Spatio-temporal microstructure evolution in directional solidification processes

Abstract

Experimental studies in Al-4.0 wt% Cu alloys were conducted in samples of different sizes in which the effect of convection increases with increasing sample diameter. Detailed measurements of dendrite tip radii and the primary arm spacing have been carried out under both diffusive and convective growth conditions. The experimental results on tip radius and primary spacing show a good agreement with the microsolvability theory and Hunt-Lu model, respectively, for diffusive growth processes. In larger samples where convection effects are present, an inhomogeneous microstructure develops. A localized growth model is proposed to explain the spatio-temporal microstructure formation under convective growth conditions. The key parameter in this model is the effective diffusion coefficient which increases with the sample diameter and plays the decisive role in selecting the length scales of the solidification microstructures under convective growth conditions.

Solidification microstructures and solid-state parallels: Recent developments, future directions

“…specimen diameter) [124,251]. The stability parameter r was found to be the same for solidification with or without convection only when the effective diffusion coefficient was used to compute r in the case with convection.…”

“…One reason is that anisotropy is difficult to measure experimentally in metallic systems, although progress in this direction has been made recently [6][7][8]. Liu et al [124] examined an Al-4%Cu alloy under conditions of diffusion-controlled solidification. Their measurements show that the dendrite tip selection follows microsolvability theory.…”

The Growth of a Single Cell/Dendrite in a Directional Solidification Process

“…[4] Hunt et al have not only studied the shape evolution of a single cell but the competitive growth of an array of cells as well. [13,17] The work on the array stability has been well appreciated and verified through precisely controlled experiments; [18][19][20][21] however, for the simpler case where the growth of a single cell has been simulated, [5,13] critical experimental results that may verify the calculation are still lacking. This is because growth of a single cell/dendrite requires the use of a capillary tube as an ampoule, and unique experimental difficulties are encountered for such a configuration, which will be addressed in Section II-A.…”

Experimental investigation of free dendritic growth of succinonitrile-acetone alloys

“…Consequently, more realistic predictions are expected from this theory. In fact, phase-field simulations [58-60, 101,123] and an experimental investigations [90] agree quantitatively with MST.…”

“…However, substantial advances have been recently achieved in order to overcoming such inconveniences[97][98]. Besides, some recent measurements carried out by Liu et al[90] using an Al-4%Cu alloy under conditions of diffusion controlled solidification validate the MST. 2.2.5 Numerical simulations Further analytical advances in the study of free dendritic growth are rather challenging.…”