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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]

Dual-phase (DP) steels were produced by a newly developed method utilizing simple cold-rolling and subsequent short intercritical annealing of a martensite-ferrite duplex starting structure. Tensile testing revealed an excellent strength-elongation balance (UTS × UE ≈ 110-150 J/cm) for the DP steels in comparison with the commercially used high strength steels. Fracture surfaces of the tensile specimens were studied by scanning electron microscopy analysis and image processing. Mechanical properties were correlated with fracture surface features. It was found that the variation of the total elongation and strength-elongation balance with the martensite volume fraction could be well correlated with the variation of the average dimple area. The variation of the yield strength and dimple areal density with the martensite volume fraction followed the same trend. [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]

Dual phase (DP) steels with different amounts of Nb were produced by utilizing cold rolling and intercritical annealing of a ferrite-martensite duplex starting structure. The effects of Nb contents (0.00, 0.06, 0.12 and 0.18 wt%) on microstructure and texture evolutions were studied. Addition of Nb promoted formation of ultra-fine grained structures with the ferrite grain size of about ∼1 μm and uniformly-dispersed martensite particles. The results showed increasing the fraction of the high angle grain boundaries and formation of {111} fiber components in the microstructures with increasing Nb content. In addition, the texture power was decreased with the addition of Nb, resulting in random texture components. [ABSTRACT FROM AUTHOR]