In the production of high-quality regenerated brass alloys from scrap copper,Fe-rich phase segregates in the form of hard particles,affecting the machining performance of brass ingots.To improve the material yield ratio,La-B-Ti composite additive was used to improve the microstructure of brass ingots with high Fe content.By thermodynamic simulation and calculation,the effect of La-B-Ti on the microstructure of Cu-Zn-Pb-Fe system was analyzed,and the microstructure,hardness and electrical conductivity of brass ingots with different mass fractions of composite additive were experimentally investigated.The results show that La easily combines with Pb to form compounds,and Ti easily combines with Fe to form compounds.The composite additive can inhibit the aggregation and precipitation of Fe-rich phase and Pb phase,and refineαphase at the same time.In addition,La-B-Ti changes the number of grain boundaries and the morphology of precipitated phases in the Cu-Zn-Pb-Fe system.When the addition of the composite additive is 0.25%of the mass of high-Fe scrap copper,the regenerated brass ingot shows the highest hardness(181 HV)and relatively high electrical conductivity(11.85%IACS).This study provides a new idea to recover high-Fe scrap copper to regenerate brass ingots.

Nd₂Fe₁₄B/PrCo₅hybrid magnets were prepared by hot pressing and hot deformation with spark plasma sintering equipment,and their magnetic properties,microstructure and intergranular interaction were investigated.There are Nd₂Fe₁₄B and PrCo₅in both the hot-pressed and hot-deformed hybrid magnets.The anisotropy and magnetic properties of the hot-deformed magnets are significantly affected by the deformation amount.With the increase of the deformation amount,the anisotropy of the magnets increases,the grains are stretched into a lath shape along the direction perpendicular to the pressure,and the coercivity and maximum magnetic energy product decrease monotonously.At the same time,the intergranular exchange coupling of the magnets gradually weakens,and the long-range magnetostatic interaction strengthens.

A large-size niobium tube target was made by perforating and extruding of niobium ingot with a diameter of 300 mm,and then annealed at different temperatures.The recovery and recrystallization temperature of the niobium tube during annealing were determined by differential scanning calorimetry(DSC),and the texture evolution of niobium tube after extrusion and annealing was analyzed by electron backscattered diffraction(EBSD)technique.The results show that different annealing heating rates have little effect on the initial recrystallization temperature of niobium tube.The deformed microstructure of the extruded niobium tube is mainly<100>and<111>silk texture,and<110>predominant recrystallization texture is obtained after annealing.This study is helpful to improve the annealing process for the microstructure homogenization of extruded niobium tubes.

The effects of gradient extrusion on evolution of the grain orientation,grain size,and grain boundary orientation difference and mechanical properties of Ti₂AlNb-based alloy were studied by EBSD combined with microhardness test.The results show that preferred orientation<101>in the microstructure of Ti₂AlNb-based alloy gradually disappears after the gradient extrusion deformation,the grain size is gradiently distributed,and the structure of fine grains on the surface and coarse grains in the core is formed.The average grain size in the edge region decreases from the initial 20.64μm to 3.92μm,and the average grain size in the core region decreases to 11.24μm after gradient extrusion from two forming units.At the same time,the length of high-angle grain boundary in the edge region gradually increases from the initial 11166.5μm to 34905.8μm.The microhardness of the deformed sample shows an increasing gradient distribution from the core to the edge,and the average microhardness values of the first gradient and the second gradient increase by 9.9%and 11.5%respectively,compared with the initial sample.It provides theoretical support for the study of the large plastic deformation process of high temperature titanium alloy.

The effect of annealing temperature on the microstructure and second-phase particles of coldrolled industrial zirconium alloy plate was studied by means of annealing microstructure and second-phase particle observation,electrochemical corrosion test and corrosion morphology analysis.It is found that the microstructure of the plate after annealing at 470℃is mainly deformed microstructure,and its electrochemical corrosion resistance is the worst.After annealing at 500℃and above,a completely recrystallized microstructure is formed in the plate,where the number and size of second-phase particles have a significant influence on the corrosion resistance of zirconium alloy in nitric acid medium.At the annealing temperature of 500℃,the number and size of second-phase particles precipitated from zirconium alloy are small.At the annealing temperature of 550℃,the number and size of second-phase particles in the alloy increases.When the annealing temperature rises to 600℃,the number of second-phase particles in the alloy changes little,but the size coarsens obviously.The sample annealed at 600℃has low self-corrosion potential E_corr,its passivation film is repeatedly broken down and repaired,and there are the most corrosion pits with relatively large size on the surface of the sample.Coarse second-phase particles are preferentially corroded in nitric acid medium,so it is necessary to control the low annealing temperature while the formation of completely recrystallized microstructure is ensured,to obtain fine second-phase particles and then improve the corrosion resistance of zirconium alloy in nitric acid.In this experiment,the zirconium alloy sample annealed at 500℃has fine second-phase particles with small number and the best corrosion resistance.

HfO₂ high-K dielectric films were prepared by vacuum electron beam evaporation,and graphene was prepared without transfer on the surface of HfO₂ substrate by PECVD.The effects of growth temperature on the microstructure,surface morphology,and dielectric properties of HfO₂ films were studied by GIXRD,AFM,impedance analyzer,and laser Raman spectrometer,as well as the effect of total reaction pressure on the growth of graphene on the surface of HfO₂ substrate.The results indicate that the HfO₂ film grown at 250℃exhibits an optimal surface morphology(RMS=0.232 nm),with amorphous structure and the highest relative dielectric constant(22.34).Appropriate total reaction pressure can balance the transport of carbon species and the growth rate of graphene,promote the uniform distribution of reactants,and thus improve the quality of graphene films.With the increase of total reaction pressure,the quality of graphene films increases first and then decreases.The few-layer graphene film with smooth surface and minimal defect level can be obtained at the pressure of 150 Pa.

Synthesizing gold nanoparticles with controllable particle size becomes very crutial because many of their properties depend on their particle size.This study employed a green reduction method to synthesize gold nanoparticles by varifing reaction conditions,with chloroauric acid solution as a precursor and capsicum extract as both a protective agent and reducing agent.The synthesized samples were characterized by X-ray diffractometer,infrared spectrometer,UV-Vis spectrometer,Malvern particle size analyzer,transmission electron microscope,field emission scanning electron microscope,and energy disperse spectrometer.The results demonstrate that the gold particles synthesized by this method in the sol are uniform spheroidal nanoparticles,and primarily composed of elementary substance gold.In addition,their dispersion is good and particle size is small with an average particle size of about 25 nm,which is a result from SEM analysis.The reaction conditions,including the consumption of capsicum extract and chloroauric acid solution,significantly affect the morphology and size of the gold particles in the sol.And the smallest gold nanoparticles can be obtained at room temperature when the consumption of capsicum extract and chloroauric acid solution is 15 mL and 10 mL,respectively.The capsicum extract contains polyhydroxyl compounds that can reduce chlorauric acid to gold atoms and impose an steric effect of long-chain polymers in the extract on the assembly of gold atoms into gold nanoparticles.

In order to systematically discuss the effect of Cu doping on the arc erosion resistance of Ag/SnO₂ contact materials,Ag/SnO₂ contact materials and Cu-doped Ag/SnO₂ contact materials with different Cu additions were prepared.The phase composition,microstructure,and component distribution of SnO₂ powder and Ag/SnO₂ contact materials before and after arc erosion were characterized using XRD,TEM,SEM,and EDS,respectively.The physical properties and arc ersion resistance of Ag/SnO₂ contact materials were tested,and the mechanism of Cu doping affecting the properties of Ag/SnO₂ contact materials was explored.The results indicate that doped Cu ions dissolve into the crystal structure of SnO₂,resulting in lattice distortion,inhibiting the growth of SnO₂ grains and reducing their grain size.With the increase of Cu addition,the hardness,resistivity and mass loss caused by arc erosion of Cu-doped Ag/SnO₂ contact materials first decrease and then increase,while the density first increases and then decreases.The Cu-doped Ag/SnO₂ contact material with a molar ratio of Cu to Sn of 0.12(Ag/0.12Cu-SnO₂)has the lowest resistivity,hardness and mass loss caused by arc erosion,and the highest density.Compared with the undoped Ag/SnO₂ contact material,the microstructure uniformity of Ag/0.12Cu-SnO₂ contact material is significantly improved,and its average resistivity,average hardness and mass loss caused by arc erosion of Ag/0.12Cu-SnO₂ contact material are reduced by 13.33%,6.87%and 59.40%respectively,while the average density is increased by 4.11%.The arc erosion resistance of Ag/SnO₂ electrical contact materials can be significantly improved by appropriate Cu addition,but excessive addition could reduce the resistance.The reason is that the grain size of Cu-doped SnO₂ is reduced,which improves the interfacial bonding strength and wettability between SnO₂ and the Ag matrix,inhibits SnO₂ particles from escaping from the silver melt pool and enriching on the surface of the contact materials,and thus improves the arc erosion resistance of the Ag/SnO₂ contact materials.

Ultrafine WC-Co composite powders were prepared by high-energy ball milling method,the effects of ball milling methods(individual pre-milling method,wet milling and open-jar method),ball milling time,and forming processes(ordinary molding,cold isostatic pressing)on the microstructure and mechanical properties of ultrafine WC-Co cemented carbide containing composite carbides were investigated.The results show that compared with the individual pre-milling method,the ultrafine cemented carbide obtained by the wet milling and open-jar method has uniform microstructure and fine grains,which meets the requirements of ultrafine cemented carbide,the distribution of complosite carbides is basically uniform,and the comprehensive physical and mechanical properties of the cemented carbide are better.With the prolongation of ball milling time using the wet milling and open-jar method,WC powder is constantly crushed and refined,the obtained cemented carbide has gradually reduced WC grain size and slightly increased hardness and coercive force,but its densification,relative magnetic saturation strength and transverse rupture strength decrease.Comprehensively for the wet milling and open-jar method,a suitable pre-milling time for composite carbides is 12 h.Compared with ordinary molding,the ultrafine WC-Co cemented carbide with composite carbides prepared by cold isostatic pressing has a lower linear shrinkage and slightly improved hardness,density and transverse rupture strength.

Y³⁺doped porous Na₃V₂(PO₄)₃/C(written as NVP/C)composites were successfully synthesized by a modified sol-gel combustion method.The structure and sodium storage performance of the composites were characterized by XRD,BET,SEM,HRTEM and electrochemical tests.The results show that Y³⁺with larger radius replaces part of V³⁺in NVP crystal structure,which leads to lattice expansion,expands the transport channel of Na⁺and accelerates the migration of Na⁺.In the process of preparing the modified samples,Y³⁺reacts with PO₄^3-to form a new conductive phase YPO₄,which improves the electronic conductivity of the composites.In addition,Y³⁺doping results in spheroidization of irregular polygonal NVP particles and a slight reduction in their size.Benefiting from the appropriate Y³⁺doping amount,uniform amorphous carbon coating layer and porous structure,the NVP/C-Y0.10 sample has excellent sodium storage performance with a high initial discharge specific capacity of 96.3 mA·h/g at a high rate of 5 C and a reversible capacity of 82.2 mA·h/g after 1000 cycles.