Y. Jirásková

Structure and composition of expanded austenite produced by nitrogen plasma immersion ion implantation of stainless steels X6CrNiTi1810 and X2CrNiMoN2253

Abstract The structure and phase composition of the modified surface of two different stainless steels (austenitic steel X6CrNiTi1810 and austenitic–ferritic steel X2CrNiMoN2253) after 3 h plasma immersion ion implantation of nitrogen at 400°C were compared using XRD, SEM, TEM and Mossbauer spectroscopy. Both steels show a surface layer with very similar composition. The major phase found is expanded austenite. Very fine precipitates in the near surface region are most likely decomposition products (ferrite/martensite and CrN) of the metastable expanded austenite. The stability of the expanded austenite in the austenitic–ferritic steel is lower and the amount of decomposition products is higher under the same treatment conditions.

Defect and atomic ordering studies in highly deformed and disordered Fe72Al28 alloy

Abstract The results of positron annihilation and Mossbauer spectroscopies in Fe 72 Al 28 alloy with different structural morphology obtained by severe deformation and by quenching from a high temperature are presented. The changes in atomic ordering and in defect arrangements after recovery and ordering annealing in both highly deformed and highly disordered samples are also pursued and discussed. It is shown that the dominant component of 184 ps in the positron lifetime spectrum of a highly disordered sample corresponds to the annihilation in vacancies which prefer to occupy that sublattice in D0 3 superstructure containing both aluminium and iron atoms. Important changes in vacancy concentration take place only when an annealing above D0 3 →B2 (823 K) is performed. Temperature treatment below this phase transformation temperature is characterized above all by changes in the density of dislocations.

AFM and Mössbauer spectrometry investigation of the nanocrystallization process in Fe–Mo–Cu–B rapidly quenched alloy

In this paper, the effect of heat treatment on the development of nanocrystallites in rapidly quenched Fe79Mo8Cu1B12 alloy is investigated. The surface morphology is examined using non-contact mode atomic force microscopy (AFM). The results are compared with those obtained by transmission Mossbauer spectroscopy (TMS), conversion electron Mossbauer spectrometry (CEMS) and x-ray diffraction (XRD). It was found that the sample is not fully amorphous even in the as-quenched state. Minor amounts of bcc-Fe grains were detected on the wheel side of the ribbon-shaped samples while no indications of the crystalline phase were observed in the bulk. The crystallization onset is observed after annealing at 410 ◦ C, when bcc-Fe nanograins are quite well developed. More intense crystallization is evidenced after annealing at higher temperatures, when the content of the crystalline phase increases progressively. The second crystallization, not discussed in the present paper, is characterized by the occurrence of additional crystalline phases, and appears after annealing at 650 ◦ C. We suggest a crystallization model assuming no drastic change in the size of the primarily formed bcc-Fe nanograins with temperature as proved by XRD. The increase in annealing temperature induces the formation of a higher number of crystalline particles, which form large irregular agglomerates (80- 130 nm in height), in accordance with the AFM data. (Some figures in this article are in colour only in the electronic version)

Thermal Stability of Stainless Steel Surfaces Nitrided by Plasma Immersion Ion Implantation

The thermal stability and the magnetic nature of metastable nitrided surface layers produced by plasma immersion ion implantation at 300°C on an austenitic X6CrNiTil810 (f.c.c.) and a ferritic X10CrA118 (b.c.c.) stainless steels were examined. The surface phase analysis was performed by the Conversion Electron Mossbauer Spectroscopy (CEMS) and the results were correlated with X-ray diffraction and microhardness measurements. The dominant phase in the as-nitrided surfaces of both steels was found to be expanded austenite (S-phase). The first structure changes of phase composition of the surface of the ferritic X10CrA118 steel were detected after an annealing at 200 °C while in the case of the austenitic X6CrNiTi1810 steel at 250°C. The lower stability of the ferritic steel is ascribed to higher diffusion of nitrogen atoms in b.c.c. structure and to a lack of other austenite stabilising elements besides nitrogen.

Iron-based granules in body of bumblebees

The paper deals with the presence of iron-based granules in body parts of bumblebees. Two groups of bumblebees were collected from their natural habitat, industrial landscape, and from a breeding station. Detection of the magnetic particles was performed by a vibratory magnetometer and their morphology and elemental composition was analysed by scanning electron microscopy with EDX microanalysis. By means of the EDX spectra, wild bumblebees were found to have many magnetic and non-magnetic particles on their body, containing Fe, O, Al, Si, Bi, Mg, K, and Ni, likely having origin in the industrial pollution of the environment. In the case of bred bumblebees the presence of iron-rich granules, which occurred more abundantly in subsurface tissues on the head and wings, was observed. Phase analysis based on X-ray diffraction shows that iron-based granules contain magnetite and wuestite and Mössbauer spectroscopy admits a superparamagnetic form of these minerals. Magnetoreception, i.e. the sensory function of these granules, is discussed within the paper.

Fe3Si surface coating on SiFe steel

Abstract Fe3Si layers were prepared using chemical vapor deposition of Si on the surface of GO steel and its subsequent heat treatment. The changes in the structure and phase composition after different heat treatment conditions have been analyzed. The coating is characterized by high hardness, good corrosion resistance, high electrical resistivity, and the spin texture which differs from the steel substrate.

Evolution of structural changes in nanocrystalline alloys with temperature

Structural features of the NANOPERM-type alloys Fe91 − xMo8Cu1Bx with x = 12, 15, and 17 have been investigated by Mössbauer spectroscopy. The room-temperature Mössbauer spectra of the as-quenched alloys are characteristic of disordered structural arrangement, but traces of bcc-Fe(Mo) as well as a FeMo2B2 phase have been revealed by X-ray diffraction in all the samples. These results have been confirmed by conversion-electron Mössbauer spectroscopy. The differences between the opposite sides of the ribbon-shaped samples have been shown to stem from structural distinctions. From the point of view of hyperfine interactions, the x = 12 sample exhibits paramagnetic behavior. With increasing x, a contribution from ferromagnetic regions appears gradually, thus leading to an increase in the magnetic ordering temperature in the as-quenched state. Partially crystallized samples have been prepared by controlled annealing of the original precursors for one hour at temperatures ranging from 330 to 650°C in a vacuum. The temperature of the onset of crystallization has been determined to be of 430, 450, and 470°C for x = 12, 15, and 17, respectively. During the first step of crystallization, bcc-Fe(Mo) nanosized grains are formed. Surface features of the samples investigated have also been characterized by using atomic force microscopy.

Influence of Magnetostriction on Cross-Sectional Magnetic Properties in Bilayered Ribbons

This paper is devoted to the surface and cross-sectional microstructural and magneto-optical investigations of the bilayered (BL) CoFeCrSiB-based ribbon of dissimilar Co/Fe content in the layers and to the comparison with the CoSiB/FeSiB ribbon, both prepared by planar flow casting. It is shown that the interface properties are strongly influenced by chemical compositions of the layers and mainly by the magnetostriction coefficients. This results in different magnetic domain patterns in the layers and across the interlayer and their changes with applied magnetic field intensity. While in the BL sample of a similar layer composition, the magnetic domains concentrate inside the layers, at the sample with completely different layer composition, the domains cross the interlayer.

Influence of Annealing Temperature and Atmosphere on Surface Microstructure and Magnetism in FINEMET-Type FeSiNbCuB Ribbons

Paper is primarily devoted to the surface investigations of the FINEMET-type Fe73.5Si13.5Nb3Cu1B9 ribbons. As-quenched (AQ) samples were subsequently annealed at different temperatures from 733 K to 923 K in vacuum and hydrogen in order to follow the influence of both treatment parameters on microstructure and magnetic properties. Two-phase magneto-optical (MO) hysteresis loops observed at AQ ribbons correspond to an amorphous structure composed of clusters of the size in units of nm (calculated from XRD). The annealing temperatures are responsible for the origin of the α-Fe and/or α-Fe(Si) nanocrystals of various size formed at the surface and consequently penetrating into the ribbon volume while the atmospheres influence surface oxidation. An interesting occurrence of the asymmetric reversal of longitudinal magnetization, clearly observed after annealing at 733 K and 743 K, is discussed from the viewpoint of quadratic magneto-optical effects. The loop asymmetry decreases with increasing annealing temperature and disappears at 923 K.

Surface microstructure changes in the mechanically strained Fe-Al based intermetallics

Abstract Surface microstructural changes in Fe–28Al and Fe–28Al–5Cr–0.5Nb–0.2C (in at%) alloys during compressive creep tests at 873 and 923 K are investigated by optical and scanning electron microscopy. The differences in microstructure between the pure and alloyed Fe–Al intermetallic alloys are discussed using additional data on vacancy and dislocation formation derived from positron annihilation lifetime measurements and the hyperfine magnetic characteristics obtained from Mossbauer phase analysis. It has been found that an addition of Cr and Nb increases the thickness of the oxide Al 2 O 3 surface layer formed at higher temperatures, influences grain size, defect structure, and rupture life of the specimen. Formation of an Al 2 O 3 oxide layer leads to a reduction of Al content in Fe–Al and to a surface magnetic softening.