Structure and anelasticity of Fe-Ge alloys

Several ternary Fe-Ge-C alloys with Ge contents ranging between 3 and 27 at. % have been studied. The structure, anelastic, thermodynamic and kinetic phenomena in Fe-3,-12,-19/21 and-27 Ge have been examined by X-ray diffraction (XRD), heat flow (DSC), vibrating sample magnetometry (VSM), optical-light and scanning electron microscopy, and internal friction (IF) methods. The Fe-3Ge and Fe-12Ge alloys form b.c.c. solid solutions. A Snoek-type internal friction (P1) peak is recorded in the Fe-3Ge alloy with parameters similar to those for α-Fe: Н = 0.86 eV, Δ = 0.015, β = 0.72 and τ0 = 2 × 10^-15 s, showing that Ge atoms have little influence on the diffusivity of carbon in iron. The Fe-12Ge alloy, with a Curie point around 1008 K, has several IF peaks: a broad Snoek-type (P1 and P2), the P3 peak caused by structural changes in as quenched specimens during annealing, and a P4 (Zener) peak at higher temperature (T_m ≈ 773 K at f = 2 Hz, β ≈ 0.7). The Fe-21Ge alloy has bcc or bcc plus hexagonal structure depending on heat treatment. The structure of the Fe3Ge-type alloy (Fe-27Ge) consists mainly of hexagonal phases, i.e. hexagonal ε (D0₁₉), β (B₈₁), and cubic ε’ (L₁₂), and exhibits corresponding magnetic ordering transitions below 873 K which are not well-reflected in the common Fe-Ge phase diagrams. In particular a high stability of the hexagonal ε phase at room temperature is noted. A broad internal friction relaxation peak with Δ = 0.0036, H ≈ 1.8 eV and τ 0 = 2·10^-17 s is found in Fe-27 Ge and is classified as a double Zener peak in the ε and β two-phase mixture.