Thermodynamic properties of melts in Al–TI(Zr, Hf) binary systems

Abstract

Aluminum-based alloys are widely used in different industries. We need to know the physical and chemical properties of these materials to improve the methods to produce them and to identify their optimal service conditions. Hence, the objective of this paper is to examine the thermodynamic properties of Al–Ti(Zr, Hf) binary melts by isoperibolic calorimetry at 1770 ± 5 K and 1790 ± 5 K. The experimental and data processing methods are described in [1]. Aluminum AV000 (99.999%), titanium, zirconium, and hafnium (99.9%) were used. Aluminum was placed into an yttria-lined corundum crucible in a massive molybdenum block. The calorimeter was calibrated against aluminum at the beginning of the experiment and against tungsten A2 (99.96%) at the end. Prior to the experiment, the calorimeter was warmed up under constant evacuation using forevacuum and diffusion pumps up to 773 K. After that, the chamber was filled with purified argon. The relative errors of the partial and integral mixing enthalpies were ±10 and ±2%, respectively. The reproducibility of the results is within 3%. During the experiment, we recorded variations in temperature that occurred when group IVb metal samples were introduced into liquid aluminum. The chamber heating rate is limited by the evacuation speed. The temperature variations during the experiment were recorded with a self-recorder and thermal effects were determined with the gravimetric method. The partial mixing enthalpies for Ti, Zr, Hf and integral mixing enthalpies for Al–Ti(Zr, Hf) binary melts are shown in Fig. 1. The thermodynamic properties of Al–Ti(Zr, Hf) binary melts are compared with similar data [2–8]. There are few experimental data on the thermodynamic properties of Al–Ti melts over a wide concentration range. At low concentrations, all mixing enthalpies of Al–Ti melts correlate with each other within experimental errors (Fig. 2a). However, the formation enthalpies turned out to be more exothermal at x Ti > 0.15 than Δ m H [3] determined calorimetrically at 2000 K. This is evidence of the temperature dependence of the mixing enthalpies of