The crankshaft is a key component of the engine,and its induction quenching process is critical to its eventual performance,machining costs,efficiency,and service life.Currently,the induction coils used for high-frequency quenching are manufactured by traditional machining and welding processes,which suffer from uneven water flow in the cooling channels and low precision of welding assembly,and result in poor performance as well as low efficiency in production line changeovers.Selective laser melting(SLM)is a well-established additive manufacturing technique renowned for its capability to produce complex,customized structures,making it particularly suitable for the integrated fabrication of components like an induction coil.However,the use of pure copper in SLM is hindered by its high thermal conductivity and low laser absorptivity,which present significant challenges during the process.The high thermal conductivity causes rapid heat dissipation,preventing effective localized melting and solidification.Simultaneously,the low laser absorptivity reduces the efficiency of energy absorption,leading to inadequate fusion and insufficient layer bonding.But the addition of chromium and zirconium can significantly reduce the thermal conductivity and improve laser absorptivity compared to pure copper,allowing for better heat retention during the laser melting process.The current study on CuCrZr alloy mainly focuses on improving its properties,and there are fewer studies on the industrial application.Therefore,this study investigated the feasibility of SLM process in the fabrication of CuCrZr alloy with high electrical conductivity and high mechanical properties and its advantages in engineering applications(induction hardening of engine camshafts).First,the experimental CuCrZr alloy samples were fabricated according to the high-relative-density process parameters using SLM technology under Ar atmosphere(99.99%).Subsequently,those samples were subjected to direct aging(DA)or solid solution treatment(ST)and ST+DA process.The influences of heat treatment durations and temperatures on the microstructure,hardness and tensile properties of CuCrZr were discussed.It was found that the electrical conductivity and mechanical properties of SLM-ed CuCrZr alloy were significantly improved after heat treatment.The hardness and the ultimate tensile strength of DA-treated samples reached HV 170 and 492.08 MPa,respectively,while the elongation reduced to 20.71%.This increase in hardness could be attributed to the precipitation of Cr phases distributed more evenly during DA treatment,which enhanced the matrix strength by impeding dislocation motion,but the presence of precipitates also contributed to a reduction in the ability to suffer from plastic deformation and leading to a notable decrease in elongation.Based on the above studies and our team's previous study on the electrical conductivity of this alloy,the process and heat treatment parameters of the CuCrZr induction coil were set.In addition,this study analyzed the influence of induction coil fabricated by different methods on induction hardening cams.The operating voltage and current of the CuCrZr induction coil were determined based on the power output of the heat treatment equipment used for conventional induction hardening.The results demonstrated that:the integrally formed CuCrZr induction coil had a relative density of 95.42%,an electrical conductivity of(85±0.2)%IACS and increased instantaneous and steady-state flow rates of 109~111 L·min1.Additionally,the flow rate fluctuation of CuCrZr induction coil had been reduced to less than 1.25 L·min-1,while instantaneous and steady-state flow rate fluctuation rates were 4.29%and 6.19%,respectively,and those for the conventional induction coil were 0.46%and 1.82%,respectively.The rate of change between the instantaneous and the steady-state flow rate was reduced from-5.53%~4.90%to-0.91%~0.91%.The dimensional accuracy of the induction coil between the two coils had increased by 37.12%,while the dimensional accuracy of the entire part had more than doubled.Further experiments determined that the rated power of induction hardening equipment in parameters was 54%power when quenching the crankshaft using CuCrZr induction coil.As the manufacturing precision of the induction coil was improved,the temperature reached at the crankshaft surface under the effect of CuCrZr induction coil would be higher than that achieved with a traditional one,according to the skin effect in current distribution characteristics of electromagnetic induction heating.Therefore,the amount of retained austenite in the camshaft increased after quenching.Meanwhile,owing to the increased cooling rate and stability of the CuCrZr induction coil,the martensite structure in the camshaft hardened was finer and more uniform,with an increased grain dislocation density,which resulted in hardness reached to HRC(57.7±0.62)and exhibited a metallographic grade of 3.To summarize,this study demonstrated that an additive-manufactured CuCrZr induction coil not only met application requirements but also enhanced stability and consistency in the cam heat treatment,which proved the advantages of additive-manufactured parts in induction hardening.

With the rapid rise of the microelectronics industry,integrated circuits are gradually developing in the direction of miniaturization and intelligence.This puts forward higher requirements for lead frame materials,including high strength,high conductivity,corrosion resistance and so on.In this study,the properties of Cu-Cr-Zr-Si alloy and its aging precipitation kinetics were studied,which would provide a basis for controlling the microstructure and properties of Cu-Cr-Zr-Si alloy.Adding Si to Cu-Cr-Zr alloy could refine the grain but excessive Si would cause the decrease of the conductivity.Therefore,in this study,a small amount of Si was selected to be added,and two kinds of alloys with different chemical composition of Cr,Alloy 1#(Cu-0.31Cr-0.20 Zr-0.03Si)and Alloy 2#(Cu-0.56Cr-0.20Zr-0.03Si),were prepared.Firstly,Alloy 2#solid solution alloy was rolled at 80%room temperature and aged at different temperatures(400,450 and 500℃).The variation of hardness and conductivity of the alloy with aging process was observed,and the optimum aging temperature was determined.Then,the hardness and conductivity of the two alloys with different compositions were measured at the optimum aging temperature,and the effects of different Cr content on the comprehensive properties of the alloys were compared.Finally,the aging methods of Alloy 2#alloy was applied at 400,450,500,550,600 and 650℃for 0,0.5,1,2,3,4,5,6,8,10 and 12 h,respectively.The aging precipitation kinetics of Alloy 2#was studied according to the relationship between the electrical conductivity and the new phase transformation rate of Cu-Cr-Zr-Si alloy.Avrami precipitation kinetics equation and electrical conductivity equation of Alloy 2#at different aging temperatures were obtained,and the isothermal transformation kinetics S curve and TTT curve was plotted,which provided methods for controlling the microstructure and properties of Cu-Cr-Zr alloy.The experimental results showed that the hardness of Alloy 2#increased rapidly with the increase of aging time while decreased gradually after reaching the peak value.The electrical conductivity of Alloy 2#increased rapidly at the initial stage and reaches a higher level after aging for 1 h,and then slowly increased with the further increased aging time.In addition,the conductivity of Alloy 2#increased significantly with the increase of aging temperature.It was considered that the hardness and conductivity of supersaturated solid solution increased rapidly at the initial stage of aging because of the high solute concentration and high precipitation driving force in supersaturated solid solution.With the aging process,the solute content in the matrix and the precipitation rate simultaneously decreased,which induced the hardness and conductivity curve increased slowly.In addition,the increase of aging temperature made the solute atoms in the matrix get enough energy to precipitate from the matrix,which improved the conductivity of the alloy.However,the increase of aging temperature also accelerated the diffusion rate of solute atoms and promoted e segregation of solute atoms,promoting the coarsening of precipitated phase,and then led to the weakening of precipitation strengthening effect.According to the above experiments,a heat treatment system(solution treatment at 970℃for 1 h+rolling at room temperature with 80%deformation+peak aging treatment at 450℃)was selected.At 450℃,the hardness and conductivity of Alloy 1#and Alloy 2#had the same trend with the increase of aging time,but the peak hardness(208 HV)of Alloy 2#was slightly higher than that of Alloy 1#(HV 204),and their conductivity was not significant difference.Cr content in Alloy 2#was higher than that in Alloy 1#,and the precipitation strengthening effect was enhanced with the increase of Cr content,so the hardness value of Alloy 2#was higher.For Alloy 1#and Alloy 2#,there was little difference in solubility of solute elements in copper matrix at 450℃,so the conductivity curves basically coincided.According to experimental results,it was found that the comprehensive properties of Cu-Cr-Zr-Si alloy could be improved by increasing appropriate Cr content.After solution treatment,room temperature rolling,the peak aging of Alloy 1#(Cu-0.31Cr-0.20Zr-0.03Si)appeared at aging time of 1 h(aging temperature of 450℃),and the hardness and conductivity of the alloy were HV 204 and 71.4%IACS,respectively.The peak aging of Alloy 2#(Cu-0.56Cr-0.20 Zr-0.03Si)appeared at aging time of 2 h,at which time the hardness was HV 208 and the conductivity was 72.6%IACS.The precipitation kinetics and conductivity of Alloy 2#during aging treatment at 400~650℃were obtained by Avrami empirical equation,and the isothermal transformation kinetics S curve and TTT curve were drawn.

Industrial pure titanium TA1 is widely used in various sectors such as chemistry,energy,aerospace and biomedical fields due to its excellent properties including low density,high strength ratio and corrosion resistance.Diverse sizes and shapes of industrial pure titanium products are needed.Hot deformation is the most important part of processing and forming,so it is of great significance to study the hot deformation behavior for the production of industrial pure titanium TA1.Previous studies on the hot deformation behavior of industrial pure titanium mainly focused on the deformation mechanism and properties,and the effects of temperature and strain rate on the constitutive equation were considered.The phase transition process is almost not considered.However,the phase transformation process plays an important role in the flow stress of industrial pure titanium during high temperature thermal processing.It is particularly important to study the influence of phase transition on thermal deformation behavior and establish an accurate prediction model.The accuracy of the constitutive equation is very important as a link between the flow stress of the material and the simulation of the deformation process parameters.The Arrhenius-type equation is widely used to express the relationship between flow stress,deformation temperature and strain rate,especially at high temperature deformation.In this paper,the high temperature deformation behavior of industrial pure titanium TA1 was studied by using Gleeble-3500 thermal simulation testing machine at the deformation temperature of 750~950℃and the strain rate of 0.1~20 s-1.The high-precision constitutive equation of industrial pure titanium TA1 considering the effect of phase transformation was established by using Arrhenius-type equation with temperature compensation function.The results showed that the flow stress of industrial pure titanium TA1 increased with the decrease of deformation temperature and the increase of strain rate during hot deformation.The peak stress,serving as a marker point where processing hardening and dynamic recrystallization or recovery counterbalance each other,rapidly decreased with increasing temperature and decreasing strain rate.Under conditions of 750℃and 20 s^-1,the peak stress reached as high as 181 MPa,whereas under conditions of 950℃and 0.1 s^-1,it reduced to 10 MPa.The peak stress between 800 and 850℃curved at different deformation rates decreased greatly.For example,when the deformation rate was 20 s^-1,the peak stress decreased by 108 MPa.When deformed below the phase transition temperature,the peak stress decreased with the increase of temperature,which was much larger than that when deformed above the phase transition temperature.When the strain rate was 1 s^-1,the temperature increased from 750 to 800℃,and the peak stress decreased by about 60 MPa.However,when the temperature increased from 900 to 950℃,the peak stress only decreased by about 3.2 MPa.This had a lot to do with the phase structure.β-Ti was a body-centered cubic structure,and the slip system was superfluous to the slip system ofα-Ti.The slip ofβ-Ti became easier and the flow stress decreased significantly.However,when the phase transition occurred completely,the influence of deformation parameters on the peak stress became smaller.Industrial pure titanium TA1 was very sensitive to temperature and strain rate when deformed below the phase transition point.Based on the experimental data,Arrhenius constitutive model was used to construct a constitutive equation suitable for the industrial pure titanium TA1 coveringβ-αphase transition temperature range.When comparing the calculated data with the experimental data,it was found that when the deformation temperature was below the phase transition temperature,the error between the calculated data and the experimental data was large.The temperature compensation function was proposed to correct it.It could be seen that the phase transition process had a significant effect on the model.The model modified by the temperature compensation function could accurately predict the data of the deformation temperature below the phase transition point.Finally,the correlation coefficient(R)between the model prediction data and the experimental data at different deformation temperatures was greater than 0.98,and the average relative error(ARRE)was within 4%.The model could fully describe the change of flow stress of industrial pure titanium TA1 during high temperature compression.In conclusion,the relationship between phase transformation and thermal deformation behavior of industrial pure titanium TA1 was studied,and a more accurate constitutive equation was established to achieve more accurate simulation in the thermal deformation process,which provided data guidance for the actual deformation process of industrial pure titanium TA1.

High-entropy alloy is a new type of alloy system,with high wear resistance,high strength,high hardness,and other good properties,but the production process requires high equipment and technology,the preparation cost is also high,and the study of high-entropy alloy is relatively difficult.In principle,the first-principles calculation does not need to rely on any empirical parameters or specific model assumptions.It only needs to know the type and arrangement of the atoms that constitute the substance to obtain the calculation results,greatly saving research and development costs and shortening the preparation cycle.Therefore,this paper used the first-principles calculation method to study.Firstly,the phase structure of((Ti_0.4W_0.15Mo_0.15Cr_0.15)_100-xAl_x(x=5,10,15,20,25,30,35,40,45 and 50;mass fraction)high-entropy alloys was determined by calculating the mixing entropy,mixing enthalpy,atomic size difference,thermodynamic parameter,and valence electron concentration.Later,in the Materials Studio software,((Ti_0.4W_0.15Mo_0.15Cr_0.15)_100-xAl_x high-entropy alloys crystal models were built.The CASTEP package was used to optimize the structure of the high-entropy alloys,and the elastic constants of the high-entropy alloys under different Al content and pressure were calculated.The bulk modulus,Young's modulus,shear modulus,Poisson's ratio,Cauchy pressure,hardness,and melting point of high-entropy alloys could be calculated using the results of the first principles.After the above calculation,it was found that when Al content was in the range of 5%to 50%,the mixing entropy was between 11.781 and 12.636 J·mol^-1·K^-1,the mixing enthalpy was between-18.157 and-8.522 kJ·mol^-1,the atomic size difference was between 0.044 and 0.052,the thermodynamic parameters were between 1.27 and 3.28,and the valence electron concentration was between 4.296 and 4.945.Except for mixing entropy,the other four terms decreased with the increase in Al content.In the first-principles calculation,the lattice constant of the high-entropy alloys could be obtained by structural optimization.The lattice constants of((Ti_0.4W_0.15Mo_0.15Cr_0.15)_100-xAl_x high-entropy alloys ranged from 0.321 to 0.408 nm,and the lattice constants of high-entropy alloys increased gradually with the increase of Al content in high-entropy alloys.In calculating the elastic constants of((Ti_0.4W_0.15Mo_0.15Cr_0.15)_100-xAl_x high-entropy alloys,only C₁₁,C₁₂,and C₄₄ components were selected for analysis.Based on C₁₁ and C₁₂,C₁₁-C₁₂ and C₁₁+2C₁₂ were calculated.According to the calculation results,both C44 and C11+2C12 were greater than 0,while C₁₁-C₁₂ was greater than 0 only when the Al content was 15%,20%,25%,35%,40%,and 50%.It was proven that the mechanical properties were theoretically stable when the Al content was 15%,20%,25%,35%,40%,and 50%.The bulk modulus,Young's modulus,and shear modulus of((Ti_0.4W_0.15Mo_0.15Cr_0.15)_100-xAl_x high-entropy alloys showed a decreasing trend with increasing Al content.Moreover,when the Al content was 0.1 and 0.3,the shear modulus and Young's modulus appeared to have negative values,which proved that the mechanical structure was unstable and conformed to the judgment of mechanical stability.In the six stable mechanical properties of((Ti_0.4W_0.15Mo_0.15Cr_0.15)_100-xAl_x high-entropy alloys,Poisson's ratio(v),ratio of bulk modulus to shear modulus(B/G),and Cauchy pressure(C₁₂-C₄₄)all increased slowly with the increase of Al content.When Al content was 15%,v0.26,B/G>1.75,C₁₂-C₄₄>0.Calculate(Ti_0.4W_0.15Mo_0.15Cr_0.15)₈₅Al₁₅ high-entropy alloy under a pressure of 0~40 GPa.The lattice constant of(Ti_0.4W_0.15Mo_0.15Cr_0.15)₈₅Al₁₅ high-entropy alloy slowly decreased from 0.350 to 0.322 nm with increasing applied pressure,and the magnitude of the decrease continuously decreased.The calculated elastic constants C₄₄,C₁₁-C₁₂,and C₁₁+2C₁₂ were all greater than 0.In addition,C₁₂ kept increasing with the increase of pressure,while C₁₁ and C₄₄ increased first and then decreased with the increase of pressure,reaching the maximum value when the pressure was 30 GPa.The bulk modulus of(Ti_0.4W_0.15Mo_0.15Cr_0.15)₈₅Al₁₅ high-entropy alloy increased continuously with the pressure increase at 0~40 GPa.Young's modulus and shear modulus both increased first and then decreased with the increase of pressure,reaching their maximum values at pressure of 25 GPa.At pressures ranging from 0 to 40 GPa,Poisson's ratio,the ratio of bulk modulus to shear modulus,and the trend of Cauchy pressure changes were similar,increasing with increasing pressure.When the pressure was 0~10 GPa,v0.26,B/G>1.75,C₁₂-C₄₄>0.The hardness of high-entropy alloy first increased and then decreased with the increase of pressure,and reached the maximum value when the pressure was 25 GPa.At the same time,the melting point of(Ti_0.4W_0.15Mo_0.15Cr_0.15)₈₅Al₁₅ high-entropy alloy increased with the increase of pressure.

The dynamic mechanical properties of ZTC4 and ZTA15 titanium alloys after casting,hot isostatic pressing and stress reduction annealing were tested by separated Hopkinson pressure bar test in this study.Adiabatic shear bands of cracked samples were analyzed and characterized.ZTC4 and ZTA15 titanium alloys were typicalα+βtwo-phase titanium alloys.The original as-cast structure was composed of largeβgrains,and the grain interior was composed of grain boundaryαand parallel lamellarαphases.After annealing ZTC4 titanium alloy at different temperatures,it could be seen that the lamellar morphology did not change significantly with the increase of annealing temperature.When the annealing temperature reached 950℃,the lamellar tip dissolves and formed a"fork"shape.When the alloy was annealed at 1020℃/2 h air cooling+700℃/2 h air cooling,the alloy microstructure was preserved inβsingle phase zone,andα-phase was dissolved and air-cooled,and the microstructure characteristics were similar to that of 700℃/2 h air cooling.Compared to ZTC4 titanium alloy,ZTA15 titanium alloy appeared"fork shape"after annealing at 950℃.The microstructure evolution of ZTC4 and ZTA15 titanium alloys was consistent by comparing the as-cast microstructure after heat treatment.The maximum plastic strain of ZTC4 titanium alloy could reach 0.19,the minimum of 0.155,the average flow stress was 1213~1241 MPa,and the impact absorption energy was 190.5~231 J·cm^-3.As forZTA15 titanium alloy,its maximum plastic strain reached 0.185 and the minimum of 0.11.The average flow stress of ZTA15 titanium alloy was 1388.5~1410 MPa,which was significantly higher than that of ZTC4 titanium alloy,and the impact absorption energy was 150~257 J·cm^-3,which was similar to that of ZTC4 titanium alloy.After adiabatic shear deformation of ZTC4 titanium alloy,local tearing occurred in the as-cast structure,and the main crack direction was about 45°angle with the deformation direction.An adiabatic shear band appeared in the untorn part connected to the main crack tip,with a width of about 20μm and an angle of about 30°from the deformation direction.In addition,discontinuous microcracks were also generated at the front end of the adiabatic shear band and at a distance of 500μm.After loading ZTA15 titanium alloy under dynamic load,a crack with a length of about 120μm and a maximum width of about 20μm appeared in the as-cast structure,and the crack direction and deformation direction were about 45°.In addition,an adiabatic shear band with a width of about 50μm appeared at the location connected to the crack tip and in the same direction.Unlike ZTC4 titanium alloy,no micro-cracks were found near the deformation zone of ZTA15 titanium alloy.The strip contrast diagram showed that a large number of dislocation network structures also appeared near the adiabatic shear zone,and smaller nanocrystals were also present inside the shear zone.The lamella adjacent to the shear zone was severely bent,and a few small grains with different orientations appeared.ZTA15 titanium alloyβsheet width was thin;deformation occurred after bearing impact load.The original lamellar boundary large angle grain boundary had been broken into dots,and the lamellar deformation absorbed part of the impact energy,while ZTC4 titanium alloy lamella formed twin grain boundary or large angle grain boundary inside the lamella under the impact,which had little effect on the impact energy absorption.Refining grain size and sheet width was beneficial to absorbing impact energy and increasing average flow stress,but had little effect on maximum plastic strain.These results indicated that lamellar thinning improved the dynamic hardening effect,but failed to improve the anti-crack propagation ability.The thermal influence of adiabatic shear on the as-cast structure had little influence on the matrix structure.After adiabatic shear occurred,a crack feature of"crack+adiabatic shear band"was formed.As could be seen from the uneven interface profiles on both sides of the non-crack,adiabatic shear occurred before crack cracking,and the interface melted,and finally cracked,without forming dispersed small cracks.The average flow stress of ZTA15 titanium alloy was about 70 MPa higher than that of ZTC4 titanium alloy,that was,the dynamic compressive strength of ZTA15 titanium alloy was higher.

Aluminum alloy is extensively utilized in aerospace,transportation,machinery manufacturing,and shipbuilding and so on.Among them,A356 aluminum alloy,a typical Al-Si alloy,is widely used in the casting of automotive parts such as manifolds,engine cylinder blocks,and heads.Due to their complex structure,these parts are suitable for production using lost foam casting(LFC).In LFC,the assembled foam group is initially embedded in dry sand molds and subjected to negative pressure,followed by pouring the metal liquid onto the foam mold.The foam then vaporizes and is replaced by the metal liquid to obtain the desired casting.However,because the pouring temperature of the metal liquid is 30~50℃higher than that of traditional casting,and the heat conduction coefficient of the dry sand used in the molds is low,the microstructure of the casting tends to be coarse,leading to reduced mechanical properties.This presents an urgent problem to be addressed.Consequently,refining the microstructure and enhancing the properties of A356 castings produced by LFC are the primary focuses.To refine the microstructure and improve the properties of aluminum alloy,methods such as adding modifiers,increasing supercooling,and applying vibration are employed.Compared to other methods,adding modifiers to aluminum alloy can rapidly introduce heterogeneous nucleation and significantly increase the nucleation rate during solidification,thus achieving the goal of modifying the alloy.Rare earth elements such as La or Ce are commonly used in the modification of aluminum alloys.The addition of La or Ce to aluminum alloys also results in a relatively significant fine-crystal strengthening effect.However,there are few studies on the use of La-Ce composite rare earth to modify A356 aluminum alloy produced by LFC.The effects of La-Ce composite rare earth on the microstructure and properties of A356 aluminum alloy made by LFC are not well understood,and the mechanism of composite strengthening with La-Ce requires further exploration.Therefore,in this study,La-Ce composite rare earth was added to A356 aluminum alloy produced by LFC in concentrations of 0,0.2%,0.4%,0.6%,and 0.8%,and the effects of La-Ce addition on the microstructure and properties of A356 aluminum alloy were investigated.The results indicated that the secondary dendrite arm spacing ofα-Al could be significantly refined.In unmodified A356 aluminum alloy,α-Al exhibited coarse dendritic structure with non-uniform distribution,and the eutectic Si phase was coarse flake-like.After the addition of La-Ce to A356 aluminum alloy produced by LFC,the size of the primaryα-Al phase,primary silicon,and eutectic silicon decreased,and the secondary dendrite arm spacing of primaryα-Al first decreased and then increased with increasing La-Ce content,reaching a minimum in A356 aluminum alloy with 0.6%La-Ce addition.The tensile strength,yield strength,elongation,and Brinell hardness of A356 aluminum alloy produced by LFC initially increased,then decreased,and then increased again with the increase in La-Ce content.When La-Ce content was 0.6%,A356 aluminum alloy achieved optimal comprehensive mechanical properties,with its tensile strength,yield strength,elongation,and Brinell hardness being 117 MPa,97 MPa,1.35%,and HBW 69.5,respectively.These values represent improvements of 27.17%,14.12%,193.48%,and 16.81%,respectively,compared to those without La-Ce modification.This was primarily due to the composite mechanism of fine crystal strengthening of the primaryα-Al phase and silicon phase,along with dispersion strengthening of the silicon phase.

Compared with pure copper components,copper-aluminum composite components not only substantially reduce the cost and weight of the workpiece but also exhibit superior comprehensive performance.Therefore,they hold significant value in both academic research and industrial applications.As a widely adopted welding process,contact reaction brazing has garnered considerable attention in relevant fields due to its advantages of simple operation,environmental friendliness,and high production efficiency.In this study,the contact reaction brazing process was employed to conduct butt welding experiments on T2 pure copper plates and 1060 industrial pure aluminum plates.The influence of various holding times on the macroscopic morphology,microstructure,and shear strength of the joint was systematically investigated.Additionally,the evolutionary pattern of the interface microstructure in the brazed joint was summarized.The results indicated that atomic diffusion extent under different holding time led to notable differences in the types and thicknesses of intermetallic compounds.When the holding time was 5 min,a diffusion bonding layer composed ofγ-Cu9Al4,η-CuAl,andθ-CuAl2 phases formed at the joint interface.Upon extending the holding time to 10 min,the elemental composition at the interface reached the eutectic point of copper-aluminum,initiating the generation and spreading of the eutectic liquid phase within the interface.Following completion of the holding process,the eutectic liquid phase simultaneously precipitatedα-Al phase andθ-CuAl2 phase,forming a layered or fishbone-like eutectic structure.Consequently,the interfacial bonding layer evolved into a four-layer structure.The thickness of the bonding layer at the joint interface increased progressively with the extension of holding time,with the eutectic structure constituting the predominant portion.This phenomenon could be attributed to the significantly higher diffusion rate of Cu/Al atoms in the eutectic liquid phase compared to that in the intergranular regions and grain boundaries.Driven by the concentration gradient,the eutectic liquid phase continued to form in the interface region until the reaction terminated or one of the matrix materials was completely depleted.When the welding process parameters were set to a welding temperature of 570℃and holding time of 20 min,the joint achieved a maximum shear strength of 36.3 MPa.With increasing holding time,the shear strength initially increased and then decreased.Under short holding time,elemental diffusion occurred only at localized contact regions,which resulted in discontinuous interfacial bonding and the formation of cracks and porosity defects.As holding time was further prolonged,copper and aluminum atoms underwent sufficient diffusion,a continuous and dense intermetallic compound layer could form at the interface.Concurrently,the eutectic liquid phase effectively filled micro-porosities,promoting joint microstructure homogenization and significantly enhancing interfacial bonding strength.However,when holding time exceeded 20 min,the shear strength exhibited a downward trend,which was primarily attributed to excessive growth of brittle intermetallic compounds,grain coarsening effects,and the emergence of localized melting corrosion defects in the aluminum matrix.The joint fracture predominantly occurred within the eutectic structure layer.The fracture surface exhibited pronounced quasi-cleavage fracture characteristics.

Hot-end components,such as high-pressure turbine blades in advanced aero-engines and gas turbines,have widely adopted thermal barrier coating technology.Currently,the widely used ceramic materials for thermal barrier coatings are Y₂O₃ partially stabilized ZrO₂ with a mass fraction of 6%~8%(8YSZ).8YSZ coatings are susceptible to sintering at high temperatures.Sintering results in reduced porosity,increased Young's modulus,decreased strain tolerance,and a higher likelihood of cracking and detachment.These issues ultimately lead to a failure in the thermal protection function of the coating.The search for ceramic materials that can withstand higher temperatures for thermal barrier coatings has become a prominent research focus in this field.The rare earth zirconate-like material A₂B₂O₇(A=La,Nd,Sm,Gd,Dy,Er,Yb,and other rare earth elements;B=Ce,Ti,Zr,Hf,etc.)with a pyrochlore/defected fluorite structure possesses characteristics such as low thermal conductivity,high melting point,and no phase transition below the melting point.This material has become a focal point for research on the new generation of ultra-high-temperature thermal barrier coating materials.Among them,Gd₂Zr₂O₇has become one of the ideal next-generation alternative materials to replace the traditional YSZ coating due to its excellent high-temperature stability,lower thermal conductivity,and resistance to reacting with the glassy deposit CMAS.The comprehensive mechanical properties of Gd₂Zr₂O₇can be further enhanced by doping.Among them,(Gd_0.9Yb_0.1)₂Zr₂O₇ performs better.Compared with YSZ coatings,(Gd_0.9Yb_0.1)₂Zr₂O₇ ceramic coatings exhibit greater sintering resistance and can endure higher temperatures.To further optimize the thermophysical properties of(Gd_0.9Yb_0.1)₂Zr₂O₇ ceramic materials and to seek new ultrahigh-temperature thermal barrier coating materials with low thermal conductivity,this study investigated the impact of Hf doping on the thermophysical properties of Gd₂Zr₂O₇ceramic materials through first-principle calculations.The elasticity coefficient matrix of Gd₂(Zr_1-xHf_x)₂O₇(x=0,0.25,0.5,0.75,1)was calculated using the stress-strain method.The elastic modulus,cell parameters,and elastic modulus of the material were calculated from the elastic coefficient matrix,respectively.The ultimate thermal conductivity,fracture toughness,high-temperature coefficient of thermal expansion,Vickers hardness model,and brittleness criterion were utilized to calculate the thermophysical property index of Gd₂(Zr_1-xHf_x)₂O₇.Yb-Hf co-doped Gd₂Zr₂O₇ceramics were prepared by hot pressing.The mold size for hot pressing was 135 mm×40 mm.The hot pressing temperature was 1600℃.The pressure was about 46 MPa.The pressure of hot pressing was about 46 MPa.The holding time of the sample was 5 h.Afterward,the ceramic blocks obtained from hot pressing were annealed in a muffle furnace.The annealing process conditions were as follows:a holding time of 1500°C for 10 h and a temperature increase rate of 5℃·min^-1.Finally,the ceramic blocks were machined into test samples of the desired dimensions for measuring thermal conductivity and coefficient of thermal expansion.X-ray diffractometer(XRD),scanning electron microscope(SEM),thermal expansion meter,and thermal conductivity meter were used to study the impact of Yb-Hf co-doping on the physical phase,microstructure,thermal expansion coefficient,and thermal conductivity of Gd₂Zr₂O₇ceramics.The main findings are as follows:1)The combined results of first-principle calculations and experiments indicated that Hf doping in Gd₂Zr₂O₇caused the contraction of the Gd₂Zr₂O₇cell and a reduction in cell parameters.2)First-principle calculations showed that Hf doping decreased the thermal conductivity and high-temperature coefficient of thermal expansion of Gd₂Zr₂O₇;meanwhile,the modulus of elasticity,Vickers hardness,fracture toughness,and brittleness increased with the increase in Hf content.However,an increased elastic modulus decreased the strain tolerance of the coating,and higher brittleness made the structural material susceptible to destabilization.The increase in these two indicators was detrimental to the thermal barrier coating.Therefore,the concentration of Hf doping to enhance the thermophysical properties of Gd₂Zr₂O₇should not be excessively high.3)With the increase in hafnium doping,grain refinement occurred in the(Gd_0.9Yb_0.1)₂(Zr_1-xHf_x)₂O₇(x=0,0.1,0.3,0.5)solid solution.4)The combined effect of both the decrease in cell parameters and the transformation of cell structure led to insignificant changes in the coefficient of thermal expansion of(Gd_0.9Yb_0.1)₂(Zr_1-xHf_x)₂O₇.5)Hf doping could enhance thermal conductivity in rare-earth zirconates by promoting thermal radiation at high temperatures.The thermal conductivity of(Gd_0.9Yb_0.1)₂(Zr_0.7Hf_0.3)₂O₇at 1500 K could be reduced to as low as 1.19 W·m^-1·K^-1.(Gd_0.9Yb_0.1)₂(Zr_0.7Hf_0.3)₂O₇was one of the potential candidates for ultra-high-temperature thermal barrier coatings.

Lithium-ion batteries have been widely used in many fields such as portable electronic devices owing to their excellent electrochemical performance,but the limited lithium resources restrict their long-term development and wide application.Sodium-ion batteries have the advantages of abundant resources,high safety and low cost,and are regarded as an important candidate to replace lithium-ion batteries.However,the Na+diffusion rate is relatively poor due to the large sodium ion radius.Therefore,the development of electrode materials with fast ion diffusion kinetics,high specific capacity and excellent cycle stability is the key to realizing the commercial application of sodium-ion batteries.At present,the anode materials of sodium ion batteries mainly include alloys,metal oxides and sulfide materials,organic materials and carbon-based materials.FeS₂,as a kind of metal sulfide anode material with abundant resources,high theoretical specific capacity,low cost and environmental friendliness,has been widely concerned by researchers.However,its low electronic conductivity,slow ion migration rate and significant volume expansion seriously restrict its rate performance and cycle stability.Carbon materials are widely used in electrode material design because of their good conductivity,circularity and low cost.Thus,embedding FeS₂nanoparticles into conductive carbon matrix is an effective method to combine the advantages of the two materials in the hope of overcoming the above problems,thereby improving the electrochemical properties of the material.In this paper,a kind of FeS₂@C nanocomposite with microsphere structure was successfully prepared by the coordination of phenol(Ph),hydroquinone(Hq)and pyrotrimol(Phl)with FeCl₃,combined with calcination and vulcanization processes.Firstly,a solution was formed by ultrasonically dispersing 0.3242 g Phl,0.2202 g hydroquinone Hq or 0.1882 g phenol Ph into 30 ml deionized water.Then 1.6218 g ferric chloride hexahydrate was added to the above solution and stirred until completely dissolved.The resulting solution was transferred to a high-pressure reactor for hydrothermal reaction at 150℃for 12 h.After cooling down to room temperature,the collection was poured into a centrifugal tube and collected after centrifugation.The obtained product was washed three times with deionized water and dried in a 60℃oven for 12 h to obtain the precursor material.Secondly,the precursor material was heated to 600℃in a nitrogen atmosphere at a heating rate of 5℃·min^-1 and held for 2 h.Then the obtained product was vulcanized by sulfur powder in nitrogen atmosphere at the mass ratio of 1∶4,and finally,FeS₂@C nanocomposite was obtained.The surface morphology and internal structure of the composite were investigated by scanning electron microscopy(SEM)and transmission electron microscopy(TEM),and the phase and electronic structure were characterized by X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The valence bond analysis of FeS₂@C nanocomposites was carried out by Fourier transform infrared spectroscopy.The results showed that the uniformly distributed solid spherical structure with FeS₂phase was successfully synthesized.No carbon peak was found in XRD pattern,indicating that the carbon in the structure was amorphous.The carbon composite not only significantly enhanced the overall electronic conductivity of the material,but also relieved the volume expansion during the charging and discharging process,ensuring the excellent cycling stability.Meanwhile,the electrochemical performance of FeS₂@C nanocomposites was analyzed by cyclic voltammetry(CV)and galvanostatic charge-discharge test.The results showed that FeS₂@C nanocomposites prepared from pyroquinone showed excellent rate capacity and cycle stability.In addition,the influence of structural engineering on electrochemical properties was also explored.The structure of FeS₂@C could be regulated by optimizing the ratio of pyrogallol to iron source.When the ratio of pyrogallol to iron source was 1∶3,the structure of FeS₂@C nanocomposites was regular nanosphere.FeS₂@C nanosphere could maintain a specific capacity of 395 mAh·g^-1after 100 cycles at a current density of 0.5 A·g^-1.Although after 1500 cycles at a high current density of 5 A·g^-1,the discharge specific capacity of 226.1 mAh·g^-1was retained,corresponding to a capacity retention rate of 75.1%,which fully confirmed the great potential of FeS₂@C nanocomposite electrodes in excellent cycling stability sodium ion battery.In addition,at the current densities of 0.2,0.5,1,2,4,5,10 and 20 A·g^-1,FeS₂@C nanosphere electrode exhibited the specific capacities of 448,359,318,274,236,214,168 and 138 mAh·g^-1,respectively.When the current density returned to 0.2 A·g^-1,the specific capacity of 402 mAh·g^-1could be achieved,indicating the excellent rate capacity.To sum up,the successful doping of carbon provided the overall electronic conductivity of the material and more reactive activation sites of Na+for promoting the cycle performance,and effectively alleviated the volume expansion caused by charging and discharging for improving stability of the battery.This work provided a candidate method for designing and preparing FeS₂/C composite for anodes of sodium ion batteries with excellent cycling stability and rate capability.

Sphalerite and pyrite are common sulfide minerals,and their flotation separation is crucial for the efficient recovery and utilization of zinc and sulfur resources.Traditional flotation reagents have the characteristics of weak collection ability and environmental pollution,so it is crucial to choose new,efficient and environmentally friendly collectors.At present,new efficient and environmentally friendly collectors have certain applications in the field of sulfide mineral flotation.The new efficient and environmentally friendly collector used in this article was sulfur nitrogen benzoyl ester(SNBJX)synthesized by Shenyang Youyan Mineral Chemical Co.,Ltd.This paper used methods such as single mineral flotation test,zinc sulfur artificial mixed ore test,Zeta potential test,Fourier transform infrared(FTIR)spectroscopy measurement,X-ray photoelectron spectroscopy(XPS)measurement,and density functional theory(DFT)calculation to investigate the selectivity and separation efficiency of SNBJX on sphalerite and pyrite.Through single mineral experiments,the collection efficiency and selectivity of collector SNBJX on sphalerite and pyrite were compared with butyl xanthate(JBX)and butylammonium black powder(JAB).The results showed that under the conditions of pH 8 and SNBJX dosage of 125 g·t^-1,SNBJX had significant selectivity for pyrite and sphalerite,with a maximum difference in recovery rates of 46.67%.The separation effect of SNBJX on artificial mixed ore(with a mass ratio of sphalerite to pyrite of l∶1)was investigated using SNBJX as a collector.The results showed that when the dosage of SNBJX was 75 g·t^-1,the sulfur grade in the sulfur concentrate was 84.02%,and the zinc grade in the zinc concentrate was 29.40%.Zeta potential tests of the samples before and after the interaction between minerals and SNBJX showed that after the addition of SNBJX,the potential of pyrite showed a significant negative shift under neutral and alkaline conditions.FTIR analysis of the samples before and after the interaction between minerals and SNBJX showed that the bonding mode of the agent on the mineral surface was C=O,C=S,and the adsorption mode was chemical adsorption.XPS analysis of the samples before and after the interaction between minerals and SNBJX showed stronger adsorption intensity of SNBJX on pyrite compared to sphalerite.Using B3LYP function in Gaussian 09 to simulate the adsorption model of sulfide minerals and reagents,DFT was used for calculations.It was found that S and O atoms in C=S and C=O groups of SNJBX could chelate with Fe and Zn,and form a six membered chelating ring,it could be seen that the effect of reagents on Fe sites was stronger than that on Zn sites,therefore,its effect on pyrite was stronger than that of sphalerite.