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In this work, electrochemical behavior of annealed (micro-) and nano-grained pure copper (fabricated by accumulative roll bonding process) in phosphate buffer solutions of various pH values ranging from 10.69 to 12.59 has been studied. Before any electrochemical measurements, evaluation of microstructure was obtained by optical microscope and transmission electron microscopy. To investigate the electrochemical behavior of the samples, the potentiodynamic polarization, Mott-Schottky analysis, and electrochemical impedance spectroscopy (EIS) were carried out. Potentiodynamic polarization plots and EIS measurements revealed that as a result of grain refinement, the passive behavior of the nano-grained sample was improved compared to that of annealed pure copper. Also, Mott-Schottky analysis indicated that the passive films behaved as p-type semiconductors and grain refinement did not change the semiconductor type of passive films. [ABSTRACT FROM AUTHOR]

Surface A356 aluminum alloy matrix composites containing micro and nanosized AlO are prepared by a new approach utilizing high-velocity oxy-fuel spraying and friction stir processing (FSP). Optical and scanning electron microscopy, microhardness, and wear tests were used to characterize the surface composites. Results indicated that, the presence of AlO in matrix can improve the mechanical properties of specimens. The microhardness of surface composites containing micro and nanosized AlO were 89.8 ± 2.6 HV and 109.7 ± 2.5 HV, respectively, which were higher than those for the as-received (79.6 ± 1.1 HV) and the FSPed A356-T6 with no alumina powder (66.8 ± 0.9 HV). Surface composites revealed low friction coefficients and wear rates, which were significantly lower than those obtained for substrate. The wear mass losses of the as-received, the FSPed, and surface micro and nanocomposite specimens after 500-m sliding distance were 50.5, 55.6, 31, and 17.2 mg, respectively. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens. [ABSTRACT FROM AUTHOR]

Mechanical alloying (MA) has been used to fabricate the Co2FeAl Heusler alloy with a nanocrystalline structure. The formation mechanism of the alloy has been investigated. Rietveld analysis showed that all the samples that were milled for >15 h had an L21 structure with a space group of Fm3m. The crystallite size and internal strain of the samples were calculated using the Williamson-Hall equation. The crystallite size of Co2FeAl increased to ∼22 nm by increasing the MA time from 15 to 20 h, and after 20 h of MA, the crystallite size decreased. In contrast, the internal strain has increased with the increase in milling time. The powder obtained after 20 h of MA was split into three parts and separately annealed at 300, 500 and 700°C for 5 h. A considerable increase was observed in the hardness value of powder particles with the increase in annealing temperature up to 500°C. However, the hardness value of the sample annealed at 700°C decreased. It seems that this feature is related to parameters such as increase in crystallite size, enhancement of lattice ordering, change in density of defects and impurities and non-stoichiometric effects. [ABSTRACT FROM AUTHOR]