The constitution of the ternary system Fe–Ni–Si

Abstract

The ternary system Fe–Ni–Si was investigated using X-ray diffraction (XRD), metallography (SEM), energy dispersive spectroscopy (SEM/EDS), magnetic susceptibility measurements, and differential thermal analysis (DTA). The existence of the ternary phase τ is corroborated and its crystal structure is confirmed to be isostructural to Cr 3Ni 5Si 2. At 700 °C the homogeneity of this phase extends from 43 to 55 at.% iron at constant 20 at.% Si. Furthermore, for the binary phases NiSi 2, Ni 2Si and Ni 31Si 12 extensive solubilities for iron are found, while the solubility of Fe in NiSi, Ni 3Si 2 or Ni 3Si does not exceed 5 at.%. On the other side of the system, the phases FeSi and Fe 3Si have large solubilities for Ni, while this is rather limited in FeSi 2. The (binary high temperature) phase Fe 5Si 3 is stabilized by Ni at least down to 700 °C. Tie lines exist between τ and solid solutions based on Fe 3Si, Ni 31Si 12 as well as γ (Ni). DTA measurements for the vertical section Fe 2Si–Ni 2Si strongly indicate that Fe 2Si and θNi 2Si form a complete series of solid solutions θ(Fe, Ni) 2Si and are thus isostructural. A critical evaluation of the available crystal structure data for Fe 2Si supports this assumption. Iron rich θ(Fe, Ni) 2Si is a weak ferromagnet. The magnetic moment of ∼1 μB per Fe-atom in θ(Fe, Ni) 2Si is only half of the magnetic moment per Fe-atom measured for τ Fe 5Ni 3Si 2. A reaction scheme accounting for all DTA data of the entire system is established and in combination with observations on the first crystallizing phase(s) the liquidus surface of Fe–Ni–Si is revised.