In this research, porous W matrixes for dispenser Ba-W cathodes were prepared by metal injection molding (MIM) using W powders with different particle shapes as raw materials. Other than investigating the effect of the powder particle shape on the pore characteristics of the porous W matrix, the influence of the powder particle shape on the emission properties of the Ba-W cathode was also investigated. Irregular W powder particles had higher surface roughness and specific surface area than the spherical W particles, resulting in sinuous pore channels and higher pore-specific surface area in the prepared W matrix. The emission current density of the cathode processed from the irregular powder was thus improved as the level of Ba-O dipoles, covered on the emission surface, was increased. This is due to the high pore-specific surface area offering a high contact area between W and impregants in the cathode.& COPY; 2023 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
The effects of melt-spinning speed ( v=15, 20, 25, 30, 35 m/s) and heat-treatment process on the magnetic properties and microstructure of melt-spun Nd26Pr3FebalCo4Ga0.42B0.92 ribbons were investigated. The ribbons show an obvious orientation when the speed is less than 25 m/s in the free side, and c-axis is perpendicular to the strip surface; the orientation decreases with the increase of melt-spinning speed. The grain can be refined by increasing the melt-spinning speed. When v<25 m/s, the initial magnetization curve shows a one-step magnetization process, and demagnetization curve have good squareness. When v >= 25 m/s, the amorphous phase content increases obviously, the initial magnetization curve changes to two-step magnetization process, and the demagnetization curve collapses obviously. The best magnetic properties B-r=0.80 T, mu H-0(cj)=1.56 T, ( BH)(max)=108.22 kJ/m(3) are obtained under v=25 m/s. After optimum crystallization annealing treatment, the amorphous phase content reduces significantly, all of the magnetic properties of ribbons improve obviously at v <= 25 m/s. Squareness and coercivity increase remarkable at v> 25 m/ s; The ribbon prepared at v=35 m/s possesses the highest coercivity (mu H-0(cj)=2.10 T). The best magnetic properties B-r=0.91 T, mu H-0(cj)=1.82 T, (BH)(max)=141.65 kJ/m(3) are obtained under v= 30 m/s. The microstructure changes along with the thickness direction. The wheel side is composed of amorphous and fine grains, the free side is composed of larger grains. After the heat-treatment, the amorphous phase content is reduced significantly.
The electrical conductivity of binary composite is closely related to the microstructure, and its morphological distribution of composition phase have fractal characteristic. Based on fractal theory and general effective medium（GEM）equations, the conductivity model of binary composite was established, and the relationship between the conductivity of composite and conductivity of component phase and fractal dimensions was determined.And the model was applied to the calculation of the conductivity of three molybdenum-based cermet: Mo-ZrO 2 ,Mo-SiO 2 and Mo-Al 2 O 3 system. The results show that the critical exponent t in the GEM equation has a certain functional relationship with the fractal dimension and tortuosity fractal dimension of the highly conductive phase.The fractal dimension Dfgradually increases with the increasing of the volume fraction, and the tortuosity fractal dimension DTgradually decreases with the increasing of the volume fraction. The calculated results of the conductivity model for the three Mo-based cermet are in good agreement with the experimental results.
The microstructural evolution and high-temperature oxidation behavior of bentonite modified MoSi 2 composite coating prepared by spark plasma sintering were studied. The results show that the composite coating is mainly composed of MoSi 2 phase and a small amount of Mo 5 Si 3 phase, and the addition of bentonite reduces the CTE mismatch between the coating and substrate, thus the composite coating presents a crack-free morphology.During oxidation at 1 500 ℃, the composite coating maintains slow mass gain since a dense and complete layer of SiO 2 forms on the surface during the oxidation process, which inhibits the high-temperature diffusion of oxygen and effectively avoids the further oxidation inside the coating. Compared with single MoSi 2 coating, the oxide scale of the bentonite modified composite coating is thinner with a crack-free morphology, therefore showing relatively better high-temperature oxidation resistance.
Based on the practical demand of raw materials quality control stability, with single particle size graded fused silica powder as the matrix material and zircon as the mineralizer, silica-based ceramic cores were prepared.Excellent high-temperature flexural strength and creep resistance was obtained through doping alumina powders and adjusting the sintering temperature. The effects of alumina and sintering temperature on the high temperature dimensional stability of silica-based ceramic cores were discussed. The results show that the increasing of the alumina amount and the sintering temperature are beneficial to the crystallization of cristobalite and the sintering level of silica-based cores, leading to significantly improves of the creep resistance of silica-based cores, but slightly deteriorates the high-temperature flexural strength. As the alumina doping ratio increases from 0 to 0.3%, the 1 550 ℃/30 min thermal deformation of the ceramic cores is significantly reduced from 3.86 mm to 0.54 mm,while the flexural strength at 1 550 ℃ is decreased from 27.86 MPa to 21.79 MPa. With the increasing of the sintering temperature from 1 180 ℃ to 1 240 ℃, the thermal deformation is reduced from 3.86 mm to 0.47 mm, while the flexural strength at 1 550 ℃ is deteriorated from 27.86 MPa to 19.67 MPa.
As an important gas-solid two-phase separation equipment in industrial production, cyclone separator is widely used in shipbuilding, petrochemical, coal-fired power, resource development. According to the theory of turbulent mixing laminar flow separation, regarding the actual physical parameters of particles in dusty air and the structure size of cyclone dust collector as the variable, the corresponding mathematical model of collecting efficiency was established, which based on the semi-empirical design method of cyclone dust collector proposed by classical Leith-Licht theory. According to mathematical model, the optimization objective function was proposed, which was used to optimize the size of cyclone separator by self code. Finally, combined computational fluid dynamics（CFD）method, the dust removal efficiency of the optimized model was verified. The simulation results show that the theoretical calculation of the mathematical model is in great agreement with the simulation results, the error is only 1.41%. This method overcomes some shortcomings such as long period of experimental verification and poor economy, which also has important engineering application value to the optimum design of cyclone separator.
Cobalt-based alloy is a common surface modification material, because of its excellent properties of wear resistance, corrosion resistance and high temperature resistance, it has a wide application prospect in the fields of surface modification and remanufacturing of aerospace, energy, heavy industry and marine equipment. Laser cladding is a new surface engineering technology with high economic benefit, which can realize the rapid and high quality molding of material surface coating. Using laser cladding technology, high performance alloy coating can be prepared on the surface of cheap metal matrix materials, which can improve the surface properties of materials without affecting the properties of the matrix materials, and can save precious and rare metals and reduce the cost. In recent decades, laser cladding technology of cobalt-based alloy has been widely concerned by scholars at home and abroad, and many achievements have been made in the improvement of coating hardness, wear resistance and corrosion resistance, crack sensitivity and other properties. In this paper, the research status of laser cladding technology on cobalt-based alloy was reviewed, and the research status at home and abroad was summarized and analyzed from the aspects of material system, process parameters and industrial application. The shortcomings of current research were summarized and the potential development direction in the future was analyzed.
In order to improve the electrostatic separation efficiency of inclusions in Ni-based superalloy,mixed powder was prepared by adding 53～150 μm size Al 2 O 3 particles into the same range of superalloy powders. Such mixed powders was treated with electrostatic separation method and the result was observed under stereoscope.The effects of corona voltage（U）,rotation speed（n）and electrode distance（S）on the removal inclusions were studied. The results show that the removing effect increases with the increase of corona voltage and the decrease of distance between electrode and roller. In the above experiment conditions,the best operation parameters are follows: electrode voltage is 30 kV,rotation rate of the roller is 70 r/min.
The development general situation and analysis of iron powder and copper powder trade in China and abroad are presented. The application of steel powder in powder metallurgy industry is emphatically analyzed.Some suggestions for further development are put forward.
Laser cladding was carried out to prepare Ni 3 Al based alloy coatings on 45 steel. Microstructure and wear resistance of the cladding materials was investigated using scanning electron microscopy, X-ray diffraction and wear tribometer. The results indicate that the microstructure of the Ni 3 Al based cladding materials contains mainly Ni 3 Al and in situ-formed M 7 C 3 , and coarse Cr 3 C 2 occurs in the cladding materials at the powder feeding rate of 1.45 kg/h. The wear resistance of the Ni 3 Al based cladding materials increases significantly with an increase in the powder feeding rate, which is much higher than that of the vermicular graphite cast iron. At the powder feeding rate of 1.16 kg/h, the specific wear rate of the cladding materials is 0.74×10 -5 mm~3/N·m, and that of the counterpart is also small, which is respectively about 19.6% and 67.7% of the vermicular graphite cast iron and its counterpart.
The oxidation behavior of SiC particles at 1 000, 1 100、1 200 and 1 300 ℃ were studied. The morphology and phase changes of SiC particles before and after oxidation were investigated using SEM and XRD, and the thickness calculation formula of oxidation layer（SiO 2 ）were also derived based on the conservation of mass. The results show that when the oxidation temperature is lower than 1 200 ℃, the oxidation rate is mainly controlled by the oxidation temperature. When the oxidation temperature is higher than 1 200 ℃, the oxidation rate of the initial oxidation is mainly controlled by the oxidation time. At 1 000 ℃, the morphology change of SiC particles is not obvious, and the oxidation product is amorphous phase. At 1 200 and 1 300 ℃, the surface deactivation of SiC particles is obvious, and the amorphous SiO 2 is gradually converted into square quartz crystals. The formula established by mass conservation could be used to predicting the thickness of oxidation layer.
Nickel-based powder metallurgy（PM）superalloy FGH4107 with five varied Zr contents were prepared by the high-throughput preparation,including vacuum induction melting（VIM）,electrode induction-melting gas atomization（EIGA）,and hot isostatic pressing（as-HIPed）processes.The effects of Zr content（mass fraction 0～0.50%）on the equilibrium phases thermodynamics,kinetic behavior and γ/γ′lattice misfit degree were studied by the calculation and simulation of JMatPro 6.5 software,combined with differential scanning calorimetry（DSC）and X-ray diffraction（XRD）.The results show that in the range of 600-1 400℃,the Zr content has little effect on the types of equilibrium phases,which are mainly composed of L,γ,MC,MB 2 ,γ′,M 3 B 2 ,M 23 C 6 ,μandσphases,Zr atoms enter γ,γ′,MC and Ni 7 Zr 2 phase in turn.With the increasing of Zr content from 0 to 0.50%,the initial melting temperature is greatly reduced but the final melting temperature is slightly decreased,and the temperature range of the solid-liquid two-phase region is enlarged.However,the Zr content has little effect on the solvus temperature of the γ′phase.With the addition of Zr from 0 to 0.50%,γ′/γ lattice misfit degree increases from 0.215%to 0.265%,indicating that Zr enters γ′phase and enhances the precipitation strengthening effect.
The high velocity oxy-fuel spraying（HVOF）technology was adopted to deposited coating on ironbased substrate using magnetostrictive materials as raw material. The effects of spraying process on the substrate material of 316L stainless steel and Q345 steel was investigated, and the mechanical properties and stress changes of the substrate material after spraying and sandblasting process were analyzed by tensile test and ultrasonic stress measurement method. The results indicate that the tensile strength and elastic modulus of the substrate slightly increase due to the processing hardening and thermal effects of spraying process on the substrate, the corresponding maximum tensile strength of 316L and Q345 steel is about 350 MPa and 450 MPa, respectively. The surface residual stress of the substrate is slightly increased, and the maximum change in residual stress for the two substrate materials under 180 MPa tensile load is 24 MPa and 30 MPa respectively. The study of the effect of the spray treatment on the mechanical properties and stress state of the substrate material can provide data to support the subsequent application of magnetostrictive coating guided wave.
A copper matrix composite（Cu-MMC for short）for brake pads used to high-speed trains was made by powder metallurgy technology. The effect of contact pressure on tribological properties of Cu-MMC under wet and dry conditions was studied, and the wear laws of Cu-MMC and its dual material（namely cast steel）were investigated. The results indicate that the frictional stabilities increases at first and then decrease, average coefficients of friction decrease continuously, the wear rate of Cu-MMC increases significantly at first and then decreases slightly,and the wear rate of cast steel increases rapidly at first and then increases gradually with increasing contact pressure under dry and wet conditions. The delamination of Cu-MMC under low contact pressure and abrasive wear of Cu-MMC under high contact pressure are obviously alleviated in wet environment, resulting in low friction coefficient and wear rate.
The types and hazards of nuclear radiation are introduced in this paper. It is proposed that the main task for the nuclear shielding design is shielding neutron and γ-ray. Meanwhile, the research status of nuclear radiation shielding materials at home and abroad are summarized in detail. The principal problems for the current comprehensive neutron and γ-ray shielding materials are discussed. The conflict between shielding effectiveness and other performances needs to be settled. The research on radiation shielding materials is prospected. It is pointed out that the development of structure（mechanical performance, heat resistant stability and etc）-function（neutron and γ-ray shielding properties）integration radiation shielding materials is the future developing trend.
Manganese trioxide was prepared with manganese sulfate as raw material and oxygen as oxidant.The effects of different PH regulators（sodium hydroxide,ammonia and compound additives）on the phase composition,microstructure and specific surface area of the product were studied.The results show that sodium impurity（Na 2 Mn 3 O 7 ）and manganese ammonia complex[（NH 4 ）Mn 8 O 16 ]are introduced into the preparation of Mn 3 O 4 with sodium hydroxide and ammonia as PH regulator,respectively.The content of manganese was low and the purity of the product was poor.Manganese trioxide prepared with compound additives as PH regulator has good crystallinity,no other peaks are generated and no introduction of other impurity ions.Micromorphology is spherical particles,particle size is about 120 nm,pore is small,specific surface area is 10.15 m~2/g,hysteresis loop type is H 3 ,pore structure is rich.
Chromium coatings with different arc currents were prepared on the surface of zirconium alloy by arc ion plating technology. The effect of arc currents on the oxidation resistance of zirconium alloy at high temperature was studied. The microstructure and phase composition of the coating were characterized by scanning electron microscopy（SEM）and X-ray diffractometry（XRD）, and the effect of arc current on the oxidation resistance of Cr coated zirconium alloy at 1 200 ℃was analyzed. The results show that higher arc current can obtain thicker Cr coating per unit time. When the arc current is 80 A, the coating surface is the smoothest and the film-base binding performance is the best. After oxidation at high temperature, Cr coating mainly consists of Cr 2 O 3 , Cr and Cr-Zr.When the arc current is 80 A, the Cr coating on Zr matrix has the best protection performance.
Nickel-cobalt-manganese ternary materials have become the best choice of lithium cathode materials for 3C,power tool and selectric vehicles due to its high capacity and high density.In order to avoid side reaction between electrolyte and cathode materials and enhance the conductivity of cathode material,it is particularly important to modify the cathode material.In this paper,Al 2 （SO 4 ） 3 and CoSO 4 were used as coating raw materials.NaOH was used as precipitator.The surface of the precursor was coated with a layer of aluminum hydroxide and cobalt hydroxide by wet coating,and then oxidized to obtain AlOOH and CoOOH.The materials were characterized by LS-POP9,BET,TD,SEM,XRD and electrochemical test.The results show that the sintered cathode material has good capacity retention and cycle performance.In the test for 0.2C（3.0-4.3 V）,the specific capacity reaches 175 m Ah/g,the initial charge-discharge efficiency,and it is excellent with 100%capacity retention rate after 50cycles.It can be seen that the double-layer composite coating method provides a way to improve the performance of lithium anode materials.
The powder rolling process is introduced. The process parameters and technological improvement of powder rolling technology and the semi-solid powder rolling technology developed based on powder rolling are discussed. The application of powder rolling technology in recent years is elaborated. Finally, the technologies are summarized and prospected.
Bronze is one of the earliest metal materials used by mankind,and it is still widely used today.Metal additive manufacturing technology breaks through the limitations of traditional processing on the structure of bronze parts,and adds vitality to the application of this material.However,due to the high reflectivity of copper alloys to laser light,laser additive manufacturing is difficult,and copper/tin composite spherical powder is an important way to solve this problem.To this end,the experimental study on the preparation of copper/tin composite spherical powder by spray drying-sintering process was carried out.On the basis of the pre-test,an orthogonal test scheme was designed to systematically study the influence of the binder,the solid content of the slurry,the atomization pressure and the atomization temperature on the properties of the powder.The copper/tin composite spherical powder prepared by optimized process parameters has a particle size of 10-40μm,of which D 50 is 25μm,D 90 is 31.2μm,and the powder particles are spherical.After vacuum sintering at 300℃,the composite powder is mainly composed of copper and tin raw material particles,and a small amount of Cu 6 Sn 5 and Cu 3 Sn intermetallic compounds are formed between the copper and tin raw material particles.The sintered copper/tin composite powder has better resistance to crushing strength.
