MIXING ENTHALPIES OF LIQUID Cu–Hf–Ti ALLOYS STUDIED BY HIGH-TEMPERATURE CALORIMETRY

Abstract

The partial enthalpies of mixing of titanium and hafnium in liquid Cu–Hf–Ti alloys were investigated at 1873 K along the x_Cu/x_Hf = 3 (at x_Ti = 0–0.25) and x_Cu/x_Ti = 3 (at x_Hf = 0–0.5) sections by a high-temperature isoperibolic calorimeter. The limiting partial enthalpy of mixing of supercooled liquid titanium in liquid Cu–Hf alloy is 2.0 ± 1.5 kJ/mol. The limiting partial enthalpy of mixing of supercooled liquid hafnium in liquid Cu–Ti alloy is –43.0 ± 4.5 kJ/mol. The integral mixing enthalpies of components along the investigated sections are calculated by integrating the Gibbs–Duhem equation. The integral mixing enthalpy is negative in the investigated composition range. The comparison of our experimental results with the calculations according to Miedema’s model shows that this model’s prediction for the Δ_mixH function should be treated with caution.