Experimental investigation and thermodynamic assessment of Al–Ca–Ni ternary system

Abstract

The Al–Ca–Ni ternary system has been experimentally investigated and thermodynamically assessed to contribute to the development of a novel Al-base amorphous alloy. A new approach in alloy preparation was used due to the special properties of calcium. With selected equilibrated alloys, the isothermal sections of the Al–Ca–Ni system at 873 and 673 K were obtained by means of scanning electron microscopy, electron probe micro-analysis (EPMA) and powder X-ray diffractometry (XRD). Phase transformation temperatures were measured by differential scanning calorimetry (DSC) analysis. The liquidus projection of this ternary system was determined by identification of primary crystallization phases in as-cast samples and from the liquidus temperatures obtained from DSC analysis. A new ternary compound Al78Ca9Ni13 (referred to as τ 3 here after) has been confirmed to exist in both the 873 and 673 K isothermal sections on the basis of EPMA and XRD analysis. All sample compositions are Al-rich: A1–A4 samples > 72.64 at.% Al, B1–B10, C1–C11 > 45 at.% Al, with only C12 at 36.8 at.% Al. Based on the available data of the binary systems Al–Ni, Al–Ca, Ca–Ni and the ternary system Al–Ca–Ni from the literature and present work, thermodynamic modelling of the Al–Ca–Ni ternary system was performed using the calculation of phase diagram method coupled with first-principle calculations. A set of consistent thermodynamic parameters for the Al–Ca–Ni ternary system was obtained with good agreement with the experimental results in the Al-rich region. The calculated data in the Al-poor region are a very plausible prediction, but not validated.