Columnar to Equiaxed Transition Analysis During Directional Solidification of Different Alloy Systems

ARES, ALICIA;; CARAM, RUBENS;; RIOS, CARLOS; SCHVEZOV, CARLOS

The Extraction & Processing Division and Fundamentals of Advanced Materials for Energy Conversion

Mark E. Schlesinger, editor. A publication of the Minerals, Metals, & Materials Society.

Lugar: Charlotte, North Carolina. USA.; Año: 2004; p. 247 - 259

Experiments were carried out in which the conditions of columnar to equiaxed transition (CET) in directional solidification of dendritic alloys are known, in alloy systems such as Al-Cu, Al-Si, Al-Si-Cu, Al-Mg, Al-Zn, commercial brass, and stainless steel. These experiments allow determine that two interfaces are defined, assumed to be macroscopically flat. The transition does not occur in abrupt form in the samples and is presented when the gradient in the liquid ahead of the columnar dendrites reaches critical and minimum values, being negative in most of cases. The transition occurs when the temperature gradients in the melt ahead of the columnar dendrites are in the range of – 3.89 °C/cm to 0.91 °C/cm for Al-2wt%Cu, – 0.55 °C/cm to 0.67 °C/cm for Al-4wt%Cu, – 2.05 °C/cm to 0.56 °C/cm for Al-10wt%Cu, – 2.8 °C/cm to 1.25 °C/cm for Al-20wt%Cu, – 11.41 °C/cm to 0.52 °C/cm for Al-33.2wt%Cu, 0.42 °C/cm to 0.50 °C/cm for Al-5wt%Si, -4.2 °C/cm to 0.67 °C/cm for Al-7wt%Si, -3.1 °C/cm to 0.48 °C/cm for Al-10wt%Si-2.5wt%Cu, -1.54 °C/cm to 0.91 °C/cm for Al-2wt%Mg, -1.67 °C/cm to 0.09 °C/cm for Al-4wt%Mg, -1.54 °C/cm to 0.91 °C/cm for Al-2wt%Zn,  -11.38 °C/cm to -0.02 °C/cm for Al-4wt%Mg, -2.23 °C/cm to 1.05 °C/cm for commercial brass, -13.4 °C/cm to -3.76 °C/cm for stainless steel. When the CET occurs, the liquidus interface velocities were 0.02 to 0.13 cm/s, 0.08 to 0.35 cm/s, 0.16 to 0.25 cm/s, 0.08 to 0.27 cm/s, 0.48 to 0.56 cm/s, 1.15 to 1.87 cm/s, 1.12 to 1.89 cm/s, 0.04 to 0.90 cm/s, 0.11 to 0.33 cm/s, 0.10 to 0.14 cm/s, 0.12 to 0.18 cm/s, 0.10 to 0.14 cm/s, 0.12 to 0.18 cm/s, 0.10 to 0.12 cm/s, respectively. Also, it was also possible to identify a short period of recalescence, being of the order of 0.59 °C for Al-2wt%Cu, 0.61 °C for Al-4wt%Cu, 0.72 °C for Al-10wt%Cu, 0.83 °C for Al-20wt%Cu, 1.08 °C for Al-33.3wt%Cu, 0.80 °C for Al-5wt%Si, 0.68 °C for Al-7wt%Si, 0.86 °C for Al-10wt%Si-2.5wt%Cu, 0.77 °C for Al-2wt%Mg, 0.54 °C for Al-4wt% Mg; 0.97 for the Al-2wt%Zn alloys and 1.25 °C for Al- 4wt%Zn, 0.67 °C for commercial brass and 4.40 °C for stainless steel. Recalescence is the result of the latent heat released by the equiaxed grains that nucleate ahead of the liquid interface. The results obtained in all alloys systems are presented and discussed.