Milan Hampl

Thermodynamic description of the Ti–O system

Abstract Phase diagram and thermodynamic data of the complete binary Ti–O system are assessed using the Calphad method. The main focus is on the proper description of high temperature titanium monoxide TiOx phase using the common compound energy formalism. The structural data of this complex solid solution phase could be successfully modeled together with the phase equilibrium and thermodynamic data, embedded in the comprehensive Ti–O assessment. The presentation of all original phase equilibrium data in the entire system indicates the well or less well established regions in comparison with the calculated phase diagram.

Experimental investigation and thermodynamic assessment of the Al–Ca–Ti system

Ternary Al–Ca–Ti alloy samples and diffusion couples Al2Ca–Ti were investigated using scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray powder diffraction, and metallographic analysis. The experiments turned out to be very difficult, as expected by this combination of elements, and adapted techniques were used. The results indicate that ternary solubilities of Ca in Al–Ti phases were not observed and no ternary phase was found in the ternary mid-composition range. The binary Ca–Ti and the ternary Al–Ca–Ti phase diagrams are developed for the first time. They are based on consistent thermodynamic calculation by combining the binary edge systems and incorporating the Al-rich Al20CaTi2 phase.

Thermodynamics of phase formation in Mg-La-Ce-Nd alloys

Experimentally validated thermodynamic descriptions have been developed for the ternary Mg-La-Ce, Mg-La-Nd, and Mg-Ce-Nd systems by selecting key alloys in both systems and analyzing the phase formation in both the as-cast and heat treated state by SEM/EDS and DSC. These results were combined to form the validated thermodynamic Calphad-type description for quaternary Mg-La-Ce-Nd alloys. It is shown that for these light rare earth elements (La, Ce, Nd) the intermetallic phases with Mg exhibit significant mutual solid solubility in the ternary systems, extending into the quaternary alloy system. This is reflected by considering the shared crystal structures in the thermodynamic modeling. Simulated solidification paths of three Mg-La-Ce-Nd alloys with different La:Ce:Nd ratios and a common total content of 5 wt.% rare earth (RE) metals are evaluated using computational thermodynamics. Unexpected and distinctly different solidification behavior of these three alloys is revealed. The sequence La→Ce→Nd in the periodic table is not at all reflected in a monotonous solidification behavior. The demonstrated individual impact of each of these elements forbids treating the RE additions as a mere wt.% sum of RE elements.