To investigate the effect of solution treatment and aging process parameters on the microstructure and mechanical properties of TB18 titanium alloy,process optimization research was conducted based on the mixed-level ...To investigate the effect of solution treatment and aging process parameters on the microstructure and mechanical properties of TB18 titanium alloy,process optimization research was conducted based on the mixed-level orthogonal experiment design of factor levels.Results show that through range analysis,the significance order of process parameters is determined as follows:solution cooling method>solution temperature>aging time>aging temperature>solution time.Considering the strength-ductility matching and engineering application requirements,the benchmark parameters are selected as solution time of 1 h,solution cooling method of air cooling(AC),aging temperature of 525℃,and aging time of 4 h.Furthermore,the effects of solution temperature in the range of 790–870℃ on the impact toughness and micro-fracture characteristics of the alloy were studied.The results reveal that the larger the area of shear lip and fibrous zone,and the smaller the area of radiation zone,the better the toughness of the alloy.With the increase in solution temperature,the length of secondary cracks on the fracture surface increases,the number of dimples increases,and the toughness is enhanced.Based on the collaborative optimization of strength and toughness,the optimal heat treatment process for TB18 alloy is determined as 870℃/1 h,AC+525℃/4 h,AC.展开更多
A polylactide(PLA)blend with simultaneous enhancement of strength,toughness,and heat resistance was successfully achieved by adding biodegradable poly(propylene carbonate)(PPC)and uniaxial pre-stretching.The effects o...A polylactide(PLA)blend with simultaneous enhancement of strength,toughness,and heat resistance was successfully achieved by adding biodegradable poly(propylene carbonate)(PPC)and uniaxial pre-stretching.The effects of the PPC content(0 wt%-50 wt%)on the phase morphology and performance of the blends before and after pre-stretching were systematically investigated.Blending PPC initially reduced the strength,modulus,and heat resistance,but pre-stretching significantly enhanced these properties.In blends containing≤30 wt%PPC,where PPC formed a well-dispersed island-like phase within the PLA matrix,pre-stretching simultaneously enhanced strength,toughness,and heat resistance.The optimized pre-stretched 70/30 PLA/PPC(ps-70/30)blend achieved exceptional performance:tensile strength increased from 66.9MPa to 84.5 MPa,elongation at break dramatically improved from 6.8%to 115.1%,impact strength reached 55.1 k J/m^(2)(far exceeding neat PLA's 3.5 k J/m^(2)),and Vicat softening temperature(VST)increased by 60.6%to 101.8℃.Notably,the ps-70/30 blend retained excellent mechanical properties even after six months of aging.These improvements were attributed to the synergistic effects of the PPC incorporation and prestretching.PPC not only promoted the high orientation of the PLA molecular chains but also facilitated the formation of a stable crystalline phase during pre-stretching,thereby enhancing both the mechanical properties and heat resistance.However,when the PPC content exceeded 30wt%,phase inversion occurred,resulting in a continuous amorphous PPC phase that degraded the overall performance.This study demonstrated that a combination of controlled PPC incorporation and pre-stretching can effectively overcome PLA's brittleness of PLA while improving its heat resistance,offering a promising strategy for developing high-performance,fully biodegradable PLA materials suitable for industrial applications.展开更多
Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed...Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed.For all of water,oil,air and furnace cooling,there is almost-complete martensite with the favorable hardenability.The increase in cooling rate mainly increases the density of dislocation and residual strain in the as-solution annealed matrix.After aging treatment,the cooling rate dominates the ratio of high-angle grain boundaries(HAGBs)instead of the size of martensite blocks.The ratio of HAGBs continuously increases with the decreased cooling rate,while the width of blocks maintains 2.40-2.49μm.Meanwhile,more reversed austenite distributes at the martensite sub-grain boundaries.By comparison,the increased rate of water cooling contributes to a favorable precipitation of NiAl with fine size and dispersive distribution caused by more accumulated internal defects of vacancies and dislocations.With the decrease of cooling rate,NiAl precipitates exhibits a similar diameter of~7 nm while a larger inter-particle distance of~22 nm.In the case of low cooling rate(oil,air and furnace),the stable precipitation strengthening effect contributes to a high yield strength of~1.3 GPa and ultimate tensile strength of~1.4 GPa.The high-ratio HAGBs,reversed austenite and NiAl precipitates with larger-interparticle distance synergistically improve the impact toughness(V-notched Charpy impact energy of 100-110 J).展开更多
In ultraviolet cured-in-place-pipe(UV-CIPP)pipeline rehabilitation,resin performance critically determines repair effectiveness.Current UV-curable resins exhibit high volatile organic compound(VOC)emissions and inadeq...In ultraviolet cured-in-place-pipe(UV-CIPP)pipeline rehabilitation,resin performance critically determines repair effectiveness.Current UV-curable resins exhibit high volatile organic compound(VOC)emissions and inadequate post-cure toughness,which compromise fatigue resistance during service.To address these issues,we synthesized hydroxyl-terminated polyurethane acrylate prepolymers using diphenylmethane diisocyanate(MDI),polypropylene glycol(PPG),and hydroxyethyl methacrylate(HEMA).Fourier transform infrared spectroscopy(FTIR)confirmed successful prepolymer synthesis.We developed UV-curable resins by incorporating various crosslinking monomers and optimized the formulations through mechanical property analysis.Testing revealed that the polyurethane-acrylic UV-cured resin system combines polyurethane's mechanical excellence with acrylics'high UV-curing activity.The PPG200/MDI/HEMA formulation achieved superior performance,with a tensile strength of 55.31 MPa,an impact toughness of 22.7 kJ/m^(2),and a heat deflection temperature(HDT)of 132℃.The optimized system eliminates volatile components while maintaining high reactivity,addressing critical limitations in trenchless pipeline rehabilitation.The improved mechanical properties meet the operational demands of underground pipes,suggesting practical applicability in trenchless pipeline repair.展开更多
Bio-based 2,5-furandicarboxylic acid polyesters offer significant promise for reducing energy and environmental crises.However,their intrinsic flammability remains a critical limitation,and conventional flame-retardan...Bio-based 2,5-furandicarboxylic acid polyesters offer significant promise for reducing energy and environmental crises.However,their intrinsic flammability remains a critical limitation,and conventional flame-retardant strategies often compromise their mechanical properties,hindering their practical applications.Herein,a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO)-based comonomer(DDP)was used to synthesize flame-retardant poly(ethylene furandicarboxylate-co-phosphaphenanthrene)(PEFDn).The covalent integration of DDP confers intrinsic flame retardancy,avoiding the plasticization and migration issues associated with additive-type systems.Upon thermal decomposition,the DOPO-derived moieties release phosphoric acid and radical scavengers,promoting char formation and suppressing flame propagation.Furthermore,density functional theory(DFT)calculations combined with non-covalent interaction(NCI)analysis revealed that DOPO dimer molecules adopt a stable parallel-displaced π-π stacking configu ration,potentially facilitating microphase separation and enhancing the energy dissipation capability.PEFD_(10)achieves a UL-94 V-0 rating while simultaneously increasing impact toughness from 1.5 kJ/m^(2) to 14.7 kJ/m^(2).Im portantly,PEFDn maintained acceptable oxygen-barrier properties.PEFD10 also exhibited high transparency and UV-shielding performance.The combination of intrinsic flame safety,im pact-toughness resistance,UV shielding,and an oxygen barrier ensures reliable protection of electrical components and long-term operational stability.The integration of multiple critical properties within a single bio-based material represents a novel approach fo r enabling sustainable polymer solutions for high-pe rformance electrical applications.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 influence of different solution and aging conditions on the microstructure,impact toughness,and crack initiation and propagation mechanisms of the novel α+β titanium alloy Ti6422 was systematically investigated....The influence of different solution and aging conditions on the microstructure,impact toughness,and crack initiation and propagation mechanisms of the novel α+β titanium alloy Ti6422 was systematically investigated.By adjusting the furnace cooling time after solution treatment and the aging temperature,Ti6422 alloy samples were developed with a multi-level lamellar microstructure,in-cluding microscaleαcolonies and α_(p) lamellae,as well as nanoscale α_(s) phases.Extending the furnace cooling time after solution treatment at 920℃ for 1 h from 240 to 540 min,followed by aging at 600℃ for 6 h,increased the α_(p) lamella content,reduced the α_(s) phase content,expanded theαcolonies and α_(p) lamellae size,and improved the impact toughness from 22.7 to 53.8 J/cm^(2).Additionally,under the same solution treatment,raising the aging temperature from 500 to 700℃ resulted in a decrease in the α_(s) phase content and a growth in the thickness of the α_(p) lamella and α_(s) phase.The impact toughness increased significantly with these changes.Samples with high α_(p) lamellae content or large α_(s) phase size exhibited high crack initiation and propagation energies.Impact deformation caused severe kinking of the α_(p) lamellae in crack initiation and propagation areas,leading to a uniform and high-density kernel average misorientation(KAM)distribu-tion,enhancing plastic deformation coordination and uniformity.Moreover,the multidirectional arrangement of coarserαcolonies and α_(p) lamellae continuously deflect the crack propagation direction,inhibiting crack propagation.展开更多
Fe-based metallic glass(MG)coatings draw great attentions due to their excellent mechanical properties.The recently developed extreme high-speed laser cladding(EHLC)provides a promising method for their fabrication bu...Fe-based metallic glass(MG)coatings draw great attentions due to their excellent mechanical properties.The recently developed extreme high-speed laser cladding(EHLC)provides a promising method for their fabrication but its application is challenged by pronounced cracking behavior.In this study,crack-free Fe-based MG coatings were prepared for the first time via EHLC.The effects of precipitated phases(i.e.,(Fe,Ni),(Fe,Ni)_(3)P and Fe_(7)C_(3))on cracking in the Fe-Ni-P-C MG coatings were investigated.展开更多
This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the pre...This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the prepared surfaces are placed on top of each other and by rolling with reduction more than 50%,the bonding between layers is established.In this research,the roll bonding process was done at room temperature,without the use of lubricants and with a 70%thickness reduction.Then,the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling.Before cold rolling,it should be noted that to decrease the hardness created due to plastic deformation,the roll-bonded samples were subjected to annealing heat treatment at 400℃for 90 min.Thus,the final samples were annealed at 200,300 and 400℃for 90 min and cooled in a furnace to examine the annealing temperature effects.The uniaxial tensile and microhardness tests measured mechanical properties.Also,to investigate the fracture mechanism,the fractography of the cross-section was examined by scanning electron microscope(SEM).To evaluate the formability of Ag/Al bilayer sheets,forming limit curves were obtained experimentally through the Nakazima test.The resistance of composites to failure due to cracking was also investigated by fracture toughness.The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reduces the ultimate tensile strength and fracture toughness.However,the changing trend is not the same at different temperatures,and according to the results,the most significant effect is obtained at 300℃and aluminum layers.It was also determined that by increasing annealing temperature,the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.展开更多
Ultra-high strength steels with a strength level of 2000 MPa are critical structural materials for some extreme service environments but face problems of low ductility and bad toughness.Current research effort s often...Ultra-high strength steels with a strength level of 2000 MPa are critical structural materials for some extreme service environments but face problems of low ductility and bad toughness.Current research effort s often focus on improving individual property,such as elongation or toughness.Therefore,it re-mains a significant challenge to unify both features of high strength,high ductility,and high toughness in one material.Adding precious metals such as Ni and Co and using aging treatment can achieve good strength and ductility in the maraging steels,but the cost is too high.In this study,we report a lean 2.4 GPa ultra-high-strength steel with a uniform elongation of 7.7%and a V-notched impact toughness of 29 J/cm^(2),which shows a competitive advantage compared with existing aircraft landing gear steels.The alloy composition design of“Mn+microalloying”and simple possessing route of quenching,deep cryo-genic treatment,and low-temperature annealing(Q-D-L)are used to achieve low-cost preparation.The transformation behaviors and mechanisms of strengthening,ductilizing,and toughening are discussed.The developed steel possesses a fine banded-equiaxed heterogeneous original austenite structure,where the CP4 occupies most of the equiaxed austenite,with more high-angle grain boundaries,and the marten-sitic variant of the banded structure is selectively weakened,resulting in a more uniform deformation,so that the crack nucleation energy and propagation energy can be simultaneously improved.Besides,the low aspect ratio structure originating from the fine parent austenite is beneficial to stimulating out-of-lath plane and in-lath plane multiple slip systems,compared with the coarse martensite with geometric lath constraints,thus increasing the deformation capability of martensite.Consequently,with the yield strength of the sample increased to 1960 MPa,the uniform elongation remained as high as 7.7%,indi-cating a notable improvement in both strength and ductility compared to samples with coarse banded austenite structures(1718 MPa&7.6%).This study provides new insights into alloy design and processing strategies for the synergistic enhancement of multiple properties in ultra-high-strength steels.展开更多
This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that ...This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.展开更多
[Objectives]To explore the mediating effect of social support between depression and resilience in elderly patients with first-episode stroke.[Methods]The general information questionnaire,PHQ-9 depression screening s...[Objectives]To explore the mediating effect of social support between depression and resilience in elderly patients with first-episode stroke.[Methods]The general information questionnaire,PHQ-9 depression screening scale,Social Support Rating scale and Connor-Davidson Resilience Scale were used to construct and test the mediation model.[Results]The total score of depressive symptoms was(8.64±3.28)points,the detection rate of depressive symptoms was 51.65%,the score of social support was(37.28±5.98)points,and the score of psychological resilience was(22.05±5.25)points.The resilience of patients was positively correlated with social support(r=0.470,P<0.01),and negatively correlated with depressive symptoms(r=-0.470,P<0.01).Social support was negatively correlated with depressive symptoms(r=-0.523,P<0.01).Social support played a partial mediating role between depression and resilience in elderly patients with first-episode stroke,and the mediating effect accounted for 16.1%of the total effect.[Conclusions]Social support can mediate the effect of depression on resilience in elderly patients with first-episode stroke.Medical staff can improve patients'psychological resilience by psychological counseling of depression and improving their social support,so as to promote their subjective well-being and maintain a healthy and positive mental state.展开更多
Coal and rock dynamic disasters are always major hidden dangers threatening mine safety production.Many researchers use cement concrete material as filling and energy-absorption materials.However,the current material ...Coal and rock dynamic disasters are always major hidden dangers threatening mine safety production.Many researchers use cement concrete material as filling and energy-absorption materials.However,the current material toughness is not sufficient to meet the requirements of mine disaster prevention.Based on this,in order to find the optimal-ratio material that combines strength and toughness,the synergistic mechanism of lithium slag(LS),ethylene-vinyl acetate(EVA)copolymer,and polyvinyl alcohol(PVA)fiber mixtures in improving the mechanical properties of cement concrete,as well as the mechanism of microscopic phase evolution,was analyzed through macroscopic experiments,mesoscopic characterization,microscopic analysis,theoretical calculations,and comprehensive evaluation.The stress-strain curves obtained from the uniaxial compressive strength tests of specimens with different admixtures and fibers were investigated,and the characteristics of different stages were analyzed.The mechanical properties of different admixtures and fiber-reinforced materials,including their advantages and disadvantages,were compared through weighted comprehensive evaluation.The entire process of material failure,ranging from pore compaction,crack initiation,crack propagation,specimen instability to crack penetration,was explained via macroscopic fracture morphology,and the mechanical mechanism of how different admixtures affect the mechanical properties of concrete materials was revealed.The microscopic mechanism and the phase-evolution process of how the admixture affects concrete properties were elucidated using X-ray diffraction(XRD),hydration reaction theory,and Fourier transform infrared spectroscopy(FTIR).Furthermore,scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS)was used to reveal the interfacial pore state and element distribution of the internal microstructure of concrete.The results show that PVA fiber bars can play the role of a“skeleton bridge”to improve the toughness of materials.LS can effectively promote the hydration process and cooperate with PVA fiber bars to enhance the mechanical properties of the material.EVA will inhibit the hydration reaction and degrade the material’s mechanical properties through the“organic isolation”effect.In addition,the on-site application has proven that the R3-group materials in this study can effectively inhibit the deformation of the roadway and possess strong reliability.Finally,the advantages and feasibility of LS-and-fiber-reinforced concrete were discussed from four perspectives:environmental protection,economy,disaster prevention,and development.This paper is expected to provide technical reference for the large-scale disposal of solid waste LS,the performance-optimization direction of concrete materials,and the prevention and control of coal and rock dynamic disasters.展开更多
The interfacial strength has a significant impact on mechanical properties of diamond composites.In this work,polycrystalline diamonds(PCDs)with medium-entropy alloy(MEA)binders and traditional Co binder were prepared...The interfacial strength has a significant impact on mechanical properties of diamond composites.In this work,polycrystalline diamonds(PCDs)with medium-entropy alloy(MEA)binders and traditional Co binder were prepared at high-pressure and high-temperature.Microstructures and interfacial strengths are carefully characterized using TEM.The results show that diamond particles are well bonded to form skeletons in all PCDs.The interfaces between MEA binders and diamond can be fully coherent.Due to the effect of Cr element and Cr-carbide,the PCD with Co_(50) Ni_(40) Fe_(10)-Cr_(3)C_(2) binder exhibits the highest interfacial bonding strength(1176.6 MPa)and highest fracture toughness(9.97 MPa m^(1/2)).The mechanical analyses indicate that both the interface and diamond skeleton have important effects on the fracture toughness of PCD.The interface with a higher bonding strength,a higher engineering strain and a higher elastic modulus can endure more stress,thereby improving the fracture toughness.展开更多
The effect ofωiso andαprecipitation on microstructure,microhardness,tensile properties and impact toughness of Ti-25Nb-10Ta-1Zr-0.2Fe(TNTZF)alloy was investigated.The results showed that the solution treated TNTZF a...The effect ofωiso andαprecipitation on microstructure,microhardness,tensile properties and impact toughness of Ti-25Nb-10Ta-1Zr-0.2Fe(TNTZF)alloy was investigated.The results showed that the solution treated TNTZF alloy with a small amount of nano-sizedωath particles inβmatrix possesses tensile strength of 697 MPa,elongation of~34%,Young’s modulus(YM)of 75 GPa,and impact toughness of 58.7 J/cm^(2).After aging at relatively lower temperatures of 400℃,the hardness and modulus of the alloy increased significantly,while the plasticity and toughness dropped sharply due to the precipitation ofωiso phase.ωiso phase displayed an ellipsoidal morphology with high volume fraction and a size of about 50 nm after aging at 400℃,leading to the highest hardness of 364 HV and YM of 108 GPa,along with completely embrittlement since elongation and toughness were almost zero.A brittle impact fracture morphology was observed in the alloy,which is dominated by intergranular fracture,with a mixed fracture characteristics of cleavage surfaces,terraces and tiny dimples.When aged at 550℃,plate-likeαdistributed inβmatrix uniformly and inβgrain boundaries in parallel,resulting in the high strength of 804 MPa,as well as lowest YM of 72 GPa,elongation of 9%and toughness of 35.8 J/cm^(2).The fracture morphology of the alloy aged at 550℃showed a ductile fracture mechanism with a large number of dimples.展开更多
The effects of isocyanate(IA)incorporation on the toughness and volume stability of AAFS were systematically investigated.Various IA dosages were introduced into AAFS,and their influence on mechanical properties,micro...The effects of isocyanate(IA)incorporation on the toughness and volume stability of AAFS were systematically investigated.Various IA dosages were introduced into AAFS,and their influence on mechanical properties,microstructure,and shrinkage behavior was evaluated.The experimental results indicate that,with the incorporation of 5%IA,the 28-day compressive strength reaches 48.6 MPa,the 56-day drying shrinkage decreases by 35.91%,and minimal cracking is observed in the ring test.Microstructural analyses using SEM,XRD,and FTIR reveal that IA reacts with water to form urethane and biuret,which crosslinks into a durable network structure.This network fills pores,reducing internal stresses and improving both toughness and volume stability.These findings offer new insights into optimizing alkali-activated materials for construction applications and provide a potential pathway for the development of more durable and stable geopolymers.展开更多
The demand for oil casing steel with ultra-high strength and excellent impact toughness for safe application in ultra-deep wells is pressing.In improving the combination of strength,ductility,and impact toughness,the ...The demand for oil casing steel with ultra-high strength and excellent impact toughness for safe application in ultra-deep wells is pressing.In improving the combination of strength,ductility,and impact toughness,the designed Cr-Mo-V micro-alloyed oil casing steel was quenched at 800,900,and 1000℃,followed by tempering at 600,680,and 760℃,respectively,to obtain distinct microstruc-tures.The results showed that the microstructure of the samples quenched at 800℃ followed by tempering comprised untransformed ferrite and large undissolved carbides,which considerably deteriorated tensile strength and impact toughness.For other conditions,the nuc-leated carbides and the boundaries are key factors that balance the tensile strength from 1226 to 971 MPa and the impact toughness from 65 to 236 J.From the perspective of carbide,optimal precipitation strengthening is achieved with a smaller carbide size obtained by a low tempering temperature of 600℃,while larger-sized carbides would remarkably soften the matrix to improve the toughness but deteriorate the tensile strength.Additionally,an increase in prior austenite grain size with the corresponding enlarged sub-boundaries obtained by high quenching temperatures substantially diminishes grain refinement strengthening,dislocation strengthening,and the energy absorbed in the crack propagation process,which is unfavorable to strength and toughness.展开更多
Impact deformation behaviors of CT20 Ti-alloy with lamellar microstructure(LM),equiaxed microstruc-ture(EM)and bimodal microstructure(BM)at 77 K were investigated systematically.The results indicated the cryogenic imp...Impact deformation behaviors of CT20 Ti-alloy with lamellar microstructure(LM),equiaxed microstruc-ture(EM)and bimodal microstructure(BM)at 77 K were investigated systematically.The results indicated the cryogenic impact toughness of the CT20 alloy with LM(∼30 J/cm^(2))is∼30%,∼11%and∼50%higher than that of EM(∼23 J/cm^(2)),BM(∼27 J/cm^(2))and Ti-6Al-4V alloy,respectively.The twinning and its syn-ergistic interactions with multiple factors are the decisive factors.The factors include fan and bifurcation twins,dislocations,α/βinterfaces,shear bands,stacking faults(SFs)and micro-cracks ultimately inducing the highest impact toughness of LM specimens.The strongest twinning induced plasticity(TWIP)effect in LM weakened the cryogenic suppression of dislocation slip and delayed the crack initiation.The EM and BM specimens exhibited higher stress peaks as finer equivalent grains.The unique<c>type dislocations and formation of SFs were found in Ti-alloy under cryogenic impact load firstly.From atomic arrange-ment,the formation mechanisms of SFs induced by consecutive Shockley and Frank partial dislocations,the twin growth mechanisms induced by boundary steps and coarsening mechanisms induced by screw dislocations were revealed.In addition,cryogenic temperature increased the risks of crack initiation and propagation during impact deformation.展开更多
The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by c...The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by comparing with traditional quenching and tempering(QT) heat treatment. Following the various QLT heat treatments, a dual-phase microstructure consisting of “soft” ferrite and “hard” tempered bainite is obtained, exhibiting significantly refined grain sizes(38.87 to 46.51 μm for QLT samples) compared to QT samples(64.93 μm). As the lamellar quenching temperature increases from 750 ℃ to 810 ℃, the yield strength and tensile strength of the QLT samples increase, although they remain lower than those of the QT samples. Conversely, elongation at fracture, reduction of area, and the product of strength and elongation synergy decrease, yet consistently exceed QT levels. Notably, the QLT samples demonstrate superior cryogenic impact toughness within the range of-80 ℃ to-120 ℃, achieving optimal values after 910 ℃ quenching + 780 ℃ lamellar quenching + 670 ℃ tempering: 215.97 J at-80 ℃, 207.80 J at-100℃, and 183.17 J at-120 ℃. This exceptional cryogenic toughness is attributed to two key mechanisms in the dual-phase microstructure:(i) a low dislocation density that suppresses crack initiation, and(ii) crack-tip passivation by soft ferrite, coupled with crack deflection and hindrance at high-angle grain boundaries(HAGBs). The results establish QLT as a viable method for enhancing cryogenic toughness in ZG14Ni3Cr1Mo V HSLA steels.展开更多
Two experimental X80 steels with different Cr contents(0.13,0.40 wt.%)were designed to study the influence of Cr content on the microstructure transformation and properties in the coarse-grained heat-affected zone by ...Two experimental X80 steels with different Cr contents(0.13,0.40 wt.%)were designed to study the influence of Cr content on the microstructure transformation and properties in the coarse-grained heat-affected zone by using a Formastor-F II thermal dilatometer and to simulate the microstructure of the subcritically reheated coarse-grained heat-affected zone(SCGHAZ)by means of the Gleeble-3500 thermal simulator,along with the scanning electron microscope,transmission electron microscope,and electron backscattering diffraction test methods to characterize the microstructures at 650℃.The findings indicate that a higher Cr content can promote the formation of bainitic ferrite(BF),while the microhardness and impact toughness of SCGHAZ are improved.Granular bainite and BF dominated the microstructures formed by the two experimental steels at 650℃,respectively.For experimental steels mainly composed of BF,they have a high proportion of high-angle grain boundaries(HAGB),and the misorientation angle of HAGB is mostly greater than 55°.Moreover,the distribution of martensite-austenite(M-A)constituents in SCGHAZ altered from dense to sparse,and the form altered from elongated to island-like when the Cr concentration was changed from 0.13 to 0.40 wt.%.Consequently,by suitably increasing the concentration of Cr,it is possible to raise the density of HAGB and improve the shape of M-A constituents,allowing SCGHAZ to have a higher toughness.展开更多
基金Key Program of National Natural Science Foundation of China(52431001)。
文摘To investigate the effect of solution treatment and aging process parameters on the microstructure and mechanical properties of TB18 titanium alloy,process optimization research was conducted based on the mixed-level orthogonal experiment design of factor levels.Results show that through range analysis,the significance order of process parameters is determined as follows:solution cooling method>solution temperature>aging time>aging temperature>solution time.Considering the strength-ductility matching and engineering application requirements,the benchmark parameters are selected as solution time of 1 h,solution cooling method of air cooling(AC),aging temperature of 525℃,and aging time of 4 h.Furthermore,the effects of solution temperature in the range of 790–870℃ on the impact toughness and micro-fracture characteristics of the alloy were studied.The results reveal that the larger the area of shear lip and fibrous zone,and the smaller the area of radiation zone,the better the toughness of the alloy.With the increase in solution temperature,the length of secondary cracks on the fracture surface increases,the number of dimples increases,and the toughness is enhanced.Based on the collaborative optimization of strength and toughness,the optimal heat treatment process for TB18 alloy is determined as 870℃/1 h,AC+525℃/4 h,AC.
基金supported by the Science and Technology Development Plan of Jilin Province(No.YDZJ202403009CGZH)Engineering Research Center of Coalbased Ecological Carbon Sequestration Technology of the Ministry of Education(No.MJST2025-1)+2 种基金Chinese Academy of Sciences(Changchun Branch)(No.2024SYHZ0038)Development and Reform Commission of Jilin Province of China(No.2024C019-5)Science and Technology Bureau of Changchun City of China(No.23SH08)。
文摘A polylactide(PLA)blend with simultaneous enhancement of strength,toughness,and heat resistance was successfully achieved by adding biodegradable poly(propylene carbonate)(PPC)and uniaxial pre-stretching.The effects of the PPC content(0 wt%-50 wt%)on the phase morphology and performance of the blends before and after pre-stretching were systematically investigated.Blending PPC initially reduced the strength,modulus,and heat resistance,but pre-stretching significantly enhanced these properties.In blends containing≤30 wt%PPC,where PPC formed a well-dispersed island-like phase within the PLA matrix,pre-stretching simultaneously enhanced strength,toughness,and heat resistance.The optimized pre-stretched 70/30 PLA/PPC(ps-70/30)blend achieved exceptional performance:tensile strength increased from 66.9MPa to 84.5 MPa,elongation at break dramatically improved from 6.8%to 115.1%,impact strength reached 55.1 k J/m^(2)(far exceeding neat PLA's 3.5 k J/m^(2)),and Vicat softening temperature(VST)increased by 60.6%to 101.8℃.Notably,the ps-70/30 blend retained excellent mechanical properties even after six months of aging.These improvements were attributed to the synergistic effects of the PPC incorporation and prestretching.PPC not only promoted the high orientation of the PLA molecular chains but also facilitated the formation of a stable crystalline phase during pre-stretching,thereby enhancing both the mechanical properties and heat resistance.However,when the PPC content exceeded 30wt%,phase inversion occurred,resulting in a continuous amorphous PPC phase that degraded the overall performance.This study demonstrated that a combination of controlled PPC incorporation and pre-stretching can effectively overcome PLA's brittleness of PLA while improving its heat resistance,offering a promising strategy for developing high-performance,fully biodegradable PLA materials suitable for industrial applications.
基金supported by the National Key Research and Development Program(Grant No.2024YFB3714200)the National Natural Science Foundation of China(Grant Nos.52173305,52233017,52203384,U244120568 and U2441261)+1 种基金the Key Program of the Chinese Academy of Sciences(Grant No.RCJJ-145-24-40)LingChuang Research Project of China National Nuclear Corporation,and Special Funds for Science and Technology Planning of Jiangsu Province(No.BZ2024059).
文摘Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed.For all of water,oil,air and furnace cooling,there is almost-complete martensite with the favorable hardenability.The increase in cooling rate mainly increases the density of dislocation and residual strain in the as-solution annealed matrix.After aging treatment,the cooling rate dominates the ratio of high-angle grain boundaries(HAGBs)instead of the size of martensite blocks.The ratio of HAGBs continuously increases with the decreased cooling rate,while the width of blocks maintains 2.40-2.49μm.Meanwhile,more reversed austenite distributes at the martensite sub-grain boundaries.By comparison,the increased rate of water cooling contributes to a favorable precipitation of NiAl with fine size and dispersive distribution caused by more accumulated internal defects of vacancies and dislocations.With the decrease of cooling rate,NiAl precipitates exhibits a similar diameter of~7 nm while a larger inter-particle distance of~22 nm.In the case of low cooling rate(oil,air and furnace),the stable precipitation strengthening effect contributes to a high yield strength of~1.3 GPa and ultimate tensile strength of~1.4 GPa.The high-ratio HAGBs,reversed austenite and NiAl precipitates with larger-interparticle distance synergistically improve the impact toughness(V-notched Charpy impact energy of 100-110 J).
基金Funded by the National Natural Science Foundation of China(No.52473077)China Three Gorges Corporation(No.202403190)。
文摘In ultraviolet cured-in-place-pipe(UV-CIPP)pipeline rehabilitation,resin performance critically determines repair effectiveness.Current UV-curable resins exhibit high volatile organic compound(VOC)emissions and inadequate post-cure toughness,which compromise fatigue resistance during service.To address these issues,we synthesized hydroxyl-terminated polyurethane acrylate prepolymers using diphenylmethane diisocyanate(MDI),polypropylene glycol(PPG),and hydroxyethyl methacrylate(HEMA).Fourier transform infrared spectroscopy(FTIR)confirmed successful prepolymer synthesis.We developed UV-curable resins by incorporating various crosslinking monomers and optimized the formulations through mechanical property analysis.Testing revealed that the polyurethane-acrylic UV-cured resin system combines polyurethane's mechanical excellence with acrylics'high UV-curing activity.The PPG200/MDI/HEMA formulation achieved superior performance,with a tensile strength of 55.31 MPa,an impact toughness of 22.7 kJ/m^(2),and a heat deflection temperature(HDT)of 132℃.The optimized system eliminates volatile components while maintaining high reactivity,addressing critical limitations in trenchless pipeline rehabilitation.The improved mechanical properties meet the operational demands of underground pipes,suggesting practical applicability in trenchless pipeline repair.
基金financially supported by the National Key Research and Development Program of China(No.2021YFB3700300)the National Natural Science Foundation of China(Nos.52573017 and U21B2093)+1 种基金Key Research and Development Program of Ningbo(No.2022Z200)the Zhejiang Provincial Natural Science Foundation(No.LY23E030005)。
文摘Bio-based 2,5-furandicarboxylic acid polyesters offer significant promise for reducing energy and environmental crises.However,their intrinsic flammability remains a critical limitation,and conventional flame-retardant strategies often compromise their mechanical properties,hindering their practical applications.Herein,a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO)-based comonomer(DDP)was used to synthesize flame-retardant poly(ethylene furandicarboxylate-co-phosphaphenanthrene)(PEFDn).The covalent integration of DDP confers intrinsic flame retardancy,avoiding the plasticization and migration issues associated with additive-type systems.Upon thermal decomposition,the DOPO-derived moieties release phosphoric acid and radical scavengers,promoting char formation and suppressing flame propagation.Furthermore,density functional theory(DFT)calculations combined with non-covalent interaction(NCI)analysis revealed that DOPO dimer molecules adopt a stable parallel-displaced π-π stacking configu ration,potentially facilitating microphase separation and enhancing the energy dissipation capability.PEFD_(10)achieves a UL-94 V-0 rating while simultaneously increasing impact toughness from 1.5 kJ/m^(2) to 14.7 kJ/m^(2).Im portantly,PEFDn maintained acceptable oxygen-barrier properties.PEFD10 also exhibited high transparency and UV-shielding performance.The combination of intrinsic flame safety,im pact-toughness resistance,UV shielding,and an oxygen barrier ensures reliable protection of electrical components and long-term operational stability.The integration of multiple critical properties within a single bio-based material represents a novel approach fo r enabling sustainable polymer solutions for high-pe rformance electrical applications.
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(No.52090041).
文摘The influence of different solution and aging conditions on the microstructure,impact toughness,and crack initiation and propagation mechanisms of the novel α+β titanium alloy Ti6422 was systematically investigated.By adjusting the furnace cooling time after solution treatment and the aging temperature,Ti6422 alloy samples were developed with a multi-level lamellar microstructure,in-cluding microscaleαcolonies and α_(p) lamellae,as well as nanoscale α_(s) phases.Extending the furnace cooling time after solution treatment at 920℃ for 1 h from 240 to 540 min,followed by aging at 600℃ for 6 h,increased the α_(p) lamella content,reduced the α_(s) phase content,expanded theαcolonies and α_(p) lamellae size,and improved the impact toughness from 22.7 to 53.8 J/cm^(2).Additionally,under the same solution treatment,raising the aging temperature from 500 to 700℃ resulted in a decrease in the α_(s) phase content and a growth in the thickness of the α_(p) lamella and α_(s) phase.The impact toughness increased significantly with these changes.Samples with high α_(p) lamellae content or large α_(s) phase size exhibited high crack initiation and propagation energies.Impact deformation caused severe kinking of the α_(p) lamellae in crack initiation and propagation areas,leading to a uniform and high-density kernel average misorientation(KAM)distribu-tion,enhancing plastic deformation coordination and uniformity.Moreover,the multidirectional arrangement of coarserαcolonies and α_(p) lamellae continuously deflect the crack propagation direction,inhibiting crack propagation.
基金financially supported by the National Natural Science Foundation of China(No.U23A20621)
文摘Fe-based metallic glass(MG)coatings draw great attentions due to their excellent mechanical properties.The recently developed extreme high-speed laser cladding(EHLC)provides a promising method for their fabrication but its application is challenged by pronounced cracking behavior.In this study,crack-free Fe-based MG coatings were prepared for the first time via EHLC.The effects of precipitated phases(i.e.,(Fe,Ni),(Fe,Ni)_(3)P and Fe_(7)C_(3))on cracking in the Fe-Ni-P-C MG coatings were investigated.
基金Project(4013311)supported by the National Science Foundation of Iran(INSF)。
文摘This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the prepared surfaces are placed on top of each other and by rolling with reduction more than 50%,the bonding between layers is established.In this research,the roll bonding process was done at room temperature,without the use of lubricants and with a 70%thickness reduction.Then,the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling.Before cold rolling,it should be noted that to decrease the hardness created due to plastic deformation,the roll-bonded samples were subjected to annealing heat treatment at 400℃for 90 min.Thus,the final samples were annealed at 200,300 and 400℃for 90 min and cooled in a furnace to examine the annealing temperature effects.The uniaxial tensile and microhardness tests measured mechanical properties.Also,to investigate the fracture mechanism,the fractography of the cross-section was examined by scanning electron microscope(SEM).To evaluate the formability of Ag/Al bilayer sheets,forming limit curves were obtained experimentally through the Nakazima test.The resistance of composites to failure due to cracking was also investigated by fracture toughness.The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reduces the ultimate tensile strength and fracture toughness.However,the changing trend is not the same at different temperatures,and according to the results,the most significant effect is obtained at 300℃and aluminum layers.It was also determined that by increasing annealing temperature,the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.
基金financially supported by the National Natural Science Foundation of China(Nos.52104371 and U21A20116)the Liaoning Province Science and Technology Plan Project(No.2022-MS-109)the State Key Laboratory of Solidification Processing in NWPU(Grant No SKLSP202311).
文摘Ultra-high strength steels with a strength level of 2000 MPa are critical structural materials for some extreme service environments but face problems of low ductility and bad toughness.Current research effort s often focus on improving individual property,such as elongation or toughness.Therefore,it re-mains a significant challenge to unify both features of high strength,high ductility,and high toughness in one material.Adding precious metals such as Ni and Co and using aging treatment can achieve good strength and ductility in the maraging steels,but the cost is too high.In this study,we report a lean 2.4 GPa ultra-high-strength steel with a uniform elongation of 7.7%and a V-notched impact toughness of 29 J/cm^(2),which shows a competitive advantage compared with existing aircraft landing gear steels.The alloy composition design of“Mn+microalloying”and simple possessing route of quenching,deep cryo-genic treatment,and low-temperature annealing(Q-D-L)are used to achieve low-cost preparation.The transformation behaviors and mechanisms of strengthening,ductilizing,and toughening are discussed.The developed steel possesses a fine banded-equiaxed heterogeneous original austenite structure,where the CP4 occupies most of the equiaxed austenite,with more high-angle grain boundaries,and the marten-sitic variant of the banded structure is selectively weakened,resulting in a more uniform deformation,so that the crack nucleation energy and propagation energy can be simultaneously improved.Besides,the low aspect ratio structure originating from the fine parent austenite is beneficial to stimulating out-of-lath plane and in-lath plane multiple slip systems,compared with the coarse martensite with geometric lath constraints,thus increasing the deformation capability of martensite.Consequently,with the yield strength of the sample increased to 1960 MPa,the uniform elongation remained as high as 7.7%,indi-cating a notable improvement in both strength and ductility compared to samples with coarse banded austenite structures(1718 MPa&7.6%).This study provides new insights into alloy design and processing strategies for the synergistic enhancement of multiple properties in ultra-high-strength steels.
基金supported by the National Natural Science Foundation of China(No.52271089)the financial support from the C hina Postdoctoral Science Foundation(No.2023M732192)。
文摘This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.
基金Supported by the National Natural Science Foundation of China(71774049).
文摘[Objectives]To explore the mediating effect of social support between depression and resilience in elderly patients with first-episode stroke.[Methods]The general information questionnaire,PHQ-9 depression screening scale,Social Support Rating scale and Connor-Davidson Resilience Scale were used to construct and test the mediation model.[Results]The total score of depressive symptoms was(8.64±3.28)points,the detection rate of depressive symptoms was 51.65%,the score of social support was(37.28±5.98)points,and the score of psychological resilience was(22.05±5.25)points.The resilience of patients was positively correlated with social support(r=0.470,P<0.01),and negatively correlated with depressive symptoms(r=-0.470,P<0.01).Social support was negatively correlated with depressive symptoms(r=-0.523,P<0.01).Social support played a partial mediating role between depression and resilience in elderly patients with first-episode stroke,and the mediating effect accounted for 16.1%of the total effect.[Conclusions]Social support can mediate the effect of depression on resilience in elderly patients with first-episode stroke.Medical staff can improve patients'psychological resilience by psychological counseling of depression and improving their social support,so as to promote their subjective well-being and maintain a healthy and positive mental state.
基金supported by the National Natural Science Foundation of China(Nos.U23B2093 and 52034009)the National Key R&D Program of China(No.2024YFC3013801)the Fundamental Research Funds for the Central Universities(Ph.D.Top Innovative Talents Fund of CUMTB)(No.BBJ2025001).
文摘Coal and rock dynamic disasters are always major hidden dangers threatening mine safety production.Many researchers use cement concrete material as filling and energy-absorption materials.However,the current material toughness is not sufficient to meet the requirements of mine disaster prevention.Based on this,in order to find the optimal-ratio material that combines strength and toughness,the synergistic mechanism of lithium slag(LS),ethylene-vinyl acetate(EVA)copolymer,and polyvinyl alcohol(PVA)fiber mixtures in improving the mechanical properties of cement concrete,as well as the mechanism of microscopic phase evolution,was analyzed through macroscopic experiments,mesoscopic characterization,microscopic analysis,theoretical calculations,and comprehensive evaluation.The stress-strain curves obtained from the uniaxial compressive strength tests of specimens with different admixtures and fibers were investigated,and the characteristics of different stages were analyzed.The mechanical properties of different admixtures and fiber-reinforced materials,including their advantages and disadvantages,were compared through weighted comprehensive evaluation.The entire process of material failure,ranging from pore compaction,crack initiation,crack propagation,specimen instability to crack penetration,was explained via macroscopic fracture morphology,and the mechanical mechanism of how different admixtures affect the mechanical properties of concrete materials was revealed.The microscopic mechanism and the phase-evolution process of how the admixture affects concrete properties were elucidated using X-ray diffraction(XRD),hydration reaction theory,and Fourier transform infrared spectroscopy(FTIR).Furthermore,scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS)was used to reveal the interfacial pore state and element distribution of the internal microstructure of concrete.The results show that PVA fiber bars can play the role of a“skeleton bridge”to improve the toughness of materials.LS can effectively promote the hydration process and cooperate with PVA fiber bars to enhance the mechanical properties of the material.EVA will inhibit the hydration reaction and degrade the material’s mechanical properties through the“organic isolation”effect.In addition,the on-site application has proven that the R3-group materials in this study can effectively inhibit the deformation of the roadway and possess strong reliability.Finally,the advantages and feasibility of LS-and-fiber-reinforced concrete were discussed from four perspectives:environmental protection,economy,disaster prevention,and development.This paper is expected to provide technical reference for the large-scale disposal of solid waste LS,the performance-optimization direction of concrete materials,and the prevention and control of coal and rock dynamic disasters.
基金financially supported by the Regional Innova-tion and Development Joint Funds of the National Natural Science Foundation of China(No.U20A20236)the Central South Univer-sity Innovation-Driven Research Programme(No.2023CXQD030)the Huaqiao University Engineering Research Center of Brittle Materials Machining(MOE,No.2023IME-002).
文摘The interfacial strength has a significant impact on mechanical properties of diamond composites.In this work,polycrystalline diamonds(PCDs)with medium-entropy alloy(MEA)binders and traditional Co binder were prepared at high-pressure and high-temperature.Microstructures and interfacial strengths are carefully characterized using TEM.The results show that diamond particles are well bonded to form skeletons in all PCDs.The interfaces between MEA binders and diamond can be fully coherent.Due to the effect of Cr element and Cr-carbide,the PCD with Co_(50) Ni_(40) Fe_(10)-Cr_(3)C_(2) binder exhibits the highest interfacial bonding strength(1176.6 MPa)and highest fracture toughness(9.97 MPa m^(1/2)).The mechanical analyses indicate that both the interface and diamond skeleton have important effects on the fracture toughness of PCD.The interface with a higher bonding strength,a higher engineering strain and a higher elastic modulus can endure more stress,thereby improving the fracture toughness.
基金supported by the Natural Science Foundation of Hunan Province(2023JJ50055,2023JJ30081)the Science Research Foundation of Hunan Provincial Education Department(21A0546)+1 种基金the Youth Project of the National Natural Science Foundation of China(62003056)the Open Fund of Hunan Engineering Research Center of Research and Development of Degradable Materials and Molding Technology(2023KFKT05).
文摘The effect ofωiso andαprecipitation on microstructure,microhardness,tensile properties and impact toughness of Ti-25Nb-10Ta-1Zr-0.2Fe(TNTZF)alloy was investigated.The results showed that the solution treated TNTZF alloy with a small amount of nano-sizedωath particles inβmatrix possesses tensile strength of 697 MPa,elongation of~34%,Young’s modulus(YM)of 75 GPa,and impact toughness of 58.7 J/cm^(2).After aging at relatively lower temperatures of 400℃,the hardness and modulus of the alloy increased significantly,while the plasticity and toughness dropped sharply due to the precipitation ofωiso phase.ωiso phase displayed an ellipsoidal morphology with high volume fraction and a size of about 50 nm after aging at 400℃,leading to the highest hardness of 364 HV and YM of 108 GPa,along with completely embrittlement since elongation and toughness were almost zero.A brittle impact fracture morphology was observed in the alloy,which is dominated by intergranular fracture,with a mixed fracture characteristics of cleavage surfaces,terraces and tiny dimples.When aged at 550℃,plate-likeαdistributed inβmatrix uniformly and inβgrain boundaries in parallel,resulting in the high strength of 804 MPa,as well as lowest YM of 72 GPa,elongation of 9%and toughness of 35.8 J/cm^(2).The fracture morphology of the alloy aged at 550℃showed a ductile fracture mechanism with a large number of dimples.
基金Funded by the National Key R&D Program of China(No.2022YFC3803400)。
文摘The effects of isocyanate(IA)incorporation on the toughness and volume stability of AAFS were systematically investigated.Various IA dosages were introduced into AAFS,and their influence on mechanical properties,microstructure,and shrinkage behavior was evaluated.The experimental results indicate that,with the incorporation of 5%IA,the 28-day compressive strength reaches 48.6 MPa,the 56-day drying shrinkage decreases by 35.91%,and minimal cracking is observed in the ring test.Microstructural analyses using SEM,XRD,and FTIR reveal that IA reacts with water to form urethane and biuret,which crosslinks into a durable network structure.This network fills pores,reducing internal stresses and improving both toughness and volume stability.These findings offer new insights into optimizing alkali-activated materials for construction applications and provide a potential pathway for the development of more durable and stable geopolymers.
基金supported from the National Nat-ural Science Foundation of China(Nos.52274342 and 52130408)the Fundamental Research Funds for the Central Universities of Central South University,China(No.1053320213826).
文摘The demand for oil casing steel with ultra-high strength and excellent impact toughness for safe application in ultra-deep wells is pressing.In improving the combination of strength,ductility,and impact toughness,the designed Cr-Mo-V micro-alloyed oil casing steel was quenched at 800,900,and 1000℃,followed by tempering at 600,680,and 760℃,respectively,to obtain distinct microstruc-tures.The results showed that the microstructure of the samples quenched at 800℃ followed by tempering comprised untransformed ferrite and large undissolved carbides,which considerably deteriorated tensile strength and impact toughness.For other conditions,the nuc-leated carbides and the boundaries are key factors that balance the tensile strength from 1226 to 971 MPa and the impact toughness from 65 to 236 J.From the perspective of carbide,optimal precipitation strengthening is achieved with a smaller carbide size obtained by a low tempering temperature of 600℃,while larger-sized carbides would remarkably soften the matrix to improve the toughness but deteriorate the tensile strength.Additionally,an increase in prior austenite grain size with the corresponding enlarged sub-boundaries obtained by high quenching temperatures substantially diminishes grain refinement strengthening,dislocation strengthening,and the energy absorbed in the crack propagation process,which is unfavorable to strength and toughness.
基金financially supported by the National Key Research and Development Program of China(No.2022YFB3705605)the Science and Technology Major Project of Shaanxi Province of China(No.2020zdzx04-01-02)+1 种基金the National Natural Science Foundation of China(No.52101122)Scholarship Fund by China Scholarship Council.
文摘Impact deformation behaviors of CT20 Ti-alloy with lamellar microstructure(LM),equiaxed microstruc-ture(EM)and bimodal microstructure(BM)at 77 K were investigated systematically.The results indicated the cryogenic impact toughness of the CT20 alloy with LM(∼30 J/cm^(2))is∼30%,∼11%and∼50%higher than that of EM(∼23 J/cm^(2)),BM(∼27 J/cm^(2))and Ti-6Al-4V alloy,respectively.The twinning and its syn-ergistic interactions with multiple factors are the decisive factors.The factors include fan and bifurcation twins,dislocations,α/βinterfaces,shear bands,stacking faults(SFs)and micro-cracks ultimately inducing the highest impact toughness of LM specimens.The strongest twinning induced plasticity(TWIP)effect in LM weakened the cryogenic suppression of dislocation slip and delayed the crack initiation.The EM and BM specimens exhibited higher stress peaks as finer equivalent grains.The unique<c>type dislocations and formation of SFs were found in Ti-alloy under cryogenic impact load firstly.From atomic arrange-ment,the formation mechanisms of SFs induced by consecutive Shockley and Frank partial dislocations,the twin growth mechanisms induced by boundary steps and coarsening mechanisms induced by screw dislocations were revealed.In addition,cryogenic temperature increased the risks of crack initiation and propagation during impact deformation.
基金supported by the Science and Technology Planning Joint Program of Liaoning Province(Applied Basic Research Project,No.2023JH2/101700054).
文摘The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by comparing with traditional quenching and tempering(QT) heat treatment. Following the various QLT heat treatments, a dual-phase microstructure consisting of “soft” ferrite and “hard” tempered bainite is obtained, exhibiting significantly refined grain sizes(38.87 to 46.51 μm for QLT samples) compared to QT samples(64.93 μm). As the lamellar quenching temperature increases from 750 ℃ to 810 ℃, the yield strength and tensile strength of the QLT samples increase, although they remain lower than those of the QT samples. Conversely, elongation at fracture, reduction of area, and the product of strength and elongation synergy decrease, yet consistently exceed QT levels. Notably, the QLT samples demonstrate superior cryogenic impact toughness within the range of-80 ℃ to-120 ℃, achieving optimal values after 910 ℃ quenching + 780 ℃ lamellar quenching + 670 ℃ tempering: 215.97 J at-80 ℃, 207.80 J at-100℃, and 183.17 J at-120 ℃. This exceptional cryogenic toughness is attributed to two key mechanisms in the dual-phase microstructure:(i) a low dislocation density that suppresses crack initiation, and(ii) crack-tip passivation by soft ferrite, coupled with crack deflection and hindrance at high-angle grain boundaries(HAGBs). The results establish QLT as a viable method for enhancing cryogenic toughness in ZG14Ni3Cr1Mo V HSLA steels.
基金support from the PipeChina Engineering Technology Innovation Co.,Ltd.(CLZB202301).
文摘Two experimental X80 steels with different Cr contents(0.13,0.40 wt.%)were designed to study the influence of Cr content on the microstructure transformation and properties in the coarse-grained heat-affected zone by using a Formastor-F II thermal dilatometer and to simulate the microstructure of the subcritically reheated coarse-grained heat-affected zone(SCGHAZ)by means of the Gleeble-3500 thermal simulator,along with the scanning electron microscope,transmission electron microscope,and electron backscattering diffraction test methods to characterize the microstructures at 650℃.The findings indicate that a higher Cr content can promote the formation of bainitic ferrite(BF),while the microhardness and impact toughness of SCGHAZ are improved.Granular bainite and BF dominated the microstructures formed by the two experimental steels at 650℃,respectively.For experimental steels mainly composed of BF,they have a high proportion of high-angle grain boundaries(HAGB),and the misorientation angle of HAGB is mostly greater than 55°.Moreover,the distribution of martensite-austenite(M-A)constituents in SCGHAZ altered from dense to sparse,and the form altered from elongated to island-like when the Cr concentration was changed from 0.13 to 0.40 wt.%.Consequently,by suitably increasing the concentration of Cr,it is possible to raise the density of HAGB and improve the shape of M-A constituents,allowing SCGHAZ to have a higher toughness.
