Combining Differential Scanning Calorimetry and Cooling-Heating Curve Thermal Analysis to Study the Melting and Solidification Behavior of Al-Ce Binary Alloys

Abstract

Two common techniques of thermal analysis, Differential Scanning Calorimetry (DSC) and Cooling/Heating Curve Thermal Analysis (CCTA), based on different signal collected and utilizing samples with a weight difference of three orders of magnitude, were used to assess the solidification and melting behavior of Al-Ce binary alloys, containing from 5 to 20 wt. % Ce. Thermal analysis was accompanied by microscopic observations of solidified structures. For heating/cooling rates of 0.2–0.4 °C/s, temperatures of eutectic transformation L ↔ Al + Al11Ce3 in the Al-10Ce alloy along with additional proeutectic reactions L ↔ Al in the Al-5Ce hypoeutectic alloy and L ↔ Al11Ce3 in Al-15Ce and Al-20Ce hypereutectic alloys, were determined. Although there was a general agreement in major transformations, registered by DSC and CCTA during melting and solidification, differences in the reaction temperature determined exceeded the typical measurement errors for each technique. In addition, DSC and CCTA exhibited differences in detecting some proeutectic reactions and minor non-equilibrium effects, accompanying the eutectic transformation. Some factors that could contribute to differences observed and their implications for engineering practice were discussed.

On the continuous mechanics first- and second-order formulations for non-equilibrium nucleation: Derivation and applications

“…Similar pattern can be seen in DTA-DSC for asymmetric heating and cooling cycles [28]. Regarding the direction of heat extraction, associated with melting and cooling, Aniolek and co-workers [29] state that during heating, due to the specific microstructure of the eutectic, where phases are aligned with each other, both phases melt very close to a common temperature on both sides of the eutectic for a high solid fraction. In contrast, on cooling you have a liquid that will transform into an alpha phase to later transform into a eutectic, however near the Liquidus isotherm, the liquid fraction is high.…”

On the Continuous Mechanics First and Second-Order Formulations for Nonequilibrium Nucleation: Derivation and Applications

“…A similar pattern can be seen in DTA-DSC for asymmetric heating and cooling cycles [33]. Regarding the direction of heat extraction, associated with melting and cooling, Aniolek and coworkers [34] state that during heating, due to the specific microstructure of the eutectic, where phases are aligned with each other, both phases melt very close to a common temperature on both sides of the eutectic for a high solid fraction. In contrast, upon cooling, you have a liquid that will transform into an alpha phase to later transform into a eutectic; however, near the liquidus isotherm, the liquid fraction is high.…”

Solidification Kinetics of an Al-Ce Alloy with Additions of Ni and Mn

“…The initial liquidus and solidus temperatures were determined by Scheil ThermoCalc TM simulations to be 733 • C and 632 • C, respectively. Therefore, the temperature range of the DSC experiment was set from 20 to 750 • C. The heating and cooling rate was selected to be 10.00 • C /min (~0.17 • C /s) based on similar studies previously conducted on Al-Ce alloys [18,29]. Each sample was 0.020 +/− 0.003 g and taken from the locations outlined in Figure 1.…”

“…The results of the DSC experiment offer insight into the specifics of solidification kinetics, such as the solidus, liquidus, and latent heat of fusion of the eutectic reaction. The solidus and liquidus temperatures were determined by extrapolating the tangent reaction rate near the tip of the characteristic peak and projecting it to intersect the baseline of the DSC data [18,31,32]. The extrapolation of the onset and end temperatures of the characteristic peak was performed according to ASTM E794 [32] standards.…”