The effect of rare earth magnesium modification concentration on the structure,hardness and wear resistance of Cr26 high chromium cast iron was studied by metallographic microscope,scanning electron microscopy,Rockwell hardness tester and dynamic abrasive wear tester,and the wear mechanism was discussed through the relationship between wear amount and wear trace morphology.The results show that the addition of rare earth magnesium changes the formation and growth environment of carbides,the morphology of carbides changes from long sheet and strip distribution to lump and nearly spherical distribution,and reduces the degree of matrix splitting.When the addition amount of rare earth magnesium reaches 0.6%,the microstructure and the distribution of carbides reaches its optimal state.The main role of rare earth is to purify the alloy liquid,refine the as-cast structure of the alloy,and the main role of magnesium is to deoxidize,desulfurize,purify the molten iron and reduce inclusions.The morphology of wear marks is mainly plough grooves,curls,pits and a small number of microcracks.The main wear mechanisms are cutting wear,multiple plastic deformation and chisel wear.

Sr2MgSi2O7∶Eu2+,Dy3+,Yb3+long afterglow phosphors were prepared via high-temperature solid state reaction.Microstructure and optical properties of Sr2MgSi2O7∶Eu2+,Dy3+,Yb3+long afterglow phosphors were characterized through XRD,SEM,excitation spectrum,emission spectrum and decay curves.The results show that the crystal structure and microstructure of Sr2MgSi2O7∶Eu2+,Dy3+,Yb3+have not changed significantly.The addition of Yb3+ions shows a remarkable change in fluorescent properties and afterglow performance.The introduction of Yb3+makes Sr2MgSi2O7∶Eu2+,Dy3+,Yb3+have better fluorescence performance and afterglow properties.Different Yb3+doping amounts have a significant effect on the trap depth and electron transport rate of the long afterglow phosphors.When the doping amount of Yb3+equals to 0.03,experiments show that the Sr2MgSi2O7∶Eu2+,Dy3+,Yb3+has the strongest fluorescence intensity and the best afterglow attenuation performance.

Lithium-oxygen batteries,as a new type of battery system with ultra-high theoretical specific energy density,have good application prospects in the field of electric vehicles.Reduced graphene oxide was prepared by modified Hummers method and thermal expansion method,and different noble metals Ru,Ir,Au and Ag were loaded by impregnation reduction method,and the effect of graphene catalysts with different noble metals on the performance of lithium-oxygen batteries were studied.The results show that the reversibility and charge-discharge cycle stability of lithium-oxygen batteries with Ru/RGO and Ir/RGO catalysts with high catalytic activity for oxygen precipitation are better than those of lithium-oxygen batteries with Ag/RGO and Au/RGO catalysts.

Using polyethylene glycol as dispersants and adhesives,nano-sized Al2O3 ceramic particles were assembled to the surface of Ni-based superalloy spherical particle to prepare Al2O3/Ni-based superalloy powder by the two steps method of ultrasonic dispersion and high speed stirring.Molding Al2O3/Ni-based superalloy composites were prepared by the laser 3 D printing.The results show that the composite powder used for laser 3 D printing technology can be successfully prepared by two steps process of ultrasonic dispersion and high speed stirring.After laser 3 D printing,the microstructure of molding materials is mainly represented by the columnar crystal and isometric crystal structure,uniform and compact,the nano-Al2O3 granules are uniformly distributed in the matrix.The microhardness(HV)of the composites can reach to 405.81.

Pure cobalt was hot processed into wire at temperatures above 600℃.The wire ends were welded by resistance welding method.The microstructure,mechanical properties and fracture mechanism of hot-processed wire and welded wire joints with different welding currents were investigated by optical microscope,universal testing machine and scanning electron microscope.The results show that the hot-processed wire has a recrystallized structure with twins and fine subgrains,and there is a residual FCC structure,locally.The fracture mechanism is micro-void coalescence.As the welding current increasing,the defect of the joint structure gradually decreases.When the current is 16.1 A,the joint structure recrystallizes and the joint strength is the highest.After the welding current is increased to 18.4 A,the joint structure has holes and the strength is reduced.The joint changes from crystal fracture to quasi-cleavage fracture with the welding current gradually increasing.When the current is 16.1 A,the fracture mechanism is micro-void coalescence and cleavage mixed fracture.The location of the fracture is in the heat affected zone at the boundary between coarse and fine grains.

Using two kinds of YG20 C cemented carbides with or without W powder added in the mixing stage as experimental subjects,the effects of W powder on the conventional properties(magnetic force,Rockwell hardness,flexural strength,etc.)and microstructure of the alloy after sintering at different temperatures were studied.The results show that the addition of W powder can promote the grain growth of YG20 C cemented carbide and even lead to the formation of abnormal coarse grains;The amount of solid solution W(or WC)in theγphase of the alloy with W powder decreased from 10.5%at 1 410℃to 10%at 1 480℃,while that without W powder increased from 10.4%to 11.6%;The bending strength of the alloy with W powder decreases sharply with the increase of the sintering temperature,and the decreasing amplitude reaches 580 N/mm^2 from 1 410℃to 1 480℃,while that without W powder is basically stable at 2 500 N/mm^2.

Tungsten carbide as an important cemented carbide material has been widely used in the fields of national economy,social life and national defense construction.In recent years,tungsten carbide production process has made great progress.The three major categories of tungsten carbide powders preparation processes include solid-phase,liquid-phase and gas-phase processes are described and their advantages and problems are briefly analyzed.The future development trend of tungsten carbide preparation process is prospected.

The research progress of binder phase in cemented carbides at home and abroad in recent years was reviewed.The possibility of substituting Ni binder phase,intermetallic compound binder phase and high-entropy alloy binder phase for Co binder phase was analyzed.The development prospect and the key points for future research of binder phase in cemented carbides were prospected.

The effect mechanism of different carbides on bending strength and wear resistance of cemented carbides was explicated by three point bending and wear tests,and the influence of carbide percentage content on cemented carbides comprehensive properties was revealed.Through standard turning and milling experiments,the data of the influence of single and multiple carbides on tool performance and working life were obtained.At the same time,the carbide percentage data for maximizing tool performance under different Co content were further obtained.The research can provide reference for the optimization of domestic tool matrix materials.

In order to explore the mechanism of oxidation leaching of stone coal,the vanadium was leached directly from stone coal vanadium ore by sulfuric acid solution at atmospheric pressure.By adding sodium persulfate in the process of acid leaching,the effects of various conditions on vanadium leaching rate were investigated.The results show that V leaching rate reached 88.9% under the experimental conditions of sodium persulfate 2% ,sulfuric acid 35 %,solid-liquid ratio 1:1,leaching temperature 95℃ and leaching time 11 h.Fitting the V leaching rate-time curves at different reaction temperatures shows that the oxidation leaching process conforms to the shrinking core model and the leaching process is controlled by the chemical reaction on the particle surface.According to Arrhenius equation,the apparent activation energy of the reaction was approximately calculated to be 66.08 kJ ·mol^-1 by using curve fitting method.