EFFECT OF HEAT TREATMENT ON THE STRUCTURAL AND MAGNETIC PROPERTIES OF THE SYSTEM Fe56.25Al43.75 PREPARED BY MECHANICAL ALLOYING

Abstract

The study of the Fe56.25Al43.75 system prepared by Mechanical Alloying (MA), using elementary powders, at milling times of 12, 24, 48, 72, and 96 hours, named MA0 samples, showed that the alloy is consolidated at 48 hours. Samples that were consolidated at this time were heat treated. This procedure consisted in heating the encapsulated specimens in quartz tubes under inert atmosphere conditions (Ar gas) at 700 ºC for 9 days in a furnace. After this time, the samples were mechanically alloyed for times ranging from 1 to 48 hours. These samples, named MA1, were studied using Mössbauer Spectrometry (MS) and (X-Ray Diffraction) XRD aiming to obtain information on their magnetic and structural properties. XRD results of MA0 samples allow us to prove that they are nanostructured with a single FeAl BCC disordered phase with an approximately constant lattice parameter of 2.900 Å, and crystallite size which decreases with the increase of milling time. For the MA1 samples XRD results show that they exhibit some degree of ordering. The X-ray diffraction spectra allow to identify the FeAl, Fe3Al, FeO and α-Fe phases. All the phases tend to disappear  except the FeAl phase. The MS results of the MA0 samples prove that the FeAl phase is ferromagnetic. An increase of the mean hyperfine field (MHF) was found due the increase of the structural disorder induced by the MA process. From MS of MA1 samples it was found that for times of 0, 1, 4, 8, and 12 hours, there is a disordered tendency and it was necessary to add a doublet, associated to paramagnetic sites of the FeAl phase, in order to obtain a better fit. Likewise for milling times of 24 and 48 hours, the doublet was changed by another which is associated with the FeO phase (wüstite), maybe due to an oxidation promoted by a leak in the seal of the jars.