Additive manufacturing(AM)of SiC_(P)/Al composites has shown significant potential for expanding the application of aluminum matrix composites(AMCs)due to their outstanding mechanical properties and wear performance.H...Additive manufacturing(AM)of SiC_(P)/Al composites has shown significant potential for expanding the application of aluminum matrix composites(AMCs)due to their outstanding mechanical properties and wear performance.However,conventional mechanically mixed powders for AM are limited due to the possible powder agglomeration and poor fluidity.In this study,the spherical SiC_(P)/AlSi10Mg composite powders prepared by spray granulation were employed to fabricate SiC_(P)-reinforced AlSi10Mg composites using laser powder bed fusion(LPBF).The impacts of laser power on microstructure evolution and wear properties of composites were systematically investigated.The results indicated that an in-situ reaction between the aluminum matrix and SiC_(P)during the LpBF process,resulted in the formation of particle-like and strip-like strengthening phase Al_(4)SiC_(4).By adjusting the laser power(from 270 W to 350 W)to change the ratio of SiC_(P)to Al_(4)SiC_(4),micro-defects could be effectively limited,and wear performance could be improved.Consequently,with an optimized ratio of SiC_(P)to Al_(4)SiC_(4),the composite exhibited a mixed strengthening mechanism caused by the SiC_(P)and Al_(4)SiC_(4)reinforcing phases.At a laser power of 310 W,the sample exhibited minimal porosity with a microhardness value reaching 265.38HV,while maintaining relatively low average friction coefficient and wear rate.In addition,compared with other studies,the hardness obtained was superior to that of the AlSi10Mg and other reported SiC_(P)/AlSi10Mg composites with similar volume fractions using the mixed powders.展开更多
In order to improve the efficient and high-value recycling utilization rate of waste red bricks from construction waste,this study crushed and ground the waste red bricks to produce recycled brick powder(RBP)with diff...In order to improve the efficient and high-value recycling utilization rate of waste red bricks from construction waste,this study crushed and ground the waste red bricks to produce recycled brick powder(RBP)with different fineness,used the Andreasen model to explore the influence of RBP on the compact filling effect of cementitious material system based on the basic characteristics of RBP.The influence of grinding time(10,20,30 min)and content(0%,5%,10%,15%,20%)of RBP on the macroscopic mechanical properties of cementitious materials was investigated.We analyzed the significant impact of RBP particle characteristics on the compressive strength of the specimen with the aid of grey entropy theory,and revealed the influence mechanism of RBP on the microstructure of cementitious materials by scanning electron microscope(SEM)and nuclear magnetic resonance(NMR).The results show that the fineness of RBP after grinding is smaller than that of cement.The fineness of recycled brick powder increases gradually with the extension of grinding time,which is manifested as the increase of<3μm particles and the decrease of>18μm particles.Compared with the unitary cement cementitious material system,the particle gradation of the RBP-cement binary cementitious material system is closer to the closest packing state.With the increase of RBP content and grinding time,the compactness of the binary cementitious system gradually decreases,indicating that the incorporation of RBP reduces the mechanical strength of the specimen.The results of grey entropy show that the specific surface area D(0.1)and<45μm particles are the significant factors affecting the mechanical properties of cementitious materials mixed with RBP.RBP mainly affects the macroscopic properties of cementitious materials by affecting the internal compactness,the number of hydration products and the pore structure.The results of SEM show that when the RBP content is less than 15%,the content of C-S-H in cement paste increase,and the content of Ca(OH)2 decreases,and the content of C-S-H decreases and the content of Ca(OH)2 increases when the RBP content is more than 15%.The NMR results show that with the extension of grinding time,the pore size of micropore increases gradually,that of middle-small pores decreases gradually,and that of large pores remains unchanged.With the increase of RBP content,the micropores first decrease and then increase,and the middle-small pores and large pores gradually decrease.In summary,the compactness of cementitious material system can be improved by adjusting the fineness of RBP.Considering the performance of cementitious materials and the utilization rate of RBP,it is recommended that the grinding time of RBP is 20 min and the content is 10%-15%.展开更多
Improving the high-temperature performance of Inconel 718(IN718)alloys manufactured via laser powder bed fusion(LPBF)has been the most concerned issue in the industry.In this study,the effects of Ti_(2)AlC inoculants ...Improving the high-temperature performance of Inconel 718(IN718)alloys manufactured via laser powder bed fusion(LPBF)has been the most concerned issue in the industry.In this study,the effects of Ti_(2)AlC inoculants on microstructures and high-temperature mechanical properties of the as-built IN718 composites were investigated.According to statistical results of relative density and unmelted particle area in as-built alloys,the optimal energy of 112 J/mm^(3)was determined.It was observed that the precipitation of the MC carbide was significantly enhanced with the addition of Ti_(2)AlC,restricting the precipitation of the Laves phase.The MC particles were uniformly distributed along the subgrain boundaries,which contributed to the dispersion strengthening.Meanwhile,the MC particles served as nucleation sites for heterogeneous nucleation during the solidification process,facilitating the refinement of columnar and cellular grains.The simulated Scheil-Gulliver curves showed that the precipitation sequence of phases did not change with Ti_(2)AlC inoculants.The as-built 1%Ti_(2)AlC/IN718 sample demonstrated an ultimate tensile strength of 998.78 MPa and an elongation of 18.04%at 650℃,revealing a markedly improved mechanical performance compared with the LPBF-manufactured IN718 alloys.The high-temperature tensile strength of 1%Ti_(2)AlC/IN718 sample increased to 1197.99 MPa by heat treatment.It was suggested that dislocation strengthening and ordered strengthening were two most important reinforcement mechanisms.展开更多
GF/Pb compositeswerefabricated by the method of powder metallurgy, and the density, microstructure and tensile propertywerecharacterized considering the size and content ofglass fibre （GF）. The results show that rel...GF/Pb compositeswerefabricated by the method of powder metallurgy, and the density, microstructure and tensile propertywerecharacterized considering the size and content ofglass fibre （GF）. The results show that relative densities decrease with increasing GF fraction, and the 50μm-GF reinforced specimens exhibit a better densification than the 300μm-GF reinforced ones. The GF particles distribute quite uniformly inPb matrix, and the composites fabricated at low sintering temperature （〈200℃） possess fine-grain microstructure. The addition of GF significantly improves the strength of the Pb composites, and the ultimate tensile strength of the Pb composite reinforcedwith the addition of 50μm-0.5% GF（mass fraction）is about 30MPa higher than that of GF-free sample. For all composites groups, increasing the reinforcement content from 0.5%to 2%（mass fraction）results in a decrease in both tensile strength and ductility.展开更多
To enhance the mechanical properties of Mo alloys prepared through laser powder bed fusion(LPBF),a hot isostatic pressing(HIP)treatment was used.Results show that following HIP treatment,the porosity decreases from 0....To enhance the mechanical properties of Mo alloys prepared through laser powder bed fusion(LPBF),a hot isostatic pressing(HIP)treatment was used.Results show that following HIP treatment,the porosity decreases from 0.27%to 0.22%,enabling the elements Mo and Ti to diffuse fully and to distribute more uniformly,and to forming a substantial number of low-angle grain boundaries.The tensile strength soars from 286±32 MPa to 598±22 MPa,while the elongation increases from 0.08%±0.02%to 0.18%±0.02%,without notable alterations in grain morphology during the tensile deformation.HIP treatment eliminates the molten pool boundaries,which are the primary source for premature failure in LPBFed Mo alloys.Consequently,HIP treatment emerges as a novel and effective approach for strengthening the mechanical properties of LPBFed Mo alloys,offering a fresh perspective on producing high-performance Mo-based alloys.展开更多
This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensit...This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing(AM) utilizing electron-beam powder bed fusion(EPBF). The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes[100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L stainless-steel.In addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm^2, and a homogeneous distribution of Cr_(23)C_6 precipitates. Precipitates were formed within the grains(with ~3 μm interparticle spacing),but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainlesssteel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685?C for50 h precipitated Cr_(23)C_6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle(and low energy) subgrain boundaries. In contrast, Cr_(23)C_6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy coherent {111} twin boundaries. Consequently, the Inconel690 subgrain boundaries essentially serve as surrogates for coherent twin boundaries with regard to avoiding carbide precipitation and corrosion sensitization.展开更多
Selective laser melting(SLM)technology is the prevailing method of manufacturing components with complex geometries.However,the cost of the additive manufacturing(AM)fine powder is relatively high,which significantly ...Selective laser melting(SLM)technology is the prevailing method of manufacturing components with complex geometries.However,the cost of the additive manufacturing(AM)fine powder is relatively high,which significantly limits the development of the SLM.In this study,the 316L fine powder and coarse powder with a mass ratio of 80:20,70:30 and 60:40 were mixed using a ball milling and the samples with a relative density greater than 97%were prepared by SLM.The results show that the intricate temperature gradients and surface tension gradients in SLM will produce Marangoni flow,forming a typical molten pool morphology,cellular and strip subgrain structures.And as the proportion of coarse powder increases,the scanning track morphology changes from smooth to undulating;the morphology of the molten pool and subgrain structure are weakened.Meanwhile,the unmelted particles appear on the surface of the SLM sample.On the premise of an introducing appropriate amount of large particle size powder(20%),the SLM samples still have good mechanical properties(662 MPa,47%).展开更多
To reduce geological disasters caused by expansive soil,it is crucial to use a new type of modified material to rapidly improve soil strength instead of traditional soil improvement materials such as lime and cement.N...To reduce geological disasters caused by expansive soil,it is crucial to use a new type of modified material to rapidly improve soil strength instead of traditional soil improvement materials such as lime and cement.Nanographite powder(NGP)has excellent properties,such as high adsorption,conductivity,and lubrication,since it has the characteristics of small size,large specific surface area,and high surface energy.However,previous studies on the improvement of expansive soil with NGP are not processed enough.To study the improvement effect of NGP on expansive soil,non-load swelling ratio tests,consolidation tests,unconfined compressive strength tests,mercury injection tests,and micro-CT tests on expansive soil mixed with different NGP contents were performed.The results show that the non-load swelling ratio,mechanical properties,and porosity of expansive soil show some increasement after adding NGP.The strength of expansive soil reaches the maximum when the NGP content is 1.450%.The cumulative mercury volume and compressive strain of expansive soil reach the maximum with the 2.0%NGP content.Finally,the modification mechanism of swelling,compressibility,microstructure,and compressive strength of expansive soil by NGP is revealed.展开更多
Achieving the simultaneous enhancement of strength and ductility in laser powder bed fused (LPBF-ed) titanium (Ti) is challenging due to the complex, high-dimensional parameter space and interactions between parameter...Achieving the simultaneous enhancement of strength and ductility in laser powder bed fused (LPBF-ed) titanium (Ti) is challenging due to the complex, high-dimensional parameter space and interactions between parameters and powders. Herein, a hybrid intelligent framework for process parameter optimization of LPBF-ed Ti with improved ultimate tensile strength (UTS) and elongation (EL) was proposed. It combines the data augmentation method (AVG ± EC × SD), the multi-model fusion stacking ensemble learning model (GBDT-BPNN-XGBoost), the interpretable machine learning method and the non-dominated ranking genetic algorithm (NSGA-Ⅱ). The GBDT-BPNN-XGBoost outperforms single models in predicting UTS and EL across the accuracy, generalization ability and stability. The SHAP analysis reveals that laser power (P) is the most important feature affecting both UTS and EL, and it has a positive impact on them when P < 220 W. The UTS and EL of samples fabricated by the optimal process parameters were 718 ± 5 MPa and 27.9 % ± 0.1 %, respectively. The outstanding strength-ductility balance is attributable to the forward stresses in hard α'-martensite and back stresses in soft αm'-martensite induced by the strain gradients of hetero-microstructure. The back stresses strengthen the soft αm'-martensite, improving the overall UTS. The forward stresses stimulate the activation of dislocations in hard α'-martensite and the generation of 〈c + a〉 dislocations, allowing the plastic strain to occur in hard regions and enhancing the overall ductility. This work provides a feasible strategy for multi-objective optimization and valuable insights into tailoring the microstructure for improving mechanical properties.展开更多
Control of the columnar to equiaxed transition(CET)is a major challenge in additively manufacturedβtitanium alloys.In this work,the promotion of CET was successfully achieved through in-situ fabrication of Ti-5Cu(wt....Control of the columnar to equiaxed transition(CET)is a major challenge in additively manufacturedβtitanium alloys.In this work,the promotion of CET was successfully achieved through in-situ fabrication of Ti-5Cu(wt.%)alloys with additions of 5,15,and 25 wt.%Nb using elemental Ti,Cu,and Nb powders by employing laser powder bed fusion(LPBF).The alloy containing 5 wt.%Nb consisted ofαlamellae,Ti2 Cu precipitates,and unmeltedβ-Nb inclusions,whereas the 25 wt.%Nb alloy consisted of equiaxedβgrains,ωprecipitates,and Ti2 Cu precipitates at the grain boundaries.In terms of mechanical proper-ties,despite the presence of Nb inclusions and liquation cracks in the 5 wt.%Nb alloy,it showed a yield strength of 1051±40 MPa and an elongation of 5.2%±1.3%.Both the strength and ductility decreased with increasing Nb content,e.g.,the 25 wt.%Nb alloy exhibited a yield strength of 808±53 MPa and an elongation of 1.6%±0.2%.As the Nb content increased from 5 to 25 wt.%,the Young’s modulus decreased from 110 to 65 GPa.The 25 wt.%Nb alloy showed a high ratio of hardness to Young’s mod-ulus(H/E)and yield pressure(H3/E2).However,due to its brittle nature,the material manifested high wear rates.These findings provide a basis for the future development of novel low-modulus isotropicβ-titanium alloys using LPBF.展开更多
In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand li...In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand lithology(tuff,limestone,basalt,granite),stone powder content(0,5%,10%,15%)and concrete strength grade(C60,C80,C100)as variables.The evolution of mechanical properties of HMC and the correlation between cubic compressive strength and other mechanical properties are studied.Compared to river sand,manufactured sand enhances the cubic compressive strength,axial compressive strength and elastic modulus of concrete,while its potential microcracks weaken the flexural strength and splitting tensile strength of concrete.Stone powder content displays both positive and negative effects on mechanical properties of HMC,and the stone powder content is suggested to be less than 10%.The empirical formulas between cubic compressive strength and other mechanical properties are proposed.展开更多
Ti-6Al-4Zr-2Sn-6Mo alloy is one of the most recent titanium alloys processed using powder bed fusion-laser beam(PBF-LB)technology.This alloy has the potential to replace Ti-6Al-4V in automotive and aerospace applicati...Ti-6Al-4Zr-2Sn-6Mo alloy is one of the most recent titanium alloys processed using powder bed fusion-laser beam(PBF-LB)technology.This alloy has the potential to replace Ti-6Al-4V in automotive and aerospace applications,given its superior mechanical properties,which are approximately 10%higher in terms of ultimate tensile strength(UTS)and yield strength after appropriate heat treatment.In as-built conditions,the alloy is characterized by the presence of soft orthorhombicα″martensite,necessitating a postprocessing heat treatment to decompose this phase and enhance the mechanical properties of the alloy.Usually,PBFed Ti6246 components undergo an annealing process that transforms theα″martensite into anα-βlamellar microstructure.The primary objective of this research was to develop a solution treatment and aging(STA)heat treatment tailored to the unique microstructure produced by the additive manufacturing process to achieve an ultrafine bilamellar microstructure reinforced by precipitation hardening.This study investigated the effects of various solution temperatures in theα-βfield(ranging from 800 to 875℃),cooling media(air and water),and aging time to determine the optimal heat treatment parameters for achieving the desired bilamellar microstructure.For each heat treatment condition,differentα-βmicrostructures were found,varying in terms of theα/βratio and the size of the primaryα-phase lamellae.Particular attention was given to how these factors were influenced by increases in solution temperature and how microhardness correlated with the percentage of the metastableβphase present after quenching.Tensile tests were performed on samples subjected to the most promising heat treatment parameters.A comparison with literature data revealed that the optimized STA treatment enhanced hardness and UTS by13%and 23%,respectively,compared with those of the annealed alloy.Fracture surface analyses were conducted to investigate fracture mechanisms.展开更多
Surface structural engineering is desirable in modifying the surface performance of carbonyl iron powder(CIP)to enhance microwave absorption(MA)and anti-oxidation performance.Herein,the surface shape-dependent CIP abs...Surface structural engineering is desirable in modifying the surface performance of carbonyl iron powder(CIP)to enhance microwave absorption(MA)and anti-oxidation performance.Herein,the surface shape-dependent CIP absorbers are designed via surface coating with zinc oxide(ZnO)nanoparticles and then a thermal annealing treatment.The morphology of ZnO nanoparticles which can be easily regulated by controlling the annealing temperature ultimately affects the MA performance of CIP coating with ZnO nanoparticles(CIP@ZnO).The core-shell CIP@ZnO particles with cubic cone ZnO nanoparticles exhibit ex-cellent MA performance and thermal stability in comparison to the original CIP.Specifically,the CIP@ZnO annealed at 350 ℃(CIP@ZnO-350)samples which have the cubic cone ZnO nanoparticles exhibit a min-imum reflection loss(RLmin)of-55.35 dB at a thickness of 2.1 mm and a maximum effective absorp-tion bandwidth(EAB)of 7.09 GHz at a thickness of 2.0 mm.In addition,the antioxidant property of the CIP@ZnO composite particles is abruptly enhanced,which breaks the restriction of the application of CIP at high temperatures.The superior MA performance of CIP@ZnO particles with cubic cone ZnO nanoparti-cles comes from the enhancement in surface shape-dependent multiple microwave scattering,interfacial polarization,and electromagnetic-dielectric synergism between ZnO and CIP.展开更多
Laser powder bed fusion(LPBF)is a widely recognized additive manufacturing technology that can fabricate complex components rapidly through layer-by-layer formation.However,there is a paucity of research on the effect...Laser powder bed fusion(LPBF)is a widely recognized additive manufacturing technology that can fabricate complex components rapidly through layer-by-layer formation.However,there is a paucity of research on the effect of laser scanning speed on the cellular microstructure and mechanical properties of martensitic stainless steel.This study systematically investigated the influence of laser scanning speed on the cellular microstructure and mechanical properties of a developed Fe11Cr8Ni5Co3Mo martensitic stainless steel produced by LPBF.The results show that increasing the laser scanning speed from 400 to 1000 mm/s does not lead to a noticeable change in the phase fraction,but it reduces the average size of the cellular microstructure from 0.60 to 0.35μm.The scanning speeds of 400 and 1000 mm/s both had adverse effects on performances of sample,resulting in inadequate fusion and keyhole defects respectively.The optimal scanning speed for fabricating samples was determined to be 800 mm/s,which obtained the highest room temperature tensile strength and elongation,with the ultimate tensile strength measured at(1088.3±2.0)MPa and the elongation of(16.76±0.10)%.Furthermore,the mechanism of the evolution of surface morphology,defects,and energy input were clarified,and the relationship between cellular microstructure size and mechanical properties was also established.展开更多
With the development of aerospace and transportation,high-strength structural materials manufactured by additive manufacturing techniques get more attention,which allows the production of counterparts with complex str...With the development of aerospace and transportation,high-strength structural materials manufactured by additive manufacturing techniques get more attention,which allows the production of counterparts with complex structures.This work investigates Al-added CoCrFeMnNi high-entropy alloys(Al-HEAs)pre-pared by laser powder bed fusion(PBF-LB),adding 4.4 wt.%Al reducing approximately 7%density.The contribution of post-heat-treatment to microstructure,mechanical properties,and corrosion behaviors are explored.Hot cracking along with grain boundaries in the as-built PBF-LB Al-HEAs is determined,which comes from the residual liquid film as a larger solidification temperature range by adding Al.The PBF-LB Al-HEAs mainly consist of a face-centered cubic(FCC)matrix with Al/Ni/Mn decorated dislocation cells therein and a minor body-centered cubic(BCC)phase.Upon 850℃ annealing treatment,massive BCC phases(ordered NiAl and disordered Cr-rich precipitates)generate at the dislocation cell/grain bound-aries and the dislocation cells are still retained.However,the volume fraction of BCC phases and the dislocation cells vanish after 1150℃ solution treatment.As a result,Al-HEA850 shows an over 1000 MPa yield strength with nearly no ductility(<3%);the Al-HEA1150 exhibits considerable strength-ductility properties.Meanwhile,the Al-HEA850 demonstrates the worst pitting corrosion resistance due to the preferential dissolution of the NiAl precipitates in chloride-containing solutions.After comparatively de-liberating the evolution of strength-ductility and localized corrosion,we built a framework about the effects of the heat treatment on the mechanical property and degradation behavior in additively manu-factured Al-added high-strength HEAs.展开更多
Introduction The widespread use of cement in concrete leads to increased carbon emissions,so the demand for supplementary cementitious materials increases significantly.Limestone powder and steel slag powder are widel...Introduction The widespread use of cement in concrete leads to increased carbon emissions,so the demand for supplementary cementitious materials increases significantly.Limestone powder and steel slag powder are widely used as supplementary cementitious materials in modern concrete.However,for UHPC and self-compacting concrete,an extremely low water/binder(W/B)ratio is on one hand a key factor in achieving ultra-high strength and ultra-low porosity of the materials,on the other hand,also leads to the deterioration of the rheological properties of the fresh paste.Meanwhile,the existing researches focus on the influence of single limestone powder or steel slag powder on the mechanical properties or microstructure of cement-based materials.Little work on the influence of steel slag powder or limestone powder on the rheological properties of composite paste at an extremely low water/binder ratio has been investigated quantitatively.The mechanism of the effect of steel slag powder or limestone powder on the rheological properties of composite paste at extremely low water/binder ratios is still unclear.In this work,the effects of steel slag powder and limestone powder on the rheological properties of composite paste at different low water/binder ratios were analyzed via determining the flow diameter,setting time,marsh cone flow time,rheological parameters,and total organic carbon content.Methods A composite paste was prepared with P.I 42.5 ordinary Portland cement,steel slag powder,limestone powder,blast furnace slag and silica fume as raw materials in a certain proportion.To achieve the preparation of composite paste with extremely low water/binder ratios,a polycarboxylate superplasticizer with a water/reducing rate of 40%(Jiangsu Subot New Materials Co.,Ltd.,China)was used.The dosage of polycarboxylate superplasticizer for the composite paste with different water/binder ratios of 0.16 and 0.21 was 2%and 0.8%,respectively.Composite pastes with different proportions of steel slag powder or limestone powder at water/binder ratios of 0.16 and 0.21 were prepared.The flow diameter(i.e.,the larger the flow diameter,the better the fluidity),setting time(i.e.,the time when the fluidity is lost)and marsh cone flow time(i.e.,the shorter the flow time,the better the fluidity)were determined to analyze the fluidity of the composite pastes.the rheological properties of composite paste at a water/binder ratio of 0.16 for rheological properties tests were determined,and the rheological parameters were obtained by the H-B model.The adsorption performance of the polycarboxylate superplasticizer was analyzed by testing the TOC content.Results and discussion When the ratio of water/binder is 0.16,both limestone powder and steel slag powder initially increase the flow diameter of the composite paste.However,the fluidity of the composite paste decreases over time,and the reduction is more pronounced with steel slag powder.This is because the nucleation and hydration promotion effect of limestone powder can reduce the loss rate of flow diameter,while the rough particles of steel slag powder increase the internal friction force,resulting in a decrease in the flow diameter of composite paste.Adding limestone powder and steel slag powder both shortens the setting time and marsh cone flow time of the composite paste.However,the steel slag powder addition of 30%delays the final setting time due to its delaying effect.Also,limestone powder can enhance the thixotropy and reduce the yield stress and plastic viscosity,thereby improving the rheological properties.In contrast,steel slag powder can increase the yield stress and plastic viscosity,thereby weakening the rheological properties and thixotropy.Steel slag powder and limestone powder both can enhance the adsorption effect of polycarboxylate superplasticizer.Steel slag powder has a stronger adsorption effect.The composite paste containing limestone powder has a higher free water content.This is because the rough and porous surface of steel slag itself and the uneven particle shape lead to the physical adsorption of polycarboxylate superplasticizer molecules on the surface of steel slag particles,thereby reducing the effective content of the water reducer dispersion.Increasing the water/binder ratio to 0.21 results in a decrease in the flow diameter of the composite paste.Furthermore,the setting time and marsh cone flow time can prolong due to the reduction in the dosage of polycarboxylate superplasticizer.Conclusions The results showed that the fluidity loss rate of composite paste with limestone powder could be lower than that of composite paste with steel slag powder.Compared to steel slag powder,the addition of limestone powder reduced the setting time and marsh cone flow time of the composite paste.The addition of limestone powder could shorten the yield stress and plastic viscosity of the composite paste.Therefore,the composite paste with limestone powder had better rheological properties and stronger thixotropy rather than that with steel slag powder.The addition of limestone powder could improve the rheological properties of the composite paste.Compared to composite paste with limestone powder,a better adsorption effect of polycarboxylate superplasticizer on the surface of the composite binder with steel slag powder could be obtained.The free water content of the composite paste with limestone powder was still higher than that of the composite paste with steel slag powder.The fluidity and rheological properties of the composite paste with limestone powder could be better.The comprehensive analysis indicated that a positive effect of limestone powder on rheological properties of composite paste at an extremely low water/binder ratio could be more dominant than that of steel slag powder.展开更多
Four types of resins,P1–P4,are used as binders for FeSiBC amorphous powder,which are then press-molded and heat-treated to fabricate magnetic powder cores(MPCs).By testing the permeability,loss,density,and radial cru...Four types of resins,P1–P4,are used as binders for FeSiBC amorphous powder,which are then press-molded and heat-treated to fabricate magnetic powder cores(MPCs).By testing the permeability,loss,density,and radial crush strength of MPCs,the effect of the binder on the magnetic properties of the cores is investigated and the best resin is found.The results show that the silicone resin P3 exhibits the best thermal stability,retaining 82.1%of its mass after heat treatment at 430°C.This contributes to improving the insulation of MPCs and reducing the eddy current loss,which is 46.06 mW cm^(−3)(150 kHz,20 mT)with the mechanical strength of 11.13 MPa.The bonding of epoxy resin P4 is superior to that of other resins,which significantly improves the powder compactness and makes MPCs density reach 5.67 g cm^(−3),and its permeability is as high as 28.7.The two types of resins have different advantages,and both lead to MPCs with excellent properties.展开更多
Powder engine as a novel type of engine using high-energy metal powder as fuel and gas,liquid,or solid as oxidizer.These engines exhibit remarkable adaptability,flexible thrust regulation,and multi-pulse start-stop,wh...Powder engine as a novel type of engine using high-energy metal powder as fuel and gas,liquid,or solid as oxidizer.These engines exhibit remarkable adaptability,flexible thrust regulation,and multi-pulse start-stop,which have significant application potentials in the fields of near-Earth space development,space propulsion systems,and deep-sea exploration.The scope of this review encompasses the classification and application of powder engines,the classification of powdered fuel supply systems,and the prospective trajectories and pivotal challenges of powder engines and fuel supply technologies.This work points out that although certain ground-based experimental challenges on powder engines have been solved,the relative technology remains in the nascent stages of feasibility demonstration and testing.The pneumatic and motor-driven piston methods currently dominate as the primary means for supplying fuel,and the structure of the piston and intake should be further optimized in the future to promote fuel fluidization and delivery efficiency.The adaptability of powder engines and powdered fuels under different pre-treatment and loading methods should be evaluated.Furthermore,the stability of powdered fuel delivery across varying operational environments,the accuracy of CFD modeling,and the precision of mass flow rate measurement and prediction technologies necessitate further enhancement and refinement.These advancements are crucial for the maturation of powder engine technology and its integration into practical applications.展开更多
In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)wit...In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)with limestone powder(stone powder)as a mineral admixture on the micro,meso,and macro properties of mortar.First,the applicability of stone powder was examined based on the physical filling and heat of hydration of stone powder-cement.Second,micro-meso testing methods,such as X-ray diffraction,scanning electron microscopy,thermogravimetry-differential scanning calorimetry,and nuclear magnetic resonance,were utilized to reveal the influencing mechanisms of stone powder on the microstructure of the mortar.Furthermore,the effect of stone powder on the compressive strength and gas permeability of the mortar was analyzed.Additionally,the time-dependent variations in the gas permeability and its functional relationship with the mechanical properties were determined.Finally,the correlation between the compressive strength and gas permeability with respect to the pore size of stone powder-doped mortar was established via gray-correlation analysis.The results show that an appropriate amount of stone powder(5%)can effectively improve the particle gradation,decelerate the release of the heat of hydration,increase the amount of hydration products,and improve the pore structure,thereby increasing the compressive strength and reducing the gas permeability coefficient.The gas permeability of stone powder-doped mortar was found to exhibit good time-dependent characteristics as well as a quadratic linear correlation with the compressive strength.The gray-correlation analysis results indicate that air pores exhibit the highest influence on the compressive strength and that the gas permeability coefficient is most significantly affected by large pores.展开更多
Laser powder bed fusion(LPBF)additive manufacturing of zinc(Zn)offers promising advantages for biodegradable metal bone implants,including tailorable microstructures,controllable porous structures,and appropriate degr...Laser powder bed fusion(LPBF)additive manufacturing of zinc(Zn)offers promising advantages for biodegradable metal bone implants,including tailorable microstructures,controllable porous structures,and appropriate degradation rates.However,the layer-by-layer construction during LPBF often leads to microstructural and performance anisotropy within metallic materials.In this work,the anisotropic mechanical and degradation properties of pure Zn processed using LPBF were comprehensively investigated for the first time.Specifically,the influence of microstructural characteristics on the mechanical and degradation properties of LPBF-processed Zn in both horizontal and vertical planes was revealed,while the underlying deformation mechanisms in different planes were illustrated.The results demonstrated that the horizontal plane exhibited higher mechanical strength compared to the vertical plane,with ulti-mate tensile strength of 123.6 and 107.86 MPa,respectively,significantly surpassing that of the tradition-ally cast counterpart(52.7 MPa).Importantly,abundant deformation twins coupled with infrequent microbands and pyramidal(c+a)slip systems activated during tensile loading along the vertical plane enabled multiple deformation modes,which sustained durable work hardening ability while delaying plastic instability,resulting in extraordinary plasticity(elongation of 14.2%).Additionally,synergistic effects between high-density grain boundaries including low-angle grain boundaries and pre-existing dislocations promoted the stable presence of a passive film along the horizontal plane,thus exhibiting relatively low corrosion sensitivity.Furthermore,the LPBF-processed Zn also demonstrated favorable biological activity and osteogenic potential.These findings provide valuable insights into multiple mechanisms underlying anisotropy in mechanical and degradation properties of laser additively manufactured Zn-based materials.展开更多
基金Project(20224BBE51044)supported by the Key R&D Program of Jiangxi Province,China。
文摘Additive manufacturing(AM)of SiC_(P)/Al composites has shown significant potential for expanding the application of aluminum matrix composites(AMCs)due to their outstanding mechanical properties and wear performance.However,conventional mechanically mixed powders for AM are limited due to the possible powder agglomeration and poor fluidity.In this study,the spherical SiC_(P)/AlSi10Mg composite powders prepared by spray granulation were employed to fabricate SiC_(P)-reinforced AlSi10Mg composites using laser powder bed fusion(LPBF).The impacts of laser power on microstructure evolution and wear properties of composites were systematically investigated.The results indicated that an in-situ reaction between the aluminum matrix and SiC_(P)during the LpBF process,resulted in the formation of particle-like and strip-like strengthening phase Al_(4)SiC_(4).By adjusting the laser power(from 270 W to 350 W)to change the ratio of SiC_(P)to Al_(4)SiC_(4),micro-defects could be effectively limited,and wear performance could be improved.Consequently,with an optimized ratio of SiC_(P)to Al_(4)SiC_(4),the composite exhibited a mixed strengthening mechanism caused by the SiC_(P)and Al_(4)SiC_(4)reinforcing phases.At a laser power of 310 W,the sample exhibited minimal porosity with a microhardness value reaching 265.38HV,while maintaining relatively low average friction coefficient and wear rate.In addition,compared with other studies,the hardness obtained was superior to that of the AlSi10Mg and other reported SiC_(P)/AlSi10Mg composites with similar volume fractions using the mixed powders.
基金Funded by National Natural Science Foundation of China(No.52108219)Lanzhou University of Technology Hongliu Outstanding Young Talent Program,China(No.062407)The High Quality of Green Machine-made Aggregate and the Evolution Mechanism of Concrete Life Cycle Performance in the Harsh Environment of Northwest China(No.U21A20150)。
文摘In order to improve the efficient and high-value recycling utilization rate of waste red bricks from construction waste,this study crushed and ground the waste red bricks to produce recycled brick powder(RBP)with different fineness,used the Andreasen model to explore the influence of RBP on the compact filling effect of cementitious material system based on the basic characteristics of RBP.The influence of grinding time(10,20,30 min)and content(0%,5%,10%,15%,20%)of RBP on the macroscopic mechanical properties of cementitious materials was investigated.We analyzed the significant impact of RBP particle characteristics on the compressive strength of the specimen with the aid of grey entropy theory,and revealed the influence mechanism of RBP on the microstructure of cementitious materials by scanning electron microscope(SEM)and nuclear magnetic resonance(NMR).The results show that the fineness of RBP after grinding is smaller than that of cement.The fineness of recycled brick powder increases gradually with the extension of grinding time,which is manifested as the increase of<3μm particles and the decrease of>18μm particles.Compared with the unitary cement cementitious material system,the particle gradation of the RBP-cement binary cementitious material system is closer to the closest packing state.With the increase of RBP content and grinding time,the compactness of the binary cementitious system gradually decreases,indicating that the incorporation of RBP reduces the mechanical strength of the specimen.The results of grey entropy show that the specific surface area D(0.1)and<45μm particles are the significant factors affecting the mechanical properties of cementitious materials mixed with RBP.RBP mainly affects the macroscopic properties of cementitious materials by affecting the internal compactness,the number of hydration products and the pore structure.The results of SEM show that when the RBP content is less than 15%,the content of C-S-H in cement paste increase,and the content of Ca(OH)2 decreases,and the content of C-S-H decreases and the content of Ca(OH)2 increases when the RBP content is more than 15%.The NMR results show that with the extension of grinding time,the pore size of micropore increases gradually,that of middle-small pores decreases gradually,and that of large pores remains unchanged.With the increase of RBP content,the micropores first decrease and then increase,and the middle-small pores and large pores gradually decrease.In summary,the compactness of cementitious material system can be improved by adjusting the fineness of RBP.Considering the performance of cementitious materials and the utilization rate of RBP,it is recommended that the grinding time of RBP is 20 min and the content is 10%-15%.
基金supported by the National Natural Science Foundation of China(Nos.52374396 and 52122409).
文摘Improving the high-temperature performance of Inconel 718(IN718)alloys manufactured via laser powder bed fusion(LPBF)has been the most concerned issue in the industry.In this study,the effects of Ti_(2)AlC inoculants on microstructures and high-temperature mechanical properties of the as-built IN718 composites were investigated.According to statistical results of relative density and unmelted particle area in as-built alloys,the optimal energy of 112 J/mm^(3)was determined.It was observed that the precipitation of the MC carbide was significantly enhanced with the addition of Ti_(2)AlC,restricting the precipitation of the Laves phase.The MC particles were uniformly distributed along the subgrain boundaries,which contributed to the dispersion strengthening.Meanwhile,the MC particles served as nucleation sites for heterogeneous nucleation during the solidification process,facilitating the refinement of columnar and cellular grains.The simulated Scheil-Gulliver curves showed that the precipitation sequence of phases did not change with Ti_(2)AlC inoculants.The as-built 1%Ti_(2)AlC/IN718 sample demonstrated an ultimate tensile strength of 998.78 MPa and an elongation of 18.04%at 650℃,revealing a markedly improved mechanical performance compared with the LPBF-manufactured IN718 alloys.The high-temperature tensile strength of 1%Ti_(2)AlC/IN718 sample increased to 1197.99 MPa by heat treatment.It was suggested that dislocation strengthening and ordered strengthening were two most important reinforcement mechanisms.
文摘GF/Pb compositeswerefabricated by the method of powder metallurgy, and the density, microstructure and tensile propertywerecharacterized considering the size and content ofglass fibre （GF）. The results show that relative densities decrease with increasing GF fraction, and the 50μm-GF reinforced specimens exhibit a better densification than the 300μm-GF reinforced ones. The GF particles distribute quite uniformly inPb matrix, and the composites fabricated at low sintering temperature （〈200℃） possess fine-grain microstructure. The addition of GF significantly improves the strength of the Pb composites, and the ultimate tensile strength of the Pb composite reinforcedwith the addition of 50μm-0.5% GF（mass fraction）is about 30MPa higher than that of GF-free sample. For all composites groups, increasing the reinforcement content from 0.5%to 2%（mass fraction）results in a decrease in both tensile strength and ductility.
基金National Natural Science Foundation of China(52105385)Stable Support Plan Program of Shenzhen Natural Science Fund(20220810132537001)+2 种基金Guangdong Basic and Applied Basic Research Foundation(2022A1515010781)Joint Fund of Henan Province Science and Technology R&D Program(225200810002)Fundamental Research Funds of Henan Academy of Sciences(240621041)。
文摘To enhance the mechanical properties of Mo alloys prepared through laser powder bed fusion(LPBF),a hot isostatic pressing(HIP)treatment was used.Results show that following HIP treatment,the porosity decreases from 0.27%to 0.22%,enabling the elements Mo and Ti to diffuse fully and to distribute more uniformly,and to forming a substantial number of low-angle grain boundaries.The tensile strength soars from 286±32 MPa to 598±22 MPa,while the elongation increases from 0.08%±0.02%to 0.18%±0.02%,without notable alterations in grain morphology during the tensile deformation.HIP treatment eliminates the molten pool boundaries,which are the primary source for premature failure in LPBFed Mo alloys.Consequently,HIP treatment emerges as a novel and effective approach for strengthening the mechanical properties of LPBFed Mo alloys,offering a fresh perspective on producing high-performance Mo-based alloys.
基金Support for this project was provided by US Department of Energy grant DE-SC0011826
文摘This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing(AM) utilizing electron-beam powder bed fusion(EPBF). The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes[100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L stainless-steel.In addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm^2, and a homogeneous distribution of Cr_(23)C_6 precipitates. Precipitates were formed within the grains(with ~3 μm interparticle spacing),but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainlesssteel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685?C for50 h precipitated Cr_(23)C_6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle(and low energy) subgrain boundaries. In contrast, Cr_(23)C_6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy coherent {111} twin boundaries. Consequently, the Inconel690 subgrain boundaries essentially serve as surrogates for coherent twin boundaries with regard to avoiding carbide precipitation and corrosion sensitization.
基金Projects(51671152,51304153,51504191,51874225)supported by the National Natural Science Foundation of ChinaProject(14JK512)supported by the Natural Science Foundation of Shaanxi Educational Committee,China+1 种基金Project(18JC019)supported by Shaanxi Provincial Department of Education Industrialization Project,ChinaProject(14JK1512)supported by Shaanxi Provincial Department of Education Natural Science Special Project,China
文摘Selective laser melting(SLM)technology is the prevailing method of manufacturing components with complex geometries.However,the cost of the additive manufacturing(AM)fine powder is relatively high,which significantly limits the development of the SLM.In this study,the 316L fine powder and coarse powder with a mass ratio of 80:20,70:30 and 60:40 were mixed using a ball milling and the samples with a relative density greater than 97%were prepared by SLM.The results show that the intricate temperature gradients and surface tension gradients in SLM will produce Marangoni flow,forming a typical molten pool morphology,cellular and strip subgrain structures.And as the proportion of coarse powder increases,the scanning track morphology changes from smooth to undulating;the morphology of the molten pool and subgrain structure are weakened.Meanwhile,the unmelted particles appear on the surface of the SLM sample.On the premise of an introducing appropriate amount of large particle size powder(20%),the SLM samples still have good mechanical properties(662 MPa,47%).
基金Project(2017TFC1503102)supported by the National Key Research and Development Project,ChinaProjects(51874065,U1903112)supported by the National Natural Science Foundation of China。
文摘To reduce geological disasters caused by expansive soil,it is crucial to use a new type of modified material to rapidly improve soil strength instead of traditional soil improvement materials such as lime and cement.Nanographite powder(NGP)has excellent properties,such as high adsorption,conductivity,and lubrication,since it has the characteristics of small size,large specific surface area,and high surface energy.However,previous studies on the improvement of expansive soil with NGP are not processed enough.To study the improvement effect of NGP on expansive soil,non-load swelling ratio tests,consolidation tests,unconfined compressive strength tests,mercury injection tests,and micro-CT tests on expansive soil mixed with different NGP contents were performed.The results show that the non-load swelling ratio,mechanical properties,and porosity of expansive soil show some increasement after adding NGP.The strength of expansive soil reaches the maximum when the NGP content is 1.450%.The cumulative mercury volume and compressive strain of expansive soil reach the maximum with the 2.0%NGP content.Finally,the modification mechanism of swelling,compressibility,microstructure,and compressive strength of expansive soil by NGP is revealed.
基金supported by the National Natural Sci-ence Foundation of China(Nos.52274359 and 52304379)the China National Postdoctoral Program for Innovative Talents(No.BX20220034)+2 种基金the China Postdoctoral Science Foundation(No.2022M720403)the AECC University Research Cooperation Project(No.HFZL2021CXY021)the Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Research Funds for the Central Universities)(No.FRF-IDRY-23-025).
文摘Achieving the simultaneous enhancement of strength and ductility in laser powder bed fused (LPBF-ed) titanium (Ti) is challenging due to the complex, high-dimensional parameter space and interactions between parameters and powders. Herein, a hybrid intelligent framework for process parameter optimization of LPBF-ed Ti with improved ultimate tensile strength (UTS) and elongation (EL) was proposed. It combines the data augmentation method (AVG ± EC × SD), the multi-model fusion stacking ensemble learning model (GBDT-BPNN-XGBoost), the interpretable machine learning method and the non-dominated ranking genetic algorithm (NSGA-Ⅱ). The GBDT-BPNN-XGBoost outperforms single models in predicting UTS and EL across the accuracy, generalization ability and stability. The SHAP analysis reveals that laser power (P) is the most important feature affecting both UTS and EL, and it has a positive impact on them when P < 220 W. The UTS and EL of samples fabricated by the optimal process parameters were 718 ± 5 MPa and 27.9 % ± 0.1 %, respectively. The outstanding strength-ductility balance is attributable to the forward stresses in hard α'-martensite and back stresses in soft αm'-martensite induced by the strain gradients of hetero-microstructure. The back stresses strengthen the soft αm'-martensite, improving the overall UTS. The forward stresses stimulate the activation of dislocations in hard α'-martensite and the generation of 〈c + a〉 dislocations, allowing the plastic strain to occur in hard regions and enhancing the overall ductility. This work provides a feasible strategy for multi-objective optimization and valuable insights into tailoring the microstructure for improving mechanical properties.
基金the National Natural Science Foun-dation of China(Grant Nos.12374022,U23A20540)the Natu-ral Science Foundation of Hunan Province for Distinguished Young Scholars(Grant No.2023JJ10075)+3 种基金the China Postdoctoral Science Foundation(Grant Nos.GZC20241335,2024MD753962)the YueLuShan Center Industrial Innovation(Grant No.2024YCII0106)the Scientific and Technological Project of Yunnan Precious Met-als Laboratory(Grant No.YPML-2023050247)the Central South University Research Programme of Advanced Interdisci-plinary Studies(Grant No.2023QYJC039).
文摘Control of the columnar to equiaxed transition(CET)is a major challenge in additively manufacturedβtitanium alloys.In this work,the promotion of CET was successfully achieved through in-situ fabrication of Ti-5Cu(wt.%)alloys with additions of 5,15,and 25 wt.%Nb using elemental Ti,Cu,and Nb powders by employing laser powder bed fusion(LPBF).The alloy containing 5 wt.%Nb consisted ofαlamellae,Ti2 Cu precipitates,and unmeltedβ-Nb inclusions,whereas the 25 wt.%Nb alloy consisted of equiaxedβgrains,ωprecipitates,and Ti2 Cu precipitates at the grain boundaries.In terms of mechanical proper-ties,despite the presence of Nb inclusions and liquation cracks in the 5 wt.%Nb alloy,it showed a yield strength of 1051±40 MPa and an elongation of 5.2%±1.3%.Both the strength and ductility decreased with increasing Nb content,e.g.,the 25 wt.%Nb alloy exhibited a yield strength of 808±53 MPa and an elongation of 1.6%±0.2%.As the Nb content increased from 5 to 25 wt.%,the Young’s modulus decreased from 110 to 65 GPa.The 25 wt.%Nb alloy showed a high ratio of hardness to Young’s mod-ulus(H/E)and yield pressure(H3/E2).However,due to its brittle nature,the material manifested high wear rates.These findings provide a basis for the future development of novel low-modulus isotropicβ-titanium alloys using LPBF.
基金Funded by the National Natural Science Foundation of China(Nos.U1934206,52108260)China Academy of Railway Sciences Fund(No.2021YJ078)+1 种基金Railway Engineering Construction Standard Project(No.2023-BZWW-006)New Cornerstone Science Foundation through the XPLORER PRIZE。
文摘In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand lithology(tuff,limestone,basalt,granite),stone powder content(0,5%,10%,15%)and concrete strength grade(C60,C80,C100)as variables.The evolution of mechanical properties of HMC and the correlation between cubic compressive strength and other mechanical properties are studied.Compared to river sand,manufactured sand enhances the cubic compressive strength,axial compressive strength and elastic modulus of concrete,while its potential microcracks weaken the flexural strength and splitting tensile strength of concrete.Stone powder content displays both positive and negative effects on mechanical properties of HMC,and the stone powder content is suggested to be less than 10%.The empirical formulas between cubic compressive strength and other mechanical properties are proposed.
基金financed by the European Union-Next Generation EU(National Sustainable Mobility Center CN00000023,Italian Ministry of University and Research Decree n.1033-17/06/2022,Spoke 11-Innovative Materials&Lightweighting)。
文摘Ti-6Al-4Zr-2Sn-6Mo alloy is one of the most recent titanium alloys processed using powder bed fusion-laser beam(PBF-LB)technology.This alloy has the potential to replace Ti-6Al-4V in automotive and aerospace applications,given its superior mechanical properties,which are approximately 10%higher in terms of ultimate tensile strength(UTS)and yield strength after appropriate heat treatment.In as-built conditions,the alloy is characterized by the presence of soft orthorhombicα″martensite,necessitating a postprocessing heat treatment to decompose this phase and enhance the mechanical properties of the alloy.Usually,PBFed Ti6246 components undergo an annealing process that transforms theα″martensite into anα-βlamellar microstructure.The primary objective of this research was to develop a solution treatment and aging(STA)heat treatment tailored to the unique microstructure produced by the additive manufacturing process to achieve an ultrafine bilamellar microstructure reinforced by precipitation hardening.This study investigated the effects of various solution temperatures in theα-βfield(ranging from 800 to 875℃),cooling media(air and water),and aging time to determine the optimal heat treatment parameters for achieving the desired bilamellar microstructure.For each heat treatment condition,differentα-βmicrostructures were found,varying in terms of theα/βratio and the size of the primaryα-phase lamellae.Particular attention was given to how these factors were influenced by increases in solution temperature and how microhardness correlated with the percentage of the metastableβphase present after quenching.Tensile tests were performed on samples subjected to the most promising heat treatment parameters.A comparison with literature data revealed that the optimized STA treatment enhanced hardness and UTS by13%and 23%,respectively,compared with those of the annealed alloy.Fracture surface analyses were conducted to investigate fracture mechanisms.
基金National Natural Science Foundation of China(No.52173264).
文摘Surface structural engineering is desirable in modifying the surface performance of carbonyl iron powder(CIP)to enhance microwave absorption(MA)and anti-oxidation performance.Herein,the surface shape-dependent CIP absorbers are designed via surface coating with zinc oxide(ZnO)nanoparticles and then a thermal annealing treatment.The morphology of ZnO nanoparticles which can be easily regulated by controlling the annealing temperature ultimately affects the MA performance of CIP coating with ZnO nanoparticles(CIP@ZnO).The core-shell CIP@ZnO particles with cubic cone ZnO nanoparticles exhibit ex-cellent MA performance and thermal stability in comparison to the original CIP.Specifically,the CIP@ZnO annealed at 350 ℃(CIP@ZnO-350)samples which have the cubic cone ZnO nanoparticles exhibit a min-imum reflection loss(RLmin)of-55.35 dB at a thickness of 2.1 mm and a maximum effective absorp-tion bandwidth(EAB)of 7.09 GHz at a thickness of 2.0 mm.In addition,the antioxidant property of the CIP@ZnO composite particles is abruptly enhanced,which breaks the restriction of the application of CIP at high temperatures.The superior MA performance of CIP@ZnO particles with cubic cone ZnO nanoparti-cles comes from the enhancement in surface shape-dependent multiple microwave scattering,interfacial polarization,and electromagnetic-dielectric synergism between ZnO and CIP.
基金financially supported by the National Natural Science Foundation of China(Nos.U2141205,52371002,and 52374366)the Fundamental Research Funds for the Central Universities(Nos.06109125 and 06930007)Fundamental Research Funds for the Central Universities(No.FRF-BD-23-02).
文摘Laser powder bed fusion(LPBF)is a widely recognized additive manufacturing technology that can fabricate complex components rapidly through layer-by-layer formation.However,there is a paucity of research on the effect of laser scanning speed on the cellular microstructure and mechanical properties of martensitic stainless steel.This study systematically investigated the influence of laser scanning speed on the cellular microstructure and mechanical properties of a developed Fe11Cr8Ni5Co3Mo martensitic stainless steel produced by LPBF.The results show that increasing the laser scanning speed from 400 to 1000 mm/s does not lead to a noticeable change in the phase fraction,but it reduces the average size of the cellular microstructure from 0.60 to 0.35μm.The scanning speeds of 400 and 1000 mm/s both had adverse effects on performances of sample,resulting in inadequate fusion and keyhole defects respectively.The optimal scanning speed for fabricating samples was determined to be 800 mm/s,which obtained the highest room temperature tensile strength and elongation,with the ultimate tensile strength measured at(1088.3±2.0)MPa and the elongation of(16.76±0.10)%.Furthermore,the mechanism of the evolution of surface morphology,defects,and energy input were clarified,and the relationship between cellular microstructure size and mechanical properties was also established.
基金This work is financially supported by the Shanghai Sailing Program(No.21YF1412000)the Natural Science Foundation of Shanghai(No.19ZR1417100).The authors greatly appreciate the access to Thermo-calc software in Prof.Olson’s lab at MIT.
文摘With the development of aerospace and transportation,high-strength structural materials manufactured by additive manufacturing techniques get more attention,which allows the production of counterparts with complex structures.This work investigates Al-added CoCrFeMnNi high-entropy alloys(Al-HEAs)pre-pared by laser powder bed fusion(PBF-LB),adding 4.4 wt.%Al reducing approximately 7%density.The contribution of post-heat-treatment to microstructure,mechanical properties,and corrosion behaviors are explored.Hot cracking along with grain boundaries in the as-built PBF-LB Al-HEAs is determined,which comes from the residual liquid film as a larger solidification temperature range by adding Al.The PBF-LB Al-HEAs mainly consist of a face-centered cubic(FCC)matrix with Al/Ni/Mn decorated dislocation cells therein and a minor body-centered cubic(BCC)phase.Upon 850℃ annealing treatment,massive BCC phases(ordered NiAl and disordered Cr-rich precipitates)generate at the dislocation cell/grain bound-aries and the dislocation cells are still retained.However,the volume fraction of BCC phases and the dislocation cells vanish after 1150℃ solution treatment.As a result,Al-HEA850 shows an over 1000 MPa yield strength with nearly no ductility(<3%);the Al-HEA1150 exhibits considerable strength-ductility properties.Meanwhile,the Al-HEA850 demonstrates the worst pitting corrosion resistance due to the preferential dissolution of the NiAl precipitates in chloride-containing solutions.After comparatively de-liberating the evolution of strength-ductility and localized corrosion,we built a framework about the effects of the heat treatment on the mechanical property and degradation behavior in additively manu-factured Al-added high-strength HEAs.
文摘Introduction The widespread use of cement in concrete leads to increased carbon emissions,so the demand for supplementary cementitious materials increases significantly.Limestone powder and steel slag powder are widely used as supplementary cementitious materials in modern concrete.However,for UHPC and self-compacting concrete,an extremely low water/binder(W/B)ratio is on one hand a key factor in achieving ultra-high strength and ultra-low porosity of the materials,on the other hand,also leads to the deterioration of the rheological properties of the fresh paste.Meanwhile,the existing researches focus on the influence of single limestone powder or steel slag powder on the mechanical properties or microstructure of cement-based materials.Little work on the influence of steel slag powder or limestone powder on the rheological properties of composite paste at an extremely low water/binder ratio has been investigated quantitatively.The mechanism of the effect of steel slag powder or limestone powder on the rheological properties of composite paste at extremely low water/binder ratios is still unclear.In this work,the effects of steel slag powder and limestone powder on the rheological properties of composite paste at different low water/binder ratios were analyzed via determining the flow diameter,setting time,marsh cone flow time,rheological parameters,and total organic carbon content.Methods A composite paste was prepared with P.I 42.5 ordinary Portland cement,steel slag powder,limestone powder,blast furnace slag and silica fume as raw materials in a certain proportion.To achieve the preparation of composite paste with extremely low water/binder ratios,a polycarboxylate superplasticizer with a water/reducing rate of 40%(Jiangsu Subot New Materials Co.,Ltd.,China)was used.The dosage of polycarboxylate superplasticizer for the composite paste with different water/binder ratios of 0.16 and 0.21 was 2%and 0.8%,respectively.Composite pastes with different proportions of steel slag powder or limestone powder at water/binder ratios of 0.16 and 0.21 were prepared.The flow diameter(i.e.,the larger the flow diameter,the better the fluidity),setting time(i.e.,the time when the fluidity is lost)and marsh cone flow time(i.e.,the shorter the flow time,the better the fluidity)were determined to analyze the fluidity of the composite pastes.the rheological properties of composite paste at a water/binder ratio of 0.16 for rheological properties tests were determined,and the rheological parameters were obtained by the H-B model.The adsorption performance of the polycarboxylate superplasticizer was analyzed by testing the TOC content.Results and discussion When the ratio of water/binder is 0.16,both limestone powder and steel slag powder initially increase the flow diameter of the composite paste.However,the fluidity of the composite paste decreases over time,and the reduction is more pronounced with steel slag powder.This is because the nucleation and hydration promotion effect of limestone powder can reduce the loss rate of flow diameter,while the rough particles of steel slag powder increase the internal friction force,resulting in a decrease in the flow diameter of composite paste.Adding limestone powder and steel slag powder both shortens the setting time and marsh cone flow time of the composite paste.However,the steel slag powder addition of 30%delays the final setting time due to its delaying effect.Also,limestone powder can enhance the thixotropy and reduce the yield stress and plastic viscosity,thereby improving the rheological properties.In contrast,steel slag powder can increase the yield stress and plastic viscosity,thereby weakening the rheological properties and thixotropy.Steel slag powder and limestone powder both can enhance the adsorption effect of polycarboxylate superplasticizer.Steel slag powder has a stronger adsorption effect.The composite paste containing limestone powder has a higher free water content.This is because the rough and porous surface of steel slag itself and the uneven particle shape lead to the physical adsorption of polycarboxylate superplasticizer molecules on the surface of steel slag particles,thereby reducing the effective content of the water reducer dispersion.Increasing the water/binder ratio to 0.21 results in a decrease in the flow diameter of the composite paste.Furthermore,the setting time and marsh cone flow time can prolong due to the reduction in the dosage of polycarboxylate superplasticizer.Conclusions The results showed that the fluidity loss rate of composite paste with limestone powder could be lower than that of composite paste with steel slag powder.Compared to steel slag powder,the addition of limestone powder reduced the setting time and marsh cone flow time of the composite paste.The addition of limestone powder could shorten the yield stress and plastic viscosity of the composite paste.Therefore,the composite paste with limestone powder had better rheological properties and stronger thixotropy rather than that with steel slag powder.The addition of limestone powder could improve the rheological properties of the composite paste.Compared to composite paste with limestone powder,a better adsorption effect of polycarboxylate superplasticizer on the surface of the composite binder with steel slag powder could be obtained.The free water content of the composite paste with limestone powder was still higher than that of the composite paste with steel slag powder.The fluidity and rheological properties of the composite paste with limestone powder could be better.The comprehensive analysis indicated that a positive effect of limestone powder on rheological properties of composite paste at an extremely low water/binder ratio could be more dominant than that of steel slag powder.
基金financially supported by the Key research and development project of Shandong province in China(Grant No.2022CXGC020308).
文摘Four types of resins,P1–P4,are used as binders for FeSiBC amorphous powder,which are then press-molded and heat-treated to fabricate magnetic powder cores(MPCs).By testing the permeability,loss,density,and radial crush strength of MPCs,the effect of the binder on the magnetic properties of the cores is investigated and the best resin is found.The results show that the silicone resin P3 exhibits the best thermal stability,retaining 82.1%of its mass after heat treatment at 430°C.This contributes to improving the insulation of MPCs and reducing the eddy current loss,which is 46.06 mW cm^(−3)(150 kHz,20 mT)with the mechanical strength of 11.13 MPa.The bonding of epoxy resin P4 is superior to that of other resins,which significantly improves the powder compactness and makes MPCs density reach 5.67 g cm^(−3),and its permeability is as high as 28.7.The two types of resins have different advantages,and both lead to MPCs with excellent properties.
基金supported by the National Natural Science Foundation of China(grant number:12102161)the Key Research and Development Program of Jiangxi Province,China(grant number:20232BBE50005)the Natural Science Foundation of Jiangxi Province,China(grant number:20224BAB214060)。
文摘Powder engine as a novel type of engine using high-energy metal powder as fuel and gas,liquid,or solid as oxidizer.These engines exhibit remarkable adaptability,flexible thrust regulation,and multi-pulse start-stop,which have significant application potentials in the fields of near-Earth space development,space propulsion systems,and deep-sea exploration.The scope of this review encompasses the classification and application of powder engines,the classification of powdered fuel supply systems,and the prospective trajectories and pivotal challenges of powder engines and fuel supply technologies.This work points out that although certain ground-based experimental challenges on powder engines have been solved,the relative technology remains in the nascent stages of feasibility demonstration and testing.The pneumatic and motor-driven piston methods currently dominate as the primary means for supplying fuel,and the structure of the piston and intake should be further optimized in the future to promote fuel fluidization and delivery efficiency.The adaptability of powder engines and powdered fuels under different pre-treatment and loading methods should be evaluated.Furthermore,the stability of powdered fuel delivery across varying operational environments,the accuracy of CFD modeling,and the precision of mass flow rate measurement and prediction technologies necessitate further enhancement and refinement.These advancements are crucial for the maturation of powder engine technology and its integration into practical applications.
基金Funded by the National Natural Science Foundation of China project(Nos.52108219 and U21A20150)the Lanzhou University of Technology Hongliu Outstanding Young Talent Program,China(No.04-062407)the Research on Quality Control Technology of High-performance Concrete Prepared by Manufactured Sand(No.2020Y21)。
文摘In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)with limestone powder(stone powder)as a mineral admixture on the micro,meso,and macro properties of mortar.First,the applicability of stone powder was examined based on the physical filling and heat of hydration of stone powder-cement.Second,micro-meso testing methods,such as X-ray diffraction,scanning electron microscopy,thermogravimetry-differential scanning calorimetry,and nuclear magnetic resonance,were utilized to reveal the influencing mechanisms of stone powder on the microstructure of the mortar.Furthermore,the effect of stone powder on the compressive strength and gas permeability of the mortar was analyzed.Additionally,the time-dependent variations in the gas permeability and its functional relationship with the mechanical properties were determined.Finally,the correlation between the compressive strength and gas permeability with respect to the pore size of stone powder-doped mortar was established via gray-correlation analysis.The results show that an appropriate amount of stone powder(5%)can effectively improve the particle gradation,decelerate the release of the heat of hydration,increase the amount of hydration products,and improve the pore structure,thereby increasing the compressive strength and reducing the gas permeability coefficient.The gas permeability of stone powder-doped mortar was found to exhibit good time-dependent characteristics as well as a quadratic linear correlation with the compressive strength.The gray-correlation analysis results indicate that air pores exhibit the highest influence on the compressive strength and that the gas permeability coefficient is most significantly affected by large pores.
基金supported by the following funds:the National Natural Science Foundation of China(No.52305358)the Fundamental Research Funds for the Central Universities(No.2023ZYGXZR061)+2 种基金the Guangdong Basic and Applied Basic Research Foundation(No.2022A1515010304)the Young Elite Scientists Sponsorship Program by CAST(No.2023QNRC001)the Young Talent Support Project of Guangzhou(No.QT-2023-001).
文摘Laser powder bed fusion(LPBF)additive manufacturing of zinc(Zn)offers promising advantages for biodegradable metal bone implants,including tailorable microstructures,controllable porous structures,and appropriate degradation rates.However,the layer-by-layer construction during LPBF often leads to microstructural and performance anisotropy within metallic materials.In this work,the anisotropic mechanical and degradation properties of pure Zn processed using LPBF were comprehensively investigated for the first time.Specifically,the influence of microstructural characteristics on the mechanical and degradation properties of LPBF-processed Zn in both horizontal and vertical planes was revealed,while the underlying deformation mechanisms in different planes were illustrated.The results demonstrated that the horizontal plane exhibited higher mechanical strength compared to the vertical plane,with ulti-mate tensile strength of 123.6 and 107.86 MPa,respectively,significantly surpassing that of the tradition-ally cast counterpart(52.7 MPa).Importantly,abundant deformation twins coupled with infrequent microbands and pyramidal(c+a)slip systems activated during tensile loading along the vertical plane enabled multiple deformation modes,which sustained durable work hardening ability while delaying plastic instability,resulting in extraordinary plasticity(elongation of 14.2%).Additionally,synergistic effects between high-density grain boundaries including low-angle grain boundaries and pre-existing dislocations promoted the stable presence of a passive film along the horizontal plane,thus exhibiting relatively low corrosion sensitivity.Furthermore,the LPBF-processed Zn also demonstrated favorable biological activity and osteogenic potential.These findings provide valuable insights into multiple mechanisms underlying anisotropy in mechanical and degradation properties of laser additively manufactured Zn-based materials.
