Experimental Investigation and Thermodynamic Modelling of the Fe-Ni-Ta System

Abstract

The liquidus surface projection and isothermal sections at 1200 and 1000 °C of the Fe-Ni-Ta system were established by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectrometry (EDS) and x-ray diffraction (XRD). Eight primary solidification regions in the liquidus surface projection were experimentally obtained. The similar phase relations were derived in the isothermal sections at 1200 and 1000 °C. Based on the experimental results in the present work and reported in the literature, the Fe-Ni-Ta system was optimized by means of CALPHAD (CALculation of PHAse Diagram) method. Solution phases (liquid, fcc, bcc) were treated as the substitutional solution. The compounds Fe2Ta, Ni2Ta, Ni3Ta and NiTa2 were treated as (Fe,Ni,Ta)m(Fe,Ni,Ta)n by a two-sublattice model, and (Fe,Ni)7Ta6 was modelled as (Fe,Ni,Ta)1(Ta)4(Fe,Ni,Ta)2(Fe,Ni,Ta)6 by a four-sublattice model. A set of self-consistent thermodynamic parameters for the Fe-Ni-Ta system was acquired.