L. Escoda

Characterization of mechanically alloyed nanocrystalline fe(Al): crystallite size and dislocation density

A nanostructured disordered Fe(Al) solid solution was obtained from elemental powders of Fe and Al using a high-energy ball mill. The transformations occurring in the material during milling were studied with the use of X-ray diffraction. In addition lattice microstrain, average crystallite size, dislocation density, and the lattice parameter were determined. Scanning electron microscopy (SEM) was employed to examine the morphology of the samples as a function of milling times. Thermal behaviour of the milled powders was examined by differential scanning calorimetry (DSC). The results, as well as dissimilarity between calorimetric curves of the powders after 2 and 20 h of milling, indicated the formation of a nanostructured Fe(Al) solid solution.

Comparison of Fe-Ni based alloys prepared by ball milling and rapid solidification

Mechanical alloying (MA) and rapid solidification (RS) are two important routes to obtain amorphous alloys. An Fe-Ni based metal-metalloid alloy (Fe50Ni30P14Si6) prepared by these two different processing routes was studied by differential scanning calorimetry, scanning electron microscopy with microanalysis, inductive coupled plasma, X-ray diffraction (XRD) and transmission Mössbauer spectroscopy (TMS). The results were compared with that obtained from other Fe-Ni based alloys of similar compositions.The structural analyses show that the materials obtained by mechanical alloying are not completely disordered after 40 h of milling whereas fully amorphous alloys were obtained by rapid solidification. TMS analyses show that, independent of the composition, after milling for 40 h, about 7% of the Fe remains unreacted.Furthermore, the thermal stability of mechanically alloyed samples is lower than that of the analogous material prepared by rapid solidification. In the MA alloys, a broad exothermic process associated to structural relaxation begins at low temperature. XRD patterns of crystallized alloys indicate that the crystallization products are bcc(Fe,Ni), fcc(Ni,Fe), and (Fe,Ni)-phosphides and -silicides.

Rapid degradation of azo-dye using Mn–Al powders produced by ball-milling

This study was conducted on the reduction reaction of the azo dye Reactive Black 5 by means of the Mn85Al15 particles prepared by melt-spinning and ball-milling processes. The morphology, the surface elementary composition and the phase structure of the powders were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The degradation efficiency of the ball milled powder was measured by using an ultraviolet-visible absorption spectrophotometer and the collected powder was analyzed by means of Fourier transform infrared spectroscopy technique to characterize the functional groups in the extract. The degradation of Reactive Black 5 and the analysis of the aromatic by-products were investigated by high performance liquid chromatography coupled with tandem mass spectrometry. The ball-milled powder shows higher degradation efficiency and the Reactive Black 5 solution was completely decolorized after 30 min. The degradation kinetics and the formation by-products depend on the pH and temperature of the solution. The analyses of the extracted product confirmed the cleavage of the (–NN–) bonds. Our findings are expected to pave the way for a new opportunity with regard to the functional applications of nanostructured metallic particles.

Magnetic Field and Annealing Influence on the Martensitic Transition in Ni45.8Mn42.6In11.6 Shape Memory Alloy Ribbons

We report the effect of shorttime vacuum annealing, during 10 minutes at 923 K, 973 K, 1023 K and 1073 K, on magnetostructural properties of as-quenched ribbons of Ni45.5Mn43In11.5 Heusler alloy. The martensitic transformation is strongly sensitive to annealing treatments. The martensitic phase starting temperature is significantly shifted from 239 K towards higher temperatures around 370 K. It suffers a break down in two peaks when a field equal or higher than 500 Oe is applied to the as-quenched sample. This effect is not detected in the transformation of annealed ribbons but its signature can be observed at low temperature. Moreover, under high magnetic field up to 30 kOe temperatures associated with both martensitic and reverse transitions do not change for annealed samples, meanwhile the magnetization difference between austenite and martensite increases with the field. Nevertheless, it almost remains unchanged in the as-quenched ribbon.

Ferromagnetic shape memory alloys: structural and thermal properties

The most extensively studied Heusler alloys are those based on the Ni-Mn-Ga system. However, to overcome the high cost of Gallium and the usually low martensitic transformation temperature, the search for Ga-free alloys has been recently attempted, particularly, by introducing In, Sn or Sb. In this work, two alloys (Mn50Ni35.5In14.5 and Ni50Mn35In15) have been obtained by melt spinning. We outline their structural and thermal behaviour. Mn50Ni35.5In14.5 alloy has the transformation above room temperature whereas Ni50Mn35In15 does not have this transformation in the temperature range here analyzed.

Recovery, grain growth and recrystallization of mechanically alloyed FeAl alloy

A nanostructured disordered Fe(Al) solid solution was obtained by mechanical alloying (MA) for 20 h in a high-energy planetary ball-mill. The phase transformations and structural changes occurring in the studied material during MA and during subsequent heat treatments were investigated by X-ray diffraction. The recovery and the recrystallization of this compound are occurred due to the ordered nature of the grain boundaries after annealing at temperature ranging from 250 and 650 oC. The evolution of the thermal behaviour of the milled and heated powders was examined by differential scanning and calorimetry. We have shown that the occurrence of Fe2Al5 Fe4Al13and Fe3Al nanocrystalline phases at elevated temperature.

Glass-coated Cu-Mn-Ga microwires produced by Taylor-Ulitovsky technique

Glass-coated Cu-Mn-Ga microwires were fabricated by Taylor-Ulitovsky technique. By means of energy dispersive spectroscopy microanalysis, an average alloy composition of Cu56Ga28Mn16 was determined. The temperature dependence of magnetization measured at a low magnetic field showed the coexistence of two ferromagnetic phases. The Curie temperature of one phase is 125 K and above room temperature for the other one. X-ray diffraction at room temperature and at 100 K reflects the presence of the same three crystalline phases corresponding to the cubic B2 Cu-Mn-Ga structure as a main phase and the minor phases of fcc Cu rich solid solution with Mn and Ga and the monoclinic CuO.

Structural and magnetic behavior of Fe(Nb,Zr) rich alloys produced by mechanical alloying

Fe80Nb7B12Cu1 and Fe80(NiZr)7B12Cu1, nanocrystalline alloys were synthesized in two high-energy ball milling devices (planetary, shaker). The microstructure, thermal and magnetic properties of the milled powders were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and vibrating sample magnetometry (VSM); respectively. Milling device influences the microstructure and properties of final products. The results suggest more energetic milling in shaker mill. The main phase is always bcc Fe rich solid solution. Nevertheless, in Fe80Nb7B12Cu1 alloy minor Nb(B) phase is found after shaker milling and in Fe80(NiZr)7B12Cu1 alloy a low crystalline size Zr rich phase after planetary milling. Crystalline grain size ranges between 9.5 and 15.1 nm; lower values correspond to alloys with a second minor phase. Coercivity values ranges between 28.6 and 36.9 Oe.

Martensitic Transformation in Mn-Ni-Sn Alloys

In this work, we analyze two Mn50Ni50-xSnx alloys with Sn content i.e., x = 5 and 7.5 respectively. These alloys are produced as ribbon-shape by melt spinning. Their structural transformation is checked by calorimetry. Martensitic transformation temperatures of these alloys strongly depend on the composition. From X-ray diffraction analysis, the 14M monoclinic phase is the main phase in both alloys, but in the alloy Sn5 appears a minor tetragonal phase too.