Liquid phase synthesis of dendritic nickel carbide alloy with high conductivity for advanced energy storage

Alloy materials have attracted increasing attentions because they possess superior electrical conductivity which can contribute to excellent electrochemical performance. Herein a dendritic Ni;C alloy material has been prepared by the pyrolysis of nickel acetylacetonate employing oleylamine as a reductant and 1-octadecene or octadecane as the solvent. The current–voltage curves indicating that the electrical conductivity of Ni;C is higher than that of nickel oxide. Electrochemical testing indicates that a high specific capacity of 390 C/g is found in alkaline electrolyte at 0.5 A/g, and deliver excellent rate characteristic as well as cycle life. The excellent electrochemical performance may be attributed to its high electrical conductivity and dendritic nanostructure that can promote diffusion of electrolyte ions. In addition, the AC//Ni;C asymmetric supercapacitor has been assembled at a cell voltages between 0 and 1.6 V, achieving a maximum energy density of 37 Wh/kg（at a power density of 0.3995 k W/kg）, and this manifests that the Ni;C alloy is a promising electrode material for electrochemical energy storage.

Effect of Titanium Content on Microstructure and Wear Resistance of Hardfacing Alloy

The hardfacing alloys with different concentrations of titanium were deposited on carbon steel substrates by shielded metal arc welding, and the effect of titanium content on the microstructure characteristics of the hardfacing alloys was investigated. The wear resistance test of the hardfacing alloys was carried out by using a slurry rubber wheel abrasion test machine, and the wear behaviour was also studied. The results indicate that the addition of titanium can effectively promote the precipitation of the complex carbides of Nb and Ti due to the prior precipitation of titanium carbide which acts as nucleation sites for complex carbides. With the increase of titanium content, the wear resistance of the hardfacing alloys is increased gradually resulting from the refinement of microstructure and dispersive distribution of fine carbide precipitates. And the wear mechanism is mainly minimum plastic deformation with interrupted grooves due to the strengthening and protecting effects of carbide precipitates.

Effect of Mg and Si on infiltration behavior of Al alloys pressureless infiltration into porous SiCp preforms

The effect of Mg and Si additon to Al matrix on infiltration kinetics and rates of Al alloys pressureless infiltration into porous SiCp preform was investigated by observing the change of infiltration distance with time as the Al alloys infiltrate into SiCp preforms at different temperatures.The results show that infiltration of SiCp preforms by Al melt is a thermal activation process and there is an incubation period before the infiltration becomes stable.With the increase of Mg content in the Al alloys from 0wt% to 8wt%,the infiltration will become much easier,the incubation period becomes shorter and the infiltration rate is faster,but these effects are not obvious when the Mg content is higher than 8wt%.As for Si addition to the Al alloys,it has no obvious effect on the incubation period,but the infiltration rate increases markedly with the increase of Si content from 0wt% to 12wt% and the rate has no obvious change when the content is bigger than 12wt%.The effect of Mg and Si on the incubation period is related to the infiltration mechanism of Al pressureless infiltration into SiCp preforms and their impact on the infiltration rate is a combined result from viscosity and surface tension of Al melt and SiC-Al wetting ability.

Low-temperature Sintering of FeCuCo based Pre-alloyed Powder for Diamond Bits

We studied the effects of sintering temperature on FeCuCo based pre-alloyed powder for diamond bits.The FeCuCo composite was fabricated by co-precipitation method.With the addition of tungsten carbide（WC）,sintering under different temperatures was investigated.Mechanical properties of the FeCuCo based matrix were systematically studied.The structure of the composite was evaluated by X-ray diffraction（XRD） and scanning electron microscope（SEM） was used to analyze the surface of the powder and matrix.The suitable sintering temperature was determined through differential scanning calorimeter（DSC）.Micro drilling experiments were performed,and 820 ℃ was identified to be the ideal sintering temperature,at which the matrix shows the best mechanical properties and drilling performance.

2D Finite Element Computer Analysis of Strength for Brazed Joint of Cemented Carbide and Silver Brazing Filler Metal

Brazing has a wide acceptance in industries and its simplicity in variety of application attracts more and more patronage. The strength of brazing joint determines the reliability of brazed engineering components. So the need to ascertain the reliability or to predict its failure （without some destructive testing） becomes high even with a computer aided analysis using the Finite Element Analysis. Here, we have employed the services of FEA software, Abaqus CAE, as a tool for the computer calculation to investigate a joint case of cemented carbide brazed with silver-based filler metal. In this paper, 2D analysis has been adopted because the thickness of the material （in 2D） does not influence the final calculation results. We have applied constant loading and constant boundary condition to explore data from the elastic and plastic strain analysis through which we were able to predict the maximum joint strength with respect to the joint thickness. The pattern of the meshing was also significant. And the result could be transferable to a real-life field situation. The final results showed that there is an optimum thickness of the filler metal with the maximum strength which matches that obtained from experiment.

STUDY OF THE MECHANISM TO IMPROVE PERFORMANCE OF CARBIDE BLADE BY LASER

The expermental research on the change of chemical composition and structure of car- bide blade surface treated by laser is carried out, and the relation between their structure and per- formance is studied. The result shows that the element Co exists as a simple substance phase in prim- itive sintering structure. while in new melt-sintering structure it forms a fine alloy phase with origi- nal carbide, and this is the main factor which improves the performance of carbide blade treated by laser.

Novel cemented carbide produced with TiN_(0.3) and high-entropy alloys

High-entropy alloys are suitable for use as a binder for cemented carbides duo to outstanding mechanical, oxidation and wear behavior. Therefore, high-entropy alloy was selected to replace Co and Ni metal bond in this study. The results of X-ray diffraction analysis show that CoCrNiCuMn high-entropy alloy is stabilized in the cemented carbide system. Scanning electron microscope（SEM） fractural morphologies of the cemented carbides added with CoCrNiCuMn show that CoCrNiCuMn distributes in grain boundaries, and the grains are bound tightly together. Furthermore, SEM fractural morphologies of the cemented carbides with 5 wt%, 7 wt%, and 10 wt% CoCrNiCuMn show that CoCrNiCuMn slows the growth of grains, which effectively binders the grains, prevents the generation and propagation of cracks, and finally, greatly improves the toughness of the cemented carbides.According to the results observed in the cemented carbides containing different amounts of CoCrNiCuMn, the hardness level gradually increases with the amount of CoCrNiCuMn; however, a reverse trend is seen in the toughness level. The cemented carbide with 10 wt% CoCrNiCuMn shows the highest toughness value of 7.05 MPa·m^1/2.

Carbide Precipitation in Austenite of a Titanium-Tungsten-Bearing Low-Carbon Steel

In this study,the carbide precipitation at 925 ℃ in austenite(γ)of a 0.04C–1.5Mn–0.10Ti–0.39 W(wt%)low-carbon steel was investigated by stress relaxation(SR)high-resolution transmission electron microscopy and atom probe tomography.First-principles calculations were employed to reveal the precipitation mechanism.Results indicate that a high dispersion of W-and Fe-rich M C-type ultrafi ne carbides(<10 nm)forms during the very early stage prior to the onset of precipitation determined by SR.These ultrafi ne carbides possess a B1-crystal structure with a lattice parameter of 3.696Å,which is quite close to that ofγ(3.56Å).It can signifi cantly decrease the misfi t of carbide/γinterface with a cube-on-cube relationship,thus assisting the carbide nucleation.As the time prolongs,a few spherical or polygonal Ti-rich(Ti,W)C particles(18–60 nm)are formed at the expense of the ultrafi ne carbides by nucleation and growth on them.These(Ti,W)C particles are identifi ed with a“core–shell”structure(Ti-rich core and Ti,W-rich shell),which leads to a better-coarsening resistance compared with pure TiC in Ti steel.Calculation results show that the composition and structure of carbides at certain stage are closely related to a combined eff ect of W,Fe,and Ti atoms together with interstitial vacancies.

Effect of Solution Annealing on Microstructure and Mechanical Properties of a Ni-Cr-W-Fe Alloy

The effect of solution annealing on the microstructure and mechanical properties of a Ni-Cr-W-Fe alloy developed for advanced 700？C ultra-supercritical power plants was investigated. Test samples in this study were subjected to different solution treatments and the same aging treatment（at 760？C for 1 h）.When solution annealing temperature was elevated from 1020？C to 1150？C, the stress-rupture life at750？C/320 MPa was increased from 60 h to 300 h, the stress-rupture elongation was enhanced from12% to 17%, and the elongation of the tensile at 750？C was improved from 11% to 24%. All tensile and stress-rupture samples displayed an intergranular dimple mixed fracture. Intergranular micro-cracks had a great relationship with the morphology of grain boundary carbides. Most carbides retained the morphology of globular shape and continuous thin plate. After tensile and stress-rupture tests, a few carbides were converted into lamellar. The results showed that intergranular micro-cracks were easier to form at continuous thin plate carbides than at globular shape carbides. Lamellar carbides hardly caused the nucleation of micro-cracks. Besides, grain boundaries sliding and elements diffusion during stressrupture tests led to the formation of precipitate free zones, which accelerated the extension of microcracks and influenced the stress-rupture life.

Plasma Transferred Arc Surface Alloying of Cr-Ni-Mo Powders on Compacted Graphite Iron

A Cr-Ni-Mo overlayer was deposited on the surface of compacted graphite iron（CGI）by the plasma transferred arc（PTA）alloying technique.The microstructure of Cr-Ni-Mo overlayer was characterized by optical microscopy（OM）,scanning electron microscopy（SEM）equipped with energy dispersive spectroscopy（EDS）,and X-ray diffractometer（XRD）.Results show that the cross-section consists of four regions：alloying zone（AZ）,molten zone（MZ）,heat affected zone（HAZ）,and the substrate（SUB）.The microstructure of AZ mainly consists of cellularγ-（Fe,Ni）solid solution,residual austenite and a network of eutectic Cr7C3 carbide while the MZ area has a typical feature of white cast iron（M3C-type cementite）.The martensite/ledeburite double shells are observed in the HAZ.With decreasing the concentration of Cr-Ni-Mo alloys,the fracture mode changes from ductile in the AZ to brittle in the MZ.The maximum hardness of the AZ（450 HV0.2）is lower than that of the MZ（800 HV0.2）.The eutectic M3 C and M7C3 carbides increase the microhardness,while the austenite decreases that of the AZ.

Secondary hardening behavior of 15CrMnMoV thin rolled tube

15CrMnMoV rolled tube is applied to many critical parts of helicopter. The secondary hardening behavior of the steel which varied with the treating process is essential for further usage. In this paper, the secondary hardening behavior of water quenched, oil quenched and air cooled steel are compared. The precipitations of alloy carbides are analyzed by electrolytic extraction, X-ray diffraction, optical microscopy as well as scanning electron microscopy. Results show that the secondary hardening effect in the air cooled steel is higher than in the water quenched and oil quenched steel, but the toughness decreases more seriously, due to more precipitation of Mo2C and VC.