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The state-of-the-art lithium-ion capacitors (LICs), consisting of high-capacity battery-type anode and high-rate capacitor-type cathode, can deliver high energy density and large power density when comparing with traditional supercapacitors and lithium-ion batteries, respectively. However, the ion kinetics mismatch between cathode and anode leads to unsatisfied cycling lifetime and anode degradation. Tremendous efforts have been devoted to solving the abovementioned issue. One promising strategy is altering high conductive hard carbon anode with excellent structural stability to match with activated carbon cathode, assembling dual-carbon LIC. In this contribution, one-pot in-situ expansion and heteroatom doping strategy was adopted to prepare sheet-like hard carbon, while activated carbon was obtained involving activation. Ammonium persulfate was used as expanding and doping agent simultaneously. While furfural residues (FR) were served as carbon precursor. The resulting hard carbon (FRNS-HC) and activated carbon (FRNS-AC) show excellent electrochemical performance as negative and positive electrodes in a lithium-ion battery (LIB). To be specific, 374.2 mAh g−1 and 123.1 mAh g−1 can be achieved at 0.1 A g−1 and 5 A g−1 when FRNS-HC was tested as anode. When combined with a highly porous carbon cathode (SBET = 2961 m2 g−1) synthesized from the same precursor, the LIC showed high specific energy of 147.67 Wh kg−1 at approximately 199.93 W kg−1, and outstanding cycling life with negligible capacitance fading over 1000 cycles. This study could lead the way for the development of heteroatom-doped porous carbon nanomaterials applied to Li-based energy storage applications.

The inhibition of Mo segregation and phase precipitation is vital for improving the hot workability and corrosion resistance of superaustentic stainless steels (SASS). The boron non-equilibrium segregation of S31254 SASS was implemented through solid solution, air cooling, and diffusion at low-temperature treatment (SADT). The precipitation process and intergranular corrosion (IGC) of S31254 SASS with various boron distributions were researched at a sensitive temperature. The second phases were observed and identified by SEM and TEM. IGC susceptibility was evaluated by double-loop potentiodynamic reactivation (DL-EPR) measurements. The SADT treatment promoted more segregation of B at the grain boundary, leading to lower amounts of grain boundary precipitation before aging for 6 h. The decrease of σ phases in B-regulated samples enhances the IGC resistance, compared with the samples without B addition specimens.

Purposes Owing to the serious segregation of Cr and Mo in super austenitic stainless steel, a large number of Mo- and Cr-rich second phases precipitate during the hot rolling process, which leads to rolling cracking and delamination. Boron microalloying is helpful for preventing the σ phase precipitation. Methods The matrices and precipitate structures of boron-free and boron-containing S31254 super austenitic stainless steels and the distribution of elements such as Cr and Mo were analyzed experimentally. Combined with the experimental results, two grain boundary structure models of γ-Fe ∑9(22-1) and γ-Fe ∑11(113) were taken as the research objects. The segregation tendency of Cr, Ni, Mn, Mo, Cu, and Si at grain boundaries was analyzed, and the influence of B on the segregation behavior of these elements at grain boundaries was discussed. Findings It was found that all of these alloying elements can be solid soluble in the grain boundary structure model of γ-Fe ∑9 and γ-Fe ∑11. Both Cr and Mo tend to segregate at the grain boundary of γ-Fe ∑9 and γ-Fe ∑11, and Mo tends to segregate most seriously at the grain boundary. When B is at the grain boundary, the segregation of Cr and Mo at the γ-Fe ∑11 boundary is inhibited, but the segregation of Mo at γ-Fe ∑9 boundary is weakly inhibited. Conclusions The essential reason why the precipitated phase can be inhibited by the addition of super austenitic stainless steel to B is explained from the atomic level, which lays a foundation for the composition optimization of super austenitic stainless steel in the future.

The influence of B addition on dissolution behavior of (σ + γ)e eutectics of a 6Mo super austenitic stainless steel S31254 during the homogenization process was investigated by SEM-BSE observations combined with EDS. The results showed that the addition of 0.005 wt% B accelerated the dissolution of the σ phase controlled by Mo diffusion, during homogenization from 30 to 90 min at 1180 °C. TOF-SIMS results showed that B segregated along the σ/γ interface in the as-cast samples. TEM observations combined with EDS investigated the phase interfaces in two as-cast samples in detail to correlate σ phase dissolution. Compared with the B-free sample, the wide transition zone (∼60 nm) with a composition gradient was more clearly observed at the σ/γ interface in the B-containing sample. The transition zone with B had two features: local segregation of B element and precipitation of R phases at the σ/γ interface. R phases owned larger contents of Mo, which was not almost observed in the as-cast S31254. The results indicated that B segregation changed the phase interface, accelerating Mo diffusion at the σ/γ interface. In addition, the results of nanoindentation indicated a more uniform distribution of hardness at the σ/γ interface after homogenization of the B-containing sample, which can be beneficial to improve the deformation compatibility of S31254 during hot working.

A systematic study was conducted on the influence of silicon on the microstructure, stress distribution, and martensitic nucleation and transformation of 301 metastable austenitic stainless steel during cold-rolling deformation. When the deformation amount of conventional 301 stainless steel is ≤20%, the amount of martensite transformation is very small. When the deformation amount is ≥30%, the amount of martensite transformation significantly increases. The introduction of Si significantly improves the amount of martensite transformation and the uniformity of deformation. 301Si-H has a significantly higher amount of martensite in the same deformation microstructure than conventional 301Si-L with a lower silicon content. Increasing the Si content decreases the stacking fault energy of 301 stainless steel. During deformation, Si tends to cluster at the grain boundaries, reducing stacking fault width and increasing dislocation density, creating sites for shear martensite nucleation at the grain boundaries. Simultaneously, significant deformation encourages the formation of deformation twins and facilitates martensite nucleation.

Grain boundary (GB) precipitation-induced cracking is a significant issue for S31254 super austenitic stainless steel during hot working. Investigating the deformation behavior based on precipitate morphology and distribution is essential. In this study, continuous smaller and intermittent larger precipitates were obtained through heat treatments at 950 °C and 1050 °C. The microstructure evolution and mechanical properties influenced by precipitates were experimentally investigated using an in situ tensile stage inside a scanning electron microscope (SEM) combined with electron backscatter diffraction (EBSD). The results showed that continuous precipitates at 950 °C had a stronger pinning effect on the GB, making grain rotation difficult and promoting slip deformation in the plastic interval. Continuous precipitates caused severe stress concentration near GB and reduced coordinated deformation ability. Additionally, the crack propagation path changed from transcrystalline to intercrystalline. Furthermore, internal precipitates were a crucial factor affecting the initial crack nucleation position. Interconnected precipitates led to an intergranular fracture tendency and severe deterioration of the material’s plasticity, as observed in fracture morphology.

Super austenitic stainless steel (SASS) is one kind of high Mo-alloy steel with excellent corrosion resistance when applied in an extremely corrosive environment. However, high contents of Cr and Mo tend to form precipitates along the grain boundary at high temperatures, leading to a great deterioration of corrosion resistance. Herein, a method of short-time aging treatment at 500 °C and 550 °C was explored, which was intended to regulate the distribution of elements at grain boundaries to improve corrosion resistance. The results indicate that before the precipitates nucleation, as the temperature rises from 500 °C to 550 °C, the Mo element has obvious diffusion behavior towards the grain boundary. Also, the uniform distribution of a small amount of Mo at the grain boundary can be conducive to improving the corrosion resistance. In addition, B inhibits the separation of Mo to grain boundary and delays the formation of the precipitated phase. The addition of B improves the intergranular corrosion resistance of SASS, especially after aging at 500 °C, which is attributed to the passivated film's Cr2O3 and Mo(VI) content. However, when the aging temperature reaches 550 °C, more Mo segregates to the grain boundaries, resulting in Mo-depleted zones, which decreases corrosion resistance.

The influence of boron (B) and cerium (Ce) grain boundary (GB) co-segregation on the precipitates formation of S31254 during 950–1050 °C was studied through a new heat treatment process. The results show that B and Ce segregate at GBs by air cooling and diffusion at 300 °C. The segregation of B and Ce at GBs inhibits formation of σ phases. B can dissolve in precipitates, which leads to the serrated GBs. Ce can't dissolve in precipitates, which makes the distribution of the precipitates more discontinuous. There is still nano-scale precipitates with the addition of B and Ce after aging for 180 min at 1050 °C. B and Ce at GBs promote mechanical properties of S31254.

6Mo super austenitic stainless steel (SASS) with nitrogen contents of 0.2 and 0.4 (wt.%) was melted, and solution treatments at 1100, 1180, and 1250 °C for 30 min were performed. The effects of nitrogen on the microstructure and pitting resistance of the two steels that signed as 0.2N and 0.4N samples were investigated. At a heat-treatment temperature of 1180 °C, the alloy demonstrates the highest corrosion resistance, attributed to the combined effects of grain size and precipitates. The structure of the passivation film changes with increasing nitrogen content, with the Cr/Fe ratio is significantly higher in the 0.4N sample compared to the 0.2N sample. Moreover, the increase in nitrogen content results in thicker Cr and Mo oxide layers and higher levels of NH3 and NH4+, thereby improving the corrosion resistance of the stainless steel.

The influence of a combined process, involving air cooling and heat treatment at 300 ℃, on precipitation behavior and corrosion resistance of a S31254-Ce steel was explored through scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), electron backscatter diffraction (EBSD) and electrochemical analysis. After air cooling and heat treatment at 300 ℃, the S31254-Ce steel was conducive to the enrichment of Ce along the grain boundary and the content of Σ3 twins in aged samples increased. The composite heat treatment process is beneficial to inhibit the precipitation of precipitates in the aging process and improve the corrosion resistance of S31254-Ce steel.

In austenitic steels, the co-segregation of C and Cr at grain boundaries can result in the formation of Cr23C6. However, the addition of B to steels can effectively reduce the amount of Cr23C6 formed and inhibit its ripening in experiments, simultaneously transforming it into Cr23(BC)6. Therefore, the effect of B on the co-segregation of C and Cr at the Σ5(210), Σ9(221) and Σ11(113) grain boundaries in austenitic steels was investigated using density functional theory. The results indicate that B, C, and Cr all tend to segregate at the three grain boundaries, with B and C showing a stronger segregation tendency. Furthermore, co-segregation of C and Cr with short distances occurs readily at the Σ5(210), Σ9(221) and Σ11(113) grain boundaries. The presence of B at grain boundaries can impede the segregation of Cr, particularly at the Σ9(221) and Σ11(113) grain boundaries. When B is pre-segregating at the Σ5(210) grain boundary, B, C, and Cr tend to co-segregate at the grain boundary. The grain boundary B hinders the accumulation of Cr near it for most grain boundaries, thereby inhibiting the co-segregation of Cr and C, making it difficult for B, C, and Cr to aggregate at most grain boundaries. This is beneficial for controlling the nucleation of Cr23(BC)6.

In order to reduce the segregation of Cr and Mo and inhibit the precipitates, we added a small amount of B and Ce to traditional S31254 steel. Using an air-cooling and low-temperature diffusion treatment, the purpose was to control B and Ce at the grain boundary. The heat-treatment process could prompt co-segregation of B, precipitate-forming elements, and Ce at the grain boundary at 950 °C. After aging at 950 °C for different amounts of time, the diffusion treatment had an obvious inhibitory effect on the precipitates that caused them to become discontinuous, fine, and serrated. The B-containing serrated precipitates were only rich in Mo, while Cr was homogeneously distributed in the probed volume. A uniform distribution of Cr reduced the Cr-depleted zone in the area adjacent to the phase interface. Ce was observed to be segregated at the grain boundary. This showed that Ce could inhibit the formation of precipitates at the grain boundary. The serrated precipitates had an obvious resistance to intergranular corrosion.

Focusing on the serious volatilization of MoO3 in super austenitic stainless steel with a high Mo content, the influence of B on the formation of oxide film and the distribution of Cr and Mo was investigated at 900 °C and 1000 °C. Without the addition of B, Mo tends to diffuse to the surface, forming porous Cr/Mo-rich oxides, causing the volatilization of Mo. The addition of B can inhibit the diffusion of Mo to the surface, facilitate the diffusion of Cr to the surface and combines with O, providing conditions for the nucleation of Cr2O3. A large amount of Cr2O3 accumulated on the surface to form a dense passive film, which inhibited the diffusion of Mo to the surface, reduced the loss of Mo, and formed Mo/Cr-rich precipitates at grain boundaries that are close to the surface. However, it was difficult to form Mo-rich precipitates at the grain boundaries of a sample without B, which aggravated the volatilization of Mo from grain boundary to surface. Therefore, the addition of B can improve the oxidation resistance of 254SMO and inhibit the volatilization of Mo.

S is a common corrosion medium for austenitic stainless steels. The severe intergranular fracture of austenitic stainless steels occurs in sulfur environments. In this paper, the permeation of S at different atomic positions for three symmetric tilt grain boundary types, i.e., Σ5(210), Σ5(310), and Σ9(114) have been computed using first-principles calculations. S has the strongest segregation tendency in the Σ5(210) grain boundary. A high content of S at the grain boundary indicates harm to the grain boundary. Sulfur segregation in the grain boundaries can weaken the strength of the metallic bond. When Mo and Cr are present at the Σ5(210) grain boundary, the sulfur-induced embrittlement is inhibited. With increased S concentration at the grain boundary, the coexistence of Mo and Cr can suppress the intergranular fracture of S on the grain boundary. The reason why high-Mo stainless steel has excellent sulfur-induced intergranular corrosion resistance is explained at the atomic level.

To protect a photovoltaic module from the hot spot effect more efficiently, an AC (alternating current) module that contains a module-level MPPT (maximum power point tracking) has been put forward. In this paper, operation states of shadowed solar cells and relevant bypass diodes were studied through MATLAB/Simulink tools, and a commercial PV module was used to reveal the temperature change when working at different LMPP (local maximum power point). Experiment results show that bypass diode can reduce power loss for the AC module to some extent but has a limited effect on protecting the AC module from the hot spot effect. Instead, it is more likely to form a local hot spot when the bypass diode turns on, and the worst shading condition for the AC module with bypass diode is about 46.5% during work states.

Abstract A combined experimental and first-principle study on the oxidation mechanism of super austenitic stainless steel S32654 at 900 °C for a short time period (1, 3, and 5 h) in air is presented. The samples exhibit excellent oxidation resistance because of the initial and gradual formation of the denser Fe- and Cr-rich layer with increasing oxidation time. Meanwhile, the Mo-rich layer gradually forms because of the Mo diffusion, which results in the formation of the oxide layer with two distinct regions: an inner Fe- and Cr-rich layer and an outer Mo-rich layer. Density functional theory is applied to investigate the diffusion behaviour of Mo atom in the Fe-Cr-Ni/Cr2O3 interface and the effects of alloying elements (Fe, Ni, and Mn) on the Mo diffusion. The Mo originating from the alloy matrix tends to diffuse into the Cr2O3 part, thereby resulting in the formation of the continuous Mo-rich layer, which is consistent with the experimental behaviour. Moreover, the introduction of Ni to the Cr2O3 part can promote the Mo diffusion and the formation of the Mo-rich oxide layer, whereas Fe and Mn can hinder the Mo diffusion. The calculated results provide a microcosmic explanation of the experimental results.

Two batches of GaAs laser power converters (LPCs) with or without a localized gradient doping layer were fabricated via metalorganic chemical vapor deposition for converting the power of 808 nm lasers. The gradient doping layer was introduced into the base layer above the back surface field layer with a doping concentration that varied exponentially from 1×1018/cm3 to 5×1018/cm3. The two batches of LPCs were tested under various 808 nm laser light intensities ranging from 100 to 2500 mW. The LPC structures with and without the gradient doping layer both displayed their highest conversion efficiency of 55.1% and 53.4%, respectively, at a laser power of 1200 mW. The addition of the gradient doping layer improved the separation efficiency of the photogenerated carriers and reduced the recombination rate in the base region of the GaAs LPCs, which increased the open-circuit voltage of the LPCs by 13.3 mV and the short-circuit current density by 3.6 mA. Furthermore, the absolute value of the fill factor increased by 1.2% at an incident light intensity of 1200 mW, resulting in a 1.7% improvement in the photoelectric conversion efficiency of the GaAs LPCs.

Cyclic oxidation tests were carried out on a Fe–13Cr–5Al–0.3Ti alloy over a temperature range of 700 °C–1100 °C in air. The composition and structure of the oxide layer were characterized by SEM and XRD, and the influence of temperature and Ti on the oxidation mechanism was analyzed. The results demonstrated that a dense α -Al _2 O _3 oxide layer was formed on the surface of the substrate at 900 °C, which inhibited the outward diffusion of Ti and made the alloy more resistant to oxidation. However, when the temperature was increased to 1000 °C, the oxide layer could not effectively inhibit the outward diffusion of the Ti. In particular, the oxide formed on alloys treated 1100 °C was divided into two layers, where the inner layer was a dense α -Al _2 O _3 oxide layer and the outer layer was TiO _2 oxide layer.

Hematite (α-Fe2O3) is a promising electrode material for cost-effective lithium-ion batteries (LIBs), and the coupling with graphene to form Gr/α-Fe2O3 heterostructures can make full use of the merits of each individual component, thus promoting the lithium storage properties. However, the influences of the termination of α-Fe2O3 on the interfacial structure and electrochemical performance have rarely studied. In this work, three typical Gr/α-Fe2O3 interfacial systems, namely, single Fe-terminated (Fe-O3-Fe-R), double Fe-terminated (Fe-Fe-O3-R), and O-terminated (O3-Fe-Fe-R) structures, were fully investigated through first-principle calculation. The results demonstrated that the Gr/Fe-O3-Fe-R system possessed good structural stability, high adsorption ability, low volume expansion, as well as a minor diffusion barrier along the interface. Meanwhile, investigations on active heteroatoms (e.g., B, N, O, S, and P) used to modify Gr were further conducted to critically analyze interfacial structure and Li storage behavior. It was demonstrated that structural stability and interfacial capability were promoted. Furthermore, N-doped Gr/Fe-O3-Fe-R changed the diffusion pathway and made it easy to achieve free diffusion for the Li atom and to shorten the diffusion pathway.

Sanicro 25 austenitic heat-resistant steel is expected to be used in superheaters and reheaters for ultra-supercritical power plants above 600 °C due to its excellent structural stability and high temperature mechanical properties. In this paper, the effects of Co and W on the structural stability, thermodynamic stability and mechanical properties of Sanicro 25 steel are analyzed by calculating the formation energy, binding energy, Gibbs free energy, elastic constant, Peierls stress and generalized stacking fault energy (GSFE) with first-principles calculation method. By calculating the formation energy, binding energy and Gibbs free energy, it concludes that alloying elements Co and W in Sanicro 25 steel can improve the structural stability and thermodynamic stability. It indicates that W and a small amount of Co can improve the plasticity and ductility of Sanicro 25 steel by calculating the bulk modulus (B), shear modulus (G), Young’s modulus (E), the B/G ratio, Poisson’s ratio and Peierls stress. It is found that when Co and W are far from the stacking fault region, it will promote the formation of partial dislocations and twins in the system, thereby improving its plastic deformation ability and mechanical properties.

The addition of B can inhibit the precipitation of σ phases at the grain boundary to improve the hot workability and corrosion resistance for super austenitic stainless steel with high Cr and Mo content. This study focused on the interaction between B and Mo at the Fe–Cr(111)/Cr2O3(0001) interface and its effect on interfacial adhesion by employing the first-principles method, especially the effect of B on the segregation behavior of Mo. The most stable O-terminated Fe/Cr2O3 interface was chosen as the basic configuration. The segregation energy and the work of separation were calculated for the metal/chromia interface with Fe–Cr as the substrate. It has been demonstrated that B can promote the diffusion of Mo atoms into the oxide layer to increase the content of Mo in the passive film. In addition, the interfacial adhesion is higher at the most segregated sites. However, it is more difficult for two or more Mo atoms than a single Mo atom to diffuse into the oxide part with the effect of B, indicating that B can only improve the Mo content of the passive film to a small extent. The electronic properties were also further discussed to analyze the interactions and the binding characters between doped atoms and their surrounding atoms and to explain the underlying reasons for the variation of interfacial adhesion.

To improve fuel use and energy-conversion efficiency and reduce the emission of pollutants, oxygenation is now deemed an effective chemical treatment of water in supercritical and ultra-supercritical power plants. Supercritical water with dissolved oxygen significantly enhances the oxidation rate of steels in the main steam pipeline and super-heater header. However, at the atomic scale, the mechanism of metal oxidation in supercritical water containing dissolved oxygen is unknown and has not been investigated by simulation. In this work, the oxidation of iron in supercritical water containing dissolved oxygen is studied by ab initio molecular dynamics and first principles calculations. The results indicate that dissolved oxygen in supercritical water dramatically accelerates the oxidation of iron. With the help of oxygen, the decomposition of water occurs on the iron surface, thereby producing more iron oxides and iron hydroxides. Additionally, hydrogen peroxide (H2O2) forms as an intermediate product, instantaneously decomposing to form iron hydroxides, and this is another reason for the enhancement in the oxidation of steel by supercritical water containing dissolved oxygen. Based on the results from ab initio molecular dynamics, we develop herein typical models of water molecules and oxygen molecules reacting directly on the iron surface and then carry out first-principles calculations. The results show that water decomposes on the iron surface only with the assistance of adjacent oxygen molecules and in the absence of surrounding water molecules. This investigation deepens our understanding of the oxidation mechanism of metal in supercritical water containing dissolved oxygen. The ideas and methods implemented in this work can also be used to study other materials exposed to supercritical water involving oxygen.

In order to promote the development of ultra-supercritical technology, the optimum composition design of three new alumina-forming austenitic heat-resistant steels, based on Fe−22Cr−25Ni (wt. %), with low cost and excellent performance, and used for 700 °C ultra-supercritical unit was carried out using Thermo-Calc software. A comparison of the mechanical properties presented that with increasing Al content, the plasticity of the system was further improved. Based on the composition system, a systematic investigation regarding the structure stability, thermodynamic properties, and mechanical properties of these new steels was carried out to reveal possible strengthening and toughening mechanisms by employing the first-principles method. Calculation results showed that when Al existed in the Fe−Cr−Ni alloy system as a solid solution, the new structures were stable, especially under high temperature. The solution of Al and Al + Si could increase the value of B/G, namely improving the plasticity of the system, particularly in case of alloying with Al + Si. The inclusion of Si in the Fe−Cr−Ni−Al system was conducive to further improving the plasticity without affecting the strength, which provided references for the subsequent optimum composition design and performance regulation of alumina-forming austenitic heat-resistant steels.

Precipitate phases often play an important role on the corrosion resistance of 2205 Duplex stainless steels (DSS). In the present paper, the microstructure and the corrosion resistance of the hot-rolled and cold-rolled 2205 steels aged for different times at 850 °C was investigated through XRD, SEM, and potentiodynamic polarization. It was discovered that the Chi(χ) phase and Sigm(σ) phase were precipitated in turn following the aging treatment of the hot-rolled and cold-rolled steels, but the precipitate amount in the cold-rolled samples was significantly higher when compared to the hot-rolled samples. The corrosion resistance of the solution-annealed cold-rolled samples was similar to the hot-rolled samples, but the corrosion resistance of the cold-rolled sample with precipitate was weaker when compared to the hot-rolled sample following aging treatment. Pitting preferentially initiates in the Cr-depleted region from the σ phase in the aged hot-rolled 2205, becoming increasingly severe during aging for a long lime. Adversely, the initiation of pitting corrosion might occur at the phase boundary, defects, and martensite in the aged cold-rolled 2205. The σ phase was further selectively dissolved through the electrochemical method to investigate the difference in microstructure and corrosion behavior of the hot-rolled and cold-rolled 2205 duplex stainless steels.

To reduce the precipitation of σ phases and to improve the hot workability of S31254 steels, boron has been added into the composition of S31254 to a concentration of 40 ppm. The precipitation behavior was investigated before and after the addition of boron in different S31254 alloys during the compression deformation, and the nose temperature at 950 °C and the phase dissolution temperature at 1074 °C were selected as the measurement temperature. The result showed that more σ phases were precipitated at the grain boundary of S31254 alloys, compared to the boron-added alloy. Meanwhile, the addition of 40 ppm boron into the alloys has obviously prevented the σ phases from the austenitic matrix, and it takes longer time for the precipitation of σ phase at 950 °C. The specific influence factors of boron on the precipitation of σ phases were also further discussed.

Hot deformation behavior and microstructure evolution of 2707 hyper duplex stainless steel (HDSS) were investigated through hot compression tests in the temperature range of 900–1250 °C and strain rate range of 0.01–10 s−1. The results showed that the flow behavior strongly depended on strain rate and temperature, and flow stress increased with increasing strain rate and decreasing temperature. At lower temperatures, many precipitates appeared in ferrite and distributed along the deformation direction, which could restrain processing of discontinuous dynamic recrystallization (DRX) because of pinning grain boundaries. When the temperature increased to 1150 °C, the leading softening behaviors were dynamic recovery (DRV) in ferrite and discontinuous DRX in austenite. When the temperature reached 1250 °C, softening behavior was mainly DRV in ferrite. The increase of strain rate was conducive to the occurrence of discontinuous DRX in austenite. A constitutive equation at peak strain was established and the results indicated that 2707 HDSS had a higher Q value (569.279 kJ·mol−1) than other traditional duplex stainless steels due to higher content of Cr, Mo, Ni, and N. Constitutive modeling considering strain was developed to model the hot deformation behavior of 2707 HDSS more accurately, and the correlation coefficient and average absolute relative error were 0.992 and 5.22%, respectively.

This study investigated the structural stability and electrochemical properties of alloying additives M (M = Mn, V, Ti, Mo, or Ni) at the γ-Fe(111)/Cr2N(0001) interface by the first-principles method. Results indicated that V and Ti were easily segregated at the γ-Fe(111)/Cr2N(0001) interface and enhanced interfacial adhesive strength. By contrast, Ni and Mo were difficult to segregate at the γ-Fe(111)/Cr2N(0001) interface. Moreover, the results of the work function demonstrated that alloying additives Mn reduced local electrochemical corrosion behavior of the γ-Fe(111)/Cr2N(0001) interface by cutting down Volta potential difference (VPD) between clean γ-Fe(111) and Cr2N(0001), while alloying additives V, Ti, Mo, and Ni at the γ-Fe(111)/Cr2N(0001) interface magnified VPD between clean γ-Fe(111) and Cr2N(0001), which were low-potential sites that usually serve as local attack initiation points.

The first-principles method is employed to study the ferromagnetic properties, as well as the electronic structure of the Cu-doped AlN. The doped AlN wide band is found to act as an effective dilute magnetic semiconductor and hence finds applications in the field of spintronics.

The effects of boron on the microstructure and intergranular corrosion behavior of UNS S31254 (S31254) austenitic stainless steels were investigated. The sensitivity to intergranular corrosion in the samples was determined by an altered double loop electrochemical potentiokinetic reactivation method. The microstructure characterization showed that the S31254 steels only precipitated sigma (σ, Fe-Cr-Mo-Ni) phases during the aging process, but boron addition decreased the amount of σ phase precipitation, reduced the size of the σ phases, and promoted the formation of small Laves phases at the grain boundaries. The precipitated σ phases lead to surrounding zones depleted of Cr and Mo, leading to intergranular corrosion. The S31254 alloy with added boron slows down the intergranular corrosion, due to microstructure manipulation at the grain boundaries. [ABSTRACT FROM AUTHOR]

The initial Li-ions nucleation on the basal plane of graphite anode with N-doped defects during the charge progress of lithium-ion battery was investigated theoretically by first-principle calculations using double-layered graphene (DLG) model. Based on the geometric structure optimization, the Li-ions are found to be accumulated on the top surface of N-doped DLG with single vacancy defect (SV-3N) in the near 2D structure. Also for the N-doped DLG with double vacancy defect (DV-4N), the Li-ions are deposit on its top surface, as well as could enter the interlayer space. The electronic analysis proves the ion character of Li layer. Therefore, the initial Li-ions nucleation on the basal plane of graphite with both N-doped SV and DV defects can be suppressed with different detailed mechanisms. The calculation of diffusion energy and lithiation potential shows that the Li-ions nucleation is inhibited via an adsorption-like and intercalation-like process on the DLG with SV-3N and DV-4N, respectively. Additionally, the calculated adsorption energy suggests that more Li atoms are adsorbed due to the presence of N, and thus the capacity of N doped graphite anode can be enhanced accordingly. [ABSTRACT FROM AUTHOR]

High-quality amorphous NiO/C/carbon nanotubes (CNTs) composite with an irregular porous structure have been successfully synthesised by a one-step combustion process at 350°C for 2 h with a heating rate of 3°C/min in air. To fully understand the potential of NiO/C/CNTs, the phase composition, morphology and electrochemical properties of materials were investigated. Benefiting from the in situ formed carbon, the addition of the CNTs and the advantages of the porous structure, the materials have shown superior electrochemical properties for supercapacitors. The specific capacitance of the composite reaches up to 1618 F/g at a current density of 1 A/g. Furthermore, the NiO/C/CNTs activate carbon asymmetric supercapacitor device demonstrates both a high energy density (25.9 Wh kg-1) and power density (5570 W kg-1), and delivers a better cycling stability (about 94%) after 7000 cycles, which is a potential material for further development of fabricating a supercapacitor electrode. [ABSTRACT FROM AUTHOR]

The connection between the austenite transformation and pitting corrosion of lean duplex stainless steel LDX 2101 was investigated at different annealing temperatures in the range 950-1200 °C. Optical microscopy, scanning electron microscopy, and electrochemical techniques were employed in the present work. Results indicated that micro-sized ferrite and austenite grains, formed with the increase of annealing temperature, influenced the pitting corrosion resistance of the studied stainless steel. As the austenite phase transformed into ferrite, the micro-sized ferrite grains were produced in austenite domains with temperature increase from 1000 °C to 1100 °C, especially at 1050 °C. In these conditions, the corrosion resistance of LDX 2101 was reduced by the micro-sized ferrite grains. A further increase of annealing temperature to 1150 °C produced the presence of micro-sized austenite grains in the ferritic phase, due to an incomplete transformation of austenite to ferrite. They represent new sites for severe pitting attacks and therefore the corrosion resistance of LDX 2101 was the weakest. The sample annealed at 1200 °C, with few micro-sized austenite grains in the ferritic matrix, exhibited excellent corrosion resistance. Moreover, a schematic was used to illustrate the pitting corrosion of the samples annealed at different temperatures. [ABSTRACT FROM AUTHOR]

This study investigates the microstructure, mechanical properties, and corrosion resistance of a friction-stir-welded joint of the hyper duplex stainless steel SAF2707. Friction stir welding (FSW) is performed at a tool rotation rate of 400 rpm and a welding speed of 100 mm/min. The microstructure of the joints is examined using scanning electron microscopy and X-ray diffraction. Tensile test and fractography are subsequently employed to evaluate the mechanical properties of the joints. Results show that the grain size of the stir zone (SZ) is smaller than that of the base metal (BM). Electron back-scattered diffraction analysis reveals that fine-equiaxed grains form in the SZ because of the dynamic recrystallization during the FSW. These grains become increasingly pronounced in the austenite phase. The tensile specimens consistently fail in the BM, implying that the welded joint is an overmatch to the BM. Moreover, the welded joints consist of finer grains and thus display higher tensile strength than their BMs. Potentiodynamic polarization curves and impedance spectroscopy both demonstrate that the corrosion resistance of the SZ is superior to that of the base material. [ABSTRACT FROM AUTHOR]

This study investigated the structural stability and electrochemical properties of alloying additives M (M = Mn, V, Ti, Mo, or Ni) at the γ-Fe(111)/Cr2N(0001) interface by the first-principles method. Results indicated that V and Ti were easily segregated at the γ-Fe(111)/Cr2N(0001) interface and enhanced interfacial adhesive strength. By contrast, Ni and Mo were difficult to segregate at the γ-Fe(111)/Cr2N(0001) interface. Moreover, the results of the work function demonstrated that alloying additives Mn reduced local electrochemical corrosion behavior of the γ-Fe(111)/Cr2N(0001) interface by cutting down Volta potential difference (VPD) between clean γ-Fe(111) and Cr2N(0001), while alloying additives V, Ti, Mo, and Ni at the γ-Fe(111)/Cr2N(0001) interface magnified VPD between clean γ-Fe(111) and Cr2N(0001), which were low-potential sites that usually serve as local attack initiation points. [ABSTRACT FROM AUTHOR]

Using density-functional calculations, we studied the interaction between interstitial impurities (N, C) and γ-Fe(111) surfaces doped, or not, with Cr, as well as the effect of Cr doping on the dissolution corrosion resistance of the γ-Fe(111) surface. The elementary processes studied afforded microscopic insights into the formation of a Cr-depleted zone, a phenomenon that leads to local corrosion of the stainless steel surface. The aim of this work was to study, at the atomic scale, the effects of N and C on the segregation behavior of Cr and the synergetic effect between co-doped atoms on the resistance to dissolution corrosion of austenitic stainless steel surfaces. The results showed that interstitial impurities prefer to be trapped at near-surface sites, which can impact the segregation behavior of Cr such that it shifts from the surface to the subsurface. Electrode potential calculations and density of states analysis demonstrated that doping with Cr or inserting interstitial impurities into the solid solution can improve the surface corrosion resistance of an fcc Fe substrate, but detrimental effects on the surface corrosion resistance are induced by interactions between Cr and interstitial impurity atoms in co-doped surfaces. The formation of near-surface Cr carbides and nitrides (speculated to be Cr2N and Cr23C6 due to the results obtained for particular co-doped surfaces) was also noted. The results of our theoretical calculations explain some of the experimental results observed at the atomic scale. [ABSTRACT FROM AUTHOR]

Effects of alloying elements in popular steels on the oxidation and dissolution corrosion of the surface of γ-Fe(111) have been investigated by performing density functional theory calculations within the local density approximation. First, the segregation of alloying atoms as well as preferential adsorption sites for oxygen and water were carefully examined, and it was found that all of the alloying elements considered had a tendency to segregate to the surface, and that the most preferred adsorption sites were the hexagonal closed packed (hcp) site and the top site for oxygen and water, respectively. The adsorption energies that characterized the tendency for oxygen or water to be adsorbed on the alloy surface showed that all ten alloying elements (especially Cr, Si, and Cu) were able to inhibit the adsorption of oxygen, and that all of the alloying elements except for Nb, Mo, and Ti inhibited water adsorption. The electrode potentials, which indicate the electrochemical stabilities of the surfaces of the alloys, suggested that all of these alloying elements (especially Cr, Mo, and Si) were able to suppress the adsorption of oxygen and water on the investigated surfaces, except for Nb and Ti in the case of water adsorption. Density of states analysis further indicated that all ten alloying elements (especially Cr, Si, Mo, and Cu) enhanced the corrosion resistance of the fcc Fe substrate, except for Nb and Ti with respect to dissolution corrosion. [ABSTRACT FROM AUTHOR]