The effect of B and Si additions on the structural and magnetic behavior of Fe-Co-Ni alloy prepared by high-energy mechanical milling

Nanocrystalline Fe50Co25Ni15X10 (X = Bamorphous, Bcrystalline, and Si) powdered alloys were prepared by mechanical alloying process. Morphological, microstructural, and structural characterizations of the powders milled several times were investigated by scanning electron microscopy and X-ray diffraction. The final crystallographic state strongly depends on the chemical composition and the grinding time; it can be single-phase or two-phase. The crystallite size reduction down the nanometer scale is accompanied by the introduction of high level of lattice strains. The dissolution of Co, Ni, B (amorphous and crystalline), and Si into the α-Fe lattice leads to the formation of highly disordered Fe-based solid solutions. Coercivity (Hc) and the saturation magnetization (Ms) of alloyed powders were measured at room temperature by a vibration sample magnetization. The magnetic measurements show a contrasting Ms and (Hc) in all alloy compositions. Conclusively, soft magnetic properties of nanocrystalline alloys are related to various factors such as metalloid addition, formed phases, and chemical compositions

Study of the nanocrystalline bulk Al alloys synthesized by high energy mechanical milling followed by room temperature high pressing consolidation

AbstractIn the present study high energy mechanical milling followed by high-pressing consolidation has been used to obtain bulk nanocrystalline Al-Fe-Si alloy. Quantitative XRD analysis and scanning electron microscopy were used to characterize the material evolution during thermal treatments in the temperature range 25–500∘C. The cold-worked structure have been synthesized with microstructure showing a mixture of a significant low size of crystallite (70 nm) and a high level of lattice strains (0.85%). Starting from the nanocrystalline specimens, isochronal experiments were carried out to monitor the reserve microstructure and transformations. The high temperature annealing is required for ameliorating the quality of room temperature consolidated materials by removing all porosity and obtaining good interparticle bonding. The thermal conductivity and the thermal diffusivity are investigated with the Photothermal deflection technique. These thermal parameters increase with the annealing temperatures. This behavior is attributed to the increase in the rate of diffusion coefficient of added elements inside the aluminum matrix

Ni-Mn-Sn-Cu Alloys after Thermal Cycling: Thermal and Magnetic Response

Heusler Ni-Mn-Sn-based alloys are good candidates for magnetic refrigeration. This application is based on cycling processes. In this work, thermal cycles (100) have been performed in three ribbons produced by melt-spinning to check the thermal stability and the magnetic response. After cycling, the temperatures were slowly shifted and the thermodynamic properties were reduced, the entropy changed at about 3–5%. Likewise, the thermomagnetic response remains similar. Thus, these candidates maintain enough thermal stability and magnetic response after cycling. Likewise, Cu addition shifts the structural transformation to higher temperatures, whereas the Curie temperature is always near 310 K. Regarding magnetic shape memory applications, the best candidate is the Ni49Mn36 Sn14Cu1 alloy.This study was funded by University of Girona PONT2020-01 and Spanish Mineco MAT2016-75967-P projects

Dealloying of Cu-Mg-Ca alloys

The chemical dealloying of Cu-Mg-Ca alloys in free corrosion conditions was investigated for different alloy compositions and different leaching solutions. For some of the precursor alloys, a continuous, pure fcc copper with nanoporous structure can be obtained by dealloying in 0.04 M H2SO4 solution. Superficial nanoporous copper structures with extremely fine porous size were also obtained by dealloying in pure water and 0.1 M NaOH solutions. The dealloying of both amorphous and partially crystalline alloys was investigated obtaining bi-phase nanoporous/crystal composites with microstructures depending on the precursor alloy state. The fast dissolution of Mg and Ca makes the Cu-Mg-Ca system an ideal candidate for obtaining nanoporous copper structures with different properties as a function of different factors such as the alloy composition, the quenching process, and leaching conditions.Peer ReviewedPostprint (published version

Microstructure and mechanical properties of AA6082-T6 by ECAP under warm processing

An AA6082 alloy deformed by equal channel angular pressing (ECAP) was studied. The evolution of microstructure as a function of the strain imparted was evaluated by optical microscopy (OM), scanning electron microscopy (SEM) coupled with an electron backscattered diffraction (EBSD) detector, X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). XRD showed that MgSi2 precipitates developed in the ECAPed specimens. Texture analysis showed the apparition of two types of textures, one associated with shearing deformation and the second due to the recrystallization phenomena. Mechanical strength properties measured by tensile tests increased in the first ECAP pass, and then progressively diminished. This phenomenon was associated to the activation of continuous softening phenomena. Calorimetric analysis indicated a slightly rise in the recrystallization temperature of the deformed specimens. Also, the stored energy increased with rising ECAP passes due to the production of new dislocations. The average geometrically necessary dislocation (GND) density, measured by EBSD, increased with increasing ECAP passes. However, the rate of increase slows down with the progress of ECAP passes.Peer ReviewedPostprint (author's final draft

Microstructure and Mechanical Properties of AA6082-T6 by ECAP Under Warm Processing

An AA6082 alloy deformed by equal channel angular pressing (ECAP) was studied. Microstructural evolution of the alloy processed by ECAP with different passes were evaluated by using optical microscope, scanning electron microscopy coupled with an electron backscattered diffraction (EBSD) detector and X-ray diffraction. Texture analysis showed the apparition of two types of textures, one associated with shearing deformation and the second due to the recrystallization phenomena. Mechanical strength properties measured by tensile tests increased in the first ECAP pass, and then progressively diminished due to the presence of concurrent softening phenomena. Calorimetric analysis indicated a slightly increase in the recrystallization temperature of the deformed specimens. Also, the stored energy increased with increasing ECAP passes due to the production of new dislocations. The average geometrically necessary dislocation density, measured by EBSD, increased with increasing ECAP passes. However, the rate of increase slows down with the progress of ECAP passes.Fil: Khelfa, T.. Northwestern Polytechnical University; China. University of Sfax; TúnezFil: Muñoz Bolaños, Jairo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Politécnica de Catalunya; EspañaFil: Li, F.. Northwestern Polytechnical University; ChinaFil: Cabrera -Marrero, J. M.. Universidad Politécnica de Catalunya; EspañaFil: Khitouni, M.. University of Sfax; Túne

Study of the microstructure and texture heterogeneities of Fe–48wt%Ni alloy severely deformed by equal channel angular pressing

International audienceA Fe-48wt%Ni alloy was processed by severe plastic deformation using equal channel angular pressing process. A stacking of 9 sheets was introduced and pressed up to two passes into die with an inner angles of Φ=90º and outer arc of curvature ψ= 17° at room temperature following route A. The same material in bulk form was also ECAPed up to one pass. The microstructure and the texture were investigated by means of electron backscattered diffraction and X-ray diffraction, respectively. To evaluate the mechanical response, Vickers microhardness was carried out. The given analyses concern the as-received sample, the peripheral and the central plates of the pressed stacks and the upper, the middle and the lower parts of the pressed bulk material. The deformation was heterogeneous and variations in texture and microstructure, resulting from different efficiencies in the shearing process, were locally noted. For the stacks samples, the microstructure evolved from equiaxed grains of 9 μm with high fraction of high-angle grain boundaries (around 90%) to a heterogeneous fine grain structure with an average grain size of 3 m after two passes. On the contrary, for the bulk sample, the evolution wa

Degradation of azo dyes by rapidly solidified metallic particles

Azo compounds are one of the most common families of dyes used in textile and leather treatments. An important step during the treatment of water polluted by these compounds, is the degradation of the compounds by decomposition of the -N=N- bonds, producing the de-colorization of the water. This de-colorization reaction can be activated by the presence of zero valent metallic particles. The metastable structures generated during rapid solidification tend to increase the chemical activity of the alloys. Recently, it has been discovered that the use of metallic particles in a metastable phase (amorphous or nanocrystalline) multiplies significantly the efficiency of the decolorization water-treatment step. Here we present the results obtained in the decolorization of water using alloys based on different metals (Fe, Mn, Ni and Al) produced by rapid solidification and posterior ball milling. For some Al-containing alloys the results show a fast reaction, even in neutral pH conditions. In this work, the efficiency of the different metastable alloys in the de-colorization process, the effects of the metastable structure and the processing conditions are presented and assessed.Peer ReviewedPostprint (published version

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

Martensitic Transformation, Thermal Analysis and Magnetocaloric Properties of Ni-Mn-Sn-Pd Alloys

Martensitic transition and magnetic response of Ni50−x Pdx,y Mn36 Sn14−y (x = 0, 1, 2 and y = 0, 1) Heusler alloys were analysed. The crystalline structure of each composition was solved by X-ray diffraction pattern fitting. For x = 1 and 2, the L21 austenite structure is formed and, for y = 1, the crystallographic phase is a modulated martensitic structure. From differential scanning calorimetry scans, we determine characteristic transformation temperatures and the entropy/enthalpy changes. The temperatures of the structural transformation increase with the addition of Pd to replace Ni or Sn, whereas the austenitic Curie temperature remains almost unvarying. In addition, the magneto-structural transition, investigated by magnetic measurements, is adjusted by suitable Pd doping in the alloys. The peak value of the magnetic entropy changes reached 4.5 J/(kg K) for Ni50Mn36Sn13Pd1 (external field: 50 kOe).This research was funded by MINECO grant MAT2016-75967-P and UdG grant PONT2020/01