A critical assessment has been performed to determine the stacking fault energy (SFE) of the austenite phase in high manganese steels using X-ray diffraction (XRD). It was found that the SFE varies substantially with the chosen elastic constants. This strong dependence induces substantial errors in the estimated values of the SFE of the austenite and, thus, the mechanical behavior of Fe-Mn-Al-C steels. The SFE of three different Fe-Mn-Al-C alloys with varying aluminum (Al) content was determined in order to establish the main plastic deformation mechanism. The aim of this work is to establish a more straightforward and reliable methodology to calculate the SFE by XRD. In this effort, it was determined that uncertainty in the elastic constants can generate errors in up to 37% of the SFE. Moreover, in the studied case, for average of elastic constant values, the predominant deformation mechanism is defined, but when considering one set of constants, these can present uncertainty of 2.7 mJ/m² and 4.4 mJ/m² for alloys of 0% Al and 3% Al, respectively. This would lead them to be within the following plastic deformation mechanism, while for 8% Al the uncertainty is negligible.

The aim of this study is to evaluate the applicability of the catalytic activity (CA) of the Fe₃O₄ magnetic system in the adsorption/degradation of methylene blue and esterification. The thermal decomposition method allowed the preparation of Fe₃O₄ nanoparticles. The crystallites of the Fe₃O₄ structural phase present an acicular form confirmed by X-ray diffraction. Transmission electron microscopy results identified the acicular shape and agglomeration of the nanoparticles. Mössbauer spectroscopy showed that the spectrum is composed of five components at room temperature, a hyperfine magnetic field distribution (HMFD), two sextets, a doublet, and a singlet. The presence of the HMFD means that a particle size distribution is present. Fluorescence spectroscopy studied the CA of the nanoparticles with methylene blue and found adsorption/degradation properties of the dye. The catalytic activity of the nanoparticles was evaluated in the esterification reaction by comparing the results in the presence and absence of catalyst for the reaction with isobutanol and octanol, where it is observed that the selectivity for the products MIBP and MNOP is favored in the first three hours of reaction.

We report on the magnetic properties of Fe_x Mn_0.3 Al_0.7-x (0.275 ≤ x ≤ 0.525) disordered alloys, which were investigated by means of Mössbauer spectroscopy, ac magnetic susceptibility and magnetization measurements. Our results are summarized in a magnetic phase diagram which includes both a re-entrant spin glass-ferromagnetic transition line for x > 0.425 and a re-entrant spin glass-antiferromagnetic transition line for x < 0.375.

A theoretical study of a diluted and random-bond Ising model applied to the magnetic properties of the fcc disordered phase of Fe-Mn-Al alloys is reported. Using the variational Bogoliubov inequality approach, it was possible to obtain mean hyperfine field data at room temperature as a function of concentration and these are in agreement with the experimental data previously reported by Pérez Alcázar, Galvão da Silva, and Paduani [Hyperfine Int. 66, 221 (1991)]. © 1996 The American Physical Society.