To investigate the aging mechanisms and elucidate the correlations between unstable microstructure and performance in biodegradable Zn alloys,the accelerated aging experiment was conducted on a high-performance wrough...To investigate the aging mechanisms and elucidate the correlations between unstable microstructure and performance in biodegradable Zn alloys,the accelerated aging experiment was conducted on a high-performance wrought Zn−0.1Mg alloy by annealing at 200℃ for varying durations.The findings reveal that the tensile strength of the alloy rapidly and significantly declines with prolonged annealing time,decreasing from 383 MPa for the as-received alloy to 102 MPa for the alloy subjected to 1440 min of annealing.The primary factors contributing to this considerable reduction in strength are static recrystallization,grain coarsening,and dislocation annihilation.Initially,the ductility of the alloy shows fluctuations,ultimately experiencing a marked decrease after extended annealing.This decline is linked to the grain growth and heightened texture intensity,while the unusual increase in ductility observed between 30 and 120 min of annealing is likely due to the formation of twins.In addition,due to rapid grain growth and an increase in precipitates and twins,the corrosion resistance of the alloy in Hank’s solution has worsened,with the corrosion rate rising from 0.037 to 0.069 mm/a following 300 min of annealing.展开更多
The role of Ca content(0.5,1.0,2.0 wt.%)on microstructure,mechanical properties and strain evolution of as-rolled Mg-Al-Ca-Zn-Mn alloy was thoroughly investigated in this work.The results indicate that the primary sec...The role of Ca content(0.5,1.0,2.0 wt.%)on microstructure,mechanical properties and strain evolution of as-rolled Mg-Al-Ca-Zn-Mn alloy was thoroughly investigated in this work.The results indicate that the primary second phase transformed from the Mg_(17)Al_(12) phase to the Al_(2)Ca phase after homogenization,and the amount of Al_(2)Ca phase increased significantly with increasing Ca content.After hot rolling,the alloys exhibited the typical bimodal microstructure composed of fine dynamic recrystallized(DRXed)grains and coarse elongated un-DRXed grains,the area fraction of the DRXed regions increased with increasing Ca content.Besides,a large number of submicron-sized as well as nano-scaled spherical Mg_(17)Al_(12) phases dynamically precipitated along the DRXed grain boundaries in all alloys,which promoted the DRX and restricted the grain growth.During rolling deformation,DRX preferentially occurred near the primary second phases and shear bands by the particle stimulated nucleation(PSN)and shear band induced nucleation(SBIN)mechanism in the alloys.The ultimate tensile strength(UTS),yield strength(YS),and elongation to failure(EF)along the rolling direction(RD)of the Mg-8.0Al-1.0Ca-1.0Zn-0.4Mn(wt.%)sheet were 393 MPa,334 MPa and 8.7%,respectively.Such high strength was mainly attributed to fine DRXed grains,high number density of dynamically precipitated Mg_(17)Al_(12) phases and strongly textured un-DRXed grains with numerous sub-structures.The reasonable DRX ratio moderated strain localization and thus stabilized tensile deformation,leading to moderate plasticity of the alloy.展开更多
Mg alloys with a combination of high strength and excellent ductility are increasingly required for structural applications.This study investigates the influence of advanced processing techniques on the mechanical pro...Mg alloys with a combination of high strength and excellent ductility are increasingly required for structural applications.This study investigates the influence of advanced processing techniques on the mechanical properties and microstructural evolution of Mg-Gd-Y-Zn-Zr alloys.Utilizing a combination of double extrusion and stepwise hot rolling followed by aging treatments,significant enhancements in the mechanical performance of these alloys are demonstrated.The processing techniques applied lead to notable refinement in grain-size and modifications in the microstructure,including the transformation of LPSO phases from 18R to 24R and the dispersion of β phase particles.These microstructural transformations contribute to a substantial increase in yield-strength,ultimate-tensile-strength,and ductility.Furthermore,findings reveal that these improvements are also supported by alterations in material texture,which influence dislocation dynamics as indicated by changes in Kernel Average Misorientation(KAM)values.The combined effect of grain boundary(GB)strengthening,phase distribution,and texture modification elucidates the observed mechanical enhancements.This research provides valuable insights into the design and optimization of Mg-Gd-Y-Zn-Zr alloys for critical applications in aerospace and automotive industries where high strength and ductility are paramount.展开更多
In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechan...In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechanical behavior.At a C content of 0.082 wt%,the microstructure of weld metal consisted of austenite,M_(6)C,and M_(23)C_(6),where M_(6)C was the main carbide.The number and average size of the M_(6)C carbides significantly decreased as the C content decreased.At a C content of 0.045 wt%,only a very small number of M_(6)C carbides were observed in the weld metal.For the tensile process,the number of deformation twins increased as the C content decreased,which introduced a stronger dynamic Hall-Petch effect,resulting in only a small decrease in the ultimate tensile strength of the weld metal.Meanwhile,the increase in deformation twins significantly enhanced the elongation of the weld metals.For the impact process,the impact energy increased from 204 to 241 J as the C content decreased.The crack initiation resistance was improved due to the reduction in M_(6)C carbide,which inhibited cracking at the interface of M_(6)C/matrix.Additionally,the crack propagation resistance was enhanced due to the increase in deformation twins,which consumed more impact energy.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
The Cu/1010 steel bimetal laminated composites(BLCs)were rolled to different thicknesses to investigate the effect of rolling direction and reduction on the microstructure evolution and mechanical properties.The diffe...The Cu/1010 steel bimetal laminated composites(BLCs)were rolled to different thicknesses to investigate the effect of rolling direction and reduction on the microstructure evolution and mechanical properties.The difference of mechanical properties between the Cu and 1010 steel causes different thickness reductions,percentage spread,and cladding ratios.The formation of strong texture induces larger strength of the rolled samples,and as the volume fraction of 1010 steel is larger in Route-A,its strength is consistently greater than that in Route-B.The obstruction of interface to crystal and dislocation slip results in the formation of interface distortion,inducing dislocation density gradient when the rolling reduction is low in Route-A.The slip planes of the Cu and 1010 steel are more prone to suffer the normal strain,while the shear strain of other crystal planes is obviously larger than the normal strain under rolling load near the interface.展开更多
The microstructural evolution,mechanical properties,and corrosion behavior of Ti-12Ni(wt.%)specimens produced by laser powder bed fusion(LPBF)using various volume energy density(VED)processing parameter values were in...The microstructural evolution,mechanical properties,and corrosion behavior of Ti-12Ni(wt.%)specimens produced by laser powder bed fusion(LPBF)using various volume energy density(VED)processing parameter values were investigated.The results showed that the alloy prepared at a low VED of 67 J/mm^(3)consisted of near-βgrains.At a VED of 133 J/mm^(3),the alloy exhibited coarse primary Ti2Ni and fine eutectoid structure.This eutectoid structure consisted ofαlaths and two types of nanoscale Ti2Ni,one in the form of short rods and the other with a spherical morphology.Further increase of the VED to 267 J/mm^(3)led to coarsening of the eutectoid structure.The dispersed Ti2Ni nanoparticles exhibited a significant strengthening effect.The alloy produced at a VED of 133 J/mm^(3)showed the greatest strength with a nanohardness of(7.8±0.1)GPa and a compressive strength of(1777±27)MPa.However,the presence of Ni segregation and holes produced by the LPBF processing adversely affected the corrosion resistance of the alloy.展开更多
The creep properties of nickel-based single crystal superalloy with [001] orientation was investigated at different test conditions. The microstructure evolution of γ′ phase, TCP phase and dislocation characteristic...The creep properties of nickel-based single crystal superalloy with [001] orientation was investigated at different test conditions. The microstructure evolution of γ′ phase, TCP phase and dislocation characteristic after creep rupture was studied by SEM and TEM. The results show that the alloy has excellent creep properties. Two different types of creep behavior can be shown in the creep curves. The primary creep is characterized by the high amplitude at test conditions of (760 °C, 600 MPa) and (850 °C, 550 MPa) and the primary creep strain is limited at (980 °C, 250 MPa), (1100 °C, 140 MPa) and (1120 °C, 120 MPa). A little change ofγ′precipitate morphology occurs at (760 °C, 600 MPa). The lateral merging of the γ′ precipitate has already begun at (850 °C, 550 MPa). Theγphase is surrounded by theγ′phase at (980 °C, 250 MPa). Theγphase is no longer continuous tested at (1070 °C, 140 MPa). At (1100 °C, 120 MPa), the thickness ofγphase continues to increase. No TCP phase precipitates in the specimens at (760 °C, 600 MPa), (850 °C, 550 MPa) and (980 °C, 250 MPa). Needle shaped TCP phase precipitates in the specimens tested at (1070 °C, 140 MPa) and (1100 °C, 120 MPa). The dislocation shear mechanism including stacking fault formation is operative at lower temperature and high stress. The dislocation by-passing mechanism occurs to form networks atγ/γ′interface under the condition of high temperature and lower stress.展开更多
X-ray diffraction （XRD）, optical microscopy （OM）, scanning electronic microscopy （SEM）, transmission electron microscopy （TEM） and tensile tests at room temperature （RT） were performed to investigate the eff...X-ray diffraction （XRD）, optical microscopy （OM）, scanning electronic microscopy （SEM）, transmission electron microscopy （TEM） and tensile tests at room temperature （RT） were performed to investigate the effect of homogenization on microstructure evolution and mechanical properties of Mg-7Gd-3Y-1Nd-1Zn-0.5Zr （mass fraction,%） alloy. The results indicate that the microstructure of the as-cast alloy is composed of α-Mg, （Mg, Zn）3RE phase and stacking fault （SF）, the homogenization results in the disappearance of （Mg, Zn）3RE phase and stacking fault （SF） as well as the emergence of 14H-type long-period stacking ordered （LPSO） phase. The ultimate tensile strength （UTS）, yield strength （YS） and elongation of the as-cast alloy are 187 MPa, 143 MPa and 3.1%, and the UTS, YS and elongation of the as-homogenized alloy are 229 MPa, 132 MPa and 7.2%, respectively.展开更多
The microstructure evolution and mechanical properties of a ZK60 magnesium alloy produced by the semi-solid thermal transformation （SSTT） route and the recrystallization and partial melting （RAP） route were studie...The microstructure evolution and mechanical properties of a ZK60 magnesium alloy produced by the semi-solid thermal transformation （SSTT） route and the recrystallization and partial melting （RAP） route were studied, respectively. The microstructure evolution during partial remelting was studied at different temperatures for different time. The tensile mechanical properties of thixoformed components by the two routes at room temperature were examined. The results show that coalescence is dominant in the SSTT alloy and Ostwald ripening is dominant in the RAP alloy. Compared with the SSTT route, the RAP route can produce finer semi-solid microstructure under the similar isothermal holding condition. The microstructure of the RAP alloy is much more spheroidized compared with the SSTT alloy. Thixoforming for the ZK60 magnesium alloy produced by the SSTT and RAP route results in successful filling of the die, and the thixoforming process improves the mechanical properties of ZK60 magnesium alloy. The RAP alloy shows significantly advantageous mechanical properties over that of the SSTT alloy.展开更多
Refractory metals,including tungsten(W),tantalum(Ta),molybdenum(Mo),and niobium(Nb),play a vital role in industries,such as nuclear energy and aerospace,owing to their exceptional melting temperatures,thermal durabili...Refractory metals,including tungsten(W),tantalum(Ta),molybdenum(Mo),and niobium(Nb),play a vital role in industries,such as nuclear energy and aerospace,owing to their exceptional melting temperatures,thermal durability,and corrosion resistance.These metals have body-centered cubic crystal structure,characterized by limited slip systems and impeded dislocation motion,resulting in significant low-temperature brittleness,which poses challenges for the conventional processing.Additive manufacturing technique provides an innovative approach,enabling the production of intricate parts without molds,which significantly improves the efficiency of material usage.This review provides a comprehensive overview of the advancements in additive manufacturing techniques for the production of refractory metals,such as W,Ta,Mo,and Nb,particularly the laser powder bed fusion.In this review,the influence mechanisms of key process parameters(laser power,scan strategy,and powder characteristics)on the evolution of material microstructure,the formation of metallurgical defects,and mechanical properties were discussed.Generally,optimizing powder characteristics,such as sphericity,implementing substrate preheating,and formulating alloying strategies can significantly improve the densification and crack resistance of manufactured parts.Meanwhile,strictly controlling the oxygen impurity content and optimizing the energy density input are also the key factors to achieve the simultaneous improvement in strength and ductility of refractory metals.Although additive manufacturing technique provides an innovative solution for processing refractory metals,critical issues,such as residual stress control,microstructure and performance anisotropy,and process stability,still need to be addressed.This review not only provides a theoretical basis for the additive manufacturing of high-performance refractory metals,but also proposes forward-looking directions for their industrial application.展开更多
Hot isostatic pressing (HIP) temperature has a significant impact on the service performance of powder metallurgy titanium alloys. In this study, a high-temperature titanium alloy, Ti-6.5Al-3.5Mo-1.5Zr-0.3Si, was prep...Hot isostatic pressing (HIP) temperature has a significant impact on the service performance of powder metallurgy titanium alloys. In this study, a high-temperature titanium alloy, Ti-6.5Al-3.5Mo-1.5Zr-0.3Si, was prepared under different HIP temperatures (880–1000℃), and the microstructural evolution and mechanical properties were systematically investigated. The results demonstrated that the HIPed alloys were predominantly composed of more than 80 vol.% α phase and a small amount of β phase, and their phase compositions were basically unaffected by the HIP temperatures. Under the typical single-temperature-maintained HIP (STM-HIP) regime, the microstructure of alloy significantly coarsened as the HIP temperature increased, and the alloy strength exhibited an obvious linear negative correlation with the HIP temperature. On the basis of Hall–Petch relation, the prediction model of grain size was established, and the mathematical equation between HIP temperature and grain size (d=M(T_(HIP-N)^(-2))) was deduced. Furthermore, a possible evolution mechanism of microstructure was proposed, which could be divided into the decomposition of initial α′ martensite for as-received powder, formation of the globular α grains in prior particle boundaries (PPBs) region, and precipitation of the platelet α grains in non-PPBs region. For these alloys prepared by the dual-temperature-maintained HIP (DTM-HIP) regime, although their tensile properties were comparable to that of alloy prepared by STM-HIP regime with same high-temperature holding stage, higher proportion of globular α grains occurred due to more recrystallization nucleation during the low-temperature holding stage, which probably provided a solution for improving the dynamic service performance of HIPed alloys.展开更多
Titanium(Ti)and its alloys are frequently utilized as critical components in a variety of engineering ap-plications because of their high specific strength and excellent corrosion resistance.Compared to conven-tional ...Titanium(Ti)and its alloys are frequently utilized as critical components in a variety of engineering ap-plications because of their high specific strength and excellent corrosion resistance.Compared to conven-tional surface strengthening technologies,laser shock peening(LSP)has increasingly attracted attention from researchers and industries,since it significantly improves the surface strength,biocompatibility,fa-tigue resistance,and anti-corrosion ability of Ti and its alloys.Despite numerous studies that have been carried out to elucidate the effects of LSP on microstructural evolution and mechanical properties of Ti and its alloys in recent years,a comprehensive review of recent advancements in the field of Ti and its alloys subjected to LSP is still lacking.In this review,the standard LSP and the novel process designs of LSP assisted by thermal,cryogenic,electropulsing and magnetic fields are discussed and compared.Microstructural evolution,with focuses on the dislocation dynamics,deformation twinning,grain refine-ment and surface amorphization,during LSP processing of Ti alloys is reviewed.Furthermore,the en-hanced engineering performance of the L SP-processed(L SPed)Ti alloys,including surface hardness,wear resistance,fatigue life and corrosion resistance are summarized.Finally,this review concludes by present-ing an overview of the current challenges encountered in this field and offering insights into anticipated future trends.展开更多
The regulation of sintering temperature in spark plasma sintering enables the achievement of grain refinement,phase control,and performance enhancement in the preparation of AZ91D magnesium alloy.This study investigat...The regulation of sintering temperature in spark plasma sintering enables the achievement of grain refinement,phase control,and performance enhancement in the preparation of AZ91D magnesium alloy.This study investigates the influence of sintering temperature on microstructural evolution and mechanical properties of the AZ91D alloy.Microstructural analysis was conducted using scanning electron microscopy,electron backscatter diffraction,and X-ray diffraction.Microscopic structures and mechanical behaviors were examined through hardness and tensile tests.Elevated sintering temperatures resulted in reduced secondary phase content,leading to a decrease in mechanical performance.The alloy exhibited optimal mechanical properties at 320℃.The nanoparticle coarsening process and particle evolution during sintering were simulated using phase field methods.By optimizing the sintering temperature,precise control over microstructural and textural evolution can be achieved,facilitating the attainment of desired hardness levels and mechanical properties.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
Low-oxygen TZM alloy(oxygen content of 0.03vol%)was subjected to solid-solution heat treatment at various temperatures followed by quenching.Results show that the tensile strength of the alloy gradually decreases with...Low-oxygen TZM alloy(oxygen content of 0.03vol%)was subjected to solid-solution heat treatment at various temperatures followed by quenching.Results show that the tensile strength of the alloy gradually decreases with the increase in solidsolution temperature,and the elongation first increases and then decreases.The the amount of nanoscale Ti-rich phases precipitated in low-oxygen TZM alloys gradually increases with the increase in solid-solution temperature.Special strip-shaped Ti-rich areas appear in the samples solidified at 1200 and 1300℃.The nanoscale Ti-rich phases ensure the uniform distribution of dislocations throughout TZM alloy,while significantly improving the plasticity of low-oxygen TZM alloy samples.展开更多
Fe-Mo functionally graded materials(FGMs)with different composition-change rates from 100%304 stainless steel to 100%Mo along the composition gradient direction were prepared by electron beam-directed energy depositio...Fe-Mo functionally graded materials(FGMs)with different composition-change rates from 100%304 stainless steel to 100%Mo along the composition gradient direction were prepared by electron beam-directed energy deposition(EB-DED)technique,including three samples with composition mutation of 100%,composition change rate of 10%and 30%.Results show that the composition-change rate significantly affects the microstructure and mechanical properties of the samples.In the sample with abrupt change of composition,the sharp shift in composition between 304 stainless steel and Mo leads to a great difference in the microstructure and hardness near the interface between the two materials.With the increase in the number of gradient layers,the composition changes continuously along the direction of deposition height,and the microstructure morphology shows a smooth transition from 304 stainless steel to Mo,which is gradually transformed from columnar crystal to dendritic crystal.Elements Fe,Mo,and other major elements transform linearly along the gradient direction,with sufficient interlayer diffusion between the deposited layers,leading to good metallurgical bonding.The smaller the change in composition gradient,the greater the microhardness value along the deposition direction.When the composition gradient is 10%,the gradient layer exhibits higher hardness(940 HV)and excellent resistance to surface abrasion,and the overall compressive properties of the samples are better,with the compressive fracture stress in the top region reaching 750.05±14 MPa.展开更多
Laser beam welding was used to join a near-β titanium alloy(Ti-3Al-6Mo-2Fe-2Zr),followed by aging treatments.The relations among aging temperature,microstructure,and tensile properties of joints were revealed.For as-...Laser beam welding was used to join a near-β titanium alloy(Ti-3Al-6Mo-2Fe-2Zr),followed by aging treatments.The relations among aging temperature,microstructure,and tensile properties of joints were revealed.For as-welded joints,the fusion zone features primarily single β phase.It is attributed to the high Mo equivalency of this alloy and the fast cooling rate in laser beam welding.After aging treatments,many α precipitates form in the fusion zone and heat affected zone.The rising aging temperature coarsens α precipitates and reduces the volume fraction of α precipitates.Compared with the as-welded joints,the aging treated joints'tensile strength and elongation are improved.The increasing aging temperature weakens the strengthening effect because of the decreasing volume fraction of α precipitates.After the aging treatment at 500℃ for 8 h,the joints obtain the optimal match between strength and plasticity.The fracture mode of joints changes from quasi-cleavage fracture in as-welded condition to microvoid coalescence fracture after heat treatments.展开更多
The transient liquid-phase(TLP)diffusion bonding of GH5188 with a BNi-5 interlayer was focused on.Parameters were chosen and optimized for GH5188 alloy according to the TLP joining mechanism.The microstructure evoluti...The transient liquid-phase(TLP)diffusion bonding of GH5188 with a BNi-5 interlayer was focused on.Parameters were chosen and optimized for GH5188 alloy according to the TLP joining mechanism.The microstructure evolution and mechanical properties of the joints were studied.Results show that the relatively complete isothermal solidification zone(ISZ)ensures a reliable connection of the base metal(BM).Within the temperature range of 1110–1190°C,higher bonding temperatures can widen ISZ and promote joint composition homogenization,thus improving mechanical properties.However,the increase in precipitated phase has an adverse effect on the mechanical properties of the joint.The maximum shear strength,reaching 482 MPa,is achieved at 1130°C,representing 84.6%of BM strength.Within the pressure range of 5–15 MPa,both precipitated phases in adiabatic solidification zone(ASZ)and voids generated by partial melting increase.On the contrary,their sizes decrease significantly under higher bonding pressure,resulting in an upward trend in alloy mechanical properties.The maximum shear strength of 490 MPa is attained at a bonding pressure of 15 MPa.The joint exhibits a typical mixed fracture pattern,with the small brittle M_(23)C_(6) phase and voids significantly impacting mechanical properties.Nano-indentation tests indicate that ASZ is a potential source of cracks.展开更多
Self-designed Al8Si0.4Mg0.4Fe aluminium alloy was modified with Sr,followed by solid solution and aging treatments to regulate its microstructure and mechanical/electrical properties.The results show that after the mo...Self-designed Al8Si0.4Mg0.4Fe aluminium alloy was modified with Sr,followed by solid solution and aging treatments to regulate its microstructure and mechanical/electrical properties.The results show that after the modification treatment,the room-temperature tensile strength of the alloy remains nearly unchanged,the elongation at break slightly increases from 1.82%to 3.34%,and the electrical conductivity significantly increases from 40.1%international annealed copper standard(IACS)to 42.0%IACS.After the modification,the alloy was subjected to solid solution treatment at 515℃for 8 h,followed by aging treatment at 180,200,220 and 240℃for 6 h.With increasing aging temperature,the electrical conductivity increases monotonously from 41.4%IACS to 45.5%IACS,while the room-temperature tensile strength initially increases and then decreases.At 200℃,the alloy achieves an optimal balance between electrical conductivity and room-temperature tensile strength:the electrical conductivity is 42.5%IACS,and the room-temperature tensile strength is 282.9 MPa.When the aging temperature continues to rise,the alloy undergoes overaging.Although the conductivity continues to increase,the room-temperature tensile strength drops sharply,and it is only 177.1 MPa at 240℃.展开更多
基金supported by the National Natural Science Foundation of China(No.52271101)Suzhou Science and Technology Project,China(Nos.SYG202312,SJC2023005,SZS2023023)+1 种基金Nanjing Major Science and Technology Project,China(No.202309015)the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology,China(No.ASMA202305)。
文摘To investigate the aging mechanisms and elucidate the correlations between unstable microstructure and performance in biodegradable Zn alloys,the accelerated aging experiment was conducted on a high-performance wrought Zn−0.1Mg alloy by annealing at 200℃ for varying durations.The findings reveal that the tensile strength of the alloy rapidly and significantly declines with prolonged annealing time,decreasing from 383 MPa for the as-received alloy to 102 MPa for the alloy subjected to 1440 min of annealing.The primary factors contributing to this considerable reduction in strength are static recrystallization,grain coarsening,and dislocation annihilation.Initially,the ductility of the alloy shows fluctuations,ultimately experiencing a marked decrease after extended annealing.This decline is linked to the grain growth and heightened texture intensity,while the unusual increase in ductility observed between 30 and 120 min of annealing is likely due to the formation of twins.In addition,due to rapid grain growth and an increase in precipitates and twins,the corrosion resistance of the alloy in Hank’s solution has worsened,with the corrosion rate rising from 0.037 to 0.069 mm/a following 300 min of annealing.
基金financially supported by National Key Research&Development Program of China(Grant No.2021YFB3703300)Natural Science Foundation of Heilongjiang Province-Outstanding Youth Fund(Grant No.YQ2020E006)+2 种基金National Natural Science Foundation(Grant No’s.52220105003 and 51971075)the Fundamental Research Funds for the Central Universities(Grant No.FRFCU5710000918)JSPS KAKENHI(Grant No.JP21H01669).
文摘The role of Ca content(0.5,1.0,2.0 wt.%)on microstructure,mechanical properties and strain evolution of as-rolled Mg-Al-Ca-Zn-Mn alloy was thoroughly investigated in this work.The results indicate that the primary second phase transformed from the Mg_(17)Al_(12) phase to the Al_(2)Ca phase after homogenization,and the amount of Al_(2)Ca phase increased significantly with increasing Ca content.After hot rolling,the alloys exhibited the typical bimodal microstructure composed of fine dynamic recrystallized(DRXed)grains and coarse elongated un-DRXed grains,the area fraction of the DRXed regions increased with increasing Ca content.Besides,a large number of submicron-sized as well as nano-scaled spherical Mg_(17)Al_(12) phases dynamically precipitated along the DRXed grain boundaries in all alloys,which promoted the DRX and restricted the grain growth.During rolling deformation,DRX preferentially occurred near the primary second phases and shear bands by the particle stimulated nucleation(PSN)and shear band induced nucleation(SBIN)mechanism in the alloys.The ultimate tensile strength(UTS),yield strength(YS),and elongation to failure(EF)along the rolling direction(RD)of the Mg-8.0Al-1.0Ca-1.0Zn-0.4Mn(wt.%)sheet were 393 MPa,334 MPa and 8.7%,respectively.Such high strength was mainly attributed to fine DRXed grains,high number density of dynamically precipitated Mg_(17)Al_(12) phases and strongly textured un-DRXed grains with numerous sub-structures.The reasonable DRX ratio moderated strain localization and thus stabilized tensile deformation,leading to moderate plasticity of the alloy.
基金financially supported by the financial supports from the National Natural Science Foundation of China(Grant No.52027805).
文摘Mg alloys with a combination of high strength and excellent ductility are increasingly required for structural applications.This study investigates the influence of advanced processing techniques on the mechanical properties and microstructural evolution of Mg-Gd-Y-Zn-Zr alloys.Utilizing a combination of double extrusion and stepwise hot rolling followed by aging treatments,significant enhancements in the mechanical performance of these alloys are demonstrated.The processing techniques applied lead to notable refinement in grain-size and modifications in the microstructure,including the transformation of LPSO phases from 18R to 24R and the dispersion of β phase particles.These microstructural transformations contribute to a substantial increase in yield-strength,ultimate-tensile-strength,and ductility.Furthermore,findings reveal that these improvements are also supported by alterations in material texture,which influence dislocation dynamics as indicated by changes in Kernel Average Misorientation(KAM)values.The combined effect of grain boundary(GB)strengthening,phase distribution,and texture modification elucidates the observed mechanical enhancements.This research provides valuable insights into the design and optimization of Mg-Gd-Y-Zn-Zr alloys for critical applications in aerospace and automotive industries where high strength and ductility are paramount.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA0410201)the Natural Science Foundation of Heilongjiang Province(No.TD2021E006)+1 种基金the Liaoning Provincial Doctoral Initiation Fund Project(No.2022-BS-008)the China Postdoctoral Science Foundation(No.2023T160654).
文摘In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechanical behavior.At a C content of 0.082 wt%,the microstructure of weld metal consisted of austenite,M_(6)C,and M_(23)C_(6),where M_(6)C was the main carbide.The number and average size of the M_(6)C carbides significantly decreased as the C content decreased.At a C content of 0.045 wt%,only a very small number of M_(6)C carbides were observed in the weld metal.For the tensile process,the number of deformation twins increased as the C content decreased,which introduced a stronger dynamic Hall-Petch effect,resulting in only a small decrease in the ultimate tensile strength of the weld metal.Meanwhile,the increase in deformation twins significantly enhanced the elongation of the weld metals.For the impact process,the impact energy increased from 204 to 241 J as the C content decreased.The crack initiation resistance was improved due to the reduction in M_(6)C carbide,which inhibited cracking at the interface of M_(6)C/matrix.Additionally,the crack propagation resistance was enhanced due to the increase in deformation twins,which consumed more impact energy.
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the National Key Research and Development Program of China(No.2018YFE0306103)the National Natural Science Foundation of China(No.52071050)+1 种基金the Science and Technology Innovation Project of Ningbo,China(No.2021Z032)the Program of China Scholarships Council(No.202106060148).
文摘The Cu/1010 steel bimetal laminated composites(BLCs)were rolled to different thicknesses to investigate the effect of rolling direction and reduction on the microstructure evolution and mechanical properties.The difference of mechanical properties between the Cu and 1010 steel causes different thickness reductions,percentage spread,and cladding ratios.The formation of strong texture induces larger strength of the rolled samples,and as the volume fraction of 1010 steel is larger in Route-A,its strength is consistently greater than that in Route-B.The obstruction of interface to crystal and dislocation slip results in the formation of interface distortion,inducing dislocation density gradient when the rolling reduction is low in Route-A.The slip planes of the Cu and 1010 steel are more prone to suffer the normal strain,while the shear strain of other crystal planes is obviously larger than the normal strain under rolling load near the interface.
基金supported by the National Natural Science Foundation of China(Nos.12374022,U23A20540)the Technological Base Project,China(No.JSHS2022206A001)+2 种基金the Natural Science Foundation of Hunan Province for Distinguished Young Scholars,China(No.2023JJ10075)the Scientific and Technological Project of Yunnan Precious Metals Laboratory,China(No.YPML-202305247)the Central South University Research Program of Advanced Interdisciplinary Studies,China(No.2023QYJC038).
文摘The microstructural evolution,mechanical properties,and corrosion behavior of Ti-12Ni(wt.%)specimens produced by laser powder bed fusion(LPBF)using various volume energy density(VED)processing parameter values were investigated.The results showed that the alloy prepared at a low VED of 67 J/mm^(3)consisted of near-βgrains.At a VED of 133 J/mm^(3),the alloy exhibited coarse primary Ti2Ni and fine eutectoid structure.This eutectoid structure consisted ofαlaths and two types of nanoscale Ti2Ni,one in the form of short rods and the other with a spherical morphology.Further increase of the VED to 267 J/mm^(3)led to coarsening of the eutectoid structure.The dispersed Ti2Ni nanoparticles exhibited a significant strengthening effect.The alloy produced at a VED of 133 J/mm^(3)showed the greatest strength with a nanohardness of(7.8±0.1)GPa and a compressive strength of(1777±27)MPa.However,the presence of Ni segregation and holes produced by the LPBF processing adversely affected the corrosion resistance of the alloy.
文摘The creep properties of nickel-based single crystal superalloy with [001] orientation was investigated at different test conditions. The microstructure evolution of γ′ phase, TCP phase and dislocation characteristic after creep rupture was studied by SEM and TEM. The results show that the alloy has excellent creep properties. Two different types of creep behavior can be shown in the creep curves. The primary creep is characterized by the high amplitude at test conditions of (760 °C, 600 MPa) and (850 °C, 550 MPa) and the primary creep strain is limited at (980 °C, 250 MPa), (1100 °C, 140 MPa) and (1120 °C, 120 MPa). A little change ofγ′precipitate morphology occurs at (760 °C, 600 MPa). The lateral merging of the γ′ precipitate has already begun at (850 °C, 550 MPa). Theγphase is surrounded by theγ′phase at (980 °C, 250 MPa). Theγphase is no longer continuous tested at (1070 °C, 140 MPa). At (1100 °C, 120 MPa), the thickness ofγphase continues to increase. No TCP phase precipitates in the specimens at (760 °C, 600 MPa), (850 °C, 550 MPa) and (980 °C, 250 MPa). Needle shaped TCP phase precipitates in the specimens tested at (1070 °C, 140 MPa) and (1100 °C, 120 MPa). The dislocation shear mechanism including stacking fault formation is operative at lower temperature and high stress. The dislocation by-passing mechanism occurs to form networks atγ/γ′interface under the condition of high temperature and lower stress.
基金Project(51204020)supported by the National Natural Science Foundation of ChinaProjects(2013CB632202,2013CB632205)supported by the National Basic Research Program of ChinaProject(2014-GX-106A)supported by the Qinghai Science and Technology Program of China
文摘X-ray diffraction （XRD）, optical microscopy （OM）, scanning electronic microscopy （SEM）, transmission electron microscopy （TEM） and tensile tests at room temperature （RT） were performed to investigate the effect of homogenization on microstructure evolution and mechanical properties of Mg-7Gd-3Y-1Nd-1Zn-0.5Zr （mass fraction,%） alloy. The results indicate that the microstructure of the as-cast alloy is composed of α-Mg, （Mg, Zn）3RE phase and stacking fault （SF）, the homogenization results in the disappearance of （Mg, Zn）3RE phase and stacking fault （SF） as well as the emergence of 14H-type long-period stacking ordered （LPSO） phase. The ultimate tensile strength （UTS）, yield strength （YS） and elongation of the as-cast alloy are 187 MPa, 143 MPa and 3.1%, and the UTS, YS and elongation of the as-homogenized alloy are 229 MPa, 132 MPa and 7.2%, respectively.
文摘The microstructure evolution and mechanical properties of a ZK60 magnesium alloy produced by the semi-solid thermal transformation （SSTT） route and the recrystallization and partial melting （RAP） route were studied, respectively. The microstructure evolution during partial remelting was studied at different temperatures for different time. The tensile mechanical properties of thixoformed components by the two routes at room temperature were examined. The results show that coalescence is dominant in the SSTT alloy and Ostwald ripening is dominant in the RAP alloy. Compared with the SSTT route, the RAP route can produce finer semi-solid microstructure under the similar isothermal holding condition. The microstructure of the RAP alloy is much more spheroidized compared with the SSTT alloy. Thixoforming for the ZK60 magnesium alloy produced by the SSTT and RAP route results in successful filling of the die, and the thixoforming process improves the mechanical properties of ZK60 magnesium alloy. The RAP alloy shows significantly advantageous mechanical properties over that of the SSTT alloy.
基金National MCF Energy R&D Program(2024YFE03260300)。
文摘Refractory metals,including tungsten(W),tantalum(Ta),molybdenum(Mo),and niobium(Nb),play a vital role in industries,such as nuclear energy and aerospace,owing to their exceptional melting temperatures,thermal durability,and corrosion resistance.These metals have body-centered cubic crystal structure,characterized by limited slip systems and impeded dislocation motion,resulting in significant low-temperature brittleness,which poses challenges for the conventional processing.Additive manufacturing technique provides an innovative approach,enabling the production of intricate parts without molds,which significantly improves the efficiency of material usage.This review provides a comprehensive overview of the advancements in additive manufacturing techniques for the production of refractory metals,such as W,Ta,Mo,and Nb,particularly the laser powder bed fusion.In this review,the influence mechanisms of key process parameters(laser power,scan strategy,and powder characteristics)on the evolution of material microstructure,the formation of metallurgical defects,and mechanical properties were discussed.Generally,optimizing powder characteristics,such as sphericity,implementing substrate preheating,and formulating alloying strategies can significantly improve the densification and crack resistance of manufactured parts.Meanwhile,strictly controlling the oxygen impurity content and optimizing the energy density input are also the key factors to achieve the simultaneous improvement in strength and ductility of refractory metals.Although additive manufacturing technique provides an innovative solution for processing refractory metals,critical issues,such as residual stress control,microstructure and performance anisotropy,and process stability,still need to be addressed.This review not only provides a theoretical basis for the additive manufacturing of high-performance refractory metals,but also proposes forward-looking directions for their industrial application.
基金support from CAS Project for Young Scientists in Basic Research(YSBR-025)and the Technology Innovation(RCJJ-145-24-39)R.P.Guo acknowledges the financial support from the National Natural Science Foundation of China(No.52401104)+1 种基金the Fundamental Research Program of Shanxi Province(No.202203021221072)the China Postdoctoral Science Foundation(No.2024M753298).
文摘Hot isostatic pressing (HIP) temperature has a significant impact on the service performance of powder metallurgy titanium alloys. In this study, a high-temperature titanium alloy, Ti-6.5Al-3.5Mo-1.5Zr-0.3Si, was prepared under different HIP temperatures (880–1000℃), and the microstructural evolution and mechanical properties were systematically investigated. The results demonstrated that the HIPed alloys were predominantly composed of more than 80 vol.% α phase and a small amount of β phase, and their phase compositions were basically unaffected by the HIP temperatures. Under the typical single-temperature-maintained HIP (STM-HIP) regime, the microstructure of alloy significantly coarsened as the HIP temperature increased, and the alloy strength exhibited an obvious linear negative correlation with the HIP temperature. On the basis of Hall–Petch relation, the prediction model of grain size was established, and the mathematical equation between HIP temperature and grain size (d=M(T_(HIP-N)^(-2))) was deduced. Furthermore, a possible evolution mechanism of microstructure was proposed, which could be divided into the decomposition of initial α′ martensite for as-received powder, formation of the globular α grains in prior particle boundaries (PPBs) region, and precipitation of the platelet α grains in non-PPBs region. For these alloys prepared by the dual-temperature-maintained HIP (DTM-HIP) regime, although their tensile properties were comparable to that of alloy prepared by STM-HIP regime with same high-temperature holding stage, higher proportion of globular α grains occurred due to more recrystallization nucleation during the low-temperature holding stage, which probably provided a solution for improving the dynamic service performance of HIPed alloys.
基金supported by the National Key R&D Plan of China(No.2022YFB3705603)the National Natural Science Foundation of China(No.52101046)+1 种基金the Excellent Youth Overseas Project of National Science and Natural Foundation of China,the Baowu Special Metallurgy Cooperation Limited(No.22H010101336)the Medicine-Engineering Interdisciplinary Project of Shanghai Jiao Tong University(No.YG2022QN076).
文摘Titanium(Ti)and its alloys are frequently utilized as critical components in a variety of engineering ap-plications because of their high specific strength and excellent corrosion resistance.Compared to conven-tional surface strengthening technologies,laser shock peening(LSP)has increasingly attracted attention from researchers and industries,since it significantly improves the surface strength,biocompatibility,fa-tigue resistance,and anti-corrosion ability of Ti and its alloys.Despite numerous studies that have been carried out to elucidate the effects of LSP on microstructural evolution and mechanical properties of Ti and its alloys in recent years,a comprehensive review of recent advancements in the field of Ti and its alloys subjected to LSP is still lacking.In this review,the standard LSP and the novel process designs of LSP assisted by thermal,cryogenic,electropulsing and magnetic fields are discussed and compared.Microstructural evolution,with focuses on the dislocation dynamics,deformation twinning,grain refine-ment and surface amorphization,during LSP processing of Ti alloys is reviewed.Furthermore,the en-hanced engineering performance of the L SP-processed(L SPed)Ti alloys,including surface hardness,wear resistance,fatigue life and corrosion resistance are summarized.Finally,this review concludes by present-ing an overview of the current challenges encountered in this field and offering insights into anticipated future trends.
基金supported by the National Natural Science Foundation of China(Nos.52074246,22008224,52275390,52205429,52201146)National Defense Basic Scientific Research Program of China(Nos.JCKY2020408B002,WDZC2022-12)+2 种基金Key Research and Development Program of Shanxi Province(202102050201011,2022ZDYF035)Science and Technology Major Project of Shanxi Province(20191102008,20191102007)Guiding Local Science and Technology Development Projects by the Central Government(YDZJSX2022A025,YDZJSX2021A027).
文摘The regulation of sintering temperature in spark plasma sintering enables the achievement of grain refinement,phase control,and performance enhancement in the preparation of AZ91D magnesium alloy.This study investigates the influence of sintering temperature on microstructural evolution and mechanical properties of the AZ91D alloy.Microstructural analysis was conducted using scanning electron microscopy,electron backscatter diffraction,and X-ray diffraction.Microscopic structures and mechanical behaviors were examined through hardness and tensile tests.Elevated sintering temperatures resulted in reduced secondary phase content,leading to a decrease in mechanical performance.The alloy exhibited optimal mechanical properties at 320℃.The nanoparticle coarsening process and particle evolution during sintering were simulated using phase field methods.By optimizing the sintering temperature,precise control over microstructural and textural evolution can be achieved,facilitating the attainment of desired hardness levels and mechanical properties.
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Outstanding Doctorate Dissertation Cultivation Fund of Xi'an University of Architecture and Technology(160842012)National Natural Science Foundation of China(52404409,52374401,52104382)+3 种基金China Postdoctoral Science Foundation(2024MD753961)Scientific and Technological Innovation Team Project of Shaanxi Innovation Capability Support Plan(2022TD-30)Key R&D Plan of Shaanxi Province(2023JBGS-14,2024QCYKXJ-116)Xi'an Science and Technology Plan Project(24ZDCYJSGG0043,2023JH-GXRC-0020)。
文摘Low-oxygen TZM alloy(oxygen content of 0.03vol%)was subjected to solid-solution heat treatment at various temperatures followed by quenching.Results show that the tensile strength of the alloy gradually decreases with the increase in solidsolution temperature,and the elongation first increases and then decreases.The the amount of nanoscale Ti-rich phases precipitated in low-oxygen TZM alloys gradually increases with the increase in solid-solution temperature.Special strip-shaped Ti-rich areas appear in the samples solidified at 1200 and 1300℃.The nanoscale Ti-rich phases ensure the uniform distribution of dislocations throughout TZM alloy,while significantly improving the plasticity of low-oxygen TZM alloy samples.
基金National Natural Science Foundation of China(51975286)。
文摘Fe-Mo functionally graded materials(FGMs)with different composition-change rates from 100%304 stainless steel to 100%Mo along the composition gradient direction were prepared by electron beam-directed energy deposition(EB-DED)technique,including three samples with composition mutation of 100%,composition change rate of 10%and 30%.Results show that the composition-change rate significantly affects the microstructure and mechanical properties of the samples.In the sample with abrupt change of composition,the sharp shift in composition between 304 stainless steel and Mo leads to a great difference in the microstructure and hardness near the interface between the two materials.With the increase in the number of gradient layers,the composition changes continuously along the direction of deposition height,and the microstructure morphology shows a smooth transition from 304 stainless steel to Mo,which is gradually transformed from columnar crystal to dendritic crystal.Elements Fe,Mo,and other major elements transform linearly along the gradient direction,with sufficient interlayer diffusion between the deposited layers,leading to good metallurgical bonding.The smaller the change in composition gradient,the greater the microhardness value along the deposition direction.When the composition gradient is 10%,the gradient layer exhibits higher hardness(940 HV)and excellent resistance to surface abrasion,and the overall compressive properties of the samples are better,with the compressive fracture stress in the top region reaching 750.05±14 MPa.
基金National Natural Science Foundation of China(51804097)Fundamental Research Funds for the Central Universities of China(B220202026)Changzhou Sci&Tech Program(CJ20220074)。
文摘Laser beam welding was used to join a near-β titanium alloy(Ti-3Al-6Mo-2Fe-2Zr),followed by aging treatments.The relations among aging temperature,microstructure,and tensile properties of joints were revealed.For as-welded joints,the fusion zone features primarily single β phase.It is attributed to the high Mo equivalency of this alloy and the fast cooling rate in laser beam welding.After aging treatments,many α precipitates form in the fusion zone and heat affected zone.The rising aging temperature coarsens α precipitates and reduces the volume fraction of α precipitates.Compared with the as-welded joints,the aging treated joints'tensile strength and elongation are improved.The increasing aging temperature weakens the strengthening effect because of the decreasing volume fraction of α precipitates.After the aging treatment at 500℃ for 8 h,the joints obtain the optimal match between strength and plasticity.The fracture mode of joints changes from quasi-cleavage fracture in as-welded condition to microvoid coalescence fracture after heat treatments.
基金National Natural Science Foundation of China(52075449,5197052086)。
文摘The transient liquid-phase(TLP)diffusion bonding of GH5188 with a BNi-5 interlayer was focused on.Parameters were chosen and optimized for GH5188 alloy according to the TLP joining mechanism.The microstructure evolution and mechanical properties of the joints were studied.Results show that the relatively complete isothermal solidification zone(ISZ)ensures a reliable connection of the base metal(BM).Within the temperature range of 1110–1190°C,higher bonding temperatures can widen ISZ and promote joint composition homogenization,thus improving mechanical properties.However,the increase in precipitated phase has an adverse effect on the mechanical properties of the joint.The maximum shear strength,reaching 482 MPa,is achieved at 1130°C,representing 84.6%of BM strength.Within the pressure range of 5–15 MPa,both precipitated phases in adiabatic solidification zone(ASZ)and voids generated by partial melting increase.On the contrary,their sizes decrease significantly under higher bonding pressure,resulting in an upward trend in alloy mechanical properties.The maximum shear strength of 490 MPa is attained at a bonding pressure of 15 MPa.The joint exhibits a typical mixed fracture pattern,with the small brittle M_(23)C_(6) phase and voids significantly impacting mechanical properties.Nano-indentation tests indicate that ASZ is a potential source of cracks.
基金Applied Basic Research Program of Liaoning Province(CN)(2022JH2/101300078)。
文摘Self-designed Al8Si0.4Mg0.4Fe aluminium alloy was modified with Sr,followed by solid solution and aging treatments to regulate its microstructure and mechanical/electrical properties.The results show that after the modification treatment,the room-temperature tensile strength of the alloy remains nearly unchanged,the elongation at break slightly increases from 1.82%to 3.34%,and the electrical conductivity significantly increases from 40.1%international annealed copper standard(IACS)to 42.0%IACS.After the modification,the alloy was subjected to solid solution treatment at 515℃for 8 h,followed by aging treatment at 180,200,220 and 240℃for 6 h.With increasing aging temperature,the electrical conductivity increases monotonously from 41.4%IACS to 45.5%IACS,while the room-temperature tensile strength initially increases and then decreases.At 200℃,the alloy achieves an optimal balance between electrical conductivity and room-temperature tensile strength:the electrical conductivity is 42.5%IACS,and the room-temperature tensile strength is 282.9 MPa.When the aging temperature continues to rise,the alloy undergoes overaging.Although the conductivity continues to increase,the room-temperature tensile strength drops sharply,and it is only 177.1 MPa at 240℃.
