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In this research, the synthesis of Co–Fe–Ni ternary alloys in different compositions (Co40Fe30Ni30, Co30Fe40Ni30 and Co30Fe30Ni40), and their structural and magnetic properties were assessed. These alloys were milled during 7 h by mechanical alloying (MA), after of the milling time, the results of the structural analysis, shown three solids solutions obtained with fcc-structure (Co(FeNi)–fcc, Fe(CoNi)–fcc and Ni(FeCo)–fcc). As a consequence of the process of synthesis, the crystal size refinement was observed in all cases, meanwhile, the particle size increased due to the powders ductility. The magnetic properties at room temperature were studied to observe the saturation magnetization (Ms), before and after of the milling, the results of the un-milled powders were 140, 130 and 110 A m2/kg for Co40Fe30Ni30, Co30Fe40Ni30 and Co30Fe30Ni40 respectively, after of mechanical alloying, the MS increased to 162, 166 and 150 A m2/kg. On the other hand, the coercive field (HC) values decreased drastically from 6.13 kA/m (~77 Oe), 4.77 kA/m (~60 Oe) and 5.57 kA/m (~70 Oe) before of the milling process, to 0.365 kA/m (~4.6 Oe), 0.296 kA/m (~3.7 Oe) and 0.306 kA/m (~3.8 Oe) after the milling for Co40Fe30Ni30, Co30Fe40Ni30 and Co30Fe30Ni40, respectively.

Elemental cobalt powder was modified by high-energy ball milling for 0–15 h, and the results obtained by X-ray diffraction (XRD) revealed a phase transformation. Initially, the unmilled powder consisted of two phases: hexagonal close-packed (hcp) and face centered cubic (fcc). From a milling time of 0–5 h, the fcc phase underwent a phase transformation to hcp, and increased milling times promoted a transformation back to the fcc phase. Moreover, the crystallite size decreased from 88.9 nm to 16.7 nm for the samples at 0 and 15 h, respectively. Conversely, the microstrain increased from 0.02% to 0.489% for the same times. On the other hand, the mean particle size increased from 6.8 μm to 68.6 μm for the first 5 h, and this effect is related to the cold welding step in the milling process and cobalt ductility. The magnetic properties of the samples were analyzed by vibrating sample magnetometry (VSM) at room temperature. The hysteresis loops exhibited an increase in saturation polarization from 1.18 to 1.33 T (145.5–163 A m2/kg) for the first hour. On the other hand, the coercivity field and magnetic anisotropy presented a progressive reduction as the milling time increased, and this effect was attributed to particle size growth and the main content of the fcc phase. Magnetic–thermogravimetric analysis revealed that the Curie temperature was ∼1391 K, which was associated with the fcc phase. In addition, other events between 700 and 900 K were identified. These events were associated with the TC of the hcp phase. Keywords: High-energy ball milling, Cobalt, Allotropic transformation, Magnetic properties, Magnetocrystalline anisotropy, Curie temperature

This research aimed to obtain a C-based coating electrochemically applied on an AA6063 alloy. Two electrochemical cells were designed and manufactured to obtain the C-based coating film on flat and cylindrical samples. Structural and microstructural characterizations were performed along with fatigue and corrosion performance testing. The structural and microstructural characterization revealed that the C-based coating deposited on AA6063 corresponded to carbon nanofibers and/or polycrystalline graphite. The performance testing showed an increase in fatigue life along with a decrease in corrosion resistance. The fracture surfaces of the fatigued samples were inspected by Scanning Electron Microscopy and 3D optical microscopy to correlate them with fatigue life estimation. The aforementioned process is a step towards the future development of a complete coating system that will overcome corrosion susceptibility. The carbon film obtained by this electrochemical route has not previously been reported elsewhere.

The present research deals with the comparative wear behavior of a mechanically milled Al-6061 alloy and the same alloy reinforced with 5 wt.% of Al2O3 nanoparticles (Al-6061-Al2O3) under different dry sliding conditions. For this purpose, an aluminum-silicon-based material was synthesized by high-energy mechanical alloying, cold consolidated, and sintered under pressureless and vacuum conditions. The mechanical behavior was evaluated by sliding wear and microhardness tests. The structural characterization was carried out by X-ray diffraction and scanning electron microscopy. Results showed a clear wear resistance improvement in the aluminum matrix composite (Al-6061-Al2O3) in comparison with the Al-6061 alloy since nanoparticles act as a third hard body against wear. This behavior is attributed to the significant increment in hardness on the reinforced material, whose strengthening mechanisms mainly lie in a nanometric size and homogeneous dispersion of particles offering an effective load transfer from the matrix to the reinforcement. Discussion of the wear performance was in terms of a protective thin film oxide formation, where protective behavior decreases as a function of the sliding speed.

The goal of this work is to demonstrate the positive effect of high energy ball milling on the magnetocaloric properties of materials based on strontium-calcium doped lanthanum manganite. We report a detailed study of crystal structure, magnetic behavior and magnetocaloric effect of La0.7Ca0.3−xSrxMnO3 (0 ≤ x ≤ 0.2, Δx = 0.05) powders, synthesized by assisted high-energy ball milling. The X-ray diffraction patterns disclose the complete formation of manganite with an orthorhombic structure for x ≤ 0.15, and rhombohedral structure for x = 0.2. Magnetic properties show a reduction of the magnetic saturation, and an increase in the Curie temperature with the strontium substitution, in all explored compositions (above room temperature). Arrot curves display that strontium doped manganites exhibit a second-order magnetic transition from ferrimagnetic to paramagnetic order. The magnetocaloric effect was calculated by measuring the isothermal magnetization around the Curie temperature, from 0 to 1.8 T, using Maxwell relations. All the synthesized manganites show magnetocaloric effect larger as compared to that of the parent compounds synthesized by other methods. The un-doped sample (x = 0) presents 7.43 J kg−1 K−1 and 93.29 J kg−1 of maximum magnetic entropy change (|ΔSM|) and the relative cooling power (RCP), respectively, under a low applied field (μoH) of 1.8 T. As it is expected, the introduction of strontium into the manganite, slightly reduces the magnetic entropy at 1.8 T, from 6.29 to 3.47 J kg−1 K−1 for x = 0.05 and x = 0.2, respectively. At the same time, the presence of strontium increases the working temperature above room temperature for strontium contents higer than 0.05, both attributed to the change in the crystal structure. These values are suitable for room-temperature magnetic refrigeration applications, using low magnetic fields (

In this paper, a systematic study on the structural and magnetic properties of Co100−xCrx alloys (0

Mechanical alloying, MA, has been successfully used to extend the limits of solid solubility in many commercially important metallic systems. The aim of this work is to demonstrate that MA modifies the solid solubility of the Co–Cr system. Co and Cr elemental powders were used as precursors and mixed in an adequate weight ratio to obtain Co 100− x Cr x (0 ≤ x ≤ 100, Δ x = 10) to study the effect of mechanical processing in the solubility of the Co–Cr system. Processing was carried out at room temperature in a shaker mixer mill using vials and balls of hardened steel as milling media with a ball:powder weight ratio of 10:1. Crystalline structure characterization of the milled powders was conducted using X-ray diffraction, and phase transformations as a function of composition were analyzed. Thermal analysis confirmed structural changes occurred in the mechanically alloyed powders. The evolution of the phase transformations with composition is reported for each composition. The results showed that after high energy ball milling for 7 h, the solid solubility between Co and Cr could be evidently extended, despite the low solid solubility at the equilibrium conditions of this system. Additionally, the micrographs of the milled powders showed that increasing composition of chromium changes the shape and size of the particles while simultaneously reducing their agglomeration; this effect is possibly attributed to the brittleness of elemental chrome.

Structural transformations and the amorphization of cobalt base alloy particles are possible when a powder mixture of Co and Cr–Mo is subjected to the mechanical alloying (MA) process. Elemental powders mixed in adequate weight ratios were used as precursors. The process was carried out at room temperature in a shaker mixer mill using vials and balls of hardened steel as milling media, with a ball:powder weight ratio of 8:1. The characterization of the crystalline structure of milled powders was carried out by means of X-ray diffraction to analyze the phase transformations as a function of milling time. The aim of this work was to demonstrate that MA can induce the amorphization of Co–Cr–Mo alloy. The evolution of the phase transformation during milling time is reported. The results showed that it is possible to produce a partial solid solution at room temperature of elemental metallic powders Co70Cr30 and Co90Mo10 by mechanical alloying. Using specific experimental conditions, it is also possible to obtain an amorphous phase in a composition Co60Cr30Mo10; first, Cr and Mo were mechanically prealloyed for 9 h to obtain a Cr80Mo20 solid solution, and Co was then added and milled in over 14 h.

We report on an alternative route for the synthesis of crystalline Co-28Cr-6Mo alloy, which could be used for surgical implants. Co, Cr and Mo elemental powders, mixed in an adequate weight relation according to ISO Standard 58342-4 (ISO, 1996), were used for the mechanical alloying (MA) of nano-structured Co-alloy. The process was carried out at room temperature in a shaker mixer mill using hardened steel balls and vials as milling media, with a 1:8 ball:powder weight ratio. Crystalline structure characterization of milled powders was carried out by X-ray diffraction in order to analyze the phase transformations as a function of milling time. The aim of this work was to evaluate the alloying mechanism involved in the mechanical alloying of Co-28Cr-6Mo alloy. The evolution of the phase transformations with milling time is reported for each mixture. Results showed that the resultant alloy is a Co-alpha solid solution, successfully obtained by mechanical alloying after a total of 10 h of milling time: first Cr and Mo are mechanically prealloyed for 7 h, and then Co is mixed in for 3 h. In addition, different methods of premixing were studied. The particle size of the powders is reduced with increasing milling time, reaching about 5 mum at 10 h; a longer time promotes the formation of aggregates. The morphology and crystal structure of milled powders as a function of milling time were analyzed by scanning electron microscopy and XR diffraction.