x, t) =ĥ(q, ω) exp (iq · x + ωt) in a three-dimensional version of the model (1). In view of the almost stationary behavior ofḣ(t) in Fig.…”