Nanocrystalline α-Fe Layer Examined by Mössbauer Spectrometry

A few micrometers thick nanocrystalline α-Fe layer with the mean crystallite size $d_{XRD}$=14 nm was deposited in low-pressure microwave plasma, using $Fe(CO)_{5}$ vapour. Its nanocrystalline character was proved on its surface under SEM (surface was formed of deposited nanoparticles) and in its volume using TEM (deposited nanoparticles were stacked up, creating columns). No significant iron oxide phases were observed in the transmission $\text{}^{57}Fe$ Mössbauer spectrum measured at 5 K nor in the surface-sensitive $\text{}^{57}Fe$ conversion electron Mössbauer spectrum measured at 293 K

Atmospheric-pressure microwave torch discharge generated gamma-Fe2O3 nanopowder

Microwave torch discharge ignited in Ar at 1 bar was used for the synthesis of gamma-Fe2O3 nanoparticles. A double-walled nozzle electrode enabled to introduce gases separately: Ar flowed in the central channel, whereas the mixture of H-2/O-2/Fe(CO)(5) was added into the torch discharge through an outer channel. The composition and properties of the synthesized nanopowders were studied by TEM, XRD, Raman and Mossbauer spectroscopies. Basic magnetic measurements at low/high temperatures were performed. The gamma-Fe2O3 phase with the mean crystallite size of 24 nm was identified by XRD in the representative sample. The measured Raman spectrum matched well those reported for gamma-Fe2O3 powders in the literature. In the transmission Mossbauer spectrum measured at 5 K the two sextets characteristic for gamma-Fe2O3 were clearly identified. No change in specific magnetic moment typical of Fe3O4 at its Verwey temperature was observed on the zero field curve, which smoothly increased with temperature. Neither Fe3O4 nor alpha-Fe2O3 were present in the sample. We also report on the high-temperature magnetic properties of the representative sample and describe its structural changes and phase transformations up to 1073 K

Elasticity of phases in Fe–Al–Ti superalloys: Impact of atomic order and anti-phase boundaries

We combine theoretical and experimental tools to study elastic properties of Fe-Al-Ti superalloys. Focusing on samples with chemical composition Fe71Al22Ti7, we use transmission electron microscopy (TEM) to detect their two-phase superalloy nano-structure (consisting of cuboids embedded into a matrix). The chemical composition of both phases, Fe66.2Al23.3Ti10.5 for cuboids and Fe81Al19 (with about 1 or less of Ti) for the matrix, was determined from an Energy-Dispersive X-ray Spectroscopy (EDS) analysis. The phase of cuboids is found to be a rather strongly off-stoichiometric (Fe-rich and Ti-poor) variant of Heusler Fe2TiAl intermetallic compound with the L21 structure. The phase of the matrix is a solid solution of Al atoms in a ferromagnetic body-centered cubic (bcc) Fe. Quantum-mechanical calculations were employed to obtain an insight into elastic properties of the two phases. Three distributions of chemical species were simulated for the phase of cuboids (A2, B2 and L21) in order to determine a sublattice preference of the excess Fe atoms. The lowest formation energy was obtained when the excess Fe atoms form a solid solution with the Ti atoms at the Ti-sublattice within the Heusler L21 phase (L21 variant). Similarly, three configurations of Al atoms in the phase of the matrix with different level of order (A2, B2 and D03) were simulated. The computed formation energy is the lowest when all the 1st and 2nd nearest-neighbor Al-Al pairs are eliminated (the D03 variant). Next, the elastic tensors of all phases were calculated. The maximum Young’s modulus is found to increase with increasing chemical order. Further we simulated an anti-phase boundary (APB) in the L21 phase of cuboids and observed an elastic softening (as another effect of the APB, we also predict a significant increase of the total magnetic moment by 140 when compared with the APB-free material). Finally, to validate these predicted trends, a nano-scale dynamical mechanical analysis (nanoDMA) was used to probe elasticity of phases. Consistent with the prediction, the cuboids were found stiffer. © 2019 by the authors. Licensee MDPI, Basel, Switzerland