Papers by Author: S. Jäger

Abstract: Carbon-containing Fe - Si and Fe - Si - Al alloys were studied with respect to the carbonrelated Snoek-type and Zener relaxation using different mechanical spectroscopy techniques. In all alloys the temperature-dependent profile of the Snoek peak, relative to that in pure iron, is modified on its high-temperature side by the substitutional atoms. At least two components, an Fe - C - Fe (which correspond to C atom jumps (diffusion) in areas where it is surrounded by Fe atoms only) and Fe - C - Me peaks, where Me = Si, Al, can be distinguished in the Snoek-peak profile. In both binary Fe - Al and Fe - Si and ternary Fe - Si - Al alloys, a higher annealing temperature prior to quenching leads to an increase in the Fe - C - Fe and a decrease in the Fe - C - Me component of the Snoek peak. Heating to 1173K and above often lowers the peak height due to thermal vacancies. Low-temperature (<670K) ageing of quenched Fe - Si - Al and Fe – Si specimens reduces both the Fe – C - Fe and Fe – C – Al / Si peaks. Ageing at T > 670 K changes the temperature- as well as the amplitude-dependent parts of internal friction due to a redistribution of carbon between solid solution and dislocations. Both the Snoek-type peak height and the dislocation mobility – as can be concluded from the slope of the amplitude-dependent internal friction – increase, and a new peak appears at temperatures higher than that of the Snoek peak, which probably is a Snoek-Köster peak resulting from the motion of weakly pinned dislocations. A Zener peak appears if the concentration of substitutional atoms is > 6 at. %. The Zener peak relaxation strength is much lower in ternary alloys than in the binary ones probably due to mutual compensation of elastic distortions in presence of Al and Si atoms which are bigger and smaller, respectively, than Fe atoms.

Abstract: 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 (Tm ≈ 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.