Crystal chemistry and thermodynamic modelling of the Al13(Fe,TM)4 solid solutions (TM = Co, Cr, Ni, Pt)

Abstract

The crystal chemistry of the Al13(Fe,TM)4 (TM = Co, Cr, Ni, Pt) solid solutions has been investigated by combining formation enthalpy measurements by differential scanning calorimetry (DSC), density functional theory (DFT) calculations and thermodynamic modelling. The formation enthalpies of seven alloys of the Al13(Fe,Co)4 solid solution were measured by DSC at 920 K, allowing the determination of the mixing enthalpy of the solution. These measurements are presented here for the first time and highlight the ideal nature of this solid solution. In addition, the mixing enthalpy of the Al13(Fe,TM)4 solid solutions (TM = Co, Cr, Ni, Pt) was determined by DFT at 0 K. These calculated and measured data (in the case of the Al13(Fe,Co)4 solid solution) were used to perform thermodynamic modelling of the solid solutions and better understand their thermodynamic stability. In addition, our modelling was used to calculate the TM occupancy on the Fe sites of the Al13(Fe,TM)4 solid solution structure at different temperatures. These data were used to quantify the chemical ordering of the solid solutions as a function of temperature. While these solid solutions show significant chemical ordering at low temperatures, only the Al13(Fe,Pt)4 solution remains highly ordered at high temperatures. These data are presented for the first time in this paper and have allowed us to design an optimal sublattice (SL) model for the Al13Fe4 solid solutions.