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 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
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
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 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
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
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
For P91 steel weldment,performing post-weld heat treatment immediately after welding can enhance welding efficiency and reduce the risk of hydrogen-induced cracking.However,determining the post-weld cooling temperatur...For P91 steel weldment,performing post-weld heat treatment immediately after welding can enhance welding efficiency and reduce the risk of hydrogen-induced cracking.However,determining the post-weld cooling temperature(PWCT)is challenging due to potential impact on the mechanical properties of weldment after subsequent heat treatment.A systematic investigation is conducted to explore the effect of PWCT on the impact toughness of P91 steel welded joints.It has been demonstrated that the impact energy of the weld metal gradually increases from 40.2 to 49.5 J as the PWCT decreases from 300 to 100℃.Microstructural analysis reveals that PWCTs above 100℃ led to an increased dislocation density in the weld metal.Furthermore,in situ observations using a high-temperature confocal laser scanning microscope confirm that excessively high PWCTs result in the formation of untempered martensite after post-weld heat treatment.Such untempered martensites are identified as the primary cause of the reduced impact toughness in the weld metal.These findings underscore the importance of carefully controlling PWCT in welding procedures for P91 steel and similar grades.展开更多
Because of the large coefficient of thermal expansion (CTE) (23 ppm K^(–1)), aluminum faces challenges in meeting the demands of high dimensional stability in precision instruments, microelectronics, and aerospace. F...Because of the large coefficient of thermal expansion (CTE) (23 ppm K^(–1)), aluminum faces challenges in meeting the demands of high dimensional stability in precision instruments, microelectronics, and aerospace. Filling negative thermal expansion (NTE) particles into aluminum can create composites with either zero or low CTEs. However, the resulting composites usually have poor thermal conductivity due to their monolithic configuration, i.e., the NTE particles are filled randomly. Thus, heat sinks should be equipped to assist their usage (e.g., in thermal management). This in turn causes strong thermal stress in the packaging system owing to the high contrast in the CTEs between those monolithic composites and heat sinks typically made of copper or aluminum. Here, we propose a gradient configuration for low-CTE aluminum composite, inspired by the bamboo structure. The gradient distribution of NTE particles (Zn_(0.5)Sn_(0.3)Mn_(0.2)NMn_(3), ZSM) was obtained by laying up several layers of ZSM/Al with the ZSM fraction ranging from 0 to 28 vol.%. In the gradient composite, the CTE near room temperature varies from 3.4 pm K^(–1) on one side to 21 ppm K^(–1) on the other side. Such a gradient CTE distribution would facilitate the low-thermal-stress designs and thus help stabilize the dimension of a precision system. Furthermore, this composite has a high thermal conductivity of 130 W m^(–1) K^(–1) and strong toughness when the flexural loading is applied on the 28 vol.% ZSM/Al side. Our research provides a novel approach to designing metallic matrix composites with unprecedented performance.展开更多
Laser additive-manufactured (AM) metallic components typically have superior uniaxial tensile strength to their conventional processing counterparts. However, the strength and toughness trade-off for most AM-fabricate...Laser additive-manufactured (AM) metallic components typically have superior uniaxial tensile strength to their conventional processing counterparts. However, the strength and toughness trade-off for most AM-fabricated metallic parts remains unsolved. Generally, the heat treatment processes can enhance the elongation and toughness of as-deposited AM samples. In this work, the fracture toughness of high-power (7600 W) laser directed energy deposition Ti-6Al-4V (Ti64) + heat treatment (short as Ti64 DED-HT) samples, were studied using fracture property tests. Combining electron backscatter diffraction (EBSD), confocal laser scanning microscope, and fractal geometry theory, we investigated their fracture mechanism and proposed a new prediction model between plane-strain fracture toughness (K_(Ic)) and conventional tensile properties. The results show that the plane-strain fracture toughness value in four states (two scanning speeds and two directions) is 81.3 ± 0.7 MPa m^(1/2), higher than that of the wrought counterparts (∼65 MPa m^(1/2)). This high plane-strain fracture toughness results from the combination of relatively fine columnar β grains and coarse α laths of the deposited parts after a specific heat-treated process. Combined with a confocal laser scanning microscope and fractal geometry analysis theory, we found that the rough surface profile leads to high fractal dimension values. In addition, we proposed a modified analytical prediction model, which can effectively predict the plane-strain fracture toughness value of AM Ti64 titanium alloys. These findings provide a guideline for obtaining a high strength-toughness and reliably predicting its KIc value in AM titanium alloys.展开更多
Polyaniline(PANi)hydrogels have a wide range of applications in artificial skin,flexible robotics,and movement monitoring.Nevertheless,limited by the modulus mismatch between rigid PANi and the soft hydrogel matrix,th...Polyaniline(PANi)hydrogels have a wide range of applications in artificial skin,flexible robotics,and movement monitoring.Nevertheless,limited by the modulus mismatch between rigid PANi and the soft hydrogel matrix,the high strength and toughness of the PANi hydrogel are mutually exclusive.Although the introduction of sacrificial bonds into the hydrogel network can alleviate this contradiction to a certain extent,it always causes pronounced energy hysteresis during hydrogel deformation.Inspired by the energy storage and release of macroscopic springs,in this work,we propose a molecular entanglement approach for the fabrication of PANi hydrogels featuring high toughness and low hysteresis,where flexible poly(ethylene glycol)(PEG)is entangled with chemically cross-linked poly(acrylic acid)(PAA)as a hydrogel matrix,and rigid PANi as a conductive filler.The resultant PAA/PEG/PANi hydrogel exhibited high mechanical properties(fracture strength of 0.75 MPa and toughness of 4.81 MJ·m^(-3))and a low energy dissipation ratio(28.2%when stretching to 300%).Moreover,the PAA/PEG/PANi hydrogel possesses a good electrical response to external forces and can be employed as a strain sensor to monitor human joint movements by producing specific electrical signals.This work provides a straightforward strategy for preparing tough conductive PANi hydrogels with low hysteresis,showing potential for the development of healthcare devices.展开更多
The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input ...The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input welding of 400 kJ/cm.With increasing the Ti/N ratio from 2.7 to 5.7,the cuboid nano-sized particles are formed,and their number density increases.The area fractions of ductile intragranular acicular ferrites(IAFs)have the highest value and the area fractions of brittle microstructures of ferrite side plates and upper bainites have the lowest value in TN30 steel.With the Ti/N ratio of about 3.0,the HAZ of steel plate has the best low-temperature toughness.With increasing the Ti/N ratio from 2.7 to 5.7,the PAG sizes after the high-temperature laser scanning confocal microscopy observation decrease linearly with increasing the number densities of nano-sized particles.The PAG size of TN30 steel is between 100 and 150μm,which is conducive to the nucleation of IAFs.展开更多
Electrically conductive carbide ceramics with high hardness and fracture toughness are promising for advanced applications.However,enhancing both electrical conductivity and fracture toughness simultaneous is challeng...Electrically conductive carbide ceramics with high hardness and fracture toughness are promising for advanced applications.However,enhancing both electrical conductivity and fracture toughness simultaneous is challenging.This study reports the synthesis of(Ti_(0.2)W_(0.2)Ta_(0.2)Hf_(0.2)Mo_(0.2))C-diamond composites with varying densities using high-pressure and high-temperature(HPHT)method.The carbides are uniformly dispersed in a titanium carbide matrix,forming conductive channels that reduce resistivity to 4.6×10^(-7)W·m.These composite materials exhibit metallic conductivity with a superconducting transition at 8.5 K.Superconducting behavior may result from d-p orbital hybridization and electron-phonon coupling in transition metal carbides,such as TaC,Mo_(2)C,and MoC.Optimizing intergranular bonding improves the fracture toughness without compromising hardness.The highest indentation toughness value is 10.1±0.4 MPa·m^(1/2),a 130%increase compare to pure TiC.Enhanced toughness arises from transgranular and intergranular fracture modes,multiple crack bridging,and large-angle crack deflection,which dissipate fracture energy and inhibit crack propagation.This study introduces a novel microstructure engineering strategy for carbide ceramics to achieve superior mechanical and electrical properties.展开更多
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.
基金supported by the National Key R&D Program of China(No.2022YFE0123300)the National Natural Science Foundation of China(Nos.U20A20277 and 52474351)Major Project of Liaoning Province Innovation Consortium(No.2023JH1/11200012).
文摘For P91 steel weldment,performing post-weld heat treatment immediately after welding can enhance welding efficiency and reduce the risk of hydrogen-induced cracking.However,determining the post-weld cooling temperature(PWCT)is challenging due to potential impact on the mechanical properties of weldment after subsequent heat treatment.A systematic investigation is conducted to explore the effect of PWCT on the impact toughness of P91 steel welded joints.It has been demonstrated that the impact energy of the weld metal gradually increases from 40.2 to 49.5 J as the PWCT decreases from 300 to 100℃.Microstructural analysis reveals that PWCTs above 100℃ led to an increased dislocation density in the weld metal.Furthermore,in situ observations using a high-temperature confocal laser scanning microscope confirm that excessively high PWCTs result in the formation of untempered martensite after post-weld heat treatment.Such untempered martensites are identified as the primary cause of the reduced impact toughness in the weld metal.These findings underscore the importance of carefully controlling PWCT in welding procedures for P91 steel and similar grades.
基金supported by the National Natural Foundation of China(No.52171146)the HFIPS Director's Fund(No.BJPY2023A08)the Natural Science Foundation of Anhui Province(No.2108085ME145).
文摘Because of the large coefficient of thermal expansion (CTE) (23 ppm K^(–1)), aluminum faces challenges in meeting the demands of high dimensional stability in precision instruments, microelectronics, and aerospace. Filling negative thermal expansion (NTE) particles into aluminum can create composites with either zero or low CTEs. However, the resulting composites usually have poor thermal conductivity due to their monolithic configuration, i.e., the NTE particles are filled randomly. Thus, heat sinks should be equipped to assist their usage (e.g., in thermal management). This in turn causes strong thermal stress in the packaging system owing to the high contrast in the CTEs between those monolithic composites and heat sinks typically made of copper or aluminum. Here, we propose a gradient configuration for low-CTE aluminum composite, inspired by the bamboo structure. The gradient distribution of NTE particles (Zn_(0.5)Sn_(0.3)Mn_(0.2)NMn_(3), ZSM) was obtained by laying up several layers of ZSM/Al with the ZSM fraction ranging from 0 to 28 vol.%. In the gradient composite, the CTE near room temperature varies from 3.4 pm K^(–1) on one side to 21 ppm K^(–1) on the other side. Such a gradient CTE distribution would facilitate the low-thermal-stress designs and thus help stabilize the dimension of a precision system. Furthermore, this composite has a high thermal conductivity of 130 W m^(–1) K^(–1) and strong toughness when the flexural loading is applied on the 28 vol.% ZSM/Al side. Our research provides a novel approach to designing metallic matrix composites with unprecedented performance.
基金supported by the National Key Re-search and Development Program of China(No.2022YFB4602301)the National Natural Science Foundation of China(No.52275381)+2 种基金the Key Research and Development Program of Shaanxi Province(No.2021LLRH-08)the 73rd batch of China Postdoctoral Science Foundation General Financial Support(No.2023MD734199)the Shaanxi Provincial Natural Science Basic Research Program(No.2023-JC-QN-0551).
文摘Laser additive-manufactured (AM) metallic components typically have superior uniaxial tensile strength to their conventional processing counterparts. However, the strength and toughness trade-off for most AM-fabricated metallic parts remains unsolved. Generally, the heat treatment processes can enhance the elongation and toughness of as-deposited AM samples. In this work, the fracture toughness of high-power (7600 W) laser directed energy deposition Ti-6Al-4V (Ti64) + heat treatment (short as Ti64 DED-HT) samples, were studied using fracture property tests. Combining electron backscatter diffraction (EBSD), confocal laser scanning microscope, and fractal geometry theory, we investigated their fracture mechanism and proposed a new prediction model between plane-strain fracture toughness (K_(Ic)) and conventional tensile properties. The results show that the plane-strain fracture toughness value in four states (two scanning speeds and two directions) is 81.3 ± 0.7 MPa m^(1/2), higher than that of the wrought counterparts (∼65 MPa m^(1/2)). This high plane-strain fracture toughness results from the combination of relatively fine columnar β grains and coarse α laths of the deposited parts after a specific heat-treated process. Combined with a confocal laser scanning microscope and fractal geometry analysis theory, we found that the rough surface profile leads to high fractal dimension values. In addition, we proposed a modified analytical prediction model, which can effectively predict the plane-strain fracture toughness value of AM Ti64 titanium alloys. These findings provide a guideline for obtaining a high strength-toughness and reliably predicting its KIc value in AM titanium alloys.
基金financially supported by the Beijing Natural Science Foundation(No.L233016)。
文摘Polyaniline(PANi)hydrogels have a wide range of applications in artificial skin,flexible robotics,and movement monitoring.Nevertheless,limited by the modulus mismatch between rigid PANi and the soft hydrogel matrix,the high strength and toughness of the PANi hydrogel are mutually exclusive.Although the introduction of sacrificial bonds into the hydrogel network can alleviate this contradiction to a certain extent,it always causes pronounced energy hysteresis during hydrogel deformation.Inspired by the energy storage and release of macroscopic springs,in this work,we propose a molecular entanglement approach for the fabrication of PANi hydrogels featuring high toughness and low hysteresis,where flexible poly(ethylene glycol)(PEG)is entangled with chemically cross-linked poly(acrylic acid)(PAA)as a hydrogel matrix,and rigid PANi as a conductive filler.The resultant PAA/PEG/PANi hydrogel exhibited high mechanical properties(fracture strength of 0.75 MPa and toughness of 4.81 MJ·m^(-3))and a low energy dissipation ratio(28.2%when stretching to 300%).Moreover,the PAA/PEG/PANi hydrogel possesses a good electrical response to external forces and can be employed as a strain sensor to monitor human joint movements by producing specific electrical signals.This work provides a straightforward strategy for preparing tough conductive PANi hydrogels with low hysteresis,showing potential for the development of healthcare devices.
基金financially supported by the National Natural Science Foundation of China(52474361).
文摘The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input welding of 400 kJ/cm.With increasing the Ti/N ratio from 2.7 to 5.7,the cuboid nano-sized particles are formed,and their number density increases.The area fractions of ductile intragranular acicular ferrites(IAFs)have the highest value and the area fractions of brittle microstructures of ferrite side plates and upper bainites have the lowest value in TN30 steel.With the Ti/N ratio of about 3.0,the HAZ of steel plate has the best low-temperature toughness.With increasing the Ti/N ratio from 2.7 to 5.7,the PAG sizes after the high-temperature laser scanning confocal microscopy observation decrease linearly with increasing the number densities of nano-sized particles.The PAG size of TN30 steel is between 100 and 150μm,which is conducive to the nucleation of IAFs.
基金support from the Science and Technology Development Project of Jilin Province(Grant No.SKL202402004)the Program for the Development of Science and Technology of Jilin Province(Grant No.YDZJ202201ZYTS308)the Open Research Fund of State Key Laboratory of Inorganic Synthesis and Preparative Chemistry(Jilin University,Grant Nos.2022-16 and 2022-23).
文摘Electrically conductive carbide ceramics with high hardness and fracture toughness are promising for advanced applications.However,enhancing both electrical conductivity and fracture toughness simultaneous is challenging.This study reports the synthesis of(Ti_(0.2)W_(0.2)Ta_(0.2)Hf_(0.2)Mo_(0.2))C-diamond composites with varying densities using high-pressure and high-temperature(HPHT)method.The carbides are uniformly dispersed in a titanium carbide matrix,forming conductive channels that reduce resistivity to 4.6×10^(-7)W·m.These composite materials exhibit metallic conductivity with a superconducting transition at 8.5 K.Superconducting behavior may result from d-p orbital hybridization and electron-phonon coupling in transition metal carbides,such as TaC,Mo_(2)C,and MoC.Optimizing intergranular bonding improves the fracture toughness without compromising hardness.The highest indentation toughness value is 10.1±0.4 MPa·m^(1/2),a 130%increase compare to pure TiC.Enhanced toughness arises from transgranular and intergranular fracture modes,multiple crack bridging,and large-angle crack deflection,which dissipate fracture energy and inhibit crack propagation.This study introduces a novel microstructure engineering strategy for carbide ceramics to achieve superior mechanical and electrical properties.
