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Ordering process in Fe-Al28Cr5 alloys studied by Mössbauer spectroscopy

Hanc-Kuczkowska A., Kansy J., Deniszczyk J.

Nukleonika

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2013

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Vol. 58, No. 1

67-71

EN

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.

2

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

Kansy J., Hanc-Kuczkowska A., Giebel D.

Nukleonika

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2013

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Vol. 58, No. 1

221-224

EN

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 centigrade. 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 centigrade generates an additional amount of defects may be ascribed to the formation of FeAl2 phase in the FeAl matrix.

3

The influence of heat treatment on point defect concentration in Fe-Al and Fe-Al-Cr systems

Kansy J., Hanc A., Giebel D.

Nukleonika

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2010

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Vol. 55, No. 1

21-25

EN

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 greater-than or equal to 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.

4

Ordering process of Fe28Al and Fe28Al5Cr alloys

Pająk L., Kansy J., Hanc A., Dercz G., Jabłońska M.

Archives of Materials Science and Engineering

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2008

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Vol. 30, nr 2

81-84

EN

Purpose: The comparison of ordering process in Fe28Al and Fe28Al5Cr alloys annealed for 8, 16 and 48 hours at 1000°C was performed. The composition of studied alloys is closed to one of Fe3Al phase. Design/methodology/approach: The studied alloys were melted in induction furnace under vacuum. Next the alloys were gravitatively casted into cylindrical graphite moulds. The alloy samples were annealed at 1000°C for 8, 16 and 48 hours. The ordering process was analyzed by X-ray diffraction,Mössbauerspectroscopy and positron annihilation methods. Findings: Different behaviour of Fe28Al and Fe28Al5Cr alloys during annealing for 8, 16 and 48 hours at 1000°C was found. The Fe3Al phase of DO3 type structure was stated only in the sample of Fe28Al alloy annealed for 48 hours. The FeAl phase appeared to be the main phase in the other samples. Research limitations/implications: The applied investigation methods appeared to be useful in the studies of long range ordering process. Application of Rietveld refinement method enabled the verification of qualitative phase analysis and the determination of lattice constant parameters. Relatively great grain sizes in studied samples made the exact determination of long range ordering parameters difficult. Practical implications: The information on the phase transformation during the heat treatment of alloys, including long range ordering, are of prime importance for technological processing. The structures with long range ordering significantly affect the properties of alloys with intermetallic phases. Originality/value: Good correlation between the results of X-ray diffraction, Mossbauer spectroscopy and positron annihilation methods were obtained. Addition of chromium made the long range ordering process slower.

5

Mössbauer and structure studies on metallic powders from Fe-Al-X (X = Ni, Cu, Cr)

Hanc A., Dercz G., Pająk L., Frąckowiak J., Kansy J.

Archives of Materials Science and Engineering

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2008

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Vol. 31, nr 1

20-24

EN

Purpose: The Fe-Al-X and Fe-Al-Ni-X metallic powders produced by the self-decomposition process and then intensive grinding in an electro-magneto-mechanical mill with X = Fe, Ni, Cu, Cr additions was determined by applying the X-ray powder diffraction (XRD) and Mössbauer spectroscopy. Design/methodology/approach: The X-ray diffraction and Mössbauer spectroscopy were applied to identify the phase composition of the studied materials. Ordering process was analyzed by X-ray diffraction methods and Mössbauer spectroscopy. Findings: The effects of solute addition (X = Fe, Ni, Cu, Cr) in the investigated Fe-Al and Fe-Al-Ni metallic powders are presented and discussed. Good correlation between the results of X-ray diffraction and Mössbauer spectroscopy studies was obtained. Research limitations/implications: The Mössbauer spectroscopy appeared to be usefull in the identification of phase composition in studied materials. Application of Rietveld refinement method enabled the verification of this composition. Practical implications: The information on the phase transformation during the self-decomposition process and then intensive grinding in an electro-magneto-mechanical mill with additions are of prime importance for technological processing. Originality/value: All the phases that exist in the milled material contain high concentrations of aluminium (over 50 at. %) and have the ordered B2 structure. Alloying additions (Ni, Fe, Cu, Cr) and intensive high-energy grinding in the EMM mill modified the chemical and phase composition of the Fe-Al-X and Fe-Al-Ni-X samples.