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

Hyperfine interaction parameters in Fe 28Al 72: 57Fe mossbauer spectroscopy and ab initio study

The paper discusses a theoretical model that associates the shape of the Mössbauer spectrum with the con guration of atoms in local surroundings of the Mössbauer nuclide. Using the model we analyse the Mössbauer spectra of Fe72Al28 alloys after various heat treatments. Basing on the model calculations the hyper ne structure parameters describing an e ect of an Al atom in the rst and the second coordination shell of 57Fe atom are evaluated. Using these parameters the values of hyper ne magnetic eld and isomers shift for the atomic con gurations present in stoichiometric Fe3Al are estimated and compared with the results of ab initio calculations

The Mossbauer Spectroscopy Studies of Cementite Precipitations during Continuous Heating from As-Quenched State of High Carbon Cr-Mn-Mo Steel

This work complements the knowledge concerning the kinetics of cementite precipitation during tempering. Investigations were performed on 120MnCrMoV8-6-4-2 steel. The samples of investigated steel were austen- itized at the temperature of 900±C and quenched in oil. Then four of five samples were tempered. Tempering consisted of heating the samples up to chosen temperatures at the heating rate of 0.05±C/s and fast cooling after reaching desired temperature. This work presents the results of investigations performed carried out using the Mossbauer spectroscopy technique and their interpretation concerning cementite nucleation and growth during tempering. The values of hyperfine magnetic field on 57Fe atomic nuclei, determined for the third component of the Mossbauer spectrum as regards to its intensity, indicate that these are the components coming from ferro- magnetic carbides. Big differences in hyperfine magnetic fields coming from Fe atoms existing in the structure of carbides, measured on samples heated up to the temperatures of 80±C and 210±C, in comparison with values for 57Fe atoms precipitated from carbides during heating up to the temperaturę of 350±C and 470±C, allow to state that these are the carbides of different crystal structure. The influence of hardened steel heating temperature on cementite precipitation was determined. The Mossbauer spectroscopy was applied not only for magnetic hyperfine fileld studies, but also to analyze the values of quadrupole splitting and isomeric shift, which resulted in significant conclusions concerning the changes in cementite precipitations morphology, chemical composition and the level of stresses being present in this research

Defect structure of Fe-AL and Fe-Al-Ni metallic powders obtained by the self-decomposition method and intensive grinding in the electro-magneto-mechanical mill

The Fe-Al and Fe-Al-Ni metallic powders produced by the self-decomposition method and then intensive grinding in an electro-magneto-mechanical mill with Fe and Ni additions were examined by X-ray powder diffraction, scanning electron microscopy and Mössbauer spectroscopy. The concentration of vacancies and Fe atoms occupying Al positions (Fe-AS atoms) was determined from the Mössbauer spectra analysis connected with distinct Fe environments. The results show that nickel addition causes both an increase in vacancy concentrations in comparison with values found for Fe-Al metallic powders and a significant increase in the antisite Fe-AS atoms concentration. Intensive highenergy grinding in the electro-magneto-mechanical mill modifies the phase composition of the studied materials and changes the concentration of point defects

Influence of heat treatment on ordering process in Fe72Al28 alloy studied by Mössbauer Spectroscopy

The paper discusses a theoretical model that associates the shape of Mössbauer spectrum with the configuration of atoms in local surroundings of the Mössbauer nuclide. The model has been implemented to a computer program which was used to analyse the Mössbauer spectra of Fe72Al28 alloys after various heat treatments. Basing on the determined configuration of atoms, the long range ordering parameter was estimated

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

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

Ab initio study of the 57 Fe electric field gradient in (FeAl)1-xTx(T=3d element) dilute alloys with B2-type structure

We present an ab initio study of the electric field gradient at Fe nuclei in the series of (FeAl)1¡xTx dilute alloys with B2-type crystal structure. The ternary additions T, of concentration x ¼ 0:06, from the group of 3d-type transition metals (Ti, V, Cr, Mn, Co, Ni, Cu) are considered. Lattice, local valence electron (3d, 4p) and weakly bound 3p core electron contributions to electric field gradient are separated out and discussed in the context of the T-atom site preference and changes of the electronic structure upon alloying. Contrary to earlier reports, we found that for most Fe nuclei the dominant contribution comes from the d-type valence electrons cancelled partially by the 3p and 4p electric field gradients which are both of opposite sign to that of the 3d one. The shielding effect of 3p semicore electrons is found and related to the electric ¯eld gradient contributed by the local valence electrons

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