CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 33 (2009) 478–486 Contents lists available at ScienceDirect CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry journal homepage: www.elsevier.com/locate/calphad A critical thermodynamic assessment of the Mg–Ni, Ni–Y binary and Mg–Ni–Y ternary systems Mohammad Mezbahul-Islam, Mamoun Medraj * Department of Mechanical Engineering, Concordia University, 1455 de Maisonneuve Blvd. West, H3G 1M8, Montreal, Canada article info Article history: Received 19 August 2008 Received in revised form 5 January 2009 Accepted 5 January 2009 Available online 17 January 2009 Keywords: Thermodynamic modeling Modified quasichemical model Mg-alloys Hydrogen storage Metallic glass abstract A thorough review and critical evaluation of phase equilibria and thermodynamic data for the phases in the Mg–Ni–Y ternary system have been carried out over the entire composition range from room temperature to above the liquidus. This system is being modeled for the first time using the modified quasichemical model which considers the presence of short range ordering in the liquid. The Gibbs energies of the different phases have been modeled, and optimized model parameters that reproduce all the experimental data simultaneously within experimental error limits have been obtained. For the liquid phases, the modified quasichemical model is applied. A sublattice model within the compound-energy formalism is used to take proper account of the structures of the binary intermediate solid solutions. The Mg–Ni and Ni–Y binary systems have been re-optimized based on the experimental phase equilibrium and thermodynamic data available in the literature. The optimized thermodynamic parameters for the Mg–Y system are taken from the previous thermodynamic assessment of the Mg–Cu–Y system by the same authors. The constructed database has been used to calculate liquidus projection, isothermal and vertical sections which are compared with the available experimental information on this system. The current calculations are in a good agreement with the experimental data reported in the literature. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Batteries can be a useful source of energy for spacecraft, military and defense, communication, power tools and consumer appliances because of their ability to store energy in a clean, convenient and efficient manner and hence there is a growing need for high-specific power, high-specific energy and low-cost batteries [1]. Currently nickel/cadmium rechargeable batteries are commonly used for these purposes. But due to the relatively low capacity and environmental concerns more efficient and safe substitutes for cadmium are urgently needed. The nickel-metal hydride battery (MH) with a hydrogen storage alloy as a negative electrode has shown a high potential in that aspect [1,2]. That is why extensive attention has been paid to the utilization of magnesium-based alloys as hydrogen storage materials owing to their high storage capacity and low specific weight [3]. The Mg–Ni–Y system is considered to be one of the promising candidates [1]. Besides, this ternary is one of the promising Mg- based metallic glass systems [4]. Hence it is becoming clear that a detailed investigation on this system is needed. The aim of the present work is to provide a comprehensive crit- ical thermodynamic evaluation and optimization of the Mg–Ni–Y system over the entire composition range from room tempera- * Corresponding author. E-mail address: mmedraj@encs.concordia.ca (M. Medraj). ture to liquidus temperature. Two of the three constituent binaries, Mg–Ni and Ni–Y, have been optimized using the modified quasi- chemical model [5–7] for the liquid phase. The Mg–Y system was optimized earlier by the same authors [8] and the model parame- ters have been used directly in this work. The Toop [9] geometric model with Mg as the asymmetric component has been used for the extrapolation of the binaries to the ternary system. 2. Literature review 2.1. Ni–Y system The phase diagram of the Ni–Y system was first investigated by Beaudry and Daane [10] and later by Domagala et al. [11]. Beaudry and Daane [10] used metallographic, thermal analysis and X-ray diffraction (XRD) methods in their investigation and reported the existence of nine intermetallic compounds; NiY 3 , Ni 2 Y 3 , Ni 2 Y, Ni 3 Y, Ni 7 Y 2 , Ni 4 Y, Ni 17 Y 2 , NiY and Ni 5 Y. Except for the last two, all other compounds undergo peritectic decomposition. Domagala et al. [11], however, reported eight compounds and missed the existence of Ni 7 Y 2 . However, another investigation by Buschow [12] on several phases of the Ni–RE (RE = rare earth) showed that an Ni 7 RE 2 phase occurs in all the heavier Ni–RE systems. So the existence of the Ni 7 Y 2 compound in the Ni–Y system is consistent with the general trend and has been included in this work. Domagala et al. [11], also, disagreed 0364-5916/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.calphad.2009.01.001