Nano WC-10 Co4 Cr coatings were prepared on ZG06 Cr13 Ni5 Mo stainless steel by using oxygen-propane HVOF,and the effects of process parameters on microstructure and performance of the coatings were studied.The phase composition and microstructure of the coatings were characterized by XRD and SEM,and the microhardness and porosity were measured by Vickers hardness tester and metallographic analyzer.The sand erosion resistance of the coatings was tested in slurry and their sand erosion wear me-chanism was analyzed.The results show that the main phases of WC-10 Co4 Cr coatings prepared under different process conditions are WC,W2C and amorphous CoCr.The phase content is greatly affected by propane flow rate.The coatings are mainly composed of CoCr metallic bonding phase and multiscale micron-nanostructured WC hard particles,as well as some defects such as micropores and microcracks.The porosity of the coatings decreases with the increase of propane flow rate and spraying angle,and decreases at first and then increases with the increase of powder feeding rate and spraying distance.The microhardness of the coatings increases at first and then decreases with the increase of propane flow rate,powder feeding rate and spraying distance,and increases with the expansion of spraying angle.The optimum process parameters are as follows:propane flow rate of 68 L/min,powder feeding rate of 45~55 g/min,spraying distance of 250 mm,and spraying angle of 90°.The maximum sand erosion resistance of nano WC-10 Co4 Cr coatings reaches 14.26 times that of stainless steel substrate,and their sand erosion wear mechanism is mainly fatigue flaking with alternating stress.

V-Mo-Sb/Ti catalyst was prepared by step impregnation method.XRD,XRF,N2-adsorption/desorption,NH3-TPD,H2-TPR,UV-Vis,and XPS were used to characterize the physicochemical properties of the catalyst.The denitrification performance and the oxidation activity of elemental mercury(Hg0)of the catalyst were evaluated by a fixed bed reactor.The results show that the loading of antimony leads to the increase of specific surface area,pore volume,surface acidity,reducibility and the content of chemi-sorbed oxygen of V-Mo/Ti catalyst,which improves the denitrification performance and the oxidation activity of Hg0.In addition,V-Mo-Sb/Ti catalyst also exhibits good resistance to SO₂ and H2O.

In order to improve the toughness and hardenability of H13 die steel,as well as prolong its service life,Stellite156 Co-based alloy coating was prepared on its surface by laser cladding.During the cladding process,in order to reduce the pores,refine the grain size and improve the hardness and wear resistance of the coating,Stellite156 Co-based alloy coatings with different Y2O3 contents(0,0.5%,1.5%,2.5%,3.5%)were prepared.The morphology and porosity of the coatings were analyzed by metallographic microscope,the microstructure and phase composition of the coatings were analyzed by SEM and XRD,the segregation of alloy elements in the coatings was analyzed by EDS,the hardness of the coatings was tested by microhardness tester,and the wear resistance of the coatings was tested by friction and wear tester.The experimental results reveals that Y₂O₃ content has little effect on the appearance of the coating,and less Y₂O₃ content can improve the heat convection in the molten pool and effectively reduce the number of pores in the coating.When Y₂O₃ content is 2.5%,the pores in the coating increase,and the coating phases mainly include Cr-Ni-Fe,Cr,Ni17W3 and a small amount of Y₂O₃ and(Cr,Co,Ni)23C6.Compared with the coating without Y₂O₃,the grain size of the coating with 2.5% Y₂O₃ is significantly reduced,the grain arrangement is more compact and orderly,and the composition segregation in crystal grains and grain boun-daries of the coating is also significantly improved.When the Y₂O₃ content increases from 0 to 2.5%,the maximum average HV microhardness of the coatings reaches 560,which is higher than 500 of the substrate.However,when the Y2O3 content continues to increase to 3.5%,the hardness of the coating significantly decreases,even lower than that without Y₂O₃.Therefore,a proper amount of Y₂O₃ can improve the pore defects,refine the grains,improve the composition segregation,increase the hardness of the coating,and then improve the wear resistance of the coating.

Using sodium bicarbonate solution as the precipitant of yttrium carbonate,the influence of reaction temperature,feeding speed,seed crystal amount and aging time on the crystallinity of yttrium carbo-nate was studied by response surface method,and the optimal technical conditions for crystallization of yttrium carbonate were obtained.The results show that the four factors have effect on the crystallinity of yttrium carbonate crystal in order:seed crystal amount>reaction temperature>aging time>feeding speed.The optimal technical conditions are reaction temperature of 72.22℃,feeding speed of 1.91 mL/min,seed crystal amount of 7.19 mL and aging time of 2.29 h.Under the optimal conditions,the average intensity of the three major XRD peaks of yttrium carbonate is 515,the particle size distribution is concentrated and large particles are dominative,the crystal grain size significantly increases,the specific surface area of the crystal decreases,and the flocculent structure on the particle surface decreases.

In order to improve the electrical conductivity and mechanical properties of Al-Cu-Sc aluminum alloy conductor materials,the response surface method(RSM)of central composite design was applied to design experiments with Design-Expert 8.0.6 software.The contents of Cu and Sc elements in Al-Cu-Sc aluminum alloy conductor materials were optimized,and a second-order response model was established regarding the effects of Cu and Sc element contents on the electrical conductivity and tensile strength of the alloy.The results show that the optimized conditions are Cu Content of 0.35%and Sc Content of 0.24%.The results of validation experiments under these conditions show that the response surface model has high reliability.The electrical conductivity of Al-0.35%Cu-0.24%Sc alloy material reaches 56.4%IACS and the tensile strength reaches 83.25 MPa,which meets the requirements for the electrical conductivity and mechanical properties of the alloy.

Zn and Ca were respectively used to modify and compound La₂O₂CO₃ carrier,and then the catalysts of Ni/La₂O₂CO₃(NL),Ni/La₂O₂CO₃-ZnO(NLZ)and Ni/La₂O₂CO₃-CaO(NLC)were prepared to catalyze reforming of ethanol steam to produce hydrogen.The crystal phase,specific surface area and comprehensive performance of the catalysts were analyzed by XRD,BET and temperature programmed reduction(TPR).The results show that compared with NL,the ethanol conversion rates of NLC and NLZ at 300℃are increased by 24.3%and 20.8%,respectively.NLC has the best low-temperature catalytic activity.The H₂ selectivity of NLC and NLZ is higher than that of NL,increased by 15.23%and 14.04%respectively at 600℃.In the range of 400~700℃,the H₂ selectivity of NLC is higher than that of NLZ,while the selectivity of CO₂,CO and CH₄ is lower than that of NLZ.NLC can better inhibit Ni coalescence and deactivation at high temperature,thus improving the efficiency of Ni catalysis for hydrogen production.

The surface mechanical attrition treatment(SMAT)process and double-sided simultaneous attrition were used to produce a gradient structure on the surface of Mg-Gd-Y alloy,and the SMAT samples were subjected to short-term annealing treatment to optimize their performance.By changing SMAT duration and sample thickness,the effect of the volume ratio of gradient-structured layer to matrix layer on mechanical properties of the alloy was studied.The results show that the SMAT samples have gradient structure in the near-surface layer,which can be divided into the severely deformed area at the most surface layer,the moderately deformed area at the sub-surface layer,and the matrix area at the bottom layer in turn.With the increase of SMAT duration,the thickness of the gradient-structured layer shows an increasing trend.The thickness of the gradient-structured layer in the relatively thin samples slowly increases due to elastic deformation and plastic deformation in the initial stage of SMAT.For samples with a thickness of more than 2 mm,their gradient-structured layers have similar thickness after SMAT for 200 min.As the volume ratio of the gradient-structured layer increases,the overall yield strength of the samples shows an upward trend.After the SMAT samples are subjected to short-term annealing,the grains of the gradient-structured layer significantly grow up,and dislocations and twins are significantly reduced,resulting in decreased yield strength and significantly improved elongation at break of the alloy.

Niobium ingot was obtained by twice vacuum electron beam melting of melted niobium prepared by aluminothermic reduction method,and then the slabs were subjected to vacuum annealing at 1100℃for 1 h after repeated upsetting and stretching with a large degree of deformation at room temperature.Finally,niobium target was made by cross rolling→cutting→annealing of finished products→leveling→machining→surface polishing.Metallographic and EBSD tests were carried out on finished producs of niobium target.The results show that using melted niobium as raw material,niobium ingot with purity above 99.99%can be obtained by twice vacuum electron beam melting.The average grain size of niobium ingot is less than 30μm after repeated upsetting and stretching,forging and cold rolling at room temperature.The main texture of niobium ingot is{001}texture,followed by{111}texture.In addition,compared with me-tallographic test,EBSD test can better evaluate the recrystallization degree and grain size of the metal.

The samples of U-0.5%Ti,U-0.75%Ti and U-0.95%Ti alloys were prepared by vacuum induction melting,and then the effect of Ti content on alloy microstructure,room-temperature tensile perfor-mance and corrosion resistance was studied.The results show that the U-Ti alloys with the above three compositions have the microstructure mainly composited of acicular and biconvex lenticular martensite,and their main phases areα′and U2Ti.The grains of U-Ti alloy are gradually refined and the content of U2Ti phase increases with the increase of Ti content.As Ti content increases,the strength of U-Ti alloy gradually increases,while the plasticity gradually decreases,and the corrosion resistance slightly decreases.

AlxFeNiSiTi(x=0.2,0.4,0.7,1.0)high-entropy alloy was prepared by mechanical alloying combined with cold isostatic pressing and vacuum sintering.The effect of Al content change on the microstructure and mechanical properties of the high-entropy alloy was studied.The results show that with the increase of Al content,phase composition of the alloy significantly changes:Ni-like FCC phase gradually transforms into Al-rich BCC2 phase.The hardness of the alloy decreases at first and then increases with Al content increasing,reaching 1015 HV when the Al content is 1.0.The nano-indentation hardness of the alloy increases with the increase of the volume fraction of FeSiTi-rich BCC1 phase.