Point defects in the B2-phase region of the Fe-Al system studied by Mössbauer spectroscopy and X-ray diffraction

In this work Mössbauer spectroscopy and X-ray powder diffraction was used to study of point defects formation in intermetallic phases of the B2 structure of the Fe-Al system as a function of Al concentration. The results are compared with the concentrations of point defects determined from positron annihilation data. The values of the 57Fe isomer shift and quadrupole splitting for the components describing the point defects in the local environment of a Mössbauer nuclide are presented. The concentration of the Fe vacancies and Fe atoms substituting Al (i.e. anti-site atom, Fe-AS) are determined. The results show that an increase in Al content causes an increase in vacancy and Fe-AS concentrations

Defect structure of Fe-Al and Fe-Al-X (X=Ni; Cu; Cr) metallic powders obtained by the self-decomposition

In the present work, the Fe-Al-X (X = Cu; Ni; Cr) metallic powders produced by the self-decomposition method of the Fe-Al doped alloys were examined by Mössbauer spectroscopy. The concentration of the Fe vacancies and the Fe atoms substituting Al (Fe-AS) was determined from the intensities of the sub-spectra in the Mössbauer analysis connected with distinct Fe environments. The results have shown that nickel and copper cause an increase of vacancy concentrations in comparison with the values found for Fe-Al metallic powders, whereas chromium decreases vacancy concentrations causing a significant increase of anti-site atoms Fe-AS concentration

Ordering process in Fe-Al28Cr5 alloys studied by Mossbauer spectroscopy

In the paper, studies of ternary Fe-Al28Cr5 alloys directed to characterization of mechanisms of the formation of ordered intermetallic phases influencing the possibilities of their practical application are shown. Also, a role of chromium as a modifier in kinetics of the formation of ordered phases is determined. Among the research method used, Mössbauer spectroscopy for the determination of hyperfine structure parameters was adopted. These parameters, sensitive to changes in spin and charge electron densities in the nearest neighbourhood of a Mössbauer isotope nucleus, caused by specific configurations of atoms, are directly connected with the degree of ordering of a compound. Spectral analysis has been carried out using the authors’ software developed based on a theoretical model relating the shape of a Mössbauer spectrum to the sample microstructure. It has been shown that Mössbauer spectroscopy enables quantitative evaluation of the degree of ordering of phases occurring in samples characterized by large graining, in the case of which it is not possible to determine the long-range order parameter by X-ray diffraction

The Influence of Heat Treatement on Point Defect Concetration in Fe-Al and Fe-Al-Cr systems

FeAl alloys of nominal Al content 28, 38 and 45 at.% and Fe28Al5Cr with minor alloying elements added to improve their application properties are studied by positron annihilation lifetime analysis. The lifetime spectra of samples FeXAl with X ≥ 38 (both quenched and cooled with furnace) are described by a single lifetime component related to the saturated positron trapping by quenched-in vacancies of concentration much higher than 100 ppm. A very strong dependence of retained vacancy concentration on the rate of cooling is shown for Fe28Al and Fe28Al5Cr alloys. After quenching, the concentration is of the order of 10–4 whereas in samples slowly cooled it is reduced to 10–5. The chromium addition to Fe28Al5Cr dismisses the vacancies concentration in comparison to the concentration in Fe28Al after the same heat treatment

Change of the defect structure in feal alloy as a result of its aging at ambient temperature

Positron annihilation lifetime spectroscopy (PALS) was used to study the defect structure of stoichiometric FeAl samples after their slow cooling or quenching from the temperatures of 1000 and 540°C. The high value of positron lifetime in the quenched-in defects suggests that they are mainly of di-vacancy type. After long storage at ambient temperature, the concentration of defects in the samples strongly decreases and mono-vacancies predominate. Annealing at 540°C generates an additional amount of defects may be ascribed to the formation of FeAl2 phase in the FeAl matrix

Structural analysis of austempered ductile iron obtained by Mossbauer spectroscopy

Purpose: The composition of metallic matrix in ductile iron as-cast and after austempering at temperatures of 280, 330 and 380oC (ADI) was examined. Design/methodology/approach: The study presents the results of these examinations obtained by Mössbauer spectroscopy. Findings: Using calculated values of the parameters of hyperfine interactions (isomeric shift IS, quadrupole splitting QS and hyperfine effective magnetic field H), isolated by deconvolution of the experimental spectrum, the constituents of the metallic matrix were identified in terms of both quantity and quality. Research limitations/implications: The measured values as well as the data compiled in literature indicate that component Z1 (the, so called, Zeeman spectrum sextet) is related with 57Fe atoms present in the structure of ferrite α1 (I stage of γo→α1 + st transformation), component Z2 is typical of ferrite α2 (II stage of st→α2 + carbides transformation), while component Z3 has its origin in 57Fe atoms seated in the structure of carbides (Fe3C, Fe2C or Fe2,4C). Practical implications: analysis of the parameters of hyperfine interactions describing the non-magnetic components (L and Q) it has been proved that they are typical of austenite. Originality/value: In the case of ADI, the determination of the composition of metallic matrix by Mössbauer spectroscopy is much more precise (the limit is the resolution power), because the experimental spectrum describes an overall volume of the examined specimen, and not only its surfaces, as does the traditional quantitative metallography

Mossbauer temperature study of the Fe80Nb6B14 amorphous alloy

Temperature studies in the range 300−800 K of amorphous Fe80Nb6B14 alloy using Mössbauer spectroscopy are presented. It is shown that at a temperature close to 700 K iron clusters with non-collinear magnetic structure are formed. The observed magnetic permeability enhancement effect in the annealed at elevated temperatures alloy, which takes place in amorphous phase, is due to the strong ferromagnetic exchange between Fe clusters via the amorphous matrix and reduction of internal stresses

Structures and phases transitions of the alloys on the bases of Fe-Al intermetallic phases

Purpose: The paper presents study the results of investigations the influence of the chemical composition and thermal treatment on the microstructures and phases transitions of intermetallics from the Fe-Al system. Design/methodology/approach: Investigated alloys with 28, 38 and 42% at. Al were melted in vacuum induction furnace. Next stage of the preparing was gravity casting for cylindrical graphite moulds in the form of bars. The structure was analyzed after annealing at 1000°C for 24 and 48 h. The phases transitions were carried out by using a DTA method on the Setsys made by Setaram. Findings: The microstructure observations indicated the presence of phases and precipitates in all investigated alloys. In all of the investigated alloys, precipitation of phases present in the structure as a result of the introduction of alloying additions, such as Zr, Cr, Mo and C, is visible. transformations connected with both disorder-order transitions and the initial temperature at which a liquid phase occurred in the alloys had taken place during heating. Research limitations/implications: The investigations showed that the very important in production of intermetallics from Fe-Al system is casting and thermal treatment process. The important is knowledge about the phases transformations in this alloys which taking the informations about the melting points, order – disorder transition and their correlations with structure and in consequence the mechanical properties. Practical implications: The formation of phases and precipitates during the heat treatment in these alloys have not been known until now. This structures aspects are significantly affect the properties of intermetallics from the Fe-Al system. In correlation with temperatures of phases transition they could take the most important informations for technological processing. Originality/value: We needed more details about intermetallic from Fe-Al system for their development. This paper are the valid supplement for development knowledge of the iron aluminides

Phase composition of urban soils by X-Ray diffraction and Mössbauer spectroscopy analysis

The m ain purpose of this study was to identify the mineral composition of soil sample taken from the upper layer of topsoil. High absorption of chemical substance is a characteristic for humus-organic layer of topsoil. The source of those substance could be a pollutant emitted to the atmosphere by human activity. The research area includes Upper Silesia region, which is the most industrial region of Poland. In the present study, the phase composition of the top soil separates were analyzed by using X-ray diffraction and Mössbauer spectroscopy. X-ray diffraction analysis revealed the presence of seven mineral phases in the material magnetic separated by lower current (quartz, illite, kaolinite, Fe3+ oxides, hematite, magnetite and pyrite). In case of higher current were identified four phases (quartz, muscovite, kaolinite and K0.94 Na0.06(AlSi3O8)). Mössbauer spectroscopy was used for an extensive analysis of iron-containing phases (pyrrhotite, magnetite, aluminosilicate oxides with Fe3+ and kaolinite/Fe2+ silicate)

Defect Creation in the Root of Single-Crystalline Turbine Blades Made of Ni-Based Superalloy

An analysis of the defects in the vicinity of the selector–root connection plane occurring during the creation of single-crystalline turbine blades made of CMSX-6 Ni-based superalloy was performed. X-ray diffraction topography, scanning electron microscopy, and positron annihilation lifetime spectroscopy were used. Comparing the area of undisturbed axial growth of dendrites to the area of lateral growth concluded that the low-angle boundaries-like (LAB-like) defects were created in the root as a result of unsteady-state lateral growth of some secondary dendrite arms in layers of the root located directly at the selector–root connection plane. Additional macroscopic low-angle boundaries (LABs) with higher misorientation angles were created as a result of concave curvatures of liquidus isotherm in platform-like regions near selector–root connections. Two kinds of vacancy-type defects, mono-vacancies and vacancy clusters, were determined in relation to the LABs and LAB-like defects. Only mono-vacancies appeared in the areas of undisturbed axial growth. Reasons for the creation of macroscopic LABs and LAB-like defects, and their relationships with vacancy-type defects were discussed