The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and micr...The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and microstructural evolution of 304 stainless steel after HPT were investigated by X-ray diffraction(XRD)analysis,electron backscatter diffraction(EBSD)analysis,transmission electron microscopy(TEM),nanoindentation test and differential scanning calorimetry(DSC)analysis.The experimental results show that HPT causes elongated nanocrystalline grains of 25 nm width along the torsion direction.After 10 turns of HPT,the deformation-induced martensitic transformation is completed and the hardness increases from 3 GPa to 8.5 GPa at the edge of the disc.However,a local reverse phase transformation from martensite to austenite is observed in the peripheral regions of the sample after 30 turns of HPT,leading to a higher volume fraction of austenite,and the hardness of the sample also decreases accordingly.展开更多
High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material...High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material cost poses substantial challenges for optimizing thermal processing parameters through repetitive experimental trials.In this work,hot compression experiments on high-purity silver were conducted using a Gleeble-3800 thermal simulator.The high temperature deformation behaviors,dynamic recovery(DRV)and dynamic recrystallization(DRX)of high-purity silver were studied by constructing an Arrhenius constitutive equation and developing thermal processing maps.The results show that plastic instability of high-purity silver occurs at high strain rates and the optimized hot processing parameters are the strain rate below 0.001 s^(−1) and the temperature of 340−400℃.Microstructural observations exhibit that DRV prefers to occur at lower deformation temperatures(e.g.,250℃).This is attributed to the low stacking fault energy of high-purity silver,which facilitates the decomposition of dislocations into partial dislocations and promotes high-density dislocation accumulation.Furthermore,DRX in high-purity silver becomes increasingly pronounced with increasing deformation temperature and reaches saturation at 350℃.展开更多
This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined wi...This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.展开更多
TC4 titanium alloy(Ti-6Al-4V),known for its excellent specific strength,corrosion resistance,and weldability,is extensively applied in aerospace,marine engineering,and advanced manufacturing.This study focuses on the ...TC4 titanium alloy(Ti-6Al-4V),known for its excellent specific strength,corrosion resistance,and weldability,is extensively applied in aerospace,marine engineering,and advanced manufacturing.This study focuses on the microstructural uniformity and mechanical properties of TC4 ingots fabricated via the electron-beam cold hearth melting(EBCHM)process.A comprehensive analysis was performed using optical microscopy,scanning electron microscopy,electron backscatter diffraction,and energy-dispersive spectroscopy to investigate the ingot’s morphology,α-phase lamellar structure,and elemental distribution.Mechanical characterization included tensile testing,and microhardness and impact toughness assessments.Results reveal that EBCHM produces a well-defined and homogeneous microstructure,with the averageαlamellae thickness varying between 1.53 and 1.71μm and minimal fluctuations across the ingot regions,indicating high process consistency.Major alloying elements(Al and V)and impurity elements(O,N,H,C,and Fe)are evenly distributed,with no observable macrosegregation.The mechanical properties are stable and reliable,with a yield strength of 694.6-701.2 MPa,a tensile strength of 711.1-716.6 MPa,an elongation of 3.35%-3.84%,and an average impact toughness of 94.7 J/cm^(2).These results provide valuable data and technical references for the application of EBCHM in manufacturing premium-quality Ti-6Al-4V ingots.展开更多
Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructur...Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructural changes during the transformation from austenite to ferrite has been clarified.It is found that ferrite side plates form preceding to acicular ferrites,although the starting temperature of respective component decreases as the cooling rate is raised.In particular,the growth rate of acicular ferrite is measured to increase significantly,rising from 30.4μm/s at a cooling rate of 3 K/s to 109.0μm/s at 15 K/s,driven primarily by an ever-increasing degree of undercooling.These findings highlight the critical role of cooling rate in dictating the sequence and growth rate of microstructural transformations,which is crucial for optimizing welding processes to obtain desired microstructures while avoiding the formation of deleterious components.展开更多
To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced materi...To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced material characterization techniques.A suitable laser output mode fell into the transition mode,allowing for the fabrication of nearly full-density samples(porosity=0.85±0.021%)with favorable mechanical properties(yield strength=351 MPa,ultimate tensile strength=417 MPa,the elongation at break=6.5%and microhardness=137.9±6.15 HV_(0.1))using optimal processing parameters(P=80 W,v=250 mm/s and d=50μm).Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal and prismatic slips.Starting from a random texture before deformation(maximum multiple of ultimate density,Max.MUD=3.95),plastic stretching led the grains to align with the Z-axis,finally resulting in a{0001}<1010>texture orientation after fracture(Max.MUD=8.755).Main phases of the SLM state are mainly composed ofα-Mg,Mg_(24)Y_(5) andβ'-Mg_(41)Nd_(5),with an average grain size of only 4.27μm(about a quarter of that in the extruded state),resulting in a favorable strength-toughness ratio.Except for the nano-β'phase and semi-coherent Mg_(24)Y_(5) phase(mismatch=16.12%)around the grain boundaries,a small amount of nano-ZrO_(2) and Y_(2)O_(3) particles also play a role in dispersion strengthening.The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening(44.41%),solid solution strengthening(34.06%)and grain boundary strengthening(21.53%),with precipitation hardening being predominantly driven by dislocation strengthening(67.77%).High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024,receiving favorable attention.This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.展开更多
Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformat...Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformation and subsequent solvus treatment was studied. The results showed that the grain size during dynamic recrystallization (DRX) did not exceed 6 μm, and the volume fraction during DRX did not exceed 45% at all reduction rates when it deformed below the γ′ solvus temperature (1080 ℃). When deformed near the γ′ solvus temperature (1110 ℃), the volume fraction and grain size increase significantly during DRX due to the dissolution and coarsening of some γ′ precipitates. When deformed above the γ′ solvus temperature (1140 ℃), even at a high reduction rate of 20 mm/s, the volume fraction during DRX reached 75%, and the grain size during DRX increased to 25 μm. At a reduction rate of 0.5 mm/s, the grain size during DRX reached 65 μm. When the sample is deformed below the γ′ solvus temperature (1080 ℃), stored strain energy accumulates in the sample, which is beneficial for the development of post dynamic recrystallization during subsequent subsolvus heat treatment, resulting in a noticeable increase in the recrystallization volume fraction. The recrystallization volume fraction of predeformed samples deformed at 1110 and 1140 ℃, followed by subsolvus heat treatment, was almost unchanged. The microstructure of the predeformed sample following supersolvus heat treatment consists of coarse equiaxed grains.展开更多
The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al all...The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.展开更多
In cold regions,slope rocks are inevitably impacted by freeze-thaw,dry-wet cycles and their alternating actions,leading to strength weakening and pore degradation.In this study,the mechanical and microstructural prope...In cold regions,slope rocks are inevitably impacted by freeze-thaw,dry-wet cycles and their alternating actions,leading to strength weakening and pore degradation.In this study,the mechanical and microstructural properties of schist subjected to four conditions were investigated:freeze-thaw cycles in air(FTA),freeze-thaw cycles in water(FTW),dry-wet cycles(DW),and dry-wet-freeze-thaw cycles(DWFT).Uniaxial compressive strength(UCS),water absorption,ultrasonication,low-field nuclear magnetic resonance,and scanning electron microscopy analyses were conducted.The integrity attenuation characteristics of the longitudinal wave velocity,UCS,and elastic modulus were analyzed.The results showed that liquid water emerged as a critical factor in reducing the brittleness of schist.The attenuation function model accurately described the peak stress and static elastic modulus of schist in various media(R2>0.97).Different media affected the schist deterioration and half-life,with the FTW-immersed samples having a half-life of 28 cycles.Furthermore,the longitudinal wave velocity decreased as the number of cycles increased,with the FTW showing the most significant reduction and having the shortest half-life of 208 cycles.Moreover,the damage variables of compressive strength and elastic modulus increased with the number of cycles.After 40 cycles,the schist exposed to FTW exhibited the highest damage variables and saturated water content.展开更多
Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)format...Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)formation and dissociation are still in controversy.In this study,montmorillonite and illite were separately mixed with quartz sand to investigate their effects on MH formation and dissociation.The microstructure of synthesized samples was observed by cryo-SEM innovatively to understand the effects of montmorillonite and illite on MH phase transition in micron scale.Results show that montmorillonite and illite both show the inhibition on MH formation kinetics and water-to-hydrate conversion,and illite shows a stronger inhibition.The 10 wt%montmorillonite addition significantly retards MH formation rate,and the 20 wt%montmorillonite has a less inhibition on the rate.The increase of illite mass ratio(0-20 wt%)retards the rate of MH formation.As the content of clay minerals increase,the water-to-hydrate conversion decreases.Cryo-SEM images presented that montmorillonite aggregates separate as individual clusters while illite particles pack as face-to-face configuration under the interaction with water.The surface-overlapped illite aggregates would make sediments pack tightly,hinder the contact between gas and water,and result in the more significant inhibition on MH formation kinetics.Under the depressurization method,the addition of clay minerals facilitates MH dissociation rate.Physicochemical properties of clay minerals and MH distribution in the pore space lead to the faster dissociation rate in clay-containing sediments.The results of this study would provide beneficial guides on geological investigations and optimizing strategies of natural gas production in marine hydrate-bearing sediments.展开更多
High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here...High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here we investigated the effect of matrix and precipitates on mechanical properties of Cr-Ni-Mo-V/Nb steel after water quenching and tempering(150-500℃).The results showed that the microstructure of the present steel is noticeably tuned by changing the tempering temperature.An excellent combination of strength(a yield strength of 1308 MPa with a total elongation of 8.2%)and toughness(Charpy V-notch impact toughness of 40.5 J/cm^(2))is obtained upon tempering at 200℃.This is attributed to the lath martensite containing high dislocation density,the martensite-twin substructure,and the strengthening effects of the precipitated needle-likeε-carbides and spherical VC particles.The acicularε-carbides are replaced by the rod-shaped Fe_(3)C at the tempering temperature of 350℃,resulting in the remarkable deterioration in strength,hardness,and elongation.Spheroidized carbides formed at a tempering temperature of 500℃ are beneficial to the enhancement of the elongation and toughness,but the strength decreases due to the matrix softening caused by the recovery of dislocation.展开更多
Ultrahigh nickel oxides(Ni content>90%)hold great promise for high-performance cathodes for the future generation of lithium-ion batteries(LIBs).However,these cathode materials cause problems such as harmful parasi...Ultrahigh nickel oxides(Ni content>90%)hold great promise for high-performance cathodes for the future generation of lithium-ion batteries(LIBs).However,these cathode materials cause problems such as harmful parasitic reactions at the cathode/electrolyte interface,degradation of the layered structure,and the creation of microcracks.Herein,a microstructural refinement and intergranular coating strategy is proposed to engineer ultrahigh nickel cathode LiNi_(0.96)Co_(0.03)Mn_(0.01)O_(2)(NCM).The W-doping-induced fine-grained microstructure not only endows NCM with excellent mechanical properties but also promotes infiltration of the fluoride-containing coating along the grain boundaries inside the secondary particles,thereby forming intergranular coatings.This combined fine-grained microstructure and intergranular coating strategy reduces the formation of microcracks and suppresses the additional parasitic electrolyte reactions caused by them,thereby inhibiting the degradation of the layered phase.Consequently,the modified NCM cathode achieved exceptional electrochemical properties,especially delivering a high initial capacity of 230.8 mA h g^(-1)(0.1 C)and a capacity retention exceeding 96% after100 cycles at 0.5 C in half cells.After 500 cycles in full cells,the capacity retention increases by 21.2% compared with NCM.This strategy mitigates multiple degradation mechanisms in Ni-rich cathodes and provides a generalized strategy for developing advanced ultrahigh-nickel cathodes for industrial application.展开更多
In the context of convection-heating-based in situ oil shale retorting,fractures serve as primary pathways for fluid migration and product extraction.This study investigates the permeability and microstructural evolut...In the context of convection-heating-based in situ oil shale retorting,fractures serve as primary pathways for fluid migration and product extraction.This study investigates the permeability and microstructural evolution of oil shale during water vapor injection in single-fracture and no-fracture scenarios.Three types of oil shale are investigated:intact oil shale,oil shale with a single straight crack,and oil shale with a single hydraulic crack.With increasing water vapor temperature,the permeabilities of the intact oil shale and oil shale with a fractured crack exhibit a trend of initial increase,followed by a decrease,and then a subsequent increase.However,the permeability of oil shale with a single straight crack consistently increases and exceeds that of oil shale with a fractured crack.The temperaturedependent permeability changes in fractured oil shale-a slight decrease in fracture cracks and a gradual increase in straight cracks-mainly occur in the range of 300℃-350℃.The permeability of oil shale with a straight crack is approximately three times that of oil shale with a fractured crack.This is attributed to the retention of viscous asphaltene and the frictional resistance caused by the rough fracture structure.For the oil shale with a single crack,the crack permeability has a dominant influence on the overall permeability of the rock.The contribution of the permeability of the straight crack exceeds 94.6%,while that of the permeability of the fractured crack is greater than 86.1%.The disparity in the contribution of these two crack structures is evident at 350℃-550℃.展开更多
The performance of welded Ni-based superalloys at high temperatures is essential to be evaluated due to their particular service environment for aero-engines and high-speed aircrafts.The tensile properties and related...The performance of welded Ni-based superalloys at high temperatures is essential to be evaluated due to their particular service environment for aero-engines and high-speed aircrafts.The tensile properties and related microstructural evolutions such as the carbide precipitate and grain of a laser-welded Ni-based alloy were experimentally and numerically investigated at different temperatures(20,300,500,800℃).The results show that at room temperature,the strength of the Base Material(BM)was slightly smaller,with a difference of less than 1%,than the Welded Material(WM),which can be attributed to the more uniformly distributed needle-shaped carbide precipitates in the WM than those nonuniformly coarser spherical ones in the BM.While at 300℃ and 500℃,the strength of WM decreased more obviously compared with that of BM due to the more apparent growth of grain:13.52%loss in yield strength in WM alloys as compared with BM alloys at 300℃,and 16.57% at 500℃.At 800℃,the strength of BM and WM both decreased to a similar level due to Dynamic Recrystallization(DRX).However,a much higher elongation was observed for the BM than WM(less than 50%of BM),which can be attributed to the enhanced dislocation accumulation capability of the large spherical carbides along grain boundaries on the fracture surface in BM.Furthermore,a unified model considering the welding effects on both microstructures(dislocation,carbides,and grain)and mechanical properties evolutions at different temperatures was developed and validated.Based on this model,the key temperature ranges(20–600℃)where apparent weakening of strength and uniform plasticity occurs for welded structures were identified,providing a direct guidance for potential structure and process design.展开更多
As primary load-bearing components extensively utilized in engineering applications,beam structures necessitate the design of their microstructural configurations to achieve lightweight objectives while satisfying div...As primary load-bearing components extensively utilized in engineering applications,beam structures necessitate the design of their microstructural configurations to achieve lightweight objectives while satisfying diverse mechanical performance requirements.Combining topology optimization with fully coupled homogenization beam theory,we provide a highly efficient design tool to access desirable periodic microstructures for beams.The present optimization framework comprehensively takes into account for key deformation modes,including tension,bending,torsion,and shear deformation,all within a unified formulation.Several numerical results prove that our method can be used to handle kinds of microstructure design for beam-like structures,e.g.,extreme tension(compression)-torsion stiffness,maximization of minimum critical buckling load,and minimization of structural compliance.When optimizing microstructures for macroscopic performance,we emphasize investigating the influence of shear stiffness on the optimized results.The novel chiral beam-like structures are fabricated and tested.The experimental results indicate that the optimized tension(compression)-torsion structure has excellent buffer characteristics,as compared with the traditional square tube.This proposed optimization framework can be further extended to other physical problems of Timoshenko beams.展开更多
The residual stress field induced by surface strengthening processes such as mechanical shot peening and other forms of plastic deformation does not generally exhibit a simple“monotonic”distribution trend.Some resea...The residual stress field induced by surface strengthening processes such as mechanical shot peening and other forms of plastic deformation does not generally exhibit a simple“monotonic”distribution trend.Some researchers have analyzed this fact from a mechanical perspective based on Hertz theory.However,the micro/nano-scale microstructural changes corresponding to the distribution of residual stress fields still appear to be lacking.In this study,we focused on a widely used material in aviation manufacturing,namely nickel-based superalloy GH4169,as our experimental material.We subjected GH4169 alloy to me-chanical strengthening treatment using a shot peening intensity of 0.25 mmA,followed by quantitative testing of micromechanical performance indicators such as microhardness and residual stress.To thoroughly investigate the relationship between micromechanical properties and microstructure changes,we utilized transmission electron microscopy(TEM)to observe and analyze shot-peened materials at different depths.Our findings revealed that the most severe microstructural distortion induced by mechanical shot peening in GH4169 alloy was likely to occur within a depth range of 25 to 75μm.This observation aligns with the actual phenomenon that the maximum microhardness and maximum residual compressive stress did not manifest on the outermost surface of the material.By presenting a detailed analysis of deformation defects such as dislocations,stacking faults,and twinning in different depths of mechan-ically strengthened layers,our study contributes to a deeper understanding and practical application of post-processing technologies based on plastic deformation.展开更多
Iron-based metal matrix composites(IMMCs)have attracted significant research attention due to their high specific stiffness and strength,making them potentially suitable for various engineering applications.Microstruc...Iron-based metal matrix composites(IMMCs)have attracted significant research attention due to their high specific stiffness and strength,making them potentially suitable for various engineering applications.Microstructural design,including the selection of reinforcement and matrix phases,the reinforcement volume fraction,and the interface issues are essential factors determining the engineering performance of IMMCs.A variety of fabrication methods have been developed to manufacture IMMCs in recent years.This paper reviews the recent advances and development of IMMCs with particular focus on microstructure design,fabrication methods,and their engineering performance.The microstructure design issues of IMMC are firstly discussed,including the reinforcement and matrix phase selection criteria,interface geometry and characteristics,and the bonding mechanism.The fabrication methods,including liquid state,solid state,and gas-mixing processing are comprehensively reviewed and compared.The engineering performance of IMMCs in terms of elastic modulus,hardness and wear resistance,tensile and fracture behavior is reviewed.Finally,the current challenges of the IMMCs are highlighted,followed by the discussion and outlook of the future research directions of IMMCs.展开更多
Based on compressive strength analysis,ultrasonic velocity testing and microstructural damage of three groups of concrete sprayed with inorganic coatings with different mix ratios were carried out under the freeze and...Based on compressive strength analysis,ultrasonic velocity testing and microstructural damage of three groups of concrete sprayed with inorganic coatings with different mix ratios were carried out under the freeze and thaw cycles(F-T).The strength attenuations of three groups of concrete were investigated,and a linear regression model showing the relationship model between acoustic parameters of three groups of concrete and their physicomechanical properties were constructed,and the micro-mechanism behind the strength decay of concrete was explained via scanning electron microscopy.The results show that in case of the same F-T cycles concrete sprayed inorganic coating adding a polypropylene fibre leads to a good anti-freezing performance.The trend in ultrasonic velocity decay in concrete under the F-T cycles is consistent with the trend in compression strength change.The ultrasonic velocity(UV)of the concrete shows a great correlation with compression strength:the greater the compression strength of concrete,the higher the UV.The losses in compressive strength of concrete in the three kinds(A,B and C,A is with silica fume,B is plain concrete,C is with polypropylene fibres)after 300 freeze-thaw cycles are 54.55%,62.25%and 22.26%,respectively,which of ultrasonic compressive wave velocities are 13.81%,16.65%and 3.77%,respectively.Concrete strength decreases during the freeze-thaw process;this is microscopically manifested as large pores,an increase in cracks,and the development of scattered primary pores affecting the centralised connectivity.The cracks of A group have a width of 5-10μm,which of B group have a width of 5-20μm,which of C group have a width of 1-2μm.The whole process of F-T is the process of generating and enlarging cracks in the inner microstructure of the concrete,which results in a markedly reduction in the mechanical characteristics of concrete.展开更多
The unclear interfacial characteristics of Ag/Cu interface during diffusion welding limit the improvement of mechanical properties of Ag/Cu bimetallic strips.The growth orientation and evolution of Ag and Cu crystals ...The unclear interfacial characteristics of Ag/Cu interface during diffusion welding limit the improvement of mechanical properties of Ag/Cu bimetallic strips.The growth orientation and evolution of Ag and Cu crystals between Ag and Cu strips were investigated by electron backscatter diffraction(EBSD)analysis,and the interfacial properties of various Ag/Cu interfacial configurations were calculated using first-principles calculations to elucidate the diversified interfacial characteristics.Three interface bonding states,including Ag(100)/Cu(100),Ag(110)/Cu(110)and Ag(111)/Cu(111),were preferentially formed in Ag/Cu bimetallic strips during roll bonding.The intensity of Ag(100)/Cu(100)interface increases with the increasing deformation amounts during cold rolling,accompanied by the decreased intensity of Ag(110)/Cu(110)and Ag(111)/Cu(111)interfaces.The largest adsorption work and lowest interface energy of Ag(100)/Cu(100)interface at the“center”position reveal the transition from Ag(110)/Cu(110)and Ag(111)/Cu(111)interfaces to Ag(100)/Cu(100)interface.展开更多
Ti_(2)AlC/TiAl composites with a network structure were successfully prepared with carbon nanotubes and Ti-45Al-8Nb pre-alloyed powder using spark plasma sintering.The effects of sintering temperature(1200-1350℃)on t...Ti_(2)AlC/TiAl composites with a network structure were successfully prepared with carbon nanotubes and Ti-45Al-8Nb pre-alloyed powder using spark plasma sintering.The effects of sintering temperature(1200-1350℃)on the microstructural evolution and mechanical properties were systematically investigated.The microstructure of Ti_(2)AlC/TiAl composites exhibits duplex,near-lamellar,and fully lamellar structures,as the sintering temperature increases from 1200 to 1350℃.The network structured Ti_(2)AlC phase can refine the microstructure and the phase becomes discontinuous at high sintering temperatures.Notably,composites sintered at 1300℃ exhibit excellent mechanical properties,with the highest compressive strength(1921 MPa)and fracture strain(26%)at room temperature.Moreover,the ultimate tensile strength and fracture strain reach 537 MPa and 3.1%at 900℃,and 485 MPa and 3.3%at 950℃,respectively.The enhancement of the mechanical properties is attributed primarily to the load bearing,particle pull-out,and inhibition of crack propagation induced by Ti_(2)AlC particles.展开更多
基金Funded by the National Natural Science Foundation of China(No.51905215)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.SJCX231233)。
文摘The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and microstructural evolution of 304 stainless steel after HPT were investigated by X-ray diffraction(XRD)analysis,electron backscatter diffraction(EBSD)analysis,transmission electron microscopy(TEM),nanoindentation test and differential scanning calorimetry(DSC)analysis.The experimental results show that HPT causes elongated nanocrystalline grains of 25 nm width along the torsion direction.After 10 turns of HPT,the deformation-induced martensitic transformation is completed and the hardness increases from 3 GPa to 8.5 GPa at the edge of the disc.However,a local reverse phase transformation from martensite to austenite is observed in the peripheral regions of the sample after 30 turns of HPT,leading to a higher volume fraction of austenite,and the hardness of the sample also decreases accordingly.
基金Project(52274369)supported by the National Natural Science Foundation of China。
文摘High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material cost poses substantial challenges for optimizing thermal processing parameters through repetitive experimental trials.In this work,hot compression experiments on high-purity silver were conducted using a Gleeble-3800 thermal simulator.The high temperature deformation behaviors,dynamic recovery(DRV)and dynamic recrystallization(DRX)of high-purity silver were studied by constructing an Arrhenius constitutive equation and developing thermal processing maps.The results show that plastic instability of high-purity silver occurs at high strain rates and the optimized hot processing parameters are the strain rate below 0.001 s^(−1) and the temperature of 340−400℃.Microstructural observations exhibit that DRV prefers to occur at lower deformation temperatures(e.g.,250℃).This is attributed to the low stacking fault energy of high-purity silver,which facilitates the decomposition of dislocations into partial dislocations and promotes high-density dislocation accumulation.Furthermore,DRX in high-purity silver becomes increasingly pronounced with increasing deformation temperature and reaches saturation at 350℃.
基金Funded by the Central Government-Guided Local Development Fund Project(No.YDZJSX2025D042)the Key R&D Program of Shanxi Province(No.202202150401018)+1 种基金the Basic Research Program of Shanxi Province(No.20210302124220)the State Key Laboratory of CAD/CG of Zhejiang University(No.A2325)。
文摘This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.
基金funding recei-ved from the National Key R&D Program of China(No.2022YFB3705602)the Scientific Research Plan Project of Shanghai,P.R.China(No.22SQBS 00600).
文摘TC4 titanium alloy(Ti-6Al-4V),known for its excellent specific strength,corrosion resistance,and weldability,is extensively applied in aerospace,marine engineering,and advanced manufacturing.This study focuses on the microstructural uniformity and mechanical properties of TC4 ingots fabricated via the electron-beam cold hearth melting(EBCHM)process.A comprehensive analysis was performed using optical microscopy,scanning electron microscopy,electron backscatter diffraction,and energy-dispersive spectroscopy to investigate the ingot’s morphology,α-phase lamellar structure,and elemental distribution.Mechanical characterization included tensile testing,and microhardness and impact toughness assessments.Results reveal that EBCHM produces a well-defined and homogeneous microstructure,with the averageαlamellae thickness varying between 1.53 and 1.71μm and minimal fluctuations across the ingot regions,indicating high process consistency.Major alloying elements(Al and V)and impurity elements(O,N,H,C,and Fe)are evenly distributed,with no observable macrosegregation.The mechanical properties are stable and reliable,with a yield strength of 694.6-701.2 MPa,a tensile strength of 711.1-716.6 MPa,an elongation of 3.35%-3.84%,and an average impact toughness of 94.7 J/cm^(2).These results provide valuable data and technical references for the application of EBCHM in manufacturing premium-quality Ti-6Al-4V ingots.
基金support from the National Natural Science Foundation of China(Grant Nos.U20A20277 and 52350610226)National Key Research and Development Plan of China(Grant No.2022YFE0123300).
文摘Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructural changes during the transformation from austenite to ferrite has been clarified.It is found that ferrite side plates form preceding to acicular ferrites,although the starting temperature of respective component decreases as the cooling rate is raised.In particular,the growth rate of acicular ferrite is measured to increase significantly,rising from 30.4μm/s at a cooling rate of 3 K/s to 109.0μm/s at 15 K/s,driven primarily by an ever-increasing degree of undercooling.These findings highlight the critical role of cooling rate in dictating the sequence and growth rate of microstructural transformations,which is crucial for optimizing welding processes to obtain desired microstructures while avoiding the formation of deleterious components.
基金supported by the National Key Research and Development Program of China(No.2022YFC2406000)the Guangdong Basic and Applied Basic Research Foundation(2024A1515011024)+5 种基金the Guangzhou Science and Technology Project(2024A04J4943)the Guangdong Academy of Sciences Development Special Fund Project(2022GDASZH-2022010107)the Guangdong province Science and Technology Plan Projects(2023B1212120008,2023B1212060045)the GDAS Projects of International cooperation platform of Science and Technology(2022GDASZH-2022010203-003)Special Support Foundation of Guangdong Province(2023TQ07Z559)Shenzhen Basic Research Project(JCYJ20210324120001003 and JCYJ20220531091802006)。
文摘To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced material characterization techniques.A suitable laser output mode fell into the transition mode,allowing for the fabrication of nearly full-density samples(porosity=0.85±0.021%)with favorable mechanical properties(yield strength=351 MPa,ultimate tensile strength=417 MPa,the elongation at break=6.5%and microhardness=137.9±6.15 HV_(0.1))using optimal processing parameters(P=80 W,v=250 mm/s and d=50μm).Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal and prismatic slips.Starting from a random texture before deformation(maximum multiple of ultimate density,Max.MUD=3.95),plastic stretching led the grains to align with the Z-axis,finally resulting in a{0001}<1010>texture orientation after fracture(Max.MUD=8.755).Main phases of the SLM state are mainly composed ofα-Mg,Mg_(24)Y_(5) andβ'-Mg_(41)Nd_(5),with an average grain size of only 4.27μm(about a quarter of that in the extruded state),resulting in a favorable strength-toughness ratio.Except for the nano-β'phase and semi-coherent Mg_(24)Y_(5) phase(mismatch=16.12%)around the grain boundaries,a small amount of nano-ZrO_(2) and Y_(2)O_(3) particles also play a role in dispersion strengthening.The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening(44.41%),solid solution strengthening(34.06%)and grain boundary strengthening(21.53%),with precipitation hardening being predominantly driven by dislocation strengthening(67.77%).High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024,receiving favorable attention.This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.
基金supported by the National Science and Technology Major Project of China(2017-VI-0018-0090).
文摘Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformation and subsequent solvus treatment was studied. The results showed that the grain size during dynamic recrystallization (DRX) did not exceed 6 μm, and the volume fraction during DRX did not exceed 45% at all reduction rates when it deformed below the γ′ solvus temperature (1080 ℃). When deformed near the γ′ solvus temperature (1110 ℃), the volume fraction and grain size increase significantly during DRX due to the dissolution and coarsening of some γ′ precipitates. When deformed above the γ′ solvus temperature (1140 ℃), even at a high reduction rate of 20 mm/s, the volume fraction during DRX reached 75%, and the grain size during DRX increased to 25 μm. At a reduction rate of 0.5 mm/s, the grain size during DRX reached 65 μm. When the sample is deformed below the γ′ solvus temperature (1080 ℃), stored strain energy accumulates in the sample, which is beneficial for the development of post dynamic recrystallization during subsequent subsolvus heat treatment, resulting in a noticeable increase in the recrystallization volume fraction. The recrystallization volume fraction of predeformed samples deformed at 1110 and 1140 ℃, followed by subsolvus heat treatment, was almost unchanged. The microstructure of the predeformed sample following supersolvus heat treatment consists of coarse equiaxed grains.
基金supported by the National Natural Science Foundation of China(Grant Nos.52074229,52371035)the Key R&D Plan of Sichuan Province(Grant No.SC2022A1C01J)the State Key Lab of Advanced Metals and Materials(Grant No.2020-ZD05).
文摘The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.
基金supported by the National Natural Science Foundation of China(Nos.42171108 and 42101136)Sichuan Science and Technology Program(Nos.2024NSFSC2007 and2025YFHZ0273)Natural Science Starting Project of SWPU(No.2024QHZ029)。
文摘In cold regions,slope rocks are inevitably impacted by freeze-thaw,dry-wet cycles and their alternating actions,leading to strength weakening and pore degradation.In this study,the mechanical and microstructural properties of schist subjected to four conditions were investigated:freeze-thaw cycles in air(FTA),freeze-thaw cycles in water(FTW),dry-wet cycles(DW),and dry-wet-freeze-thaw cycles(DWFT).Uniaxial compressive strength(UCS),water absorption,ultrasonication,low-field nuclear magnetic resonance,and scanning electron microscopy analyses were conducted.The integrity attenuation characteristics of the longitudinal wave velocity,UCS,and elastic modulus were analyzed.The results showed that liquid water emerged as a critical factor in reducing the brittleness of schist.The attenuation function model accurately described the peak stress and static elastic modulus of schist in various media(R2>0.97).Different media affected the schist deterioration and half-life,with the FTW-immersed samples having a half-life of 28 cycles.Furthermore,the longitudinal wave velocity decreased as the number of cycles increased,with the FTW showing the most significant reduction and having the shortest half-life of 208 cycles.Moreover,the damage variables of compressive strength and elastic modulus increased with the number of cycles.After 40 cycles,the schist exposed to FTW exhibited the highest damage variables and saturated water content.
基金supported by the Key Research Program of the Institute of Geology&Geophysics,CAS(Grant No.IGGCAS-201903).
文摘Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)formation and dissociation are still in controversy.In this study,montmorillonite and illite were separately mixed with quartz sand to investigate their effects on MH formation and dissociation.The microstructure of synthesized samples was observed by cryo-SEM innovatively to understand the effects of montmorillonite and illite on MH phase transition in micron scale.Results show that montmorillonite and illite both show the inhibition on MH formation kinetics and water-to-hydrate conversion,and illite shows a stronger inhibition.The 10 wt%montmorillonite addition significantly retards MH formation rate,and the 20 wt%montmorillonite has a less inhibition on the rate.The increase of illite mass ratio(0-20 wt%)retards the rate of MH formation.As the content of clay minerals increase,the water-to-hydrate conversion decreases.Cryo-SEM images presented that montmorillonite aggregates separate as individual clusters while illite particles pack as face-to-face configuration under the interaction with water.The surface-overlapped illite aggregates would make sediments pack tightly,hinder the contact between gas and water,and result in the more significant inhibition on MH formation kinetics.Under the depressurization method,the addition of clay minerals facilitates MH dissociation rate.Physicochemical properties of clay minerals and MH distribution in the pore space lead to the faster dissociation rate in clay-containing sediments.The results of this study would provide beneficial guides on geological investigations and optimizing strategies of natural gas production in marine hydrate-bearing sediments.
基金supported by the National Natural Science Foundation of China(Grant Nos.51904278,51974288 and 52071300)the Special Funding Projects for Local Science and Technology Development guided by the Central Committee(YDZJSX2021C007,YDZJSX2021B020 and YDZX20191400004587)+4 种基金the Key Research and Development Project of Shanxi Province(202102050201004,202102150401002,202202050201015)the Scientific and Technological Innovation Talent Team Project of Shanxi Province(202204051002020)the Basic Research Program of Shanxi Province(20210302123218,202203021212126,202203021221096)the Foundation of the State Key Laboratory of Advanced Metallurgy,USTB(K22-11)the Special Project for Transformation of Scientific Achievements(202204021301025).
文摘High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here we investigated the effect of matrix and precipitates on mechanical properties of Cr-Ni-Mo-V/Nb steel after water quenching and tempering(150-500℃).The results showed that the microstructure of the present steel is noticeably tuned by changing the tempering temperature.An excellent combination of strength(a yield strength of 1308 MPa with a total elongation of 8.2%)and toughness(Charpy V-notch impact toughness of 40.5 J/cm^(2))is obtained upon tempering at 200℃.This is attributed to the lath martensite containing high dislocation density,the martensite-twin substructure,and the strengthening effects of the precipitated needle-likeε-carbides and spherical VC particles.The acicularε-carbides are replaced by the rod-shaped Fe_(3)C at the tempering temperature of 350℃,resulting in the remarkable deterioration in strength,hardness,and elongation.Spheroidized carbides formed at a tempering temperature of 500℃ are beneficial to the enhancement of the elongation and toughness,but the strength decreases due to the matrix softening caused by the recovery of dislocation.
基金financially supported by the National Natural Science Foundation of China(52071073)the Fundamental Research Funds for the Central Universities(2024GFZD002)+3 种基金the Natural Science Foundation of Hebei Province(E2024501015)the Liaoning Applied Basic Research Program(2023JH2/101300011)the Basic Scientific Research Project of Liaoning Province Department of Education(LJKZZ20220024)the Shenyang Science and Technology Project(23-407-3-13)。
文摘Ultrahigh nickel oxides(Ni content>90%)hold great promise for high-performance cathodes for the future generation of lithium-ion batteries(LIBs).However,these cathode materials cause problems such as harmful parasitic reactions at the cathode/electrolyte interface,degradation of the layered structure,and the creation of microcracks.Herein,a microstructural refinement and intergranular coating strategy is proposed to engineer ultrahigh nickel cathode LiNi_(0.96)Co_(0.03)Mn_(0.01)O_(2)(NCM).The W-doping-induced fine-grained microstructure not only endows NCM with excellent mechanical properties but also promotes infiltration of the fluoride-containing coating along the grain boundaries inside the secondary particles,thereby forming intergranular coatings.This combined fine-grained microstructure and intergranular coating strategy reduces the formation of microcracks and suppresses the additional parasitic electrolyte reactions caused by them,thereby inhibiting the degradation of the layered phase.Consequently,the modified NCM cathode achieved exceptional electrochemical properties,especially delivering a high initial capacity of 230.8 mA h g^(-1)(0.1 C)and a capacity retention exceeding 96% after100 cycles at 0.5 C in half cells.After 500 cycles in full cells,the capacity retention increases by 21.2% compared with NCM.This strategy mitigates multiple degradation mechanisms in Ni-rich cathodes and provides a generalized strategy for developing advanced ultrahigh-nickel cathodes for industrial application.
基金funded by the Open Research Fund of the State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources,China University of Mining and Technology(Grant No.SKLCRSM23KF018)the National Natural Science Foundation of China(Grant No.52104144)the National Key R&D Program of China(Grant No.2019YFA0705501).
文摘In the context of convection-heating-based in situ oil shale retorting,fractures serve as primary pathways for fluid migration and product extraction.This study investigates the permeability and microstructural evolution of oil shale during water vapor injection in single-fracture and no-fracture scenarios.Three types of oil shale are investigated:intact oil shale,oil shale with a single straight crack,and oil shale with a single hydraulic crack.With increasing water vapor temperature,the permeabilities of the intact oil shale and oil shale with a fractured crack exhibit a trend of initial increase,followed by a decrease,and then a subsequent increase.However,the permeability of oil shale with a single straight crack consistently increases and exceeds that of oil shale with a fractured crack.The temperaturedependent permeability changes in fractured oil shale-a slight decrease in fracture cracks and a gradual increase in straight cracks-mainly occur in the range of 300℃-350℃.The permeability of oil shale with a straight crack is approximately three times that of oil shale with a fractured crack.This is attributed to the retention of viscous asphaltene and the frictional resistance caused by the rough fracture structure.For the oil shale with a single crack,the crack permeability has a dominant influence on the overall permeability of the rock.The contribution of the permeability of the straight crack exceeds 94.6%,while that of the permeability of the fractured crack is greater than 86.1%.The disparity in the contribution of these two crack structures is evident at 350℃-550℃.
基金co-supported by the financial support from the Fundamental Research Funds for the Central Universities,China(Nos.YWF-23-L-1012,YWF-22-L-1017)the National Natural Science Foundation of China(No.52005020)。
文摘The performance of welded Ni-based superalloys at high temperatures is essential to be evaluated due to their particular service environment for aero-engines and high-speed aircrafts.The tensile properties and related microstructural evolutions such as the carbide precipitate and grain of a laser-welded Ni-based alloy were experimentally and numerically investigated at different temperatures(20,300,500,800℃).The results show that at room temperature,the strength of the Base Material(BM)was slightly smaller,with a difference of less than 1%,than the Welded Material(WM),which can be attributed to the more uniformly distributed needle-shaped carbide precipitates in the WM than those nonuniformly coarser spherical ones in the BM.While at 300℃ and 500℃,the strength of WM decreased more obviously compared with that of BM due to the more apparent growth of grain:13.52%loss in yield strength in WM alloys as compared with BM alloys at 300℃,and 16.57% at 500℃.At 800℃,the strength of BM and WM both decreased to a similar level due to Dynamic Recrystallization(DRX).However,a much higher elongation was observed for the BM than WM(less than 50%of BM),which can be attributed to the enhanced dislocation accumulation capability of the large spherical carbides along grain boundaries on the fracture surface in BM.Furthermore,a unified model considering the welding effects on both microstructures(dislocation,carbides,and grain)and mechanical properties evolutions at different temperatures was developed and validated.Based on this model,the key temperature ranges(20–600℃)where apparent weakening of strength and uniform plasticity occurs for welded structures were identified,providing a direct guidance for potential structure and process design.
基金supported by the National Natural Science Foundation of China(grant number 11902015)the Open Fund of Deceleration and Landing Laboratory of the Fifth Academy of Aerospace Science and Technology Group(grant number EDL19092138)the Ministry of Education Chunhui Plan(HZKY20220014).
文摘As primary load-bearing components extensively utilized in engineering applications,beam structures necessitate the design of their microstructural configurations to achieve lightweight objectives while satisfying diverse mechanical performance requirements.Combining topology optimization with fully coupled homogenization beam theory,we provide a highly efficient design tool to access desirable periodic microstructures for beams.The present optimization framework comprehensively takes into account for key deformation modes,including tension,bending,torsion,and shear deformation,all within a unified formulation.Several numerical results prove that our method can be used to handle kinds of microstructure design for beam-like structures,e.g.,extreme tension(compression)-torsion stiffness,maximization of minimum critical buckling load,and minimization of structural compliance.When optimizing microstructures for macroscopic performance,we emphasize investigating the influence of shear stiffness on the optimized results.The novel chiral beam-like structures are fabricated and tested.The experimental results indicate that the optimized tension(compression)-torsion structure has excellent buffer characteristics,as compared with the traditional square tube.This proposed optimization framework can be further extended to other physical problems of Timoshenko beams.
基金supported by the National Key R&D Program of China(Nos.2023YFE0106500,GLAM)the National Natural Science Foundation of China(Nos.52171073,52075298,51801031)the National Science and Technology Major Projects(Nos.Y2022-VII-0007-0049,J2019-VII-0015-0155,P2023-B-IV-002-001,J2019-IV-0009-0077).
文摘The residual stress field induced by surface strengthening processes such as mechanical shot peening and other forms of plastic deformation does not generally exhibit a simple“monotonic”distribution trend.Some researchers have analyzed this fact from a mechanical perspective based on Hertz theory.However,the micro/nano-scale microstructural changes corresponding to the distribution of residual stress fields still appear to be lacking.In this study,we focused on a widely used material in aviation manufacturing,namely nickel-based superalloy GH4169,as our experimental material.We subjected GH4169 alloy to me-chanical strengthening treatment using a shot peening intensity of 0.25 mmA,followed by quantitative testing of micromechanical performance indicators such as microhardness and residual stress.To thoroughly investigate the relationship between micromechanical properties and microstructure changes,we utilized transmission electron microscopy(TEM)to observe and analyze shot-peened materials at different depths.Our findings revealed that the most severe microstructural distortion induced by mechanical shot peening in GH4169 alloy was likely to occur within a depth range of 25 to 75μm.This observation aligns with the actual phenomenon that the maximum microhardness and maximum residual compressive stress did not manifest on the outermost surface of the material.By presenting a detailed analysis of deformation defects such as dislocations,stacking faults,and twinning in different depths of mechan-ically strengthened layers,our study contributes to a deeper understanding and practical application of post-processing technologies based on plastic deformation.
基金funding support from the National Natural Science Foundation of China(No.52101046)Shuangjie Chu appreciates the funding support from the National Key Research and Development Program of China(No.2022YFB3705600).
文摘Iron-based metal matrix composites(IMMCs)have attracted significant research attention due to their high specific stiffness and strength,making them potentially suitable for various engineering applications.Microstructural design,including the selection of reinforcement and matrix phases,the reinforcement volume fraction,and the interface issues are essential factors determining the engineering performance of IMMCs.A variety of fabrication methods have been developed to manufacture IMMCs in recent years.This paper reviews the recent advances and development of IMMCs with particular focus on microstructure design,fabrication methods,and their engineering performance.The microstructure design issues of IMMC are firstly discussed,including the reinforcement and matrix phase selection criteria,interface geometry and characteristics,and the bonding mechanism.The fabrication methods,including liquid state,solid state,and gas-mixing processing are comprehensively reviewed and compared.The engineering performance of IMMCs in terms of elastic modulus,hardness and wear resistance,tensile and fracture behavior is reviewed.Finally,the current challenges of the IMMCs are highlighted,followed by the discussion and outlook of the future research directions of IMMCs.
基金provided by the Science for Earthquake Resilience Program of China Earthquake Administration(Grant No.XH24044A)the National Natural Science Foundation of China(Grant Nos.42330704,U1939209)+1 种基金the Scientific Research Fund of Institute of Earthquake Forecasting,China Earthquake Administration(Grant Nos.2022IESLZ03,2022 IESLZ01)the Natural Science Foundation of Gansu Province(Grant No.22JR5RA825).
文摘Based on compressive strength analysis,ultrasonic velocity testing and microstructural damage of three groups of concrete sprayed with inorganic coatings with different mix ratios were carried out under the freeze and thaw cycles(F-T).The strength attenuations of three groups of concrete were investigated,and a linear regression model showing the relationship model between acoustic parameters of three groups of concrete and their physicomechanical properties were constructed,and the micro-mechanism behind the strength decay of concrete was explained via scanning electron microscopy.The results show that in case of the same F-T cycles concrete sprayed inorganic coating adding a polypropylene fibre leads to a good anti-freezing performance.The trend in ultrasonic velocity decay in concrete under the F-T cycles is consistent with the trend in compression strength change.The ultrasonic velocity(UV)of the concrete shows a great correlation with compression strength:the greater the compression strength of concrete,the higher the UV.The losses in compressive strength of concrete in the three kinds(A,B and C,A is with silica fume,B is plain concrete,C is with polypropylene fibres)after 300 freeze-thaw cycles are 54.55%,62.25%and 22.26%,respectively,which of ultrasonic compressive wave velocities are 13.81%,16.65%and 3.77%,respectively.Concrete strength decreases during the freeze-thaw process;this is microscopically manifested as large pores,an increase in cracks,and the development of scattered primary pores affecting the centralised connectivity.The cracks of A group have a width of 5-10μm,which of B group have a width of 5-20μm,which of C group have a width of 1-2μm.The whole process of F-T is the process of generating and enlarging cracks in the inner microstructure of the concrete,which results in a markedly reduction in the mechanical characteristics of concrete.
基金supported by the National Natural Science Foundation of China(No.52474401)the Project funded by the China Postdoctoral Science Foundation(No.2022M712919)+1 种基金Open Project of State Key Laboratory of Advanced Brazing Filler Metals and Technology(SKLABFMT-2021-03)Guangdong Basic and Applied Basic Research Foundation(2023A1515140124).
文摘The unclear interfacial characteristics of Ag/Cu interface during diffusion welding limit the improvement of mechanical properties of Ag/Cu bimetallic strips.The growth orientation and evolution of Ag and Cu crystals between Ag and Cu strips were investigated by electron backscatter diffraction(EBSD)analysis,and the interfacial properties of various Ag/Cu interfacial configurations were calculated using first-principles calculations to elucidate the diversified interfacial characteristics.Three interface bonding states,including Ag(100)/Cu(100),Ag(110)/Cu(110)and Ag(111)/Cu(111),were preferentially formed in Ag/Cu bimetallic strips during roll bonding.The intensity of Ag(100)/Cu(100)interface increases with the increasing deformation amounts during cold rolling,accompanied by the decreased intensity of Ag(110)/Cu(110)and Ag(111)/Cu(111)interfaces.The largest adsorption work and lowest interface energy of Ag(100)/Cu(100)interface at the“center”position reveal the transition from Ag(110)/Cu(110)and Ag(111)/Cu(111)interfaces to Ag(100)/Cu(100)interface.
基金financially supported by the National Natural Science Foundation of China(Nos.52171120,52271106,52071188)the Natural Science Foundation of Zhejiang Province,China(No.LZY23E050001)。
文摘Ti_(2)AlC/TiAl composites with a network structure were successfully prepared with carbon nanotubes and Ti-45Al-8Nb pre-alloyed powder using spark plasma sintering.The effects of sintering temperature(1200-1350℃)on the microstructural evolution and mechanical properties were systematically investigated.The microstructure of Ti_(2)AlC/TiAl composites exhibits duplex,near-lamellar,and fully lamellar structures,as the sintering temperature increases from 1200 to 1350℃.The network structured Ti_(2)AlC phase can refine the microstructure and the phase becomes discontinuous at high sintering temperatures.Notably,composites sintered at 1300℃ exhibit excellent mechanical properties,with the highest compressive strength(1921 MPa)and fracture strain(26%)at room temperature.Moreover,the ultimate tensile strength and fracture strain reach 537 MPa and 3.1%at 900℃,and 485 MPa and 3.3%at 950℃,respectively.The enhancement of the mechanical properties is attributed primarily to the load bearing,particle pull-out,and inhibition of crack propagation induced by Ti_(2)AlC particles.
