Résumé: Microstructure as well as magnetic, thermal and magnetocaloric properties of the mechanically alloyed Fe72Nb8B20 powders have been investigated by means of Mössbauer spectrometry, differential scanning calorimetry (DSC), and magnetic measurements. The Mössbauer spectrometry results showed the formation of nanostructured Fe(B) and Fe(Nb) solid solutions, Fe2B boride, and an amorphous phase. The endothermic and exothermic peaks that are observed in the DSC curves might be related to the Curie temperature, and the crystallization of the amorphous phase, respectively. The critical exponent values around the magnetic phase transition of the amorphous phase (TC = 480 K), are deduced from the modified Arrott plots, Kouvel−Fisher curves and critical isotherm examination. The calculated values (β = 0.457 ± 0.012, γ = 0.863 ± 0.136 and δ = 3.090 ± 0.004) are near to those of the mean field model, revealing a dominating role of magnetic order arising due to long-range ferromagnetic interactions, as the critical exponents are mean-field-like. The maximum entropy change and the refrigerant capacity values are 1.45 J/kg·K and 239 J/kg, respectively, under a magnetic field of 5 T.

Résumé: The effect of the B content on the microstructural, structural, and magnetic properties of partially amorphous Fe92−xNb8Bx (x = 5, 10, 15, and 20) alloys has been investigated by means of scanning electron microscopy, X-ray diffraction, high and low-temperature extraction-type magnetometers. The XRD results reveal the formation of a nanocomposite structure where nanocrystalline bcc α-Fe and Fe2B phases are embedded into an amorphous matrix. The FeB boride is observed for higher boron contents (x = 15 and 20), and the crystallite sizes are in the range of 7–24 nm. As the B content increases, the amorphous phase-relative proportion and coercivity increase, whereas the saturation magnetization decreases. An important magnetic hardening occurs by lowering the temperature from 400 to 5 K for x = 20% B. The variation of the Curie temperature can be attributed to the heterogeneity of the amorphous matrix.

Résumé: The mechanical alloying process has been used to prepare nanocrystalline Ni20Co80 alloy from elemental Ni and Co powders in a planetary ball mill under argon atmosphere. Scanning electron microscopy, X-ray diffraction and magnetic measurements were carried out to investigate morphological, structural, microstructural and magnetic properties changes during the milling process. The interdiffusion of Co and Ni leads to a heterogeneous solid solution with Ni-rich and Co-rich environments after 12 h of milling. The end product is a mixture of a highly disordered structure, fcc-Ni(Co), fcc-Co(Ni) and hcp-Co(Ni) phases having different microstructural and structural parameters. The coercivity, Hc, decreases rapidly up to 3 h of milling to about 58.3 Oe and remains constant on further milling. The saturation magnetization, Ms, value of about 126 emu/g is obtained after 48 h of milling.

Résumé: A nanostructured Ni50Co50 mixture was prepared by high‐energy ball milling in a planetary ball mill (Frisch P7) under an argon atmosphere. Scanning electron microscopy and X‐ray diffraction (XRD) have been used to study the morphology of the powder particles, microstructure, and structure evolution. Detailed analysis of the XRD patterns was performed by the MAUD program, which is based on the Rietveld method. It reveals the complete vanishing of the Co peaks after 3 h of milling, indicating the allotropic transformation of Co from hcp to fcc structure. The reciprocal dissolution of the elemental Ni and Co powders leads to the formation of a heterogeneous solid solution with two structures: fcc‐Ni(Co) and fcc‐Co(Ni) with relative fractions of about 76 and 20%, respectively, after 24 h of milling. Microstructural parameters such as lattice parameter, crystallite size, microstrains, dislocation density, and stacking …

Résumé: Nanostructured Co50Ni50 powders were mechanically alloyed from elemental Co and Ni powders using a planetary ball mill type Fritsch P7 under argon atmosphere. The milled powders were characterized by scanning electron microscopy, X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC). The SEM micrographs show a progressive refinement of the particles size with milling time. For longer milling time, the particles morphology is homogenous indicating the formation of the alloy. The XRD reveals the interdiffusion of the Ni and Co elements as milling proceeds and the formation of an heterogeneous solid solutions with two structures: fcc-Ni(Co) and fcc-Co(Ni), having different structural and microstructural parameters. The XRD patterns refinement reveals also the Co allotropic transformation from the hcp to fcc structure form at the early stage of milling. DSC results show a broad exothermic reaction indicating a strain relaxation and a recovery process.

Résumé: In the present work, morphological, structural, thermal and magnetic properties of nanocrystalline Co50Ni50 alloy prepared by high energy planetary ball milling have been studied by means of scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry. The coercivity and the saturation magnetization of alloyed powders were measured at room temperature by a vibration sample magnetization. Morphological observations indicated a narrow distribution in the particle and homogeneous shape form with mean average particle size around 130μm2. The results show that an allotropic Co transformation hcp→fcc occurs within the three first hours of milling and contrary to what expected, the Rietveld refinement method reveals the formation of two fcc solid solutions (SS): fcc Co(Ni) and Ni(Co) beside a small amount of the undissolved Co hcp. Thermal measurement, as a function of milling time …

Résumé: Effect of the milling conditions on the amorphisation of Fe77Cr4P8C11 alloy. Fe77Cr4P8C11 powdered mixtures were mechanically alloyed from elemental Fe, Cr, P (red phosphorous) and C (activated and graphite) powders with purity of 99.9% using a planetary ball mill type Fritsch P7 under argon atmosphere. The milled powders were characterised by X-ray diffraction, using the Maud program accordingly to the Rietveld method, and Mossbauer spectrometry. Based on both X-ray diffraction (XRD) and Fe-57 Mossbauer spectrometry (MS) investigations, the formation of a disordered amorphous like phase is observed after 24 h and 32 h of milling for the G-Fe77Cr4P8C11 (graphite) and A-Fe77Cr4P8C11 (activated carbon), respectively. Further milling leads to the recrystallization by mechanical energy of the disordered amorphous like phase resulting on the formation of Fe3P, Fe7C3 and epsilon'-Fe2. 2C type …

Résumé: Mechanical alloying method was used to prepare nanocrystalline Co50Ni50 alloy. X-ray diffraction was applied to determinate the structure of the alloy. Structural and microstructural parameters (lattice parameters, microstrains, crystallite sizes and phase percentages) were deduced from the Rietveld refinement of XRD patterns, by using the MAUD program, and discussed as a function of milling time. XRD results indicated that the crystalline solid solutions were achieved after 6h of milling. SEM observations revealed that mechanical alloys consist of agglomerated fineparticles of about 24 nm in size

Résumé: Nanostructured Fe-8P (wt%) powder mixture was prepared by high energy ball milling in a planetary ball mill (Fritsch P7) under argon atmosphere. The morphology of the particles, the phase identification and the alloying evolution process as a function of milling time are studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and 57Fe Mössbauer spectrometry (MS), respectively. Refinement based on Rietveld method of the XRD patterns and the Mössbauer spectra analysis show that the Fe x P (1 x 2P phosphide phases are the main product after 3 h of milling (∼10%). From the XRD Rietveld refinement, it is observed that the Fe2P phase disappears completely after 12 h of milling, while the Fe3P nanophase appears after 9 h and remains for larger milling duration. The lattice structure distortion is evidenced by the lattice parameter changes ofthe milled products. A two structure state of the α-Fe(P …

Résumé: Nanostructured Fe-8P (wt%) powder mixture was prepared by high energy ball milling in a planetary ball mill (Fritsch P7) under argon atmosphere. The morphology of the particles, the phase identification and the alloying evolution process as a function of milling time are studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and 57Fe Mössbauer spectrometry (MS), respectively. Refinement based on Rietveld method of the XRD patterns and the Mössbauer spectra analysis show that the Fe x P (1 < x < 2) and Fe2P phosphide phases are the main product after 3 h of milling (∼10%). From the XRD Rietveld refinement, it is observed that the Fe2P phase disappears completely after 12 h of milling, while the Fe3P nanophase appears after 9 h and remains for larger milling duration. The lattice structure distortion is evidenced by the lattice parameter changes ofthe milled products. A two structure state of the α-Fe(P) solid solution: α-Fe1 and α-Fe2 is confirmed by both the XRD and MS measurements. After milling for 21 h, a mixture of a disordered two phase α-Fe(P) solid solution, Fe3P nanophase and a small amount of a paramagnetic FeP phosphide phase (∼2%) is obtained.

Résumé: Fe77Cr4P8C11 alloy was prepared by mechanical alloying (MA) of elemental Fe, Cr, P and C (graphite) powders in a planetary ball mill type Fritsch P7 under argon atmosphere. Morphological changes, microstructural and structural evolutions during ball milling were followed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and 57Fe Mössbauer spectrometry (MS) as a function of the milling time. The crystallite size refinement against the milling time is accompanied by an increase of the atomic level strain. After 6h of milling, the dissolution of phosphorous into the α-Fe matrix is evidenced by the formation of a small amount (∼4%) of the paramagnetic Fe2P phase as revealed by Mössbauer spectrometry. The complete mixing of all the elemental powders at the atomic level is achieved at 12h of milling and results, after 24h, in an amorphous matrix where nanocrystalline phosphides and carbides with …

Résumé: In an attempt to prepare amorphous Fe77Cr4P8C11 alloy by mechanical alloying, powder mixtures of Fe, Cr, P and C (activated carbon) with a purity of 99.9% have been ball milled, under argon atmosphere for several periods up to 90 h, in a planetary ball mill (Fritsch P7). The structure and microstructure of the milled powders have been characterised, as a function of milling time, by X-ray diffraction and Mössbauer spectrometry. During the first stage of milling (up to 12 h), detailed analyses of the diffraction patterns and the Mössbauer spectra reveal a complete dissolution of the elemental powders and the formation of FexP (1 < x < 2), Fe3P phosphides and Fe3C carbide in addition to α-(Fe,Cr) phase. The amorphous like state is reached after 32 h of milling. Further milling leads to the appearance of new carbides such as (Fe,Cr)7C3 and ɛ′-Fe2.2C with the phosphide (Fe,Cr)3P type phase embedded in the amorphous matrix.