Subcritical Bifurcation from Planar to Cellular Interface in Al – 0.5 wt.% Cu Directionally Solidified

Abstract

ABSTRACTSamples of the Al – 0.5wt.% Cu system were directionally grown under controlled conditions, to study the role played by the instabilities in the process relatives to the microstructure selection for a given values of interface velocity, and thermal gradient. Using an interface quenching technique and metallographic analysis in longitudinal and transversal cuts of the samples, we determine the transition mechanisms between the different stages of the growth, and associate them to the stability of the solidification front. We study the planar to a cellular transition in different conditions, and although the solidification parameters are in good agreement with the perturbations theory, when analyzing the amplitude of the perturbations during the planar to a cellular transition, the same theory is not able to predict certainly the critical wavelength in this case. Also, we found a subcritical behavior during the transition from a planar to a cellular interface for the diluted Al – Cu system, detecting a hysteresis behavior for the amplitude of the perturbations when it is increasing and then decreasing the interface velocity, through the threshold.