Mechanical properties of pure tantalum samples transversely or longitudinally formed by using selective laser melting(SLM) were investigated.The microstructure and phase composition of the prepared tantalum samples were studied by SEM and XRD,and their hardness and tensile properties at room temperature and high temperature were studied using microhardness tester and universal testing machine.The results show that the tantalum samples transversely formed by SLM exhibit a microstructure of equiaxed grains while the tantalum samples longitudinally formed by SLM show a miscrostructure of elongated grains.The phase composition of the SLM tantalum samples is BCC-Ta,with a Ta content over 99.995%.Meanwhile,the average compactness of the samples reaches 99.87% and the average microhardness is 191 HV.The SLM tantalum samples exhibit excellent strength and ductility at room temperature.How-ever,as the tensile temperature increases,their strength and ductility decrease,with the ductility reaching its worst at 600 ℃ due to dynamic strain aging.The fracture morphology at room temperature of the SLM tantalum samples is ductile fracture,and the cleavage characteristics of the fracture become more obvious as the tensile temperature increases.At 1 200 ℃,the fracture surface exhibits severe oxidation corrosion,presenting characteristics of intergranular oxidation corrosion cracking.Within the temperature range from room temperature to 1 200 ℃,the tensile properties of the tantalum samples longitudinally formed by SLM are slightly better than those of the tantalum samples transversely formed by SLM.

Tantalum powder for capacitors was prepared by the magnesium thermal reductionof Ta₂O₅.The effects of magnesium addition,holding temperature,and holding time on the composition and electrical properties of the tantalum powder were investigated.The results show that insufficient magnesium addition,low holding temperature,and short holding time result in incomplete reduction of Ta₂O₅.However,excessive magnesium addition leads to an increase in the leakage current of tantalum powder and the waste of magnesium chips and acid.And high holding temperature and long holding time lead to a decrease in the electric capacity of tantalum powder and an increase in energy consumption,thereby raising the cost.To reduce costs and improve efficiency,the optimal process conditions include the magnesium addition of twice the theoretical amount,holding temperature of around 960 ℃,and holding time of 6 hours.Under such conditions,the prepared tantalum powder exhibits an oxygen content of 0.362 0%,magnesium content of 0.001 1%,leakage current coefficient(K value) of 4.4×10^-4 μA/(μF·V),and weight-specific capacity of 15 630 μF·V/g.

Ti_2AlNb alloy was prepared by high-energy ball milling and spark plasma sintering technology.The microstructure and phase composition of the alloy were characterized by SEM,EDS and XRD,the tensile strength of the alloy at room temperature was measured by universal tensile testing machine,and the fracture morphology was observed.The effects of different sintering temperatures on the microstructure and tensile properties of Ti_2AlNb alloy were analyzed.The results show that Ti_2AlNb alloy is composed of O phase,B2 phase and α₂ phase at different sintering temperatures,and the morphology of the O phase changes with the sintering temperature.The O phase appears as Rim-O phase at 950 ℃,acicular O phase at 1 000 ℃,and lath-like O phase at 1 050 ℃ and 1 100 ℃.The tensile strength of Ti_2AlNb alloy at room temperature can reach 198 MPa under the conditions of a sintering temperature of 1 000 ℃,a holding time of 90 min and a pressure of 50 MPa,and its fracture type after tensile testing at room temperature is brittle fracture which mainly consists of cleavage fracture.

Ti₂AlNb-based alloy was subjected to three passes of isothermally restricted multi-directional forging(R-MDF) in the B2+O phase region.The microstructure of the deformed alloy samples was analyzed using metallographic microscope,X-ray diffractometer,scanning electron microscope,and transmission electron microscope.Quantitative analysis of the total volume fraction of O phase,width and volume fraction of lamellar O phase,and size of equiaxed O phase in each pass of multi-directional forging was conducted using Image software,aiming to study the deformation behavior of O phase in different passes.Vickers hardness test was conducted on Ti₂AlNb-based alloy samples in different passes to reveal the relationship between microstructure and microhardness after multi-directional forging.The research results show that after deformation,coarse lamellar O phase fragments and refines into equiaxed O phase.After different passes of multi-directional forging,the size of equiaxed O phase initially increases from 0.57 μm in the first pass to 1.24 μm in the second pass and then gradually decreases,reaching an average size of approximately 0.84 μm after the third pass.Compared with the initial sample,the microhardness of the samples in each pass increases by approximately 15.4%,22.2%,and 14.8%,respectively.

Lithium niobate(LN) powder was sintered by vacuum hot-pressing sintering to prepare LN piezoelectric ceramics,with the optimal sintering parameters determined by changing the sintering temperature and holding time.The density,microstructure,phase composition,piezoelectric and dielectric properties of the sintered samples were tested.The results show that LN piezoelectric ceramics prepared under the conditions of a sintering temperature of 900 °C,a holding time of 120 minutes,and a pressure of 35 MPa exhibit the highest density(4.62 g/cm³) and the maximum piezoelectric constant d₃₃(8.7 pC/N).Compared with the methods of traditional solid-phase sintering and CO₂ laser sintering,the piezoelectric constant of the prepared LN piezoelectric ceramics increases by 7.9 pC/N and 2.7 pC/N,respectively.When the test frequency is within 1 kHz~1 MHz,the dieletric constant of LN piezoelectric ceramics prepared under different conditions decreases rapidly and then tends to stabilize.

The research progress of the second phase composition modified cemented carbides was systema-tically discussed,the modification mechanism,types of modifiers,and mechanical properties of WC-based cemented carbides modified by adding the second phase elements or compounds were introduced,and the improvement mechanism of mechanical properties of the cemented carbide by doping second phase was analyzed and summarized.The effect of modifying cemented carbides with different types and contents of additives is different.The effects of different additives and preparation methods on the mechanical properties of cemented carbides were classified and compared.The results show that the comprehensive mechanical properties of cemented carbides are mainly related to the degree of grain refinement and micro-interface structure.The added second phase can form a certain coordination structure with the WC matrix,effectively inhibit the growth of WC grains,and thus improve the performance of the alloy.Finally,the current development bottlenecks and unresolved issues of the second phase composition modified cemented carbides are summarized.

Inhomogeneous cemented carbides were prepared by using pre-sintered higher Co content fine-grained pellets(WC-12%Co) and lower Co content ultra-coarse-grained mixed powder(WC-8.5%Co) as raw materials with a mass ratio of 3∶7.The effects of different mixing methods on the microstructure and properties of the cemented carbides were studied by field emission scanning electron microscope,metallographic microscope,coercive magnetometer,hardness tester,and electro-mechanical universal testing machine.The results show that the cemented carbides mixed by dry mixing and dry milling exhibit an inhomogeneous structure of coarse-grained WC surrounding aggregated fine-grained WC,while more Co pools are formed at the same time,deteriorating the properties of the cemented carbides.However,using high-strength wet milling method for mixing can reduce the probability of forming Co pools,promote the uniform distribution of Co phase and WC grains,improve the density of cemented carbides,and achieve supe-rior comprehensive mechanical properties.In addition,the activity of WC grains in the pre-sintered fine-grained pellets is significantly reduced,which mitigates the effect of ball milling activation,slows down the growth rate of fine grains,and maintains the inhomogeneous structure of the wet-milled cemented carbides.

The effects of different sintering pressures(4.0~6.0 GPa) on the microstructure and mechanical properties of WC-8Co cemented carbide samples were studied by using a cubic press at identical temperature(1 400 ℃) and holding time(6 min).The results show that the sintering of the WC-8Co cemented carbide samples can be completed within 6 min at 1 400 ℃ and ultra-high pressure of 4.0~6.0 GPa.As the sintering pressure increases,the average size of WC grains in WC-8Co cemented carbide samples gradually increases with local WC grains even growing abnormally,resulting in a gradual decrease in the coercivity,Vickers hardness and fracture toughness of the cemented carbide samples.Within the investigated pressure range,the mechanical properties of the WC-8Co cemented carbide samples reach the best at a sintering pressure of 4.0 GPa.And under the testing conditions of a load of 30 kgf(294 N) and a holding time of 10 s,the Vickers hardness and fracture toughness of the sample are 15.2 GPa and 14.9 MPa·m^1/2,being very close to the mechanical properties of commercial YG8 cemented carbide(Vickers hardness of 15.6 GPa and fracture toughness of 15.9 MPa·m^1/2) under the same testing conditions.As the sintering pressure increases,the fracture forms of the cemented carbide samples gradually transition from the dominant intergranular fracture to a combination of intergranular fracture and transgranular fracture,with an increasing proportion of transgranular fracture.

In order to improve the electrochemical performance of regenerated lithium-ion battery materials,a ball milling-spray method was proposed to recover and regenarate waste LiNi_0.5Co_0.2Mn_0.3O₂(NCM523).This method includes ball milling and refinement for the pretreated waste cathode material,rapid preparation of the precursor of the regenerated material through spray drying,and high temperature calcination to preduce the regenerated NCM523 material.The morphology,component,phase and chemical change of the materials during the regeneration process were analyzed by SEM,EDS,XRD,HRTEM,FT-IR,XPS and TG-DSC,and the electrochemical properties of the batteries assembled with regenerated NCM523 were also analyzed.The results show that the regenerated material has a porous structure,and the degree of lithium-nickel mixing is reduced,resulting in improved electrochemical performance.The first cycle discharge specific capacity of the regenerated NCM523 obtained under experimental conditions is 159.053 mA·h/g at 0.11 C,and the discharge specific capacity is 145.615 mA·h/g after 100 cycles,with a good capacity retention rate of 91.55%.And its first cycle discharge specific capacity is 126.974 mA·h/g at a current density of 5 C.Compared with the traditional direct regeneration method,the electrochemical properties of NCM523 prepared by ball milling-spray regeneration method are significantly improved.

在现代社会中,邪教组织常以各种形式潜伏在人们的日常生活中,通过欺骗、控制、洗脑等手段,危害个人身心安全与家庭和谐,极大程度地扰乱社会秩序,影响国家稳定。抵制邪教侵害,维护家庭与社会稳定是每个公民的责任与义务。