Correlation of work function and stacking fault energy through Kelvin probe force microscopy and nanohardness in diluteα-magnesium

Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca,Mg-Sr and Mg-Ba systems.This investigation incorporated the difference in the‘Work Function'(ΔWF)measured via Kelvin Probe Force Microscopy(KPFM),as a property directly affected by interatomic bond types,i.e.the electronic structure,nanoindentation measurements,and Stacking Fault Energy values reported in the literature.It was shown that the nano-hardness of the solid-solutionα-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba.Thus,it was shown,by also considering the nano-hardness levels,that SFE of a solid-solution is closely correlated with its‘Work Function'level.Nano-hardness measurements on the eutectics andΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys.Correlation withΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree,relatively simple atomic models and a number of assumptions.As asserted by this investigation,if the results of measurement techniques can be qualitatively correlated with those of the computational methods,it can be possible to evaluate the electronic structures in alloys,starting from binary systems,going to ternary and then multi-elemental systems.Our investigation has shown that such a qualitative correlation is possible.After all,the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level,that is,free electron density distributions.Our study indicated that the principles of‘electronic metallurgy'in developing multi-elemental alloy systems can be followed via practical experimental methods,i.e.ΔWF measurements using KPFM and nanoindentation.

Multifunctional catalytic sites regulation of atomic-scale iridium on orthorhombic-CoSe_(2)for high efficiency dual-functional alkaline hydrogen evolution and organic degradation

The earth-abundant and high-performance catalysts are crucial for commercial implementation of hydrogen evolution reaction(HER).Herein,a multifunctional site strategy to construct excellent HER catalysts by incorporating iridium(Ir)ions on the atomic scale into orthorhombic-CoSe2(Ir-CoSe_(2))was reported.Outstanding hydrogen evolution activity in alkaline media such as a low overpotential of 48.7 mV at a current density of 10 mA cm^(-2)and better performance than commercial Pt/C catalysts at high current densities were found in the Ir-CoSe_(2) samples.In the experiments and theoretical calculations,it was revealed that Ir enabled CoSe_(2)to form multifunctional sites to synergistically catalyze alkaline HER by promoting the adsorption and dissociation of H_(2)O(Ir sites)and optimizing the binding energy for H^(*)on Co sites.It was noticeable that the electrolytic system comprising the Ir-CoSe_(2)electrode not only produced hydrogen efficiently via HER,but also degraded organic pollutants(Methylene blue).The cell voltage of the dual-function electrolytic system was 1.58 V at the benchmark current density of 50 mA cm^(-2),which was significantly lower than the conventional water splitting voltage.It was indicated that this method was a novel strategy for designing advanced HER electrocatalysts by constructing multifunctional catalytic sites for hydrogen production and organic degradation.

Efficient and Stable Inverted Perovskite Solar Modules Enabled by Solid-Liquid Two-Step Film Formation

A considerable efficiency gap exists between large-area perovskite solar modules and small-area perovskite solar cells.The control of forming uniform and large-area film and perovskite crystallization is still the main obstacle restricting the efficiency of PSMs.In this work,we adopted a solid-liquid two-step film formation technique,which involved the evaporation of a lead iodide film and blade coating of an organic ammonium halide solution to prepare perovskite films.This method possesses the advantages of integrating vapor deposition and solution methods,which could apply to substrates with different roughness and avoid using toxic solvents to achieve a more uniform,large-area perovskite film.Furthermore,modification of the NiO_(x)/perovskite buried interface and introduction of Urea additives were utilized to reduce interface recombination and regulate perovskite crystallization.As a result,a large-area perovskite film possessing larger grains,fewer pinholes,and reduced defects could be achieved.The inverted PSM with an active area of 61.56 cm^(2)(10×10 cm^(2)substrate)achieved a champion power conversion efficiency of 20.56%and significantly improved stability.This method suggests an innovative approach to resolving the uniformity issue associated with large-area film fabrication.

Unveiling the influence of dendrite characteristics on the slip/twinning activity and the strain hardening capacity of Mg-Sn-Li-Zn cast alloys

This work explores the correlation between the characteristics of the cast structure(dendrite growth pattern,dendrite morphology and macro-texture)and strain hardening capacity during high temperature deformation of Mg-5Sn-0.3Li-0 and 3Zn multi-component alloys.The three dimensional(3D)morphology of the dendrite structure demonstrates the transition of the growth directions from<1123>,<1120>and<1122>to<1123>and<1120>due to the addition of Zn.The simultaneous effects of growing tendency and the decrement of dendrite coarsening rate at the solidification interval lead to dendrite morphology transition from the globular-like to the hyper-branch structure.This morphology transition results in the variation of the solidification macro-texture,which has effectively influenced the dominant deformation mechanisms(slip/twin activity).The higher activity of the slip systems increases the tendency of the dendrite arms for bending along the deformation direction and fragmentation.Apart from this,the dendrite holding hyper-branch structure with an average thickness below 20μm are more favorable for fragmentation.The dendrite fragmentation leads to considerable softening fractions,and as an effective strain compensation mechanism increases the workability of dendritic structure.

Ultralow-voltage hydrogen production and simultaneous Rhodamine B beneficiation in neutral wastewater

Electrocatalytic water splitting for hydrogen production is hampered by the sluggish oxygen evolution reaction(OER)and large power consumption and replacing the OER with thermodynamically favourable reactions can improve the energy conversion efficiency.Since iron corrodes easily and even self-corrodes to form magnetic iron oxide species and generate corrosion currents,a novel strategy to integrate the hydrogen evolution reaction(HER)with waste Fe upgrading reaction(FUR)is proposed and demonstrated for energy-efficient hydrogen production in neutral media.The heterostructured MoSe_(2)/MoO_(2) grown on carbon cloth(MSM/CC)shows superior HER performance to that of commercial Pt/C at high current densities.By replacing conventional OER with FUR,the potential required to afford the anodic current density of 10 m A cm^(-2)decreases by 95%.The HER/FUR overall reaction shows an ultralow voltage of 0.68 V for 10 m A cm^(-2)with a power equivalent of 2.69 k Wh per m^(3)H_(2).Additionally,the Fe species formed at the anode extract the Rhodamine B(Rh B)pollutant by flocculation and also produce nanosized magnetic powder and beneficiated Rh B for value-adding applications.This work demonstrates both energy-saving hydrogen production and pollutant recycling without carbon emission by a single system and reveals a new direction to integrate hydrogen production with environmental recovery to achieve carbon neutrality.

Dissolution of TiO_(2) and TiN inclusions in CaO–SiO_(2)–B_(2)O_(3)-based fluorine-free mold flux

Mold flux serves the crucial metallurgical function of absorbing inclusions, directly impacting the smoothness of the casting process as well as the cast slab quality. In this study, the dissolution behavior and mechanism of Ti O_(2)and Ti N inclusions in molten Ca O–Si O_(2)–B_(2)O_(3)-based fluorine-free mold flux were explored by in situ single hot thermocouple technology combined with X-ray photoelectron spectroscopy.The results showed that Ti O_(2) inclusions are effectively dissolved by the molten slag within 76 s, during which the original octahedral [Ti O_(6)]^(8-)structures are destroyed and convert to the networker tetrahedral [Ti O_(4)]^(4-)structures. However, the dissolution rate is much lower for Ti N inclusions than for Ti O_(2)inclusions. This can be attributed to the fact that the Ti N particles need to be oxidized and then dissolved in the molten slag to form tetrahedral [Ti O4]4-and octahedral [Ti O_(6)]^(8-)structures during the Ti N inclusion dissolution process, which is accompanied by the generation of a large amount of N_(2)gas. Moreover, Ca Ti O_(3)crystals tend to nucleate and grow on bubble surfaces with sufficient octahedral [Ti O_(6)]^(8-)structures and Ca^(2+)ions, eventually resulting in the molten slag being in a solid–liquid mixed state.

A study of highly activated hydrogen evolution reaction performance in acidic media by 2D heterostructure of N and S doped graphene on MoO_(x)

Herein,a layer of molybdenum oxide(MoO_(x)),a transition metal oxide(TMO),which has outstanding catalytic properties in combination with a carbonbased thin film,is modified to improve the hydrogen production performance and protect the MoO_(x)in acidic media.A thin film of graphene is transferred onto the MoO_(x)layer,after which the graphene structure is doped with N and S atoms at room temperature using a plasma doping method to modify the electronic structure and intrinsic properties of the material.The oxygen functional groups in graphene increase the interfacial interactions and electrical contacts between graphene and MoO_(x).The appearance of surface defects such as oxygen vacancies can result in vacancies in MoO_(x).This improves the electrical conductivity and electrochemically accessible surface area.Increasing the number of defects in graphene by adding dopants can significantly affect the chemical reaction at the interfaces and improve the electrochemical performance.These defects in graphene play a crucial role in the adsorption of H^(+)ions on the graphene surface and their transport to the MoO_(x)layer underneath.This enables MoO_(x)to participate in the reaction with the doped graphene.N^(‐)and S^(‐)doped graphene(NSGr)on MoO_(x)is active in acidic media and performs well in terms of hydrogen production.The initial overpotential value of 359 mV for the current density of−10 mA/cm^(2)is lowered to 228 mV after activation.

Influence of cooling rate on solidification behavior of sand-cast Mg-10Gd-3Y-0.4Zr alloy

The effect of the cooling rate ranging from 1.4 °C/s to 3.5 °C/s on the solidification behavior of the sand-cast Mg?10Gd?3Y?0.4Zr alloy was studied by computer aided cooling curve analysis (CA-CCA). With the increase in cooling rate, the nucleation temperature (Tα,N) increases from 634.8 °C to 636.3 °C, the minimum temperature (Tα,Min) decreases from 631.9 °C to 630.7 °C, the nucleation undercooling (ΔTN) increases from 2.9 °C to 5.6 °C, the beginning temperature of the eutectic reaction (Teut,N) increases, the time of the eutectic reaction shortens, solidus temperature decreases from 546.0 °C to 541.4 °C, and solidification temperature range (ΔTS) increases by 6.1 °C. The increased nucleation rate (N&) is supposed to be the main reason for the increased?TN. Increased value (Teut,N?Teut,G) and shortened time of the eutectic reaction cause the change in the volume fraction and morphology of the second phase.

Semisolid joining of aluminum A356 alloy by partial remelting and mechanical stirring

A method to reach the globular weld structure of A356 aluminum alloy using stirring the localized semisolid zone during butt-joining is developed.Since the heat conductivity of this alloy is very high, the accurate controlling of temperature during joining must be considered.A gas heating system was used to heat up the nitrogen gas up to the required temperature.A dried and free oxygen gas was prepared when a stream of nitrogen gas could pass closely around a hot element.Hot and pure nitrogen gas flow through a precise ceramic nozzle was used to create a localized semisolid pool.At this stage a fine stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint.Substrates were moved in direction of joint line by a small trolley to avoid the deviation of nozzle from the joint line and its distance and angle from the substrate.A fixture system was used to hold two substrates together on the trolley.A narrow hot plate was located on the trolley to heat up the joint line due to high heat conductivity of aluminum.Effect of gas temperature was investigated on the microstructure and mechanical properties of weld seam.Results showed that increase in temperature promoted the final welding properties, and also at liquid fractions less than 50% joining was not fully practical.The best mechanical properties were achieved with liquid fraction of about 70%.

Dynamic recrystallization and precipitation in high manganese austenitic stainless steel during hot compression

Dynamic recrystallization and precipitation in a high manganese austenitic stainless steel were investigated by hot compression tests over temperatures of 950-1150~C at strain rates of 0.001 s-1-1 s-1. All the flow curves within the studied deformation regimes were typ- ical of dynamic recrystallization. A window was constructed to determine the value of apparent activation energy as a function of strain rate and deformation temperature. The kinetics of dynamic recrystallization was analyzed using the Avrami kinetics equation. A range of apparent activation energy for hot deformation from 303 kJ/mol to 477 kJ/mol is obtained at different deformation regimes. Microscopic characterization confirms that under a certain deformation condition （medium Zener-Hollomon parameter （Z） values）, dynamic recrystalliza- tion appears at first, but large particles can not inhibit the recrystallization. At low or high Z values, dynamic recrystallization may occur be- fore dynamic precipitation and proceeds faster. In both cases, secondary phase precipitation is observed along prior austenite grain bounda- ries. Stress relaxation tests at the same deformation temperatures also confirm the possibility of dynamic precipitation. Unexpectedly, the Avrami＇s exponent value increases with the increase of Z value. It is associated with the priority of dynamic recrystallization to dynamic precipitation at higher Z values.

Friction-stir-welded overaged 7020-T6 alloy joint: an investigation on the effect of rotational speed on the microstructure and mechanical properties

Commercial A7020-T6 plates in the overaged state were subjected to friction stir welding with four different tool rotational speeds of 500, 710, 1000, and 1400 r/min and a single traverse feed rate of 40 mm/min. The resultant changes in the welding heat input, microstructure, and the mechanical properties of the joints were investigated. The changes were related to the processes of growth, dissolution, and re-formation of precipitates. The precipitate evolution was examined by differential scanning calorimetry, and the microstructural analysis was conducted using optical, scanning, and transmission electron microscopes. The results showed that the grain size in the stirred zone(SZ) decreased substantially compared with the base metal, but increased with tool rotational speed because of the rise in temperature. We found that the width of the heat-affected zone increased with tool rotational speed. The hardness and the tensile strength in the SZ increased with increasing heat input compared with the base metal in the overaged condition. This recovery in mechanical properties of the joints can be attributed to the dissolution and re-formation of precipitates in the SZ and the thermomechanically affected zone. This process is referred to as an "auto-aging treatment."

Evaluation of diffusion and phase transformation at Ag/Al bimetal produced by cold roll welding

Aluminum and silver strips were cold welded by rolling and a bimetallic strip was produced. To create cold weld between A1 and Ag, mating surfaces were specially prepared and various rolling thickness reductions were applied. The minimum critical thickness reduction to begin cold weld was specified as 70% which equals 0.1630 critical rolling shape factors. The bimetallic strips were treated by diffusion annealing at 400 ~C and various annealing time. The A1/Ag interface of strips was observed by scanning electron microscope to investigate the formation of hard and brittle probable phases. The effect of anneal time on diffusion distance and phase transformation was also analysed by EDS analysis and line scan. A diffusion region along the interface in the Ag side was observed and its width increased with prolonging annealing time. Some 8 phases were detected close to the interface after anneal treating for 3 h and 8 phase was thicker and more continuous by increasing annealing time. The microhardness measurement showed that in spite of formation of 8 phase due to diffusion annealing, the interface hardness was reduced.

An investigation on the hardness and corrosion behavior of MWCNT/Mg composites and grain refined Mg

In the present work,multi walled carbon nanotubes(MWCNT)reinforced magnesium(Mg)matrix composite was fabricated by friction stir processing(FSP)with an aim to explore its mechanical and electrochemical behavior.Microstructural observations showed that the thickness of the produced composite layer was in the range of 2500μm.FSP resulted uniform distribution of CNT near the surface while agglomerated layers in the subsurface.Grain refinement of Mg achieved by FSP improved the hardness but significant enhancement in the hardness value was observed for FSPed MWCNT/Mg composites.Potentiodynamic polarization studies revealed that the increase in corrosion current density was observed for MWCNT/Mg composite compared with grain refined Mg and pure Mg,implying the significance of secondary phase(MWCNT)in decreasing the corrosion resistance of the composite.

Preparation of nanostructure silver powders by mechanical decomposing and mechanochemical reduction of silver oxide

The mechanical decomposing and mechanochemical reductions of silver oxide for preparation of nanocrystalline silver powders by high planetary ball mill was investigated. XRD and HRSEM techniques were used to characterize the structural evolution and morphological changes of products. The results show that the nanostructured silver with an average crystallite size of 14 nm and internal strain of 0.75% is synthesized by mechanical decomposing of Ag2O after 95 h milling. While, the product of mechanochemical reduction of silver oxide using graphite after 22 h milling is nanostructured silver with an average crystallite size of 28 nm and internal strain of 0.44%.

Electrophoretic deposition of titanium/silicon-substituted hydroxyapatite composite coating and its interaction with bovine serum albumin

Silicon-substituted hydroxyapatite (Ca10(PO4)6-x(SiO4)x(OH)2-x, Si-HA) composite coatings on a bioactive titanium substrate were prepared by electrophoretic deposition technique with the addition of triethanolamine (TEA) to enhance the ionization degree of Si-HA suspension. The surface structure was characterized by XRD, SEM, XRF, EDS and FTIR. The bond strength of the coating was investigated. The results show that the depositing thickness and the images of Si-HA coating can be changed with the variation of deposition time. The XRD spectra of Ti/Si-HA coatings show the characteristic diffraction peaks of HA, and the incorporation of silicon changes the lattice parameter of the crystal. The FTIR spectra shows that the most notable effect of silicon substitution is the decrease of intensities of —OH and PO43- groups with the silicon contents increasing. XRD and EDS element analyses present that the content of silicon in the coating increases with increasing silicon concentration in the suspension. The bioactive TiO2 coating formed may improve the bond strength of the coatings. The interaction of Ti/Si-HA coating with BSA is much greater than that of Ti/HA coating, suggesting that the incorporation of silicon in HA is significant to improve the bioactive performance of HA.

Mechanical Properties and Dimensional Stability of Rigid PVC Foam Composites Filled with High Aspect Ratio Phlogopite Mica

High aspect ratio Phlogopite mica was used to enhance the dimensional stability and mechanical properties of extruded rigid Polyvinyl Chloride (PVC) foam. Mica was added to rigid PVC compound at different concentrations (0 - 20 wt%) and processed using a single screw profile extruder. PVC foam-Mica composites were characterized for their dimensional stability, and structural, thermal, and mechanical properties. Experimental results showed that the dimensional stability increased by 44% and heat resistance of the samples improved as the amount of mica increased in the composites. The storage modulus and tensile strength of the composites were also enhanced with the addition of mica. However, increasing the concentration of mica had no significant effect on the impact and flexural properties of the composites. SEM micrographs show good dispersion and orientation of the mica flakes along the cell walls of the PVC foam. Overall, the platy structure and physical properties of mica seemed to have played an important role in providing good interfacial bonding with the cell membranes of the foam, thus enhancing the dimensional stability of the PVC- Mica foam composites.

Preparation of Heavyweight Ultra-high Performance Concrete Using Barite Sand and Titanium-rich Heavy Slag Sand

The heavyweight ultra-high performance concrete(HUHPC)was prepared with barite sand partially replaced by titanium-rich heavy slag sand(THS)at replacement proportion of 0%,30%,50%,70%and 100%in this work.The results show that THS incorporation can effectively improve the mechanical properties and reduce the volume shrinkage of HUHPC.The HUHPC with 50%THS replacement reaches an apparent density of 2890 kg/m^(3)(for fresh HUHPC),28 d compressive strength of 129 MPa,28 d flexural strength of 23 MPa,28 d flexural toughness of 28.4,56 d volume shrinkage of 359×10^(-4) and,as expected,excellent durability.Microstructural investigation demonstrates that the internal curing of pre-wetted THS promotes the hydration of the surrounding cement paste thereby strengthening the interfacial transition zone,resulting in the“hard shell”formation around aggregate to“protect”the aggregate.Additionally,the“pin structure”significantly improves the cement paste-aggregate interfacial connection.The combination of“hard shell protection”and“pin structure”remarkably improve the mechanical properties of HUHPC produced with porous THS aggregate.

3D numerical investigation of effects of density and surface tension on mixing time in bottom-blown gas-stirred ladles

In molten phase metallurgical processes,mixing via gas injection has a vital role in obtaining a homogeneous product.The efficiency of mixing depends on operational variables such as gas flow rate and slag height as well as physical properties of the molten phases.A numerical simulation is conducted to study the above parameters in the flow behavior of a bottom-blown bath.The molten metal and the slag are modeled by water and oil,respectively.The numerical results,particularly the mixing time,are validated against experimental data.The results show that mixing time increases as the slag height increases and decreases as the density of the slag material increases.The mixing time decreases with an increase in the density of the primary phase;however,it increases as the surface tension between air and water increases.A case with properties close to a real molten metal is also modeled.The performance of the system is influenced by the momentum rather than the dissipative forces.Thus,the effect of the density of the molten phase on the mixing process is more pronounced compared to the effect of the surface tension between the air and the molten phase.

Laser metal deposition of refractory high-entropy alloys for high-throughput synthesis and structure-property characterization

Progress in materials development is often paced by the time required to produce and evaluate a large number of alloys with different chemical compositions.This applies especially to refractory high-entropy alloys(RHEAs),which are difficult to synthesize and process by conventional methods.To evaluate a possible way to accelerate the process,high-throughput laser metal deposition was used in this work to prepare a quinary RHEA,TiZrNbHfTa,as well as its quaternary and ternary subsystems by in-situ alloying of elemental powders.Compositionally graded variants of the quinary RHEA were also analyzed.Our results show that the influence of various parameters such as powder shape and purity,alloy composition,and especially the solidification range,on the processability,microstructure,porosity,and mechanical properties can be investigated rapidly.The strength of these alloys was mainly affected by the oxygen and nitrogen contents of the starting powders,while substitutional solid solution strengthening played a minor role.

Effects of rapid heating cyclic heat treatment on microstructures and compression mechanical properties of TiAl-based alloy

By means of rapid heating cyclic heat treatment, the microstructure of a TiAl-based alloy was refined. The colony size and lamellar spacing were measured to be 50 μm and 0.12 μm, respectively. The compression mechanical properties were determined at room temperature and the best comprehensive mechanical properties can reach σ0.2 of 745.1 MPa, σp of 1 672.2 MPa and δ of 19.40%. The improvement of mechanical properties is caused by the microstructural refinement and the phase interface nucleation contributes a lot to the refinement of microstructure.