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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.

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.

Currently, substantial attention has been concentrated on the preparation and practical application of complex hierarchical nanostructure composite, which exhibits excellent electrochemical properties compared to the single-structured materials. Hence, a novel electrode of NiMoO4@Co3O4–5H composite nanoarrays supported on reduced graphene oxide/Ni Foam (rGO/NF) was synthesized through the facile hydrothermal method. The composite combines the advantages of the large specific capacitance of NiMoO4 and the great rate capability of Co3O4, exhibiting the distinguished specific capacitance and rate performance. The prepared NiMoO4@Co3O4–5H composite shows an enhanced pseudocapacitive performance of about 1722.3 F g−1 at a current density of 1 A g−1, and eminent rate capability of 80.8% at 10 A g−1. Moreover, the composite delivers good long-term cycling stability with capacitance retention of 91% after 6000 cycles. An asymmetric supercapacitor (ASC) was fabricated using NiMoO4@Co3O4–5H and AC as the positive electrode and negative electrode, achieving the high energy density of 37.1 Wh kg−1 at a power density of 798.0 W kg−1, and exceptional cycling stability (100% retention after 4000 cycles). These consequences suggest that NiMoO4@Co3O4–5H could be considered as a potential electrode material for energy storage devices.

Uncontrollable electrochemical deposition of Li2S has negative impacts on the electrochemical performance of lithium-sulfur batteries, but the relationship between the deposition and the surface defects is rarely reported. Herein, ab initio molecular dynamics (AIMD) and density functional theory (DFT) approaches are used to study the Li2S deposition behaviors on pristine and defected graphene substrates, including pyridinic N (PDN) doped and single vacancy (SV), as well as the interfacial characteristics, in that such defects could improve the polarity of the graphene material, which plays a vital role in the cathode. The result shows that due to the constraint of molecular vibration, Li2S molecules tend to form stable adsorption with PDN atoms and SV defects, followed by the nucleation of Li2S clusters on these sites. Moreover, the clusters are more likely to grow near these sites following a spherical pattern, while a lamellar pattern is favorable on pristine graphene substrates. It is also discovered that PDN atoms and SV defects provide atomic-level pathways for the electronic transfer within the Li2S-electrode interface, further improving the electrochemical performance of the Li-S battery. It is found for the first time that surface defects also have strong impacts on the deposition pattern of Li2S and provide electronic pathways simultaneously. Our work demonstrated the interior relationship between the surface defects in carbon substrates and the stability of Li2S precipitates, which is of high significance to understand the electrochemical kinetics and design Li-S battery with long cycle life.

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.

The effects of B on microstructure, pitting and intergranular corrosion in solution-annealed S31254 super austenitic stainless steels were systemically investigated. After solid solution treatment at 1200 °C for different time, the precipitation and grain size of S31254 with and without B steels were analyzed. Addition of B to S31254 promotes the redissolution of detrimental sigma (σ) phases, and the optimum solid solution condition for B-containing S31254 is at 1200 °C for 2 h. The S31254 steels with B after solid solution treatment exhibited much better corrosion resistance than that without B, which is relative to the elimination of destructional σ precipitates and the decrease of chromium-depleted region near the grain boundary. Moreover, the passive films of samples with B have increased Cr2O3 and Mo-rich oxides, which may be responsible for the improvement of corrosion resistance.

Zintl phase compounds Ca9Zn4+xSb9 have promising thermoelectric properties due to their complex crystal structure and tunable interstitial Zn. In this work, we prepared nominal Ca9Zn4+xSb9 (x = 0.5...

High silica SSZ-13 zeolite was synthesized by an efficient and green steam-assisted crystallization (SAC) method under a low alkalinity and low organic templates amount system. The as-prepared samples were characterized by XRD, SEM, N2 adsorption–desorption, TG–DTG and NH3-TPD. The results showed that the SAC method can not only remarkably improve zeolite yield but also enhance the crystallization rate of SSZ-13 zeolite compare to conventional hydrothermal route. Meanwhile, it was also found that the various content of the organic structure directing agent (N,N,N-trimethyladamantammonium hydroxide, TMAdaOH) in the dry gel can adjust flexibly the crystal size, morphology and acidity of samples. The zeolite samples with smaller particles and more strong acidity amount were more likely obtained under the higher TMAdaOH/SiO2 ratio (0.2) condition. In addition, the catalytic evaluation in methanol-to-olefins (MTO) reaction showed that the high silica SSZ-13 catalysts synthesized by SAC method exhibited longer lifetime and comparative selectivity to ethylene and propene than those of the SSZ-13s obtained by conventional hydrothermal route. Thus, the SAC route is believed to be a competitive strategy to synthesize high silica SSZ-13 zeolites with improved MTO catalytic performance.

Graphene characterized with ultrahigh intrinsic strength and excellent electronic properties is an ideal material to reinforce metals without despairing their thermal and electrical properties. Here, the electronic and mechanical properties of graphene intercalated copper (graphene/Cu) composites are investigated using density functional theory calculations. Graphene/Cu systems present an excellent electrical conductivity and increasing Debye temperature from 335 K for pure Cu to over 535 K in regardless of stacking models. In addition to greatly enhanced Young's modulus (149%), shear modulus (156%) and bulk modulus (108%) compared to copper, the ultimate strength of graphene/Cu composites are enhanced by 174% and 162%, in x and y directions, respectively. The strengthening and toughening effects of graphene in the composites is originated from strain strengthening and load transfer, which is consistent with the experimental results. Based on this calculation, the strengthening mechanism can be understood, which explains many experimental observations and also provides us a guide to improve graphene/metal composites quality.

SSZ-13 zeolite with a SiO2/Al2O3 ratio in the range of 26–183 was synthesized by adding zeolite L in the synthesis gel absent from additional aluminum source, and the effects of SiO2/Al2O3 and N,N,N-trimethyladamantammonium hydroxide (TMAdaOH)/SiO2 ratios on the crystallization were investigated. The crystallization mechanism was studied with X-ray diffraction, Scanning electron microscopy, Fourier transform infrared spectroscopy and 29Si and 27Al MAS NMR spectroscopy techniques. It is shown that the SiO2/Al2O3 and TMAdaOH/SiO2 ratios have a significant effect on the acidity, and thus, the methanol-to-olefins (MTO) performance of SSZ-13. The co-presence of TMAdaOH, NaOH and extra silica source (SiO2) is necessary for formation of SSZ-13. The crystallization of SSZ-13 occurs by decomposing structure of zeolite L into double six- and four-membered rings that subsequently restructure into CHA topology under the direction of TMAdaOH, and further induce the nucleation and crystal growth. It is noteworthy that the Al species in zeolite L directly transform into those of SSZ-13 without forming monomeric species. The prepared SSZ-13 shows higher catalytic stability and selectivity to ethylene and proplyene than the conventionally synthesized sample from amorphous aluminosilicate gel in MTO reaction.

Hematite (&alpha, Fe2O3) is a promising electrode material for cost-effective lithium-ion batteries (LIBs), and the coupling with graphene to form Gr/&alpha, 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 &alpha, Fe2O3 on the interfacial structure and electrochemical performance have rarely studied. In this work, three typical Gr/&alpha, 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 &deg, 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&rsquo, s modulus (E), the B/G ratio, Poisson&rsquo, 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.

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.

Nickel composites reinforced with reduced graphene oxide (rGO) nanosheets were fabricated by a direct current electrodeposition technique. The low volume fraction of graphene can promote the cathodic polarized potential, facilitate the transport of ions and electrons on electrodes, and provide a large number of nucleation sites, consequently accelerate the formation of heterogeneous microstructure features. The graphene/Ni composite with 2 mL graphene dispersions demonstrates a tensile strength of 864 MPa and a plastic elongation of 20.6%, which are 25% and 36% higher than that of the pure bulk Ni. The enhancements in strength and ductility of the composite can be ascribed to the bimodal microstructure, for which the fine grain population provides for enhanced strength, whereas the coarse grain population enhances ductility by enabling strain hardening. On the contrary, the positive role of rGO in microstructure control will be weakened due to the agglomeration of rGO sheets in a high-volume plating bath. The low adsorption quantity of rGO is unfavourable for the nucleation of Ni matrix, accordingly produces a uniform fine-grained microstructure. The tensile strength of the composite with 5 mL rGO is 750 MPa, whereas the fracture elongation is only 7.5%. It is believed that a proper addition of rGO dispersion makes a promising microstructure for advanced graphene/Ni composite.

Designing a novel, efficient and cost-effective nanocomposite with the advantage of robust structure and outstanding conductivity is highly promising for the electrode materials of high-performance supercapacitors. Herein, we designed and synthesized a hierarchical structured NiMoO4@rGO/NF via a facile and scalable approach by growing NiMoO4 nanowires onto the skeleton of reduced graphene oxide (rGO)/Ni foam (NF). The as-made NiMoO4@rGO/NF exhibits a superior electrochemical behavior owing to the coupling effect of homogeneous NiMoO4 nanowires and high conductivity of rGO, and it exhibits a superb capacitance value of 1877 F g−1 at 1 A g−1 and shows a ultralong life span with over 98% capacitance retention after 4000 cycles at 5 A g−1 in 2 M KOH electrolyte. Moreover, an asymmetric device employing NiMoO4@rGO/NF composite and activated carbon is assembled with an aqueous electrolyte, and it displays a maximum energy density of 40 Wh kg−1 at a specific power 218.2 W kg−1. Interestingly, the asymmetric device can remain 111.2% of its initial value even after 8000 charge/discharge cycles. These results demonstrate that the NiMoO4@rGO/NF binder-free electrode provides greatly enhanced electrochemical performance and shows promising application as an anode for energy storage.

First-principles calculations have been carried out to investigate the effects of alloying elements (Zn, Li, Y and Sc) on the electronic structure, elastic and thermal properties of Mg solid solution. The calculated cohesive energies show that Mg-Sc has the highest structural stability. The calculations of the densities of states (DOS) and electronic charge density difference indicate that Mg-Y (Sc) alloys have very strong covalent bonding due to a very strong Mg p-Y(Sc) d hybridization. The bulk modulus B, shear modulus G, Young's modulus E and Poisson ratio ν are derived using Voigt-Reuss-Hill (VRH) approximation. The results show that all the alloys can exhibit ductile properties at 2.77 at% R, and Mg-Zn(Li) alloys have the better ductility and plasticity. In the end, the Debye temperature and isochoric heat capacity are also calculated and discussed.

This paper described a comprehensive DFT + U investigation on the general trends in structural stability, electronic and optical absorption properties, photocatalytic activity of BiOCl doped with 3d transition metals (TMs = Sc, V, Cr, Ti, Fe, Co, Ni, Cu, Zn). We find that it is rather difficult for Sc, V, Ti, Ni atoms to substitute Bi into BiOCl crystal lattice in experiments due to their positive formation energies, but the negative formation energies for Cr-, Mn-, Fe-, Co-, Ni-, Cu-, Zn-doped BiOCl systems exhibit the thermodynamic structure stability. Most of TMs doping could narrow the band gap of BiOCl and lead to the changes in conduction band minimum and valance band maximum as well as the formation of several impurity energy levels within the forbidden band of BiOCl, achieving the photoactivity improvement and simultaneously maintaining the stronger redox potential. With 3d TMs doping, the optical absorption intensity of BiOCl around 350 nm increased and exhibited a redshift to the different extents, in good agreement with reported experimental data. Our theoretical calculations should provide meaningful guidance for the experimentalists to design and develop more thermodynamically stable and highly effective visible light response photocatalysts.

Few-layer graphene reinforced nickel matrix (GNs/Ni) composites were fabricated by a facile in-situ processing strategy involving the transformation from solid carbon precursors to graphene reinforcements under the vacuum hot-press sintering. It enabled the homogeneous distribution of reinforcements, the effective interfacial bonding between graphene nanosheets and Ni matrix, as well as the resisted grain growth during the high-temperature consolidation process. The GNs/Ni composites exhibited exceptionally enhancement of the strength and ductility simultaneously. The composite with 0.3 wt% graphene achieved the optimal yield strength, tensile strength, and fracture elongation of 285 MPa, 611 MPa, and 56%, respectively, which were enhanced by 1.16, 1.34 and 1.37 folds compared to those of pure Ni bulk. The microstructures before and after tensile deformation demonstrated that the strengthening effect of in-situ grown graphene in the Ni matrix was attributed to the grain refinement and effective load transfer, while the toughening effect was related to the crack bridging and graphene pull-out mechanisms.

The effect of aging temperature and holding time on the precipitation of secondary phases and pitting corrosion resistance of SAF2906 super duplex stainless steel was examined. Chromium nitride and σ phase were observed to preferentially precipitate at the ferrite/austenite interface. An amount of nitrides was also observed within the ferrite grain. The precipitation of chromium nitride occurred before the σ phase. The increase in aging temperature and holding time did not affect the concentration of the nitrides but increased the area fraction of the σ phase at a faster rate. The Cr2N precipitation in SAF2906 is more evident than that of the other duplex stainless steels. The variation tendency of the precipitation concentrations is primarily consistent with the prediction results of Thermo-Calc software. The electrochemical results showed that Cr2N and σ phase significantly reduced the pitting potential. Scanning electron microscope observations revealed that pits appear mainly in regions adjacent to sigma phase and Cr2N.

First-principles calculations within density functional theory have been carried out to investigate α2 phase in the Ti3Al based alloy with Zr, Hf, and Sn (6.25at%) elements doped. The lattice constants, total energies and elastic constants were calculated for the supercells. The formation enthalpies, bulk modulus, shear modulus, Young’s modulus, and intrinsic hardness were investigated. The ductility of the doped α2 phases was analyzed by the Cauchy pressure, G/B and Poisson’s ratio. The results show that the substitution of Ti(6 h) by Zr, Hf, and the substitution of Al(2n) by Sn can make the doped α2 phase more stable. The inflexibility and hardness of α2 phase can be enhanced by doping with Zr and Hf, while Sn brings the opposite effect. Sn is more powerful to improve the ductility of the doped α2 phase than Hf, but Zr can increase the brittleness. The densities of states (DOS and PDOS) and the difference charge density are obtained to reveal the underlying mechanism of the effect of alloying elements.

This work aims to use surfactant-assisted direct current electrodeposition technique to prepare four types of bimodal nickel, under different current densities. Bimodal Ni is obtained with different grain size and spatial distribution of CG and UFG areas showing a big disparity in mechanical properties. As a result of small population of coarse-grained surrounded by quite a lot of ultrafine-grained forming a unique shell-and-core bimodal structure, bimodal one present the best comprehensive mechanical properties with an ultrahigh tensile strength (~847 MPa) and a considerable plastic strain (~16.7%). Deformation initial, bimodal structures display more positive strain hardening to meaningful strains than unimodal structure of UFG and CG. Particularly bimodal one work-hardening rate is the highest thanks to its structure (UFG occupy 76.7% in total number fraction) and the distribution of growth twins. Growth twins in this article are referred to Σ3(111) coherent twins playing an important role in improving high strength, enhancing uniform plastic deformation ability.

The pressure dependence behaviors of structural and mechanical properties as well as the effect of temperature on thermodynamic properties of Ni-Al ordered intermetallic compounds (i. e. Ni 3 Al, Ni 5 Al 3 , NiAl, Ni 2 Al 3 and NiAl 3 ) are investigated in details by implementing first-principles calculations. The calculated lattice parameters, bulk modulus and its pressure derivative are well in agreement with available experimental and theoretical values at zero pressure. All the compounds are mechanically stable with pressure going up to 50 GPa, and the volume change resistance of nickel aluminum alloys can be improved by increasing pressure and Ni concentration. The shear deformation resistance, elastic stiffness and microhardness of nickel aluminum alloys can be strengthened by increasing the content of Ni 5 Al 3 and Ni 2 Al 3 , and pressure can also enhance these properties of Ni 5 Al 3 , NiAl and Ni 2 Al 3 . The ductility of Ni 3 Al, Ni 5 Al 3 and NiAl can be improved by increasing pressure, while brittle nature turns into ductile nature in 20–30 GPa and 10–20 GPa for Ni 2 Al 3 and NiAl 3 , respectively. Furthermore, the elastic anisotropy of Ni 3 Al, Ni 5 Al 3 , Ni 2 Al 3 and NiAl 3 enhances with pressure, while NiAl shows few change with pressure increasing. In addition, Ni 3 Al is the most sensitive to pressure change among considered compounds. Finally, the Debye temperature, linear thermal expansion coefficient and heat capacity of these compounds are calculated using the quasi-harmonic Debye model in pressure ranging from 0 to 50 GPa and temperature ranging from 0 to 1200 K to elucidate the relationships between thermodynamic parameters and temperature under various pressure. The results are helpful insights into the study of nickel aluminum alloys.

Super-austenitic stainless steel S32654 sheets with 2.4 mm thickness were successfully welded by friction stir welding (FSW) at the rotational speeds of 300 and 400 rpm with a constant traverse speed of 100 mm/min using W-Re tool. The sound joints with almost no nitrogen loss were successfully produced. The microstructure evolution was characterized by optical digital microscope (ODM), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), electron backscatter diffraction (EBSD) and transmission electron spectroscopy (TEM). The results suggest that the grain structure evolution in stir zone (SZ) is dominated by continuous dynamic recrystallization (CDRX). The strain rate plays a dominated effect on obvious grain refinement. The band structures containing W and Re are generated due to the wear between tool probe and steel in SZ. Furthermore, the microhardness measurements and transverse tensile tests indicate that the grain refinement combining with high density dislocations and substructures improves the hardness and strength, but greatly reduces the plastic deformation capacity of joints. The more suitable welding parameters are determined as 300 rpm and 100 mm/min for this steel. Keywords: Friction stir welding, Super-austenitic stainless steel, S32654, Microstructure evolution, Recrystallization, Mechanical properties

The effect of pressure on structural and mechanical properties as well as the temperature dependence of thermodynamic properties, such as enthalpies of formation, elastic moduli, anisotropy, heat capacity and thermal expansion coefficient et al., of Ni2XAl (X = Sc, Ti, V) Heusler compounds are investigated implementing first-principles calculations. The influence of pressure on lattice parameters decreases as the increase of atomic number X (Sc, Ti, V). The Ni2XAl (X = Sc, Ti, V) show mechanically stable, ductility and anisotropy in 0–50 GPa, and appropriate pressure can improve their mechanical properties because the bulk modulus B, shear modulus G, Young's modulus E, G/B and microhardness H almost linearly increase with pressure. The influence of pressure on B, G, E and H gradually decreases as the order of Ni2ScAl > Ni2TiAl > Ni2VAl, while it has an inverse effect on ductility and anisotropy. In addition, the resistance to volume deformation of NiAl alloys can be improved by second-phase strengthening with Ni2VAl and Ni2TiAl precipitates. Finally, the temperature and pressure dependences of bulk modulus, Debye temperature, heat capacity as well as thermal expansion coefficient of these compounds are elucidated using the quasi-harmonic Debye model. It is inverse for the effect of temperature and pressure on thermodynamic parameters. Keywords: Heusler compounds, L21-type Ni2XAl, Mechanical properties, Thermodynamic properties, First-principles

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&ndash, 22Cr&ndash, 25Ni (wt. %), with low cost and excellent performance, and used for 700 &deg, 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&ndash, Cr&ndash, 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&ndash, Ni&ndash, 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.

To get the atomic scale understanding of impurities induced intergranular embrittlement or enhancement and the control of these effects on austenitic stainless steels, behavior of impurities B and S at gamma-Fe grain boundary (GB) and effects of alloying elements (Cr, Ni, Mn, Co, Mo) additions on the cohesive properties of the gamma-Fe GB doped by impurities are investigated by performing density functional theory (DFT) calculations. The results showed that, as the GB enhancer and embrittler respectively, impurities B and S tend to stay at the interstitial sites of gamma-Fe GB, while alloying elements also can segregate at the GB studied. The presence of all the alloying elements considered can inhibit B GB segregation to some extent due to the higher segregation energies and can impair the enhancement effect of B on GB cohesion. However, these elements almost have no impact on GB segregation and embrittlement effect of S, except for Ni, Mn and Mo: Ni and Mo inhibit and improve S GB segregation, respectively; Mn and Mo strongly enhance and reduce S-induced GB embrittlement, respectively. Moreover, the remedial effect of (Cr + Ni), (Cr + Mn) on S-induced GB embrittlement is also discussed. Additional atomic structure and total valence charge density analysis demonstrated and explained our conclusions. (C) 2015 Elsevier B.V. All rights reserved.

The effect of Tungsten (W) on the precipitate evolution and mechanical properties of the alumina-forming austenitic stainless steels (AFAs) Fe-15Cr-25Ni-3Al-NbWCu during aging at 700 °C was systematically investigated. After aging at 700 °C, microstructural characterization revealed that both of the secondary NbC and L12-ordered Ni-Cu-Al phases were precipitated in the matrix of the two steels for strengthening alloys, but W-added AFA (AFA-W) steel exhibited a smaller average size of Ni-Cu-Al phase than AFA steel. In addition, most of the precipitates in AFA steels were δ-ferrite phase with prolonging the aging time, and few Fe2Nb-type Laves phases were observed in the 1000 h-aged AFA samples. However, the addition of W promoted the precipitation of Fe2W-type Laves phases and increased its volume fraction during the aging period. The continuity of δ-ferrite at the grain boundary of AFA-W steels was also interrupted by the co-precipitated Fe2W Laves phase and B2-NiAl phase, avoiding the formation of detrimental δ-ferrite network. Compared to AFA steels, AFA-W steels exhibited higher room temperature tensile properties at the same aging time, which may be caused by the strengthening effect of more dispersed Fe2W phases and smaller sizes of Ni-Al-Cu phases in the grain interiors. Meanwhile, the stress concentration on the triple junctions caused by δ-ferrite was decreased by Fe2W precipitates; thus, further resulting in an increased ductility compared to the AFA steels without W addition.

The addition of B can inhibit the precipitation of &sigma, 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&ndash, 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&ndash, 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.

The present work reports on the hydrothermal conversion of Ni-Ti-O nanopores anodically grown on NiTi alloy into nanospindles and their cytocompatibility. The results show the amorphous nanopores can transform to anatase nanospindles with length concentrated at 70–110 nm and diameter at 16–24 nm upon hydrothermal treatment at 200 °C in pure water for 2 h. The nanospindles also can promote proliferation of bone marrow mesenchymal stem cells when compared with that of nanopores and bare NiTi alloy thus are promising as biomedical coatings of NiTi alloy.

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 &deg, C was investigated through XRD, SEM, and potentiodynamic polarization. It was discovered that the Chi(&chi, ) phase and Sigm(&sigma, ) 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 &sigma, 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 &sigma, 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 &sigma, 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 &deg, C and the phase dissolution temperature at 1074 &deg, C were selected as the measurement temperature. The result showed that more &sigma, 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 &sigma, phases from the austenitic matrix, and it takes longer time for the precipitation of &sigma, phase at 950 &deg, C. The specific influence factors of boron on the precipitation of &sigma, phases were also further discussed.

Friction stir welding (FSW) was applied to a 2.4 mm thick high nitrogen nickel-free austenitic stainless steel plate using tungsten–rhenium (W–Re) tool. The high-quality weld was successfully produced at a tool rotational speed of 400 rpm and a traveling speed of 100 mm/min. The microstructure, mechanical and corrosion properties of the weld were studied. The nitrogen content of the weld was almost identical to that of base metal (BM). FSW refined grains in the stir zone (SZ) through dynamic recrystallization and led to increase in hardness and tensile strength within the SZ, while the ductility was slightly decreased. The failure of tensile specimens occurred in the BM. TEM results revealed precipitates of Cr23C6 of size ~1 μm in the SZ, although their content was small. The precipitation of Cr23C6 and increase in δ-ferrite in the SZ led to small decrease in both pitting and intergranular corrosion resistance. Keywords: Friction stir welding, High nitrogen austenitic stainless steel, Microstructure, Mechanical properties, Corrosion resistance

This study investigated the segregation behavior of alloying additives X (X = Si, Al, V, Ti, Mo, W, Nb, Y) on the Fe(1 1 1)/Cr2O3(0 0 0 1) interface as well as the effects of these additives on the interfacial adhesive strength by using the first-principles method. The results indicated that W, Mo, and Nb atoms were easily segregated at the Fe(1 1 1)/Cr2O3(0 0 0 1) interface, however, the introduction of them would weaken the adhesive strength of the interface through weak-electron effects. Moreover, Y, Al, Si, Ti, and V were difficult to segregate at the Fe(1 1 1)/Cr2O3(0 0 0 1) interface. Comparison of separation energies and interfacial structural properties suggested that introduction of Si and Al improved the adhesive strength of the Fe(1 1 1)/Cr2O3(0 0 0 1) interface through strong interactions between Si/Al and O. Thus, Si and Al improved the adhesion of surface oxide scales and enhanced oxidation resistance.

Ilmenite-type A TiO 3 ( A =Fe, Co, Ni) crystals have been investigated via Generalized Gradient Approximation (GGA) in the scheme of Revised Perdew-Burke-Ernzerhof (RPBE) using the first-principles method. The band structures, densities of states, bond orders and charge populations, optical properties including the dielectric function e ( ω ), absorption coefficient I ( ω ), refractive index n ( ω ), extinction coefficient k ( ω ), electron energy loss function L ( ω ) and reflectivity function R ( ω ), are calculated. The results show that the GGA-optimized geometries agree well with the experimental data. FeTiO 3 has a direct band gap, but both CoTiO 3 and NiTiO 3 exhibit indirect band gap. The analysis for densities of states and atomic charge populations exhibits that Ti O bonds possess the stronger covalent bonding strength than A O bonds. The calculated optical properties along [100], [010] and [001] as well as polycrystalline directions demonstrate the significant optical anisotropy parallel and perpendicular to c -axis for A TiO 3 . Finally, the origins of main peaks for optical spectra are presented based on electron transitions. Theoretical insights into the microscopic intrinsic properties of A TiO 3 should provide fundamental investigations for further understanding the Ilmenite A TiO 3 materials and improving their practical applications.

Hierarchical mordenite with micropores and mesopores was one-pot synthesized through a soft-templating method using a special diquaternary ammonium-type surfactant as a mesoporogen. The obtained samples were characterized by XRD, N2 physisorption, SEM, TEM, TG-DTG, 27Al and 29Si NMR spectroscopy, and NH3-TPD techniques. The catalytic performance of the hierarchical mordenite compared to that of conventional mordenite and mesoporous AlMCM-41 material was evaluated in the benzylation of benzene with benzyl alcohol. The results show that the hierarchical mordenite is highly crystalline and possesses large mesopore volume and strong acidity. Moreover, the prepared hierarchical mordenite catalyst is high-efficiency for the conversion of benzyl alcohol into diphenylmethane due to the superior mass transfer ability and largely accessible acid sites. The apparent reaction rate constant for HMOR is 23 times that for CMOR and 8 times that for AlMCM-41. These results suggest that hierarchical zeolites with mesoporosity and strong acidity may be the ideal catalysts in reactions involving large molecules.

Hierarchical mesoporous zeolites with different levels of micro- and mesoporosity were prepared by dissolution and reassembling processes of MOR zeolite in the presence of mesoscale cationic surfactant cethyltrimethylammonium bromide. The obtained materials were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, Fourier transform infrared, Nitrogen (N2) adsorption/desorption, Temperature programmed desorption of NH3 (NH3-TPD) and Nuclear magnetic resonance techniques. Moreover, these hierarchical zeolites were tested as hydrocarbon traps using toluene as probe molecule and the temperature programmed desorption method. The results showed that the amount of microstructure and mesostructure in the composite was able to be favorably tuned by varying dissolution time at the first stage. The hierarchical materials displayed remarkably high desorption temperature in toluene-TPD, which is an expected performance of hydrocarbon trap in automobile tailpipes. The effect is due to the easier transport of bulky molecules provided by mesopores and increasing the number of available active sites via a fragmentation of the microporous framework. Therefore, the synthesized composite molecular sieve may be a novel catalyst for hydrocarbon trap in automobile tailpipes.

The martensitic transformation (MT) and magnetic properties have been investigated in a series of Ni50−x Fe x Mn32Al18 ferromagnetic shape memory alloys. The substitution of Fe for Ni reduces the MT temperature of Ni–Fe–Mn–Al alloys effectively, and the magnetization of the austenite was significantly enhanced in these high-doped alloys. The Fe introduction converts antiferromagnetic austenite to ferrimagnetic state, and therefore, the unique MT occurs between ferrimagnetic and antiferromagnetic state in these alloys. The MT temperatures decreased by about 15 K under the magnetic field of 30 kOe for x = 8 alloy. The positive value of magnetic entropy change was determined to 3.35 J/kg K around the MT in the field change of 30 kOe for x = 6 alloy. These results suggest that Ni50−x Fe x Mn32Al18 alloys would be the promising candidates for magnetic multifunctional materials.

The adsorption energies, geometric structures, electronic properties, work functions and surface dipole moments of monatomic Ag adsorption on the (2 × 2) BiOCl (0 0 1) surfaces, including the 1Cl-, BiO- and 2Cl-terminated BiOCl (0 0 1) surfaces, have been investigated using first-principles calculations based on density functional theory. The most energetically favorable adsorption configuration of single Ag atom is at the fourfold hollow site, with the minimum adsorption energies of −0.465, −2.954 and −8.080 eV for the 1Cl-, BiO- and 2Cl-terminated BiOCl (0 0 1) surfaces, respectively. The analysis results of electronic properties indicate that there are new intermediate energy states mainly contributed to Ag 4d and Cl 3p states for 2Cl-terminated (0 0 1) surface, and Ag 5s states for 1Cl- and BiO-terminations. In addition, Ag adsorption can induce the formation of surface dipole moment and change in work function by the interfacial charge transfer. Combined with the previously reported experiments, the charge transport mechanism and effective separation processes of photo-induced electron–hole pairs of Ag/BiOCl photocatalytic system are built up and discussed. More importantly, our calculated findings could afford the theoretical basic knowledge for further understanding the microscopic structures, electronic properties, and photocatalytic reaction mechanism of Ag/BiOCl photocatalyst, providing a new analysis calculation for potential application in the investigation on the Ag/BiOBr and Ag/BiOI as well as other noble metals/BiOCl catalytic systems.

The Ni43.3Mn31.5Fe11.7Al13.5 ribbon was obtained by melt-spinning method and the microstructure, magnetic and magnetoresistance properties of these ribbons were studied by scanning electron microscope and vibration sample magnetometer. The reverse martensitic transformation from the weak-magnetic martensite phase to the ferromagnetic austenite was confirmed in these ribbons. A moderate negative magnetoresistance in the magnetic field of 30 kOe was obtained around the martensitic transformation, which would mainly owing to the field-induced reverse martensitic transformation. Taking into account of various properties, the present Ni–Fe–Mn–Al ribbons provide an impetus for further research.