The microstructure and mechanical properties of Ti-9 Al-5.4 Mo-1.9 Zr-0.3 Si titanium alloy were studied by metallographic microscope,X-ray diffractometer,transmission electron microscope and microhardness tester.The results show that there are a lot of equiaxialαstructure andβstructure resulting fromαstructural transformation in titanium alloy matrix before and after field treatment.The content of primaryαphase in the original microstructure of the titanium alloy is 41.2%.After the treatment with pulsed electric field,magnetic field and electromagnetic field,the content of primaryαphase changes to 42.1%,44.3%and 43.6%,respectively.Compared with the original microstructure,α-Ti axis ratio of the titanium alloy is significantly larger after external field treatment,and theα-Ti axis ratio obtained by pulse electromagnetic field treatment is the largest.The entanglement dislocation in the alloy matrix is not significantly reduced after magnetic field treatment.After electric field or pulse electromagnetic field treatment,the dislocation density in the alloy matrix is generally reduced,and the number of entanglement dislocations is also significantly reduced.The hardness of the samples obtained by various methods is basically consistent,and the hardness of the sample after pulse electromagnetic field treatment is relatively low.

In order to improve the wear properties of 45#steel,(V2O5+WO3+C)/Ni60 coatings were prepared by laser cladding on steel 45#steel surface.The microstructure and phase of the cladding layer were analyzed by metallographic microscope,scanning electron microscope and X-ray diffractometer,the microhardness of the cladding layer was measured by microhardness tester,and the friction test was carried out by high-speed ring wear tester.The results show that the coating is composed of solid solutionγ(NiFe)and in-situ synthesized reinforcing phases including W2C,WC,VC and Cr3C2.The hardness and wear resistance of the(V2O5+WO3+C)/Ni60 coating are greatly improved.The average HV0.3 hardness of the cladding layer is as high as 1 400,which is one fifth of the wear weight loss of Ni60 coating.

Undoped AgSnO2 and AgSnO2/La2O3 contact materials with six kinds of SnO2 particle sizes were prepared by powder metallurgy,and the influence was studied of SnO2 particle size on physical properties and electrical contact properties of the two kinds of AgSnO2 contact materials.The results show that when SnO2 particle sizes are 1 000 nm and 500 nm,respectively,both the undoped AgSnO2 and AgSnO2/La2O3 materials have moderate hardness,high conductivity,small and stable contact resistance and arc energy.The properties of AgSnO2 contact materials can be improved by selecting appropriate SnO2 particle size.

The composite ceramic coating on 304 steel surface was prepared by coating with SiO2,Al2O3 and MgO as raw materials.The corrosion resistance and thermal shock resistance of the ceramic coating were studied.The effects of material ratio,sintering temperature and heating rate on the surface morphology and properties of the ceramic coating were analyzed.The results show that when the ratio of SiO2,Al2O3,MgO aggregate(mass ratio 65∶20∶15)to water glass is 1∶5,sintering temperature is 750℃,heating rate is 2℃/min,and sintering time is 30 min,the ceramic coating without crack and with uniform composition and good surface quality can be prepared.The ceramic coating shows excellent corrosion resistance in both NaCl solution and salt spray,which is significantly improved compared with stainless steel.The ceramic coating also has good thermal shock resistance.

Oxidation-reduction process is a simple and eco-friendly method for recycling cemented carbide scrap.The principle and impact factors of recycling cemented carbide scrap by oxidation-reduction process are introduced.The existing problems of the above process are pointed out and their solutions are proposed.The problems and countermeasures of recycling coated cemented carbide scrap by oxidation-reduction process are emphatically discussed.And then the suggestions are proposed for future oxidation-reduction process to recycle cemented carbide scrap.All these are useful for the sustainable development of tungsten resources.

The types,adding methods,dosages and action mechanism of common grain growth inhibitors are described,and the effects of different inhibitors on the physical and mechanical properties of the cemented carbides are introduced.On the basis of a large number of research results,some existing problems in this field are pointed out,such as the differences of experimental results caused by the inconsistency of research methods,experimental conditions,types and dosages of inhibitors.

The preparation methods of WC-Co gradient cemented carbides for mining at home and abroad are summarized,including carburizing,melt infiltration,layered pressing(construction)and locally coating grain inhibitor and sintering.The research status of these four methods and the application of gradient alloys are introduced.The constraints of promotion application of gradient cemented carbide as mining alloys are analyzed,and the application prospects of WC-Co gradient cemented carbides in mining and the technical problems in industrial production are prospected.

The theoretical breakthrough of the mainstream technology in hydrometallurgy of tungsten and its existing problems in engineering and technology are summarized.The factors of China's tungsten re sources, technology and environmental protection policies are also comprehensively analyzed. A new tung sten metallurgy technology, sulfuric-phosphoric mixed acid decomposition technology of scheelite, developed by Central South University is introduced. The new technology can solve these problems in the cur rent tungsten hydrometallurgy. It provides a new way for promoting the healthy development of tungsten industry in China under the new situation.

The nanofiltration process has been widely used in the metallurgical process of rare metal tung sten, molybdenum and rare light metal lithium. Because of expansion and deepening of the research on nanofiltration process,it is necessary to establish a model which can accurately predict the performance of nanofiltration membrane. Many nanofiltration process models are formed and several nanofiltration mathe matical models described in this study are as follows: the simple irreversible thermodynamics model and the solution-diffusion model, the steric hindrance-pore model concerning nanopore, the charge model, the electrostatic and steric-hindrance model and the Donnan-steric partitioning pore model introducing charge factors,and the steric, electric and dielectric exclusion model with dielectric effect. Then the differences among the models and their application ranges are respectively discussed. The study of finite element analy sis and artificial neural network in the simulation of nanofiltration process is reviewed,and research priori ties and directions are put forward.

Using waste lithium titanate from anode materials of Li-ion batteries as the raw material and after pretreatment,Li and Ti in waste materials were separated and recovered by dilute sulfuric acid preferential leaching process. The effects were investigated of sulfuric acid concentration, liquid-solid ratio, leaching temperature and leaching time on the leaching rate of lithium and titanium in the acid leaching process. The experimental results show that the optimized dilute sulfuric acid preferential leaching process parameters are as follows: sulfuric acid concentration is 4 mol/L,liquid-solid ratio is 6:1 , leaching temperature is 80℃ and leaching time is 4 h. Under these conditions, the primary leaching rate of lithium can reach 90%,and that of titanium is 1.08%.