Ionel Chicinaş

A structural investigation of SmCo5/Fe nanostructured alloys obtained by high-energy ball milling and subsequent annealing

SmCo5/Fe nanostructured alloys with 20 wt% Fe, obtained by high-energy ball milling of SmCo5 and Fe powders, were investigated by 57Fe Mossbauer spectrometry, x-ray diffraction and tomographic atom probe. The Mossbauer analysis reveals that during the first stages of milling, an interdiffusion of Co and Fe occurs, leading both to the formation of α-Fe(Co) regions in α-Fe and to the introduction of Fe in SmCo5 regions. Annealing at temperatures up to 650 °C for 0.5 h promotes interdiffusion further leading to the formation of a unique α-Fe(Co) phase and a Fe-richer Sm(Co,Fe)5 phase. The Co/Fe interdiffusion is confirmed by tomographic atom probe analysis. The data are discussed and compared with the results of previous magnetic measurements.

Synthesis of the Supermalloy Powders by Mechanical Alloying

The mixture of the Ni, Fe and Mo elemental powders with the nominal composition of the Supermalloy was milled in a planetary mill under Ar atmosphere. Several milling times have been used ranging from 4 to 16 h. A heat treatment of 30 min, 1, 2 and 4 h at temperature of 350°C has been performed in vacuum in order to improve the alloying process and remove the internal stresses. The formation of the Fe-Ni-Mo alloys by mechanical alloying was evidenced by X-ray diffraction. The nanocrystalline Supermalloy powders have been obtained after 16 h milling and after 8 h milling followed by 4 h annealing. A typical grain size of 11 ± 2 nm have been obtained after 16 h milling. The chemical homogeneity composition and the morphology of the powder particles have been studied by X-ray microanalysis and scanning electron microscopy respectively.

Magnetic properties of xCuO · (1 - x) [2B2O3 · PbO] glasses

Abstract The results of magnetic studies on xNiO.(1-x)[2B2O3.PbO] glasses with 0 ⩽ x ⩽ 40 mol.% are reported. These results evidenced that the nickel ions, in this glass system, are in a divalent state and magnetically isolated. The magnetic moments, μ, decrease from a value 3.31 μB for the 5 mol.% NiO to a value 2.90 μB for 40 mol.% NiO. These variations can be due to the result of a statistical average of the nickel sites distribution.

Influence of Wet-Milling Process on Magnetic Properties of Supermalloy Magnetic Nanocrystalline Powders

Nanocrystalline Supermalloy powders were obtained by wet milling in argon atmosphere. As process control agent the C6H6 was used. Several milling times have been used ranging from 2 up to 20 h. The formation of the alloy was evidenced by X-ray diffraction (XRD). An annealing at 623 K for 4 h was applied in order to remove the internal stresses and to finish the solid state reaction. A typical crystallite size of 11-12 nm has been obtained after 20 h of wet milling. The magnetic measurements have been performed in a magnetic field up to 8 T at 300 K. A decrease of magnetization is observed upon increasing the milling time due both to the defects induced during the milling and to adsorbed benzene on the particles surface. Differential scanning calorimetry (DSC) curves show the exothermic peaks correlated with the presence of the C6H6 on the powder particles. The benzene and the internal stresses and crystalline defects are eliminated and an increase of magnetization with milling time can be observed for samples annealed at 623 K for 4 h.

Influence of residual internal stresses on the coercive field of soft magnetic powders

Abstract We have found evidence of the existence of second- and third-order internal stresses within Fe powder grains (affected zone size: second order ≈ crystalline grains size; third order ≈ few interatomic distances) by means of X-ray diffraction. It is shown that the second-order internal stresses in powder grains induced during pulverization have qualitatively the same dependence on grain size and heat treatment as B H C .

Stability of Phases in Ball-Milled Zinc Ferrite/Iron Composite Produced by Spark Plasma Sintering

Three milling modes have been used for the synthesis of zinc ferrite/iron composite/nanocomposite powders. A partial or total reaction between zinc ferrite and iron (followed by the formation of zinc oxide and iron oxide) appears in the composite compact during Spark Plasma Sintering (SPS), for sintering temperature range of 400 to 550°C. Low sintering temperature led to a good preservation of zinc ferrite and iron when a composite powder obtained in low energetic milling mode was used. The milled powders and sintered compacts were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy, and energy dispersive X-ray spectrometry (EDX). The milling mode and sintering parameters influence on the stability of phases of composite/nanocomposites powder and compacts were investigated and discussed.

Synthesis of the Fe-10%Si Nanocrystalline Powder by Mechanical Alloying

Fe-Si alloy with a Si content of 10 wt. % was obtained in nanocrystalline state by mechanical alloying of elemental iron and silicon powders. The mechanical alloying process was carried out in a high energy ball mill (Fritsch, Pulverisette 4) in argon atmosphere. The X-ray diffraction (XRD) studies indicated that after 4 hours of milling the Fe-Si alloy is formed. The mean crystallites size decreases down to 7 nm after 8 hours of milling. The particles morphology investigated by scanning electron microscopy (SEM) showed an evolution during milling process from two different kinds of particles to a one kind of particles with irregular shape. The magnetisation of powders decreases upon increasing the milling time up to 4 hours as a consequence of the Fe-Si alloy formation.

Influence of high deformation on the microstructure of low-carbon steel

Low-carbon steel sheets DC04 used in the automotive industry were subjected to cold rolling for thickness reduction from 20% to 89%. The desired thickness was achieved by successive reductions using a rolling mill. The influence of thickness reduction on the microstructure was studied by scanning electron microscopy. Microstructure evolution was characterized by the distortion of grains and the occurrence of the oriented grain structure for high cold work. A mechanism of grain restructuring for high cold work was described. The occurrence of voids was discussed in relation with cold work. The evolution of voids at the grain boundaries and inside the grains was also considered. To characterize the grain size, the Feret diameter was measured and the grain size distribution versus cold work was discussed. The chemical homogeneity of the sample was also analyzed.

Synthesis, Structural, and Magnetic Properties of Nanocrystalline/Nanosized Manganese-Nickel Ferrite–

The nanocrystalline/nanosized mixed manganese-nickel spinel ferrite Mn0.5Ni0.5Fe2O4 was successfully synthesized by the classical ceramic method followed by mechanical milling. The refinement of the crystallite size is obtained by increasing the milling time up to 120 min. The particles size distribution performed on the milled powder showed a fine ferrite powder. The Néel temperature of Mn0.5Ni0.5Fe2O4 decreases by increasing the milling time as a result of the structural disorder and it is larger when compared with the manganese ferrite one and lower when compared with the nickel ferrite one. The saturation magnetization of the spinel structure was found to be 2.42 μB and it is close to the theoretical one 2.5 μB. The saturation magnetization and spontaneous magnetization decrease by increasing milling time. The spontaneous magnetization is reduced more drastically when compared with the saturation magnetization. One of the major causes is assumed to be the spin canted effect induced at the particles surface by milling process.

{\rm Mn}_{0.5}{\rm Ni}_{0.5}{\rm Fe}_{2}{\rm O}_{4}

This paper studies the fracture surfaces of an aluminium hot extrusion die that broke down during operation. The die was constructed, from H13 steel and was intended for the production of 60,000 Kg of aluminium profile. The male part fractured during operation after the production of 500 Kg profile. Initially, the machine and thermal treatments that were applied for construction of the die were collected and studied. The die was carefully inspected visually with a stereoscope. The fracture surfaces, some cracks, and the structure that was not affected by the failure, were investigated by optical microscopy. The thickness, quality and homogeneity of the nitrated layers were inspected. Additional information concerning the fracture was obtained by examining a primary crack using a scanning electron microscope and chemical analysis of the material was made using EDX attachment. The paper reports on some interesting observations relating to the fractured component, the type of the fractures, and the quality of the heat treatments, and presents some of the probable causes that led to the premature failure of the die.