Investigation of ordering phenomenon in Me–Pt (Me=Fe,Ni) liquid alloys

Abstract

The phase diagrams of Fe-Pt and Ni-Pt liquid alloy systems show the existence of FePt and NiPt intermetallic compounds, respectively, in their solid intermediate states, and the associative tendency between unlike atoms in these liquid alloys has been analysed using the self-association model. The concentration dependences of mixing properties such as the free energy of mixing, G M ; the concentration fluctuations, S cc (0), in the long-wavelength limits; the chemical short-range order (CSRO) parameter, α 1 ; as well as the chemical diffusion, enthalpy and entropy of the mixing of Fe-Pt and Ni-Pt liquid alloys have been investigated to determine the nature of ordering in the liquid alloys. The results show that heterocoordination occurs in the alloys at all concentrations. The effect of CSRO on S cc (0), chemical diffusion, D, and the order parameter, α 1 , has been considered. The ordering phenomenon in the liquid alloys is also related to the effect of the atomic size mismatch volume on S cc (0).

A revised model for activity–composition relations in solid and molten FePt alloys and a preliminary model for characterization of oxygen fugacity in high-pressure experiments

“…Comparison of the newly derived model for liquid FePt alloy to those proposed by Fredriksson and Sundman (2001) and Odusote (2008) shows that these previous studies predict significantly larger activity coefficients at 3000 K and 0 GPa (Fig. 7).…”

“…Constraints on the thermodynamic properties of molten FePt alloys include Knudsen cell measurements of Fe activities (Alcock and Kubik, 1968) and those that can be inferred from the properties of solid FePt alloy by matching Fe-Pt melting relations (Buckley and Hume-Rothery, 1959;Fredriksson, 2004;Isaac and Tammann, 1907). We are aware of two previous thermodynamic models for the thermodynamic mixing properties of molten FePt alloy, those of Fredriksson and Sundman (2001) and Odusote (2008), but each has some unsatisfactory features. The Odusote (2008) model is, unfortunately, calibrated only from data on FePt solid at 1123 K and therefore is not necessarily applicable to liquid solutions.…”

“…We are aware of two previous thermodynamic models for the thermodynamic mixing properties of molten FePt alloy, those of Fredriksson and Sundman (2001) and Odusote (2008), but each has some unsatisfactory features. The Odusote (2008) model is, unfortunately, calibrated only from data on FePt solid at 1123 K and therefore is not necessarily applicable to liquid solutions. Fredriksson and Sundman (2001) calibrated a Redlich-Kister model based on both the Knudsen cell and melting-loop data.…”