Victor V. Tcherdyntsev

Formation of iron-nickel nanocrystalline alloy by mechanical alloying*

Abstract Fe1-xNix alloys were prepared by mechanical alloying of elemental powders in high-energy planetary ball mill in a wide concentration range of components (10 ≤x ≤0). The structure was studied by X-ray diffractometry. It is shown that concentration ranges of single-phase solid solution of MA samples are markedly wider than that of thermodynamically stable alloys. Character of X-ray peaks indicates that there is a high density of crystalline lattice defects including stacking faults. Block sizes, calculated without considering stacking faults presence, was found to be 8 – 15 nm, and calculated with considering of stacking faults 30 – 80 nm. The results were discussed on the basis of thermodynamic model of MA.

Phase transformations in Fe–Ni system at mechanical alloying and consequent annealing of elemental powder mixtures

Fe 100-x Ni x alloys (10<x<90at%) were prepared by mechanical alloying (MA) of elemental powders in a high-energy planetary ball mill and studied by X-ray diffractometry and Mossbauer spectroscopy. It is shown that the concentration ranges of single-phase solid solutions of MA samples extend significantly as compared with those obtained by conventional techniques. In our case, the BCC phase exists in the range from 0 to 20 at% Ni and FCC phase from 30 to 100at% Ni. Block size was 10-15 nm. Consequent annealing of MA samples resulted in further extension of FCC single-phase concentration range to the relatively low Ni content (20at%). This was caused by considerable retardation of austenite-martensite transformation in MA alloys. The FCC alloys with 20-28 at% Ni were found to be non-ferromagnetic at room temperature; only the paramagnetic component was observed in the corresponding Mossbauer spectra. However, the treatments of low-nickel austenite alloys like cooling in liquid nitrogen or mechanical deformation provoked austenite-martensite transformation and led to the rise of ferromagnetic properties.

Mechanically alloyed low-nickel austenite Fe-Ni phase: evidence of single-phase paramagnetic state

Abstract Fe 100− x Ni x alloys were obtained by a mechanical alloying technique (MA) from elemental metals. The alloys consist of: single body-centered cubic phase (bcc) at nickel concentrations ⩽22 at.%, single face-centered cubic phase (fcc) – at x >28 at.% and two of these phases – at 22⩽ x ⩽28 at.%. Annealing results in formation of single fcc phase structure in the samples with x ⩾22 at.%. According to the Mossbauer spectrometry data these annealed alloys with 22–28 at.% Ni were not ferromagnetic at room temperature. Cooling austenitic samples in liquid nitrogen as well as mechanical deformation stimulated austenite–martensite transformation accompanied by the appearance of ferromagnetism.

Quasicrystalline phase formation by heating a mechanically alloyed Al65Cu23Fe12 powder mixture

Abstract Elemental powder mixtures of a Al65Cu23Fe12composition milled for two and four hours in a planetary ball mill were used to form quasicrystals. Annealing of the as-milled samples led to complex solid-state transformations. During the heat-up a sequence of solid-state reactions takes place in the as-milled powder. These reactions were studied both by differential scanning calorimetry and X-ray diffraction methods. An analysis of the phase formation shows the effect of the difference in the thermodynamic driving forces, such as the positive heats of mixing for the Cu–Fe system and the negative ones for the Al–Fe and Al–Cu systems, on the phase transformation consequence.

Fe–Mn mechanically alloyed powders characterised by local probes

Abstract High-energy ball milling of Fe–Mn elemental powder mixtures has been carried out for Mn atomic concentrations in the range 10–90%. X-ray diffraction (XRD), Mossbauer spectroscopy (MS) and perturbed angular correlations (PAC) have been used to investigate the crystalline structure in the milled samples. It is found that ball milling gives rise to concentration ranges of existence of terminal solid solutions more extended than in the equilibrium phase diagram. Particular attention has been paid to the environment of 57Fe (MS) and 111In (PAC) probe atoms: 57Fe atoms are a constituent of the system, while 111In atoms have been implanted at 400 keV into pills made from the milled powders. The PAC spectra of milled Fe show the ferromagnetic α-phase with a high fraction of a single vacancy next to the probe. Accordingly, the Mossbauer spectrum is a sextet with the characteristic splitting of α-Fe and a broadening which indicates a certain degree of atomic structure disorder. With an amount of Mn up to 15% PAC probes with one and two Mn next neighbours are identified by their smaller magnetic hyperfine field, corresponding to two distinct magnetic components in the Mossbauer spectra. At 20 and 30% of Mn the PAC magnetic signal of the a-phase disappears in favour of a distorted cubic apparently non-magnetic signal. From 40 to 70% of Mn a broad distribution of hyperfine magnetic fields is observed by PAC. Mossbauer spectra in the 20–70% of Mn range can be fitted with an unresolved low field magnetic sextet. Finally, the PAC spectra at 80 and 90% are quite similar to the one which is obtained after milling pure Mn, while the corresponding Mossbauer data can be roughly approximated to those of the α-Mn(Fe) solid solution.

The Evolution of Crystalline Precursors During the Formation of Al-Cu-Fe Quasicrystalline Intermetallics in Mechanically Alloyed Powders

Mechanical alloying (MA) of elemental powders in the Al-Cu-Fe system was carried out using two types of laboratory equipment (vibratory and planetary mills) to produce single phase, stable icosahedral quasicrystals. The sequence and nature of the solid state reactions during milling and subsequent annealing were studied in detail using qualitative and quantitative laboratory X-ray analysis and differential scanning calorimetry. The effect of milling parameters (energy intensity, temperature, milling time) on the course of transformations was elucidated. Specific reactions were identified which took place during annealing in different temperature ranges. The evolution of crystalline precursors of the quasicrystalline phase was established.

Thermal Stability of Ball Milled Al / Al-Cu-Fe Quasicrystal Metal Matrix Composites

Al65Cu23Fe12 quasicrystalline (QC) powder was used as a filling material for aluminium matrix composites. Quasicrystalline phase was prepared by mechanical alloying of elemental powders and subsequent annealing. To produce the composites, QC was milled together with pure aluminium in the ratios of Al – 20 mass. % QC and Al – 10 mass. % QC for various milling times. It was shown that the QC phase in these composites remains untransformed up to the temperatures of 350 – 400 0 C. Heating up to higher temperatures initiates the reaction between QC and Al yielding ternary crystalline Al7Cu2Fe phase; an increase in the milling time raises the reaction rate.

Structure transformation and elements redistribution at heating of Fe73.5Nb3Cu1Si13.5B9 amorphous alloy

Abstract The evolution of structure and elements redistribution in rapidly quenched Finemet-type Fe 73.5 Nb 3 Cu 1 Si 13.5 B 9 alloy at heat treatments were investigated by differential scanning calorimetry (DSC), thermomagnetic analysis, Mossbauer spectroscopy (MS), and X-ray diffraction methods. The effect of the structural relaxation on the Curie point of amorphous phase ( T c A ) has been studied using DSC and magnetic measurements. Using both heating and isothermal DSC scanning modes, we found that T c A value increases with the treatment temperature, as well as with the increase of the treatment duration. MS analysis shows that the pre-crystallization process results in the changes of fine structure of amorphous phase spectra, which are caused by the components redistribution during the relaxation process, resulting in the Cu-rich clusters formation and subsequence appearance of nanocrystals.

Effect of Deformation by High Pressure Torsion on the Phase Composition and Microhardness of Mechanically Alloyed and Rapidly Quenched Al–Fe Alloys

Aluminium-based Al-Fe alloys with Fe content of 2, 5, 8, 10 and 11 wt. % w ere prepared by two techniques: rapid quenching (RQ) from the melt at the rate of 10 K/s and mechanical alloying (MA) of pure elements in a high-energy planetary ball m il . The structure of the alloys was examined using X-ray diffraction and Mössbauer spectroscopy. It is s hown that the crystalline structure refinement and the phase composition of the alloys essentia lly depend on the techniques used for the sample preparation. Phase transformations by high pressure tor ion (HPT) of RQ and MA alloys were studied. The highest supersaturation of Fe in the al uminium-based solid solution can be reached using two subsequent techniques of alloy treatment: RQ and HPT. Microhardness measurements of HPT alloys show the significant stricture hete rogeneity of specimens, the dependence of the microhardness on the radius of the pills was found. Phase composition and microhardness at heating were investigated. At the initial step of heating (120–150°C), an increase of microhardness was observed, whereas further heating results in de crease of the microhardness value.

Mössbauer and X-Ray Diffraction Study of the Phase and Structure Transformations During Annealing of Mechanically Alloyed Al65Cu23Fe12

A powder mixture of Al65Cu23Fe12 composition milled for four hours in a planetary ball mill was used as a starting material for quasicrystalline structure formation. Phase analysis of as-milled samples shows a mixture of intermetallic phases with preponderance of A2 and D03 structures. Also the presence of residual Al and Fe was detected. Annealing the milled samples gives rise to complex solid-state transformations. Mossbauer spectroscopy shows that the residual Fe amount decreases gradually with annealing temperature and that starting from the temperature of 440°C only an asymmetrical doublet is present. The formation of a structure almost totally icosahedral was observed in the XRD patterns of samples annealed at 600°C and above. The qualitative differences in the Mossbauer spectra observed for these samples may be associated with the presence of “approximant” phases to quasicrystalline structure.