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The microstructures and strength of pure Ni ball after high speed collision process were investigated. The elongated and equiaxed nanocrystallines with high angle grain boundaries and random grain orientation were formed near the interface position due to high strain and strain rate. Sufficient intragranular recrystallization occurred due to shock induced storage energy. Sufficient recrystallization in the grain interior facilitated to activate dislocation in the process of subsequent deformation and resulted in ameliorated hardness. Moreover, the high angle grain boundaries could effectively impede the dislocation movement, which also significantly enhanced the strength of Ni ball near the interface.

The ultrafine grained pure Ni and Ni-W alloy were obtained by electrodeposition technique and subsequent annealing treatment. The effects of annealing on the microstructures, the mechanical properties and the corrosion resistance of pure nickel and Ni-W alloy were investigated. The EBSD analyses showed that annealed pure Ni displayed preferred grain orientation, while annealed Ni-W alloy showed relatively more random grain orientation. Moreover, abnormal grain growth was observed in annealed pure Ni, while annealed Ni-W alloy displayed a more uniform grain size distribution. It could be predicted that solid solution of tungsten significantly suppressed grain growth and induced uniform grain size distribution during low temperature annealing process. Moreover, comparing with annealed pure Ni, the tungsten in annealed Ni-W alloy changed the semiconducting characteristic of surface passive films. Annealed Ni-W alloy showed higher corrosion resistance than annealed pure Ni in 3.5 wt% NaCl solution and in borate buffer solution.

The effects of the ball milling on microstructures of the graphene/Ni composites and subsequent hydrogen evolution reaction in acidic solution were investigated. Ni nanoparticles with average grain size of 4 nm were uniformly dispersed on the graphene surface after short time ball milling. While amorphous characteristic was observed due to long time ball milling. The graphene/Ni composites with amorphous structure exhibited higher electrocatalytic performance than the graphene/Ni composites with nanocrystalline structure. The Volmer-Heyrovsky mechanism was found for the graphene/Ni composites with nanocrystalline structure, while the graphene/Ni composites with amorphous structure showed evident Heyrovsky mechanism. The excellent hydrogen evolution reaction and stability of the graphene/Ni composites could be attributed to superior interfacial contact, amorphous Ni, and synergistic effect between amorphous Ni and high conductive graphene.

NiMoO4 nanoparticles and quantum dots were uniformly distributed on the surface of reduced nanohole graphene oxide (rNHGO). NiMoO4@rNHGO exhibited a higher specific capacitance and better cycling stability than NiMoO4@reduced graphene oxide (rGO), which were attributed to the large surface area and high electrical conductivity. NiMoO4 nanoparticles and quantum dots (QDs) had high surface to volume ratio, which would not result in change in volume during the electro–chemical operation and induced better supercapacitor performance. Moreover, synergistic effect between NiMoO4 and the rNHGO also improved undoubtedly high specific capacitance and cycle stability.

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.

3D MoS 2 hollow spheres were successfully fabricated by hydrothermal process. Commercial bulk MoS 2 had quite large grain size and preferential (002) grain orientation, while as-prepared MoS 2 hollow spheres had refined grain and random grain orientation. Meanwhile, the hydrogen evolution reaction of the commercial bulk MoS 2 and as-prepared MoS 2 hollow spheres was systematically investigated in acidic solution. The as-prepared MoS 2 hollow spheres catalyst exhibited a lower onset overpotential for hydrogen evolution reaction than bulk MoS 2 . The superior hydrogen evolution reaction activity could be attributed to the unique 3D MoS 2 hollow spheres which provided more active edge sites. In addition, 3D MoS 2 hollow spheres also exhibited excellent high chemical stability after 1000 potential cycles.

Cotton-like NiO is formed on the surface of bare Ni foam after hydrothermal process and calcination process, while ultrathin NiO nanoflakes occur on Ni foam coated with graphene. The high specific capacitance of 1782 F g− 1 at 1 A g− 1 and 90.2% capacity retention at 1 A g− 1 after 5000 cycles charge-discharge test are found. The graphene induces the high electrical conductivity and excellent interfacial contact, in addition, the graphene facilitates the forming of ultrathin NiO nanoflakes which result in huge pseudocapacitance due to large surface area and abundant mesoporous. The unique microstructure characteristic promotes interfacial electron transport in the electrode material and improves ion diffusion during the electrochemical reaction process.

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 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 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.

The effect of the strain of 316L stainless steel on its corrosion resistance in borate buffer solution was investigated by in site tensile test and the electrochemical impedance spectroscopy measurements. It was found that the corrosion resistance of the 316L stainless steel decreased with the increasing of in site strain. The lower corrosion resistance of the stainless steel during in site strain was mainly attributed to the higher doping concentration in passive film. Especially, with the increasing of in site strain, the concentrations of acceptor (i.e., cation vacancies) in the passive films significantly increased. More acceptor concentrations reduced the compactness of the passive film and its corrosion resistance. Moreover, two exponential relationships were found between in site strain and the charge transfer resistance of the passive film and between in site strain and total doping concentrations in passive film, respectively.