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The ratio of the twin decreased after thermomechanical process for the CoCrNi medium-entropy alloy. The grain refinement decreased the passive current and increased the breakdown potential of the CoCrNi medium-entropy alloy in sodium chloride solution. The electrochemical impedance spectroscopy analysis showed that the grain refinement of the CoCrNi medium-entropy alloy facilitated to form thicker passive films and larger passive film resistance, which thus resulted into better corrosion resistance in sodium chloride solution. More nucleation sites after the grain refinement could enhance diffusion rate of alloying element and promote to form thicker and more stable passive films on refined grain CoCrNi medium-entropy alloy. Moreover, sufficient recrystallization level within refined grains for the CoCrNi MEA also improved its corrosion resistance.

Few layer graphene was formed on the surface of Ni foam using the chemical vapor deposition technique, which effectively decreased flaws and inhibited stack of graphene. The CoS nanorods were synthesized on the surface of bare Ni foam after hydrothermal method, while graphen on Ni foam facilitated to form CoS nanowires with porosity surface structure and large specific surface area. The CoS nanowires on Ni foam coated with graphene showed an high specific capacitance of 1506 F g−1 at 1 A g−1 and 88.2% capacity retention at a current density of 1 A g−1 after 5000 cycles charge-discharge test. The improved electronic conductivity of current collector Ni foam by graphene and porous microstructure of CoS nanowires catalyzed by graphene enhanced significantly supercapacitors performance. This was attributed to large CoS nanowires electrode-electrolyte contact area and reduced volume change during the charge-discharge process.

Aligned NiCo 2 S 4 nanotubes on Ni foam were obtained by the complete sulfidation of NiCo-precursor which was synthetized by hydrothermal process. The NiCo 2 S 4 nanotubes on Ni foam delivered a higher specific capacitance than NiCo 2 O 4 nanowires on Ni foam. The NiCo 2 S 4 nanotubes on Ni foam exhibited the high capacitance of 1936.2 F g −1 at 1 A g −1 . The porous NiCo 2 S 4 nanotubes on Ni foam provided a huge number of exposed active sites for electrochemical reaction. Moreover, the NiCo 2 S 4 nanotubes on Ni foam with large specific surface area facilitated the diffusion and penetration of electrolyte and improved electrochemical reaction. Therefore, after 5000 continuous charge–discharge cycles, only about 7.9% degradation in specific capacitance was observed for NiCo 2 S 4 nanotubes on Ni foam.

The effects of urea concentration on microstructures of ZnCo 2 O 4 during hydrothermal process and their supercapacitors performance were investigated. The sphere ZnCo 2 O 4 oxide with nanostructure arrays was formed after hydrothermal process containing low urea concentration. The slim and curved ZnCo 2 O 4 nanowires were formed on Ni foam due to medium urea concentration, while sharp and separated ZnCo 2 O 4 nanostructure arrays were formed on Ni foam due to high urea concentration. The sharp and separated ZnCo 2 O 4 nanostructure arrays on Ni foam showed the best electrochemical performance. ZnCo 2 O 4 nanostructure arrays obtained were composed of interconnected ZnCo 2 O 4 nanoparticles. The gaps between ZnCo 2 O 4 nanoparticles promoted penetration of the electrolyte, which induced the high supercapacitive performance. The sharp and separated ZnCo 2 O 4 nanostructure arrays on Ni foam had the lowest charge transfer resistance, which improved supercapacitive performance. In addition, the strong and separated ZnCo 2 O 4 nanowires improved significantly cycle life during the charge-discharge process due to good strain accommodation of the unique structure.

The effect of strain and low temperature sensitization on corrosion resistance of AISI 321 stainless steel in elevated borate buffer solution was investigated. The study found that the AISI 321 stainless steel with 20% strain showed the lowest degree of sensitization due to the fact that sample with 20% strain had high dislocation density which promoted chromium diffusion and a small amount of α'-martensites. The results from electrochemical impedance spectroscopy indicated that sensitized sample with 20% strain showed the best corrosion resistance after immersion test at 290 °C. A good agreement was found between the electrochemical impedance spectroscopy and the degree of sensitization. The oxide film was composed of three layers according to the results of the XPS and Raman spectra. In addition, the outer part compositions of the oxide film were mainly γ-Fe2O3 and Fe-Cr spinel and iron hydroxide, while the inner and intermediate layers were mainly Fe-Cr spinel and the mixtures of the oxides of Fe, Cr, Ni. The ratio of hydroxide in oxide film increased due to large strain, especially for chromium hydroxide. Mott-Schottky analysis showed that more hydroxides induced more donor and acceptor concentrations in oxide film. More hydroxides reduced corrosion resistance of oxide film.

The effects of urea concentration on microstructures of Ni3S2formed on nickel foam and its hydrogen evolution reaction were investigated. The Ni3S2 nanosheets with porous structure were formed on nickel foam during hydrothermal process due to low urea concentration. While high urea concentration facilitated the forming of Ni3S2 nanotube arrays. The resulting Ni3S2 nanotube arrays exhibited higher catalytic activity than Ni3S2nanosheets for hydrogen evolution reaction. This was mainly attributed to a fact that Ni3S2 nanotube arrays facilitated diffusion of electrolyte for hydrogen evolution reaction.

The nanocrystalline pure nickels with different grain orientations were fabricated by direct current electrodeposition process. The grain size slightly decreased with the increasing of electrodeposition solution temperature. However, grain orientation was affected significantly. Comparing with samples obtained at 50 °C and 80 °C, sample obtained at 20 °C had the strongest (111) orientation plane which increased electrochemical corrosion resistance of this sample. At the same time, the lowest (111) orientation plane deteriorated electrochemical corrosion resistance of sample obtained at 50 °C.

The effect of grain refinement on the corrosion resistance of the passive film formed on 2099 Al–Li alloy was investigated. The microscopic structures of cold rolled 2099 Al–Li aluminum alloy were characterized by Transmittance Electron Microscopy and surface activity was analysed by electron work function. The corrosion resistance of the passive film was studied by electrochemical techniques and Raman spectra. It was found that nano/ultrafine grained 2099 Al–Li alloy with refined precipitation phases was obtained by several plastic deformation process. The corrosion resistance of the 2099 Al–Li aluminum alloy was improved by grain refinement and refined precipitation phases. The improved corrosion resistance of 2099 Al–Li alloy after grain refinement was attributed to decreased electron work function. The grain refinement promoted the forming of thicker passive film and decreased acceptor concentration in passive film.

The results from double loop electrochemical potentiokinetic reactivation technique, potentiostatic critical pitting temperature technique and electrochemical impedance spectroscopy showed that the resistance of the 2205 duplex stainless steel to pitting corrosion decreased with the increasing of sensitization time due to a decreasing in passivation ability. The 2205 duplex stainless steel showed the increase in pitting corrosion in the ferritic phase and in intergranular corrosion between the austenitic and ferritic phases with the increasing of sensitization time. The precipitated phases changed due to the increasing of the sensitization time, which affected degree of sensitization of the 2205 duplex stainless steel.

The stain-induced nanocrystalline α'-martensite was obtained by cryogenic cold rolling at liquid-nitrogen temperature for 316L stainless steel. The electrochemical results showed nanocrystalline 316L stainless steel deteriorated its corrosion resistance in a typical proton exchange membrane fuel cell environment compared with coarse grained one. However, comparing with electrochemically nitrided coarse grained stainless steel, electrochemically nitrided nanocrystalline stainless steel improved significantly corrosion resistance in the same environment, which was supported further by Mott–Shottky analysis. X-ray photoelectron spectroscopy analysis revealed that the nanocrystalline promoted the enrichment of nitrogen and chromium and inhibited form of NH 3 on the surface, which could significantly improve the corrosion resistance of the 316L stainless steel. The present study showed that the electrochemically nitrided 316L stainless steel was more suitable for the bipolar plates in proton exchange membrane fuel cell environment than the untreated one, especially for nanocrystalline stainless steel.

The effects of electrochemical nitridation on the corrosion resistance of the 2205 duplex stainless steel were investigated. It was found that increased nitrogen content in the 2205 duplex stainless steel affected donor and acceptor concentration distribution in the passive films on the surface of the 2205 duplex stainless steel. Moreover, the total donor and acceptor concentration in passive films decreased with the increasing of nitrogen content. The electrochemically nitridation facilitated to induce compact passive film and thus improved significantly the corrosion resistance of the 2205 duplex stainless steel in borate buffer solution.

The effects of solution temperature, concentration of chloride ions, and grain refinement on the corrosion resistance of the passive film formed on 304 stainless steels in borate buffer solution were investigated by electrochemical impedance spectroscopy and Mott-Schottky measurements. The results showed that the passive films formed on the surface of 304 stainless steels possessed n- and p-type semiconductor characteristics. With the increase of solution temperature, the corrosion resistance of the passive film of coarse and nano/ultrafine grained stainless steels decreased. However, the corrosion resistance of the passive film in nano/ultrafine grained stainless steel was higher than that in the coarse grained one. Moreover, in cyclic potentiodynamic polarization tests, chloride ions changed semiconductor characteristics of the passive film formed on the surface of stainless steel.

With the increase of strain, the degree of sensitization of 304 stainless steels increased and desensitization did not occur in 240 h at 380 °C. Although the stress relaxation appeared, the reversed transformation of strain-induced martensite was scarcely observed. Therefore, strain-induced α′-martensite could lead directly to increase of degree of sensitization. Unlike the sensitization at lower temperature, tensile pre-strain promoted desensitization in higher temperature at 575 °C and 675 °C. The higher the sensitization temperature was, the lower the degree of sensitization was. The higher temperature promoted reversed transformation of strain-induced α′-martensite and facilitated recovery and recrystallization of reversed transformed austenite, which resulted in decreased degree of sensitization.

{011} planes which were medium close-packed planes were the dominating orientation in A sample (without burnishing) and B sample (a burnished sample) surfaces. There was not a common close-packed plane dominating orientation parallel to C sample (the other burnished sample) surface, and texture in this sample was abnormal. The corrosion property by electrochemical impedance spectroscopy was improved by burnishing process. Considering similar dislocation density obtained by XRD and grain boundary characteristic of two burnished samples, although the surface energy quantity for Al was (111)

The nano/ultrafine grain (NUG) with an average grain size of 230 nm was obtained by cold rolling down to 94% reduction in thickness and reversion annealing at 800 °C for 200 s. The NUG sample exhibited a lower corrosion resistance than coarse grain (CG) sample in 0.1 M NaCl solution at room temperature, indicating that the passive film formed on the surface of the NUG austenite did not improve corrosion resistance in the solution. However, the corrosion resistance of the former was higher than that of the latter in 0.5 M H 2 SO 4 solution at room temperature, which was proved by electrochemical impedance spectroscopy and Mott–Schottky plots in conjunction with the point defect model. Comparing slightly difference of acceptor density (i.e. cation vacancies) between CG and NUG samples, higher corrosion resistance of NUG sample was probably attributed to significant decreased donor density (i.e. oxygen vacancies and cation interstitials) in 0.5 M H 2 SO 4 solution. Moreover, the corrosion resistance of the passive films formed on CG and NUG samples in borate buffer solution at room temperature showed little difference.