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Guzman, D., Garcia, C., Soliz, A., Sepulveda, R., Aguilar, C., Rojas, P., et al. (2018). Synthesis and Electrochemical Properties of Ti-Si Alloys Prepared by Mechanical Alloying and Heat Treatment. Metals, 8(6), 417.
Abstract: The aim of this work was to study the synthesis and electrochemical properties of Ti 2 wt %-Si alloys prepared by mechanical alloying (MA) and heat treatment. The MA process was performed under Ar atmosphere. The structural, morphological, and compositional evolutions during the milling and subsequent heat treatment were investigated by X-ray diffraction, energy-dispersive spectroscopy, and scanning electron microscopy. The electrochemical behavior was evaluated by open circuit potential and linear sweep voltammetry measurements. The results showed that the MA process promotes the formation of a supersaturated alpha-Ti-Si solid solution. During heat treatment, the Si remaining in the mechanically alloyed powders and the Si from the alpha-Ti-Si supersaturated solid solution reacted with Ti to form Ti-Si intermetallic compounds. These compounds have a fine and homogeneous distribution in the alpha-Ti matrix, which cannot be achieved by conventional casting methods. Additionally, the electrochemical evaluations revealed that the mechanically alloyed and heat-treated Ti 2 wt %-Si powders have better corrosion resistance in 1.63 M H2SO4 than the pure Ti and MA Ti-Si samples. This is likely due to the particular microstructure produced during the milling and subsequent heat treatment.
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Martinez, C., Aguilar, C., Briones, E., Guzman, D., Zelaya, E., Troncoso, L., et al. (2018). Effects of Zr on the amorphization of Cu-Ni-Zr alloys prepared by mechanical alloying. J. Alloys Compd., 765, 771–781.
Abstract: This work presents the effects of high energy milling with different Ni and Zr ratios on the amorphization of ternary Cu-Ni-Zr alloys (initially, Cu-43Ni-7Zr, Cu-12Ni-31Zr, Cu-33Ni-7Zr, and Cu-12Ni-23Zr; and later, Cu-23Ni-15Zr and Cu-11Ni-7Zr). Microstructure was determined using X-Ray diffraction and electron microscopy. Results were compared to thermodynamic models. In the ternary alloys under study, the lattice parameter of the Cu-Ni solid solution was generally correlated to the amounts of nickel incorporated into the Cu lattice. However, longer milling times reduced that lattice parameter and facilitated Zr insertion into the solid solution. For example, after 5 h of milling time, microstructural analysis showed the formation of a solid solution with cubic structure in Cu-43Ni-7Zr. This pattern is consistent with the presence of a lattice parameter between that of Cu and Ni (alpha-phase); in contrast, the Cu-33Ni-7Zr alloy showed an alpha-phase and another similar to Zr. Results suggest that, as the amount of nickel increases, the ability to form an amorphous phase decreases. Additionally, experimental and thermodynamic data showed a solid-solution formation stage, followed by an amorphous phase formation stage that occurred as milling time and Zr content increased. (C) 2018 Published by Elsevier B.V.
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Martinez, C., Briones, F., Rojas, P., Ordonez, S., Aguilar, C., & Guzman, D. (2017). Microstructure and Mechanical Properties of Copper, Nickel and Ternary Alloys Cu-Ni-Zr Obtained by Mechanical Alloying and Hot Pressing. MRS Adv., 2(50), 2831–2836.
Abstract: Elemental powders of Cu and Ni, binary alloys (Cu-Ni and Cu-Zr) and ternary alloy (Cu-Ni-Zr) obtained by mechanical alloying and uniaxial compaction hot microstructure and mechanical properties were investigated. The alloys studied were: pure Cu, pure Ni, binary alloys (Cu-Ni; Cu-Zr) and ternary alloys (Cu-Ni-Zr) under the same mechanical milling and hot pressing conditions. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM); the mechanical properties were studied by compression tests and hardness in Vickers scale (HV0.5) on polished surfaces at room temperature. According to XRD results, hot pressing process crystallite size increase and microstrain decreases in the compact samples due to the release of crystalline defects. The compacted samples have porosity of approximately 20%. The milling powder samples have a higher hardness than the unmilled samples, this because during milling crystal defects are incorporated together with the microstructural refinement. Ternary alloy is the one with the highest hardness of all systems studied, reaching 689 HV0.5. In compression tests determined a strain 5 %, Zr-containing samples become more fragile presenting the lowest values of compressive strength. In contrast, samples of Ni and Cu-Ni binary alloy are more resistant to compression.
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Rojas, P. A.., Martinez, C., Aguilar, C., Briones, F., Zelaya, M. E., & Guzman, D. (2016). Characterization of phase changes during fabrication of copper alloys, crystalline and non-crystalline, prepared by mechanical alloying. Ing. Invest., 36(3), 102–109.
Abstract: The manufacture of alloys in solid state has many differences with the conventional melting (casting) process. In the case of high energy milling or mechanical alloying, phase transformations of the raw materials are promoted by a large amount of energy that is introduced by impact with the grinding medium; there is no melting, but the microstructural changes go from microstructural refinement to amorphization in solid state. This work studies the behavior of pure metals (Cu and Ni), and different binary alloys (Cu-Ni and Cu-Zr), under the same milling/mechanical alloying conditions. After high-energy milling, X ray diffraction (XRD) patterns were analyzed to determine changes in the lattice parameter and find both microstrain and crystallite sizes, which were first calculated using the Williamson-Hall (W-H) method and then compared with the transmission electron microscope (TEM) images. Calculations showed a relatively appropriate approach to observations with TEM; however, in general, TEM observations detect heterogeneities, which are not considered for the W-H method. As for results, in the set of pure metals, we show that pure nickel undergoes more microstrain deformations, and is more abrasive than copper (and copper alloys). In binary systems, there was a complete solid solution in the Cu-Ni system and a glass-forming ability for the Cu-Zr, as a function of the Zr content. Mathematical methods cannot be applied when the systems have amorphization because there are no equations representing this process during milling. A general conclusion suggests that, under the same milling conditions, results are very different due to the significant impact of the composition: nickel easily forms a solid solution, while with a higher zirconium content there is a higher degree of glass-forming ability.
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Sepulveda, E., Mangalaraja, R. V., Troncoso, L., Jimenez, J., Salvo, C., & Sanhueza, F. (2022). Effect of barium on LSGM electrolyte prepared by fast combustion method for solid oxide fuel cells (SOFC). MRS Adv., Early Access.
Abstract: In this work, La0.85Sr0.15-xBaxGa0.85Mg0.15O3-delta (LSBGM), with 0 <= x <= 0.075, were prepared as electrolytes for solid oxide fuel cells applications. The effect of barium and sintering temperature on the structure and electrical properties was studied. A fast combustion method was used, starting with nitrate salts and citric acid as fuel. The XRD spectra showed two main phases corresponding to LSGM orthorhombic (space group Imma) and LSGM-cubic (space group Pm-3 m). From literature, both structures are reported as high oxygen ion conductive species, but normally, they are not reported to appear together. Major secondary phases were LaSrGaO4, BaLaGaO4, and BaLaGaO7. SEM revealed a material with low porosity, indicating incomplete densification. The sample La0.85Sr0.75Ba0.075Ga0.85Mg0.15O3-delta showed a conductivity of 0.016 and 0.058 S cm(-1) at 600 degrees C and 800 degrees C, respectively. This means an improvement of 34% compared to the non-barium sample La0.85Sr0.15Ga0.85Mg0.15O3-delta at 600 degrees C. Thus, this composition could be used in SOFC.
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