The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the init...The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the initial stage of high-temperature creep,two sets of dislocations with different Burgers vectors move and meet inγmatrix channels,and react to form a quadrilateral dislocation network.Andγ′phases with raft-like microstructure are generated after the formation of dislocation networks.As creep progresses,the quadrilateral dislocation network is gradually transformed into hexagonal and quadrilateral dislocation networks.During steady stage of creep,the superalloy undergoes deformation with the mechanism that a great number of dislocations slip and climb in the matrix across the raft-likeγ′phases.At the later stage of creep,the raft-likeγ′phases are sheared by dislocations at the breakage of dislocation networks,and then alternate slip occurs,which distorts and breaks the raft-likeγ′/γphases,resulting in the accumulation of micropores at the raft-likeγ′/γinterfaces and the formation of microcracks.As creep continues,the microcracks continue to expand until creep fracture occurs,which is the damage and fracture mechanism of the alloy at the later stage of creep at high temperature.展开更多
By using fatigue crack propagation testing and microstructural characterization,the crack fracture and propagation mechanisms of K4169 superalloy under various loads were investigated.The results demonstrate that the ...By using fatigue crack propagation testing and microstructural characterization,the crack fracture and propagation mechanisms of K4169 superalloy under various loads were investigated.The results demonstrate that the grain sizes of K4169 superalloy significantly increase,and the precipitation of the needle-likeδphase and the Laves phase is observed.Voids and microcracks form at location of Laves phase enrichment,creating conditions for crack propagation.By the a−N(a is the crack length,and N is the number of cycles)relationship curve,the change in the fatigue crack growth rate with the increasing number of cycles progresses through three separate stages.The fracture process of K4169 superalloy under low-stress cyclic loading(3 kN)exhibits the ductile fracture.Subsequently,the fracture process starts to change from the ductile fracture to the brittle fracture as the stress increases to 4.5 kN.In the microstructures of fractures in both stress states,intergranular propagation is the mechanism responsible for crack propagation.Moreover,the Laves phase exists near the fracture crack,which is in line with the post-service structural phenomenon.展开更多
A thorny problem in the miscible Ti/Fe system is the unavoidable formation of numerous brittle intermetallic compounds(IMCs).Adding H62 interlayer is an essential method to reduce the brittle IMCs or decrease the brit...A thorny problem in the miscible Ti/Fe system is the unavoidable formation of numerous brittle intermetallic compounds(IMCs).Adding H62 interlayer is an essential method to reduce the brittle IMCs or decrease the brittleness.A joint with good formability and tensile properties was obtained.The microstructure and element distribution of the joint were observed by metallographic microscopy,scanning electron microscopy and electron probe microanalysis.The shear resistance exhibited an initial increase,followed by a subsequent decrease,with an increase in heat input.It reached a maximum value of 2470 N at a welding energy of 267 kJ/m.The Fe-Ti brittle IMCs in TC4/DP780 joints are replaced by Fe-Cu phase and Cu-Ti phase,which reduces the brittleness at TC4/DP780 interface.The results show that the TC4/DP780 joint forms numerousα-Cu andγ-Fe solid solutions through the mutual diffusion and solid solution between H62 and TC4 layers of metals,which effectively inhibits the diffusion of Ti atoms and reduces the formation of brittle Ti-Fe IMCs.At the H62/TC4 interface,a composite layer composed of Cu-Ti IMCs and Cu-based solid solutions is formed.The composite layer grows dendritically from the TC4 alloy to the H62 interlayer.The microstructure at the TC4/DP780 interface changes from fine dendrites to coarse dendrites with the increase in Ti content and heat input.When the heat input is lower,the interfacial elements do not react sufficiently.When the heat input is excessive,microcracks appear at the TC4/DP780 interface,which limits the improvement of mechanical properties of TC4/DP780 joint.展开更多
The traditional"trial and error"microstructural control method,with high cost and low efficiency,has become a key issue restricting the development of ultra-high strength and toughness titanium alloys.This s...The traditional"trial and error"microstructural control method,with high cost and low efficiency,has become a key issue restricting the development of ultra-high strength and toughness titanium alloys.This study adopts the molybdenum equivalent(Mo_([eq]))method to rapidly design Ti-xMo-4Al-4Zr-3Nb-2Cr-1Fe alloys(x=5-9).The as-cast alloys with different Mo_([eq])exhibit a single peak of theβphase in XRD.Theβgrains of 5Mo alloy(the lowest Mo_([eq]))exhibit elongated columnar grain characteristics.As the Mo_([eq])increases,theβgrains transition towards a more equiaxed form,resulting in a decrease in aspect ratio and a reduction in grain size.As the Mo_([eq])increases,the a phase content gradually decreases and the a phase is almost unobservable in 9Mo alloy(the highest Mo_([eq])).The a phase in 5Mo alloy exhibits short rod-shaped shapes with an average length of about2.4μm,while the a phase in 6Mo alloy shows an equiaxed and short rod shapes with the smallest size.The strength,plasticity,and toughness are the lowest in 5Mo alloy,with values of 867 MPa,7.3%,and 56 MPa·m^(1/2),respectively.However,it reaches its maximum in 6Mo alloy,where the strength,plasticity,and toughness increase to 984 MPa,12.8%,and 74 MPa·m^(1/2),respectively.The mechanical properties of Ti-xMo-4Al-4Zr-3Nb-2Cr-1Fe alloys are affected mainly by solid-solution strengthening of Mo element,refinement ofβgrain,and changes inα/βphase content.This study lays a certain theoretical foundation for the theoretical research and composition development of new ultra-high strength and toughness titanium alloys.展开更多
The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural ...The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.展开更多
（TiB2＋Al2O3）/NiAl composites were synthesized by self-propagation high-temperature synthesis, and their phase compositions, microstructures and evolution modes were studied. The microstructures and shapes vary with...（TiB2＋Al2O3）/NiAl composites were synthesized by self-propagation high-temperature synthesis, and their phase compositions, microstructures and evolution modes were studied. The microstructures and shapes vary with the TiB2＋Al2O3 content in the NiAl matrix. TiB2 particles take a great variety of elementary shapes such as white bars, plates, herringbones, regular cubes and cuboids. These results outline a strategy of self-assembly processes in real time to build diversified microstructures. Some TiB2 grains in sizes of 2-5μm are embeded in Al2O3 clusters, while a small number of TiB2 particles disperse in the NiAl matrix. It is believed that the higher the TiB2＋Al2O3 content is, the more the regular shapes and homogeneous distributions of TiB2 and Al2O3 will be present in the NiAl matrix.展开更多
The surface oxidation and subsurface microstructure evolution of Alloy 690 TT can occur during partial slip fretting corrosion in high-temperature pure water.Detailed characterization methods such as laser scanning co...The surface oxidation and subsurface microstructure evolution of Alloy 690 TT can occur during partial slip fretting corrosion in high-temperature pure water.Detailed characterization methods such as laser scanning confocal microscopy,scanning electron microscopy,electron probe micro-analyzer,and transmission electron microscopy were used to reveal the related mechanism.The results showed that Cr_(2)O_(3) oxides together with a small number of spinel oxides were formed in sticking region since a small quantity of high-temperature water could pass through the gaps between the asperities to oxidize the materials.Widespread distribution of oxides in microslip region consisted of(Ni,Fe)Cr_(2)O_(4),because Ni^(2+)and Fe^(2+) ions could react with Cr_(2)O_(3) to generate a small amount of non-stoichiometric spinel oxides.The oxides around micropitting in microslip region consisted of double-layer structure.The outermost layer contained(Fe,Cr)-rich oxides due to the effect of fretting leading to mechanical mixing between Cr_(2)O_(3) and(Ni,Fe)(Fe,Cr)_(2)O_(4).The inner layer consisted of(Fe,Ni)-rich oxides owing to the consumption of Cr_(2)O_(3) by the reaction with Ni^(2+)and Fe^(2+) ions.The reciprocating motion of oxide particles in microslip region resulted in the stress-strain supporting the recrystallization for the formation and development of a tribologically transformed structure in subsurface and plowing effect by fretting in surface.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 characterization techniques were employed like transmission electron microscope,X-ray diffraction and microstructural characterization to investigate microstructural evolution and impact of precipitate-phase preci...The characterization techniques were employed like transmission electron microscope,X-ray diffraction and microstructural characterization to investigate microstructural evolution and impact of precipitate-phase precipitation on strength and toughness of a self-developed 32Si_(2)CrNi_(2)MoVNb steel during the quenching and tempering process.Research outputs indicated that the steel microstructure under the quenching state could be composed of martensite with a high dislocation density,a small amount of residual austenite,and many dispersed spherical MC carbides.In details,after tempering at 200℃,fine needle-shapedε-carbides would precipitate,which may improve yield strength and toughness of the steel.However,as compared to that after tempering at 200℃,the average length of needle-shapedε-carbides was found to increase to 144.1±4 from 134.1±3 nm after tempering at 340℃.As a result,the yield strength may increase to 1505±40 MPa,and the impact absorption energy(V-notch)may also decrease.Moreover,after tempering at 450℃,thoseε-carbides in the steel may transform into coarse rod-shaped cementite,and dislocation recoveries at such high tempering temperature may lead to decrease of strength and toughness of the steel.Finally,the following properties could be obtained:a yield strength of 1440±35 MPa,an ultimate tensile strength of 1864±50 MPa and an impact absorption energy of 45.9±4 J,by means of rational composition design and microstructural control.展开更多
With the laser remelting of cast alloys combined with non-equilibrium liquidus projection thermodynamic calculations,a high-strength and heat-resistant Al-3Fe-2Mn alloy was designed.Incorporating Mn atoms into the met...With the laser remelting of cast alloys combined with non-equilibrium liquidus projection thermodynamic calculations,a high-strength and heat-resistant Al-3Fe-2Mn alloy was designed.Incorporating Mn atoms into the metastable nanoscale Al_(6)Fe phase,occupying some lattice sites,enhances its thermal stability.Additionally,during rapid solidification of laser powder bed fusion(L-PBF),the solubility of Fe and Mn elements in the aluminum alloy increases significantly,forming a supersaturated solid solution with improved strength.This alloy demonstrates excellent processability,achieving a relative density of over 99%,and tensile strengths of 295 MPa at 200℃ and 230 MPa at 300℃.The Al-3Fe-2Mn alloy holds great potential for wide applications due to its high strength at high temperature.展开更多
Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in thi...Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in this study.The microstructure of the WE43 and CNTs/WE43 layers was systematically compared.The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment.The spot segregation composed of Mg_(24)Y_(5),CNTs,and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content.The grain growth of both types of layers underwent three stages:slow,rapid,and steady-state.The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature,resulting in a 47%increase at 510℃ and a 35%increase at 540℃ in the grain growth exponent compared to the WE43 layers at 510℃.During the subsequent aging treatment at 225℃,the precipitation sequences from plate-shaped β″to plate-shaped and globular β′ were observed in both types of layers.CNTs can facilitate an increase in the nucleation rate of precipitates,but without accelerating precipitation hardening rate.The long and short diameters of the precipitates in peak-aged state were decreased by 48.5%and 43.1%by addition of CNTs,respectively.The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment.The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.展开更多
The hot deformation behavior of the premium GH4738 alloy was investigated in the temperature range of 1313 to 1353 K at strain rates of 0.01 to 1 s^(−1)using the hot compression test.To accurately predict flow stress,...The hot deformation behavior of the premium GH4738 alloy was investigated in the temperature range of 1313 to 1353 K at strain rates of 0.01 to 1 s^(−1)using the hot compression test.To accurately predict flow stress,three novel strain compensation constitutive equations were developed and rigorously assessed.The results indicate that the power function model(correlation coefficients r=0.98544)demonstrates greater prediction accuracy compared to other functions,with a calculated average activation energy of 507.968 kJ mol−1.Additionally,electron backscattered diffraction technology and transmission electron microscopy were used to analyze the evolution of the alloy microstructure during dynamic recrystallization under different deformation conditions.The results show that under high-temperature and large deformation conditions,the dislocation density and the degree of grain rotation increase,which promotes the formation and growth of new recrystallized grains,so that recrystallization is completed when the deformation amount reaches 30%.Besides,the increase in the temperature not only enhances the thermal activation mechanism,but also improves the grain size uniformity and texture consistency.Meanwhile,the carbide inhibits grain overgrowth by pinning grain boundaries,maintaining a fine and uniform grain structure of the alloy,and thereby improving the plasticity of the material.展开更多
(TiZrHf)_(50)Ni_(30)Cu_(20-x)Co_(x)(x=2,4,6,at%)high-entropy high-temperature shape memory alloys were fabricated by watercooled copper crucible in a magnetic levitation vacuum melting furnace,and the effects of Co co...(TiZrHf)_(50)Ni_(30)Cu_(20-x)Co_(x)(x=2,4,6,at%)high-entropy high-temperature shape memory alloys were fabricated by watercooled copper crucible in a magnetic levitation vacuum melting furnace,and the effects of Co content on microstructure and mechanical properties were investigated.The results indicate that the grain size of the alloy decreases with increasing the Co content.In the as-cast state,the alloy consists primarily of the B19′phase,with a trace of B2 phase.The fracture morphology is predominantly composed of the B19′phase,whereas the B2 phase is nearly absent.Increasing the Co content or reducing the sample dimensions(d)markedly enhance the compressive strength and ductility of the alloy.When d=2 mm,the(TiZrHf)_(50)Ni_(30)Cu_(14)Co_(6) alloy demonstrates the optimal mechanical properties,achieving a compressive strength of 2142.39±1.8 MPa and a plasticity of 17.31±0.3%.The compressive cyclic test shows that with increasing the compressive strain,the residual strain of the(TiZrHf)_(50)Ni_(30)Cu_(14)Co_(6) alloy increases while the recovery ability declines.The superelastic recovery capability of the alloy is continuously enhanced.The superelastic recovery rate increases from 1.36%to 2.12%,the residual strain rate rises from 1.79%to 5.52%,the elastic recovery rate ascends from 3.86%to 7.36%,while the total recovery rate declines from 74.48%to 63.20%.展开更多
The performance of a material is directly affected by its microstructural development during the solidification phase. Discrete cellular automaton (CA) models are widelyused in materials science to simulate and predic...The performance of a material is directly affected by its microstructural development during the solidification phase. Discrete cellular automaton (CA) models are widelyused in materials science to simulate and predict microstructural growth. This review comprehensively explains the developments and applications of CA in solidification structure simulation, including the theoretical underpinnings, computational procedures, software development, and recent advances. Summarizes the potential and limitations of cellular automata in understanding microstructure evolution during solidification, explores the evolution of microstructures during solidification, and adds to our existing knowledge of cellular automaton theory. Finally, the research trend in simulating the evolution of the solidification microstructure using cellular automaton theory is explored.展开更多
The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion a...The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion at 1150℃(A3).The results show that A2 sample,extruded at 1100℃ with uniform γ+γ′duplex microstructures,demonstrates excellent hot deformation behavior at both 1050 and 1100℃.The true stress-true strain curves of A2 sample maintain a hardening-softening equilibrium over a larger strain range,with post-deformation average grain size of 5μm.The as-HIPed A1 sample and 1150℃ extruded A3 sample exhibit a softening region in deformation curves at 1050℃,and the grain microstructures reflect an incomplete recrystallized state,i.e.combination of fine recrystallized grains and initial larger grains,characterized by a necklace-like microstructure.The predominant recrystallization mechanism for these samples is strain-induced boundary migration.At 1150℃ with a strain rate of 0.001 s^(-1),the influence of the initial microstructure on hot deformation behavior and resultant microstructure is relatively less pronounced,and postdeformation microstructures are fully recrystallized grains.Fine-grained microstructures are conducive to maximizing the hot deformation potential of alloy.By judiciously adjusting deformation regimes,a fine and uniform deformed microstructure can be obtained.展开更多
Interrupted and ruptured creep tests were conducted on single crystal superalloy DD9 at 980℃/250 MPa and 1100℃/137 MPa conditions.Microstructure evolution during creep was analyzed through scanning electron microsco...Interrupted and ruptured creep tests were conducted on single crystal superalloy DD9 at 980℃/250 MPa and 1100℃/137 MPa conditions.Microstructure evolution during creep was analyzed through scanning electron microscope and transmission electron microscope.Results show that the microstructure evolutions are similar under the creep conditions of 980℃/250 MPa and 1100℃/137 MPa.Cubicalγ′phase,which is dispersedly distributed in theγmatrix,gradually evolves into a layered structure perpendicular to the stress direction.The width of theγmatrix channel along the direction parallel to the stress increases.The relationship between the increase in width of theγmatrix channel and the strain satisfies linear relationship in logarithmic form,indicating that the width of theγmatrix can be deduced via the strain under creep state.This may provide an approach to investigate the width ofγmatrix in single crystal superalloys during creep under high temperature and low stress conditions.In the early creep stage,dislocations formed in theγphase generate mutually perpendicular networks through cross-slip at theγ/γ′interface.Then,stable hexagonal dislocation networks form as a result of the coupling effects of external stress and mismatch stress at high temperatures.In the later period of creep,dislocations shear theγ′phase,ultimately causing the fracture.展开更多
The hot deformation behavior of as-extruded Ti-6554 alloy was investigated through isothermal compression at 700–950°C and 0.001–1 s^(−1).The temperature rise under different deformation conditions was calculat...The hot deformation behavior of as-extruded Ti-6554 alloy was investigated through isothermal compression at 700–950°C and 0.001–1 s^(−1).The temperature rise under different deformation conditions was calculated,and the curve was corrected.The strain compensation constitutive model of as-extruded Ti-6554 alloy based on temperature rise correction was established.The microstructure evolution under different conditions was analyzed,and the dynamic recrystallization(DRX)mechanism was revealed.The results show that the flow stress decreases with the increase in strain rate and the decrease in deformation temperature.The deformation temperature rise gradually increases with the increase in strain rate and the decrease in deformation temperature.At 700°C/1 s^(−1),the temperature rise reaches 100°C.The corrected curve value is higher than the measured value,and the strain compensation constitutive model has high prediction accuracy.The precipitation of theαphase occurs during deformation in the twophase region,which promotes DRX process of theβphase.At low strain rate,the volume fraction of dynamic recrystallization increases with the increase in deformation temperature.DRX mechanism includes continuous DRX and discontinuous DRX.展开更多
Comprehensive characterization of the high-temperature mechanical properties was conducted on two typical micro structures of the Al-Sn-Zr-Mo-Si titanium alloy—near-equiaxedαand Widmanstatten structures—at test tem...Comprehensive characterization of the high-temperature mechanical properties was conducted on two typical micro structures of the Al-Sn-Zr-Mo-Si titanium alloy—near-equiaxedαand Widmanstatten structures—at test temperatures of 700,800,and 900℃.The results demonstrate that the lamellar and acicularαphase in the Widmanstatten structure exhibits higher resistance to slip,resulting in superior high-temperature strength,particularly at 900℃,compared with the near-equiaxed structure.As thermal stabilization temperature increases,the primaryα-phase in the sample with original near-equiaxed micro structure transitions from an equiaxed morphology to a lamellar or flake shape,and the transformedβcontent diminishes,while the width of the lamellarα-phase within the transformedβincreases substantially.The microstructure of the sample with original Widmanst?tten structure demonstrates minimal change,with the initially coarse acicularαphase undergoing further growth.After theα2 phase and other precipitates form on the grain boundaries of the coarse acicularα,subsequent cracking is likely to initiate at these precipitates.The relatively straight grain-boundary crack propagation path is shorter,leading to a decrease in overall strength.The micro structures of the Al-Sn-Zr-Mo-Si titanium alloy exhibit a creep rupture time exceeding 10 h at 800℃.The creep strain exhibited by the sample with near-equiaxed micro structure is notably higher than that of the sample with Widmanstatten structure.This discrepancy can be attributed to the elevated content of lamellar and needle-likeα,which hinders the climb creep of dislocations.Moreover,the longer crack propagation path associated with the Widmanstatten microstructure contributes to considerably enhanced high-temperature creep resistance relative to the near-equiaxed structure.Furthermore,high-temperature creep endurance tests and experiments demonstrate that the Widmanstatten-structured titanium alloy meets the requirements for short-term high-temperature applications at 900℃under a stress of 20 MPa.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
The microstructure evolution and strengthening ability of natural aging(NA),delayed aging(DA),and DA after pre-aging(PDA)of Al-Mg-Si alloy were studied.Results show that small and unstable atomic clusters are generate...The microstructure evolution and strengthening ability of natural aging(NA),delayed aging(DA),and DA after pre-aging(PDA)of Al-Mg-Si alloy were studied.Results show that small and unstable atomic clusters are generated during NA,leading to the formation of low-density coarseβʺandβ′phases,thus reducing the strength of DA alloy.However,atomic clusters and GP zones with larger sizes and high Mg/Si molar ratio form during pre-aging treatment.They prevent the generation of clusters during NA and can serve as effective nucleation sites in subsequent artificial aging,which elevates the number density of fineβʺprecipitates and improves the alloy strength.After pre-aging at 175°C,the strengthening capacity of PDA alloy is restored,with hardness and yield strength reaching 95.1%and 101.9%of peak-aged alloy.展开更多
基金Guizhou Province Science and Technology Plan Project(QKHJC-ZK[2024]yiban604)Guizhou Province Science and Technology Plan Project(CXTD[2021]008)+4 种基金Bijie City Science and Technology Project(BKLH[2023]9)Technology Project of Bijie City(BKLH[2023]36)Natural Science Research Project of Guizhou Higher Education Institutions of China(QJJ[2023]047)Science and Technology Project of Guizhou Department of Transportation(2022-121-011)Sanmenxia City Science and Technology Bureau Science and Technology Research Project(2022002005)。
文摘The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the initial stage of high-temperature creep,two sets of dislocations with different Burgers vectors move and meet inγmatrix channels,and react to form a quadrilateral dislocation network.Andγ′phases with raft-like microstructure are generated after the formation of dislocation networks.As creep progresses,the quadrilateral dislocation network is gradually transformed into hexagonal and quadrilateral dislocation networks.During steady stage of creep,the superalloy undergoes deformation with the mechanism that a great number of dislocations slip and climb in the matrix across the raft-likeγ′phases.At the later stage of creep,the raft-likeγ′phases are sheared by dislocations at the breakage of dislocation networks,and then alternate slip occurs,which distorts and breaks the raft-likeγ′/γphases,resulting in the accumulation of micropores at the raft-likeγ′/γinterfaces and the formation of microcracks.As creep continues,the microcracks continue to expand until creep fracture occurs,which is the damage and fracture mechanism of the alloy at the later stage of creep at high temperature.
基金National Natural Science Foundation of China (No. 51975200)Hunan Provincial Innovation Foundation for Postgraduate,China (No. QL20220201)。
文摘By using fatigue crack propagation testing and microstructural characterization,the crack fracture and propagation mechanisms of K4169 superalloy under various loads were investigated.The results demonstrate that the grain sizes of K4169 superalloy significantly increase,and the precipitation of the needle-likeδphase and the Laves phase is observed.Voids and microcracks form at location of Laves phase enrichment,creating conditions for crack propagation.By the a−N(a is the crack length,and N is the number of cycles)relationship curve,the change in the fatigue crack growth rate with the increasing number of cycles progresses through three separate stages.The fracture process of K4169 superalloy under low-stress cyclic loading(3 kN)exhibits the ductile fracture.Subsequently,the fracture process starts to change from the ductile fracture to the brittle fracture as the stress increases to 4.5 kN.In the microstructures of fractures in both stress states,intergranular propagation is the mechanism responsible for crack propagation.Moreover,the Laves phase exists near the fracture crack,which is in line with the post-service structural phenomenon.
基金supported by the National Natural Science Foundation of China(Grant Nos.52001141 and 52475360).
文摘A thorny problem in the miscible Ti/Fe system is the unavoidable formation of numerous brittle intermetallic compounds(IMCs).Adding H62 interlayer is an essential method to reduce the brittle IMCs or decrease the brittleness.A joint with good formability and tensile properties was obtained.The microstructure and element distribution of the joint were observed by metallographic microscopy,scanning electron microscopy and electron probe microanalysis.The shear resistance exhibited an initial increase,followed by a subsequent decrease,with an increase in heat input.It reached a maximum value of 2470 N at a welding energy of 267 kJ/m.The Fe-Ti brittle IMCs in TC4/DP780 joints are replaced by Fe-Cu phase and Cu-Ti phase,which reduces the brittleness at TC4/DP780 interface.The results show that the TC4/DP780 joint forms numerousα-Cu andγ-Fe solid solutions through the mutual diffusion and solid solution between H62 and TC4 layers of metals,which effectively inhibits the diffusion of Ti atoms and reduces the formation of brittle Ti-Fe IMCs.At the H62/TC4 interface,a composite layer composed of Cu-Ti IMCs and Cu-based solid solutions is formed.The composite layer grows dendritically from the TC4 alloy to the H62 interlayer.The microstructure at the TC4/DP780 interface changes from fine dendrites to coarse dendrites with the increase in Ti content and heat input.When the heat input is lower,the interfacial elements do not react sufficiently.When the heat input is excessive,microcracks appear at the TC4/DP780 interface,which limits the improvement of mechanical properties of TC4/DP780 joint.
基金the financial support by the National Natural Science Foundation of China(Nos.U21A2042,52425401,U2441255,52474377)the Major Science and Technology Achievement Transformation Project in Heilongjiang Province(No.ZC2023SH0075)the Henan Provincial Key Research and Development&Promotion Special Program(No.251111231400)。
文摘The traditional"trial and error"microstructural control method,with high cost and low efficiency,has become a key issue restricting the development of ultra-high strength and toughness titanium alloys.This study adopts the molybdenum equivalent(Mo_([eq]))method to rapidly design Ti-xMo-4Al-4Zr-3Nb-2Cr-1Fe alloys(x=5-9).The as-cast alloys with different Mo_([eq])exhibit a single peak of theβphase in XRD.Theβgrains of 5Mo alloy(the lowest Mo_([eq]))exhibit elongated columnar grain characteristics.As the Mo_([eq])increases,theβgrains transition towards a more equiaxed form,resulting in a decrease in aspect ratio and a reduction in grain size.As the Mo_([eq])increases,the a phase content gradually decreases and the a phase is almost unobservable in 9Mo alloy(the highest Mo_([eq])).The a phase in 5Mo alloy exhibits short rod-shaped shapes with an average length of about2.4μm,while the a phase in 6Mo alloy shows an equiaxed and short rod shapes with the smallest size.The strength,plasticity,and toughness are the lowest in 5Mo alloy,with values of 867 MPa,7.3%,and 56 MPa·m^(1/2),respectively.However,it reaches its maximum in 6Mo alloy,where the strength,plasticity,and toughness increase to 984 MPa,12.8%,and 74 MPa·m^(1/2),respectively.The mechanical properties of Ti-xMo-4Al-4Zr-3Nb-2Cr-1Fe alloys are affected mainly by solid-solution strengthening of Mo element,refinement ofβgrain,and changes inα/βphase content.This study lays a certain theoretical foundation for the theoretical research and composition development of new ultra-high strength and toughness titanium alloys.
基金supported by the National Natural Science Foundation of China (Nos. 52075449, 51975480)。
文摘The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.
基金Project(51272141)supported by the National Natural Science Foundation of ChinaProject(ts20110828)supported by the Taishan Scholars Project of Shandong Province,ChinaProject(2015AA034404)supported by the Ministry of Science and Technology of China
文摘（TiB2＋Al2O3）/NiAl composites were synthesized by self-propagation high-temperature synthesis, and their phase compositions, microstructures and evolution modes were studied. The microstructures and shapes vary with the TiB2＋Al2O3 content in the NiAl matrix. TiB2 particles take a great variety of elementary shapes such as white bars, plates, herringbones, regular cubes and cuboids. These results outline a strategy of self-assembly processes in real time to build diversified microstructures. Some TiB2 grains in sizes of 2-5μm are embeded in Al2O3 clusters, while a small number of TiB2 particles disperse in the NiAl matrix. It is believed that the higher the TiB2＋Al2O3 content is, the more the regular shapes and homogeneous distributions of TiB2 and Al2O3 will be present in the NiAl matrix.
基金financial supports of the Beijing Natural Science Foundation(Grant No.2194081)the Project funded by China Postdoctoral Science Foundation(Grant No.2018M641187)the Fundamental Research Funds for the Central Universities(Grant No.FRF-TP-18-047A1)。
文摘The surface oxidation and subsurface microstructure evolution of Alloy 690 TT can occur during partial slip fretting corrosion in high-temperature pure water.Detailed characterization methods such as laser scanning confocal microscopy,scanning electron microscopy,electron probe micro-analyzer,and transmission electron microscopy were used to reveal the related mechanism.The results showed that Cr_(2)O_(3) oxides together with a small number of spinel oxides were formed in sticking region since a small quantity of high-temperature water could pass through the gaps between the asperities to oxidize the materials.Widespread distribution of oxides in microslip region consisted of(Ni,Fe)Cr_(2)O_(4),because Ni^(2+)and Fe^(2+) ions could react with Cr_(2)O_(3) to generate a small amount of non-stoichiometric spinel oxides.The oxides around micropitting in microslip region consisted of double-layer structure.The outermost layer contained(Fe,Cr)-rich oxides due to the effect of fretting leading to mechanical mixing between Cr_(2)O_(3) and(Ni,Fe)(Fe,Cr)_(2)O_(4).The inner layer consisted of(Fe,Ni)-rich oxides owing to the consumption of Cr_(2)O_(3) by the reaction with Ni^(2+)and Fe^(2+) ions.The reciprocating motion of oxide particles in microslip region resulted in the stress-strain supporting the recrystallization for the formation and development of a tribologically transformed structure in subsurface and plowing effect by fretting in surface.
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the National Natural Science Foundation of China(Key Program)(52031004).
文摘The characterization techniques were employed like transmission electron microscope,X-ray diffraction and microstructural characterization to investigate microstructural evolution and impact of precipitate-phase precipitation on strength and toughness of a self-developed 32Si_(2)CrNi_(2)MoVNb steel during the quenching and tempering process.Research outputs indicated that the steel microstructure under the quenching state could be composed of martensite with a high dislocation density,a small amount of residual austenite,and many dispersed spherical MC carbides.In details,after tempering at 200℃,fine needle-shapedε-carbides would precipitate,which may improve yield strength and toughness of the steel.However,as compared to that after tempering at 200℃,the average length of needle-shapedε-carbides was found to increase to 144.1±4 from 134.1±3 nm after tempering at 340℃.As a result,the yield strength may increase to 1505±40 MPa,and the impact absorption energy(V-notch)may also decrease.Moreover,after tempering at 450℃,thoseε-carbides in the steel may transform into coarse rod-shaped cementite,and dislocation recoveries at such high tempering temperature may lead to decrease of strength and toughness of the steel.Finally,the following properties could be obtained:a yield strength of 1440±35 MPa,an ultimate tensile strength of 1864±50 MPa and an impact absorption energy of 45.9±4 J,by means of rational composition design and microstructural control.
基金supported by the National Natural Science Foundation of China(No.U21B2073)the Science and Technology Project of the Science and Technology Department of Hubei Province,China(No.2022EHB020)。
文摘With the laser remelting of cast alloys combined with non-equilibrium liquidus projection thermodynamic calculations,a high-strength and heat-resistant Al-3Fe-2Mn alloy was designed.Incorporating Mn atoms into the metastable nanoscale Al_(6)Fe phase,occupying some lattice sites,enhances its thermal stability.Additionally,during rapid solidification of laser powder bed fusion(L-PBF),the solubility of Fe and Mn elements in the aluminum alloy increases significantly,forming a supersaturated solid solution with improved strength.This alloy demonstrates excellent processability,achieving a relative density of over 99%,and tensile strengths of 295 MPa at 200℃ and 230 MPa at 300℃.The Al-3Fe-2Mn alloy holds great potential for wide applications due to its high strength at high temperature.
基金supported by the National Natural Science Foundation of China(52005264).
文摘Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in this study.The microstructure of the WE43 and CNTs/WE43 layers was systematically compared.The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment.The spot segregation composed of Mg_(24)Y_(5),CNTs,and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content.The grain growth of both types of layers underwent three stages:slow,rapid,and steady-state.The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature,resulting in a 47%increase at 510℃ and a 35%increase at 540℃ in the grain growth exponent compared to the WE43 layers at 510℃.During the subsequent aging treatment at 225℃,the precipitation sequences from plate-shaped β″to plate-shaped and globular β′ were observed in both types of layers.CNTs can facilitate an increase in the nucleation rate of precipitates,but without accelerating precipitation hardening rate.The long and short diameters of the precipitates in peak-aged state were decreased by 48.5%and 43.1%by addition of CNTs,respectively.The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment.The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.
基金supported by the National Key R&D Program of China(No.2021YFB3700403).
文摘The hot deformation behavior of the premium GH4738 alloy was investigated in the temperature range of 1313 to 1353 K at strain rates of 0.01 to 1 s^(−1)using the hot compression test.To accurately predict flow stress,three novel strain compensation constitutive equations were developed and rigorously assessed.The results indicate that the power function model(correlation coefficients r=0.98544)demonstrates greater prediction accuracy compared to other functions,with a calculated average activation energy of 507.968 kJ mol−1.Additionally,electron backscattered diffraction technology and transmission electron microscopy were used to analyze the evolution of the alloy microstructure during dynamic recrystallization under different deformation conditions.The results show that under high-temperature and large deformation conditions,the dislocation density and the degree of grain rotation increase,which promotes the formation and growth of new recrystallized grains,so that recrystallization is completed when the deformation amount reaches 30%.Besides,the increase in the temperature not only enhances the thermal activation mechanism,but also improves the grain size uniformity and texture consistency.Meanwhile,the carbide inhibits grain overgrowth by pinning grain boundaries,maintaining a fine and uniform grain structure of the alloy,and thereby improving the plasticity of the material.
基金National Natural Science Foundation of China(12404230,52061027)Science and Technology Program Project of Gansu Province(22YF7GA155)+1 种基金Lanzhou Youth Science and Technology Talent Innovation Project(2023-QN-91)Zhejiang Provincial Natural Science Foundation of China(LY23E010002)。
文摘(TiZrHf)_(50)Ni_(30)Cu_(20-x)Co_(x)(x=2,4,6,at%)high-entropy high-temperature shape memory alloys were fabricated by watercooled copper crucible in a magnetic levitation vacuum melting furnace,and the effects of Co content on microstructure and mechanical properties were investigated.The results indicate that the grain size of the alloy decreases with increasing the Co content.In the as-cast state,the alloy consists primarily of the B19′phase,with a trace of B2 phase.The fracture morphology is predominantly composed of the B19′phase,whereas the B2 phase is nearly absent.Increasing the Co content or reducing the sample dimensions(d)markedly enhance the compressive strength and ductility of the alloy.When d=2 mm,the(TiZrHf)_(50)Ni_(30)Cu_(14)Co_(6) alloy demonstrates the optimal mechanical properties,achieving a compressive strength of 2142.39±1.8 MPa and a plasticity of 17.31±0.3%.The compressive cyclic test shows that with increasing the compressive strain,the residual strain of the(TiZrHf)_(50)Ni_(30)Cu_(14)Co_(6) alloy increases while the recovery ability declines.The superelastic recovery capability of the alloy is continuously enhanced.The superelastic recovery rate increases from 1.36%to 2.12%,the residual strain rate rises from 1.79%to 5.52%,the elastic recovery rate ascends from 3.86%to 7.36%,while the total recovery rate declines from 74.48%to 63.20%.
文摘The performance of a material is directly affected by its microstructural development during the solidification phase. Discrete cellular automaton (CA) models are widelyused in materials science to simulate and predict microstructural growth. This review comprehensively explains the developments and applications of CA in solidification structure simulation, including the theoretical underpinnings, computational procedures, software development, and recent advances. Summarizes the potential and limitations of cellular automata in understanding microstructure evolution during solidification, explores the evolution of microstructures during solidification, and adds to our existing knowledge of cellular automaton theory. Finally, the research trend in simulating the evolution of the solidification microstructure using cellular automaton theory is explored.
基金Shenzhen Science and Technology Program(KJZD20230923113900001)Project of Industry and Information Technology Bureau of Shenzhen Municipality(201806071403422960)。
文摘The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion at 1150℃(A3).The results show that A2 sample,extruded at 1100℃ with uniform γ+γ′duplex microstructures,demonstrates excellent hot deformation behavior at both 1050 and 1100℃.The true stress-true strain curves of A2 sample maintain a hardening-softening equilibrium over a larger strain range,with post-deformation average grain size of 5μm.The as-HIPed A1 sample and 1150℃ extruded A3 sample exhibit a softening region in deformation curves at 1050℃,and the grain microstructures reflect an incomplete recrystallized state,i.e.combination of fine recrystallized grains and initial larger grains,characterized by a necklace-like microstructure.The predominant recrystallization mechanism for these samples is strain-induced boundary migration.At 1150℃ with a strain rate of 0.001 s^(-1),the influence of the initial microstructure on hot deformation behavior and resultant microstructure is relatively less pronounced,and postdeformation microstructures are fully recrystallized grains.Fine-grained microstructures are conducive to maximizing the hot deformation potential of alloy.By judiciously adjusting deformation regimes,a fine and uniform deformed microstructure can be obtained.
文摘Interrupted and ruptured creep tests were conducted on single crystal superalloy DD9 at 980℃/250 MPa and 1100℃/137 MPa conditions.Microstructure evolution during creep was analyzed through scanning electron microscope and transmission electron microscope.Results show that the microstructure evolutions are similar under the creep conditions of 980℃/250 MPa and 1100℃/137 MPa.Cubicalγ′phase,which is dispersedly distributed in theγmatrix,gradually evolves into a layered structure perpendicular to the stress direction.The width of theγmatrix channel along the direction parallel to the stress increases.The relationship between the increase in width of theγmatrix channel and the strain satisfies linear relationship in logarithmic form,indicating that the width of theγmatrix can be deduced via the strain under creep state.This may provide an approach to investigate the width ofγmatrix in single crystal superalloys during creep under high temperature and low stress conditions.In the early creep stage,dislocations formed in theγphase generate mutually perpendicular networks through cross-slip at theγ/γ′interface.Then,stable hexagonal dislocation networks form as a result of the coupling effects of external stress and mismatch stress at high temperatures.In the later period of creep,dislocations shear theγ′phase,ultimately causing the fracture.
基金National Key R&D Program of China(2022YFB3706901)National Natural Science Foundation of China(52274382)Key Research and Development Program of Hubei Province(2022BAA024)。
文摘The hot deformation behavior of as-extruded Ti-6554 alloy was investigated through isothermal compression at 700–950°C and 0.001–1 s^(−1).The temperature rise under different deformation conditions was calculated,and the curve was corrected.The strain compensation constitutive model of as-extruded Ti-6554 alloy based on temperature rise correction was established.The microstructure evolution under different conditions was analyzed,and the dynamic recrystallization(DRX)mechanism was revealed.The results show that the flow stress decreases with the increase in strain rate and the decrease in deformation temperature.The deformation temperature rise gradually increases with the increase in strain rate and the decrease in deformation temperature.At 700°C/1 s^(−1),the temperature rise reaches 100°C.The corrected curve value is higher than the measured value,and the strain compensation constitutive model has high prediction accuracy.The precipitation of theαphase occurs during deformation in the twophase region,which promotes DRX process of theβphase.At low strain rate,the volume fraction of dynamic recrystallization increases with the increase in deformation temperature.DRX mechanism includes continuous DRX and discontinuous DRX.
基金funding received from the National Key R&D Program of China(No.2022YFB3705600)。
文摘Comprehensive characterization of the high-temperature mechanical properties was conducted on two typical micro structures of the Al-Sn-Zr-Mo-Si titanium alloy—near-equiaxedαand Widmanstatten structures—at test temperatures of 700,800,and 900℃.The results demonstrate that the lamellar and acicularαphase in the Widmanstatten structure exhibits higher resistance to slip,resulting in superior high-temperature strength,particularly at 900℃,compared with the near-equiaxed structure.As thermal stabilization temperature increases,the primaryα-phase in the sample with original near-equiaxed micro structure transitions from an equiaxed morphology to a lamellar or flake shape,and the transformedβcontent diminishes,while the width of the lamellarα-phase within the transformedβincreases substantially.The microstructure of the sample with original Widmanst?tten structure demonstrates minimal change,with the initially coarse acicularαphase undergoing further growth.After theα2 phase and other precipitates form on the grain boundaries of the coarse acicularα,subsequent cracking is likely to initiate at these precipitates.The relatively straight grain-boundary crack propagation path is shorter,leading to a decrease in overall strength.The micro structures of the Al-Sn-Zr-Mo-Si titanium alloy exhibit a creep rupture time exceeding 10 h at 800℃.The creep strain exhibited by the sample with near-equiaxed micro structure is notably higher than that of the sample with Widmanstatten structure.This discrepancy can be attributed to the elevated content of lamellar and needle-likeα,which hinders the climb creep of dislocations.Moreover,the longer crack propagation path associated with the Widmanstatten microstructure contributes to considerably enhanced high-temperature creep resistance relative to the near-equiaxed structure.Furthermore,high-temperature creep endurance tests and experiments demonstrate that the Widmanstatten-structured titanium alloy meets the requirements for short-term high-temperature applications at 900℃under a stress of 20 MPa.
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supported by the National Natural Science Foundation of China(No.52261007)the Science and Technology Project of Guangxi,China(No.GKAD22035039)the Opening Fund for Key Laboratory of New Processing Technology for Nonferrous Metal&Materials,Ministry of Education,Guilin University of Technology,China(Nos.22KF-11,22KF-14).
文摘The microstructure evolution and strengthening ability of natural aging(NA),delayed aging(DA),and DA after pre-aging(PDA)of Al-Mg-Si alloy were studied.Results show that small and unstable atomic clusters are generated during NA,leading to the formation of low-density coarseβʺandβ′phases,thus reducing the strength of DA alloy.However,atomic clusters and GP zones with larger sizes and high Mg/Si molar ratio form during pre-aging treatment.They prevent the generation of clusters during NA and can serve as effective nucleation sites in subsequent artificial aging,which elevates the number density of fineβʺprecipitates and improves the alloy strength.After pre-aging at 175°C,the strengthening capacity of PDA alloy is restored,with hardness and yield strength reaching 95.1%and 101.9%of peak-aged alloy.
