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: H= 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 τ₀ = 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.