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A large number of pitting pits were formed on the surface of Ni foam by immersion corrosion in NaCl solution. The graphene was deposited on Ni foam templates, then 3D graphene foams were obtained by removing Ni foam in the mixed solution of ferric chloride and hydrochloric acid. It was found that pitting pits on Ni foam facilitated to form fewer-layers graphene, however, pitting pits on Ni foam induced more defects on 3D graphene foam. The graphene with fewer-layers exhibited better electrical and mechanical properties for strain sensor devices. Moreover, fewer-layers graphene effectively inhibited degradation of resistance during cycling stability tests.

Co 3 O 4 @MnO 2 core–shell arrays hybrid electrode directly grown on Ni foam for supercapacitor was obtained by two-step hydrothermal processes. Co 3 O 4 @MnO 2 core–shell arrays hybrid electrode exhibited a high specific capacitance of 1920 F g −1 at current density of 1 A g −1 . This was attributed to relative high conductivity of the Co 3 O 4 nanowire arrays and the large surface area provided by the ultrathin MnO 2 nanosheets. The porous MnO 2 nanosheets stack provided numerous channels for rapid diffusion of electrolyte ions and fast electron transport, which enhanced the electrochemical reactions. The synergetic effect between Co 3 O 4 nanowire and MnO 2 nanosheets also improved the supercapacitor performance. In addition, the Co 3 O 4 @MnO 2 core–shell arrangement also exhibited excellent cyclic stability.

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 pure NiMoO4 and sphere-shaped NiMoO4@rGO nanostructure were obtained by one step hydrothermal process. The sphere-shaped NiMoO4@rGO nanostructure showed higher significantly specific capacitance value than pure NiMoO4. The enhanced capacitive performance of the as-prepared sphere-shaped NiMoO4@rGO nanostructure was attributed to the mesoporous structure, large surface area of rGO nanosheets and higher electrical conductivity. These mesoporous structures could provide more electroactive sites which promoted the electrode–electrolyte contact and enhanced ion and electron transport during the chemical reaction. Moreover, high specific capacitance also could be attributed to the positive synergistic effect between rGO and NiMoO4.

Pure CoMoO4 nanoplate arrays grew on nickel foam by one-step hydrothermal process, while flower-like nanoflake CoMoO4@RGO nanocomposites grew on nickel foam. Flower-like nanoflake CoMoO4@RGO nanocomposites electrode exhibited higher capacitance than pure CoMoO4 nanoplate arrays electrode. Maximum specific capacitance of 856.2 F g−1 was obtained at current density of 1 A g−1 for CoMoO4@RGO nanocomposites electrode. In addition, after 2000 cycles of continuous galvanostatic charge–discharge cycles, only 5.5% degradation of specific capacitance was found for CoMoO4@RGO nanocomposites. CoMoO4@RGO nanocomposites exhibited lower electrochemical resistance than pure-CoMoO4. This was because that the former had larger specific surface area and average pore diameter than the latter. The flower-like nanoflake CoMoO4 facilitated electrolyte movement during charge or discharge process and provided more active sites for the electrochemical reactions. In addition, the synergetic effect between RGO and CoMoO4 also improved the supercapacitor performance.

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 thermal reduced graphene oxide deposition on nickel foam was successfully synthesized by ultrasonic and subsequent thermal reduction process. Ultrathin mesoporous Ni3S2 was formed on the bare nickel foam after hydrothermal process, while Ni3S2 nanotube arrays were formed on the surface of nickel foam with the thermal reduced graphene oxide due to catalysis action of thermal reduced graphene oxide. The resulting Ni3S2 nanotube arrays exhibited higher catalytic activity than ultrathin mesoporous Ni3S2 for hydrogen evolution reaction. In addition, and excellent stability was also obtained in Ni3S2 nanotube arrays.

The undulate bulk Ni 3 S 2 with porous surface was obtained on bare Ni foam after hydrothermal process, while plume-like Ni 3 S 2 was formed on the surface of Ni foam with the thermal reduced graphene oxide (rGO) due to catalysis action of thermal rGO. The Ni 3 S 2 on Ni foam with rGO showed better electrochemical performance than Ni 3 S 2 on Ni foam. In addition, Ni 3 S 2 on Ni foam with rGO also improved long-cycle stability. This made it become a good current collector in energy storage applications. The reason for the improvement of the supercapacitor performance of Ni 3 S 2 on Ni foam with rGO was discussed.

The effects of urea on microstructures of SnO2 during hydrothermal process and its supercapacitor performance were investigated. The sphere SnO2 was formed on Ti plate in hydrothermal solution without urea, while the SnO2 micro-flowers were assembled by numerous few-layered nanopetals due to adding to urea during hydrothermal process. The separated SnO2 nanopetals arrays showed better electrochemical performance than sphere SnO2. The gap between SnO2 nanopetals promoted penetration of the electrolyte and induced high supercapacitive performance.

3D Co 3 O 4 @CoMoO 4 core–shell architectures directly grown on nickel foam for supercapacitor electrode were obtained by two-step hydrothermal process. The Co 3 O 4 @CoMoO 4 nanocomposites electrode exhibited higher capacitance than Co 3 O 4 nanowire electrode. Maximum specific capacitance of 2530 F g − 1 was obtained at current density of 1 A g − 1 for Co 3 O 4 @CoMoO 4 core–shell architectures. In addition, after 3000 cycles of continuous galvanostatic charge–discharge cycles, only about 3.7% degradation in specific capacitance could be noticed. The CoMoO 4 nanorods stack on Co 3 O 4 nanowires arrays allowed facile electrolyte movement during charge or discharge process and provided more active sites for the electrochemical reactions. The unique architecture had a large interfacial area and numerous channels for rapid diffusion of electrolyte ions and fast electron transport. In addition, the synergetic effect between Co 3 O 4 nanowire and CoMoO 4 nanorods also improved the supercapacitor performance.

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 microscopic structures of different burnished layers in 2024 aluminum alloy were characterized by Transmission Electron Microscopy. The corrosion resistance of the burnished 2024 aluminum alloy was improved by grain refinement. The decreasing of electron work function improved corrosion resistance of the burnished 2024 aluminum alloy, moreover, less donor and acceptor concentrations in passive film also improved corrosion resistance of the burnished 2024 aluminum alloy. However, the substructures with high density dislocations deteriorated significantly the corrosion resistance of burnished 2024 aluminum alloy. More aluminum oxides improved the corrosion resistance of nanocrystalline 2024 aluminum alloy based on result of XPS.

The corrosion resistance of coarse grained and nanocrystalline Ni Fe alloys in chloride solutions and proton exchange membrane fuel cell environment was investigated. The nanocrystalline Ni Fe alloys were obtained by electrodeposition, while coarse grained Ni Fe alloys were obtained by annealing. The results from electrochemical tests showed that coarse grained Ni Fe alloys had higher corrosion resistance than nanocrystalline samples in NaCl solution due to more compact passive films formed on the surface of coarse grained Ni Fe alloys. In addition, Raman spectra test showed that many nanocrystalline boundaries in electrodeposited Ni Fe alloys promoted the diffusion of nickel, which resulted in the formation of more nickel oxides and nickel hydroxides. However, the electrochemical study showed that coarse grained sample had lower corrosion resistance than nanocrystalline one in a typical proton exchange membrane fuel cell environment. The present study showed that nanocrystalline Ni Fe alloys were more suitable for the bipolar plates in proton exchange membrane fuel cell environment.

Although the grain refinement by severe plastic deformation can obtain outstanding mechanical strength, this usually involves sacrificing the plasticity of the materials. This work therefore provided a simple processing route to achieve strength and plasticity by twice cold rolling and reversed transformation annealing for the 316L stainless steel to optimize the recrystallized microstructures. Our study revealed that applied approach of twice cold rolling and reversed transformation annealing dramatically improved strength and retained better ductility in nano/ultrafine grained 316L stainless steel. The results obtained by the transmission electron microscopy indicated that the grain refinement facilitated the forming of deformed nanotwins in austenitic stainless steels. The high strength was attributed to grain refinement, α′-martensite transformation and nanotwin, while excellent ductility resulted from α′-martensite transformation and grain boundary slip or rotation.

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 corrosion behaviors of NiTi shape memory alloy in NaCl solution, H2SO4 solution and borate buffer solution were investigated. It was found that TiO2 in passive film improved the corrosion resistance of NiTi shape memory. However, low corrosion resistance of passive film was observed in low pH value acidic solution due to TiO2 dissolution. Moreover, the corrosion resistance of NiTi shape memory alloy decreased with the increasing of passivated potential in the three solutions. The donor density in passive film increased with the increasing of passivated potential. Different solutions affect the semiconductor characteristics of the passive film. The reducing in the corrosion resistance was attributed to the more donor concentrations in passive film and thinner thickness of the passive film.

Surface enriched molybdenum 316L stainless steel was obtained by ball milling technique. The electrochemical tests showed surface enriched molybdenum improved the corrosion resistance of the 316L stainless steel. This was attributed to a fact that more molybdenum oxides improved the corrosion resistance of the 316L stainless steel in borate buffer solution. In addition, more chromium oxides in the passive film after ball milling also improved corrosion resistance of the 316L stainless steel.

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 nickel, nickel-molybdenum alloy, nickel-graphite and nickel-reduced graphene oxide composite coatings were obtained by the electrodeposition technique from a nickel sulfate bath. Nanocrystalline molybdenum, graphite and reduced graphene oxide in nickel coatings promoted hydrogen evolution reaction in 0.5 M H2SO4 solution at room temperature. However, the nickel-reduced graphene oxide composite coating exhibited the highest electrocatalytic activity for the hydrogen evolution reaction in 0.5 M H2SO4 solution at room temperature. A large number of gaps between ‘cauliflower’ like grains could decrease effective area for hydrogen evolution reaction in slight amorphous nickel-molybdenum alloy. The synergistic effect between nickel and reduced graphene oxide promoted hydrogen evolution, moreover, refined grain in nickel-reduced graphene oxide composite coating and large specific surface of reduced graphene oxide also facilitated hydrogen evolution reaction.

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 effect of grain refinement on corrosion resistance of alloy 690 was investigated. The electron work function value of coarse grained alloy 690 was higher than that of nano/ultrafine grained one. The grain refinement reduced the electron work function of alloy 690. The passive films formed on coarse grained and nano/ultrafine grained alloy 690 in borate buffer solution were studied by potentiodynamic curves and electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The results showed that the grain refinement improved corrosion resistance of alloy 690. This was attributed to the fact that grain refinement promoted the enrichment of Cr 2 O 3 and inhibited Cr(OH) 3 in the passive film. More Cr 2 O 3 in passive film could significantly improve the corrosion resistance of the nano/ultrafine grained alloy 690.

The passivation properties of deformed 304 stainless steels after immersion in borate buffer solution containing 0.2821 mol/L Cl− at 288 °C were investigated. The spinel and magnetite oxides were formed on all the samples. However, the hematite oxides reduced significantly with the increasing of strain. The sample with maximum strain possessed the poorest corrosion resistance. The hematite oxide could offer high corrosion resistance, while magnetite evidently deteriorated corrosion resistance. Moreover, the influence of the donors in outer layer of oxide film on corrosion resistance was more important than that of the acceptors in inner layer.

The passive film formed on the surface of the alloy 690 in borate buffer solution was studied by potentiodynamic curves and electrochemical impedance spectroscopy. With the increasing of the passivation potential, the corrosion resistance of the alloy 690 reduced. Moreover, the corrosion resistance of the passive film was the lowest in the vicinity of 0.6 V SCE . These results were supported by XPS and Mott–Schottky analyses. The corrosion resistance of the alloy 690 increased with the increasing of passivated potential in borate buffer solution with chloride ion. The chloride ion decreased corrosion resistance of the alloy 690 according to point defect model.

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 nano/ultrafine grained stainless steel promoted the form of more deformation nanotwins and inhibited dislocation slip and strain induced α′-martensite transformation during deformation compared with coarse grained stainless steel. The diffusivity of the point defects in passive film in coarse grain stainless steel was lower than that in nano/ultrafine one. The corrosion resistance of nano/ultrafine grained stainless steel was improved by reducing content of strain induced α′-martensite. Moreover, the donor and acceptor densities in passive film formed on the stainless steel increased due to more strain induced α′-martensites and more chloride ions. Fewer strain induced α′-martensites and more nanotwins in nano/ultrafine grained stainless steel improved its corrosion resistance.

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 effect of the strain of 316L stainless steel on its corrosion resistance in PEMFC environment was investigated. Higher tensile strain facilitated the formation of more dislocations. The 316L stainless steel with 20% strain showed the best corrosion resistance in PEMFC environment containing a few fluoride ions, however, the corrosion resistance of the stainless steel decreased with the increasing of engineering strain in PEMFC environment with a considerable amount of fluoride ions. The morphology and density of the dislocations in strained 316L stainless steel could both affect significantly its corrosion resistance in PEMFC environment. This conclusion was supported by Mott–Schottky measurement and XPS analysis.

The effect of cold rolling temperature on grain boundary characteristic of the 304 austenitic stainless steels in thermomechanical treatment was examined. Comparing to cold rolling at room temperature and annealing, the cryogenic cold deformation and annealing promoted grain refinement and reduced fraction of coincidence site lattice. Although more coincidence site lattice restrained sensitization, the grain refinement accelerated sensitization. The sensitization deteriorated corrosion resistance of 304 austenitic stainless steel obtained by thermomechanical treatment.

The effects of cold rolling temperature on grain size and grain orientation of pure iron were investigated. Comparing with sample rolled at room temperature, the grain refinement was facilitated in sample obtained by cryogenic cold rolling at liquid-nitrogen temperature. However, the grain orientation changed little for two samples. It was shown that cathodic hydrogen evolution reaction could govern the corrosion reaction for pure iron in sulfuric acid solution. The grain refinement obtained by rolling improved the corrosion resistance of iron in sulfuric acid solution, borate buffer solution and borate buffer solution with chloride ion. However, comparing with iron rolled at room temperature, the corrosion resistance of iron obtained by cryogenic temperature rolling was lower. Comparing with iron rolled at room temperature, higher dislocation density in iron rolled at cryogenic temperature reduced its corrosion resistance.

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.

The passive film of iron showed n-type semiconductor characteristic in borate buffer solution, and its donor concentration increased slightly after tensile strain in the present study. However, comparing with solution-annealed sample, the anodic passive film formed on tensile-strained one was highly protective. The more dislocations on tensile-strained sample promoted the diffusion of iron and oxygen vacancy. Moreover, more donor density (mainly oxygen vacancies) promoted the diffusion of oxygen. They all facilitated tensile-strained sample to form Fe2O3 and thicker passive film on the surface. More Fe2O3 and thicker passive film on the surface of tensile-strained iron could improve corrosion resistance. Copyright © 2014 John Wiley & Sons, Ltd.

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.

The effect of burnish process on 2024 aluminum alloy was studied by electron work function and electron backscattered diffraction (EBSD). Moreover, the corrosion resistance of thin passive films formed on 2024 aluminum alloy in borate buffer solutions was studied by the electrochemical impedance spectroscopy (EIS), the Mott–Schottky plots and the galvanostatic techniques. The composition of passive films was analyzed by Raman spectra. The results obtained indicated that the impedance increased due to burnish and this was attributed to decreased electron work function and higher current efficiency in the burnished aluminum alloy which led to thicker passive films. It was further supported by Raman spectra experiment. Moreover, the donor and acceptor concentration of passive films and their the semiconductor type have changed due to burnish.

The passive behaviors of coarse and nano/ultrafine grain austenitic stainless steels processed by cold rolling and reversion annealing were investigated. The average grain about 200 nm was obtained by cold rolling down to 94% reduction in thickness and reversion annealing at 800 °C for 250 s. Passive films formed in borate buffer solution (pH 9.2) have been characterized by electrochemical impedance spectroscopy and Mott–Schottky plots. The impedance results indicated a distinct inflection was observed with the increasing of potential, however, the Mott–Schottky analysis did not show such inflection point in the same potential range. There were not evident differences in passive properties between coarse and nano/ultrafine grain samples. This was attributed to synergistic effect of grain refinement and orientation. However, the corrosion resistance of the passive film in nano/ultrafine grain sample was higher than that in coarse grain sample after immersion test by the three-point-bend loading.

The martensitic phase transformation and reverse transformation of AISI 304 austenitic stainless steel by tensile pre-strain and sensitization at 948 K were investigated by X-ray diffraction. Martensite reversion was found to occur by an athermal shear mechanism at this temperature. A small quantity of “supposed secondary α′-martensite” was generated in a specimen suffering 40% engineering strain after being sensitized for a long time and water quenched. This could be due to the redistribution of carbon and chromium in the reverted austenitic phase and dislocations, which promoted the nucleation of the martensitic transformation.

The electrochemical measures in deformed AISI 304 stainless steels ranged from 0% to 24% were investigated. With the increasing of the strain α′-martensite was gradually increasing. Moreover, the morphologies and densities of dislocations changed with increasing strain. The Mott–Schottky plots showed that the maximum total of donor and acceptor densities in passive film occurred in borate buffer solution when ɛ-martensite was most, while in borate buffer solution with 5000 ppm Cl− the maximum total of donor and acceptor densities occurred when the content of α-martensite was most. These results were proven by further impedance spectroscopy experiments.

The degree of sensitization for tensile pre-strain (0%, 10%, 20%, 30%, 40%) of AISI 304 stainless steels and sensitization at 575 °C was investigated by the double loop electrochemical potentiokinetic reactivation technique and scanning electron microscopes (SEMs). The properties of passive films of all the sensitized specimens in borate buffer solution (pH = 9.2) with 5000 ppm Cl− were investigated by the Mott–Schottky analysis. The degree of sensitization results showed that two reactivation current peak values were obtained for the sensitized specimens after 30% and 40% pre-strain. The degree of sensitization was decreased by pre-strain, except for specimen with 10% pre-strain. The results were further confirmed by the Mott–Schottky analysis.

The ultrafine grained 2205 duplex stainless steel was obtained by cold rolling and annealing. The tensile properties were investigated at room temperature. Comparing with coarse grained stainless steel, ultrafine grained sample showed higher strength and plasticity. In addition, grain size changed deformation orientation. The strain induced α'-martensite was observed in coarse grained 2205 duplex stainless steel with large strain. However, the grain refinement inhibited the transformation of α'-martensite;nevertheless, more deformation twins improved the strength and plasticity of ultrafine grained 2205 duplex stainless steel. In addition, the grain refinement improved corrosion resistance of the 2205 duplex stainless steel in sodium chloride solution.