High spatial frequency laser induced periodic surface structures(HSFLs)on silicon substrates are often developed on flat surfaces at low fluences near ablation threshold of 0.1 J/cm2,seldom on microstructures or micro...High spatial frequency laser induced periodic surface structures(HSFLs)on silicon substrates are often developed on flat surfaces at low fluences near ablation threshold of 0.1 J/cm2,seldom on microstructures or microgrooves at relatively higher fluences above 1 J/cm^2.This work aims to enrich the variety of HSFLs-containing hierarchical microstructures,by femtosecond laser(pulse duration:457 fs,wavelength:1045 nm,and repetition rate:100 kHz)in liquids(water and acetone)at laser fluence of 1.7 J/cm^2.The period of Si-HSFLs in the range of 110–200 nm is independent of the scanning speeds(0.1,0.5,1 and 2 mm/s),line intervals(5,15 and 20μm)of scanning lines and scanning directions(perpendicular or parallel to light polarization direction).It is interestingly found that besides normal HSFLs whose orientations are perpendicular to the direction of light polarization,both clockwise or anticlockwise randomly tilted HSFLs with a maximal deviation angle of 50°as compared to those of normal HSFLSs are found on the microstructures with height gradients.Raman spectra and SEM characterization jointly clarify that surface melting and nanocapillary waves play important roles in the formation of Si-HSFLs.The fact that no HSFLs are produced by laser ablation in air indicates that moderate melting facilitated with ultrafast liquid cooling is beneficial for the formation of HSFLs by LALs.On the basis of our findings and previous reports,a synergistic formation mechanism for HSFLs at high fluence was proposed and discussed,including thermal melting with the concomitance of ultrafast cooling in liquids,transformation of the molten layers into ripples and nanotips by surface plasmon polaritons(SPP)and second-harmonic generation(SHG),and modulation of Si-HSFLs direction by both nanocapillary waves and the localized electric field coming from the excited large Si particles.展开更多
A novel, Ti-6 Al-4 V(Ti64)/Hydroxyapatite(HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion(EPBF) additive manufacturing(AM): specifically, the commerc...A novel, Ti-6 Al-4 V(Ti64)/Hydroxyapatite(HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion(EPBF) additive manufacturing(AM): specifically, the commercial electron beam melting(EBM?) process. In addition to solid Ti64 and Ti64/5% HA samples, four different unit cell(model) open-cellular mesh structures for the Ti64/5% HA composite were fabricated having densities ranging from 0.68 to 1.12 g/cm^3, and corresponding Young's moduli ranging from 2.9 to 8.0 GPa, and compressive strengths ranging from ~3 to 11 MPa. The solid Ti64/5%HA composite exhibited an optimal tensile strength of 123 MPa, and elongation of 5.5% in contrast to a maximum compressive strength of 875 MPa. Both the solid composite and mesh samples deformed primarily by brittle deformation, with the mesh samples exhibiting erratic, brittle crushing. Solid, EPBF-fabricated Ti64 samples had a Vickers microindentation hardness of 4.1 GPa while the Ti64/5%HA solid composite exhibited a Vickers microindentation hardness of 6.8 GPa. The lowest density Ti64/5%HA composite mesh strut sections had a Vickers microindentation hardness of 7.1 GPa. Optical metallography(OM) and scanning electron microscopy(SEM) analysis showed the HA dispersoids to be highly segregated along domain or grain boundaries, but homogeneously distributed along alpha(hcp) platelet boundaries within these domains in the Ti64 matrix for both the solid and mesh composites. The alpha platelet width varied from ~5 μm in the EPBF-fabricated Ti64 to ~1.1 m for the Ti64/5%HA mesh strut. The precursor HA powder diameter averaged 5 μm, in contrast to the dispersed HA particle diameters in the Ti64/5%HA composite which averaged 0.5 m. This work highlights the use of EPBF AM as a novel process for fabrication of a true composite structure, consisting of a Ti64 matrix and interspersed and exposed HA domains, which to the authors' knowledge has not been reported before. The results also illustrate the prospects not only for fabricating specialized, novel composite bone replacement scaffolds and implants, through the combination of Ti64 and HA, but also prospects for producing a variety of related metal/ceramic composites using EPBF AM.展开更多
The present study is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of duplex stainless steel welded joints. In this regard, inf...The present study is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of duplex stainless steel welded joints. In this regard, influence of different laser welding parameters was clarified. Both bead-on-plate and autogenously butt welded joints were made using carbon dioxide laser with a maximum output of 9 kW in the continuous wave mode. Welded joints were subjected to visual, dye penetrant and radiography tests before sectioning it for different destructive tests. Accelerated corrosion test was carried out based on tafel plot technique. The results achieved in this investigation disclosed that welding parameters play an important role in obtaining satisfactory properties of welded joint. High laser power and/or high welding speed together with adjusting laser focused spot at specimen surface have produced welded joints with a remarkable decrease in fusion zone size and an acceptable weld profile with higher weld depth/width ratio. Besides, acceptable mechanical and corrosion properties were obtained. Using nitrogen as a shielding gas has resulted in improving mechanical and corrosion properties of welded joints in comparison with argon shielding. This is related to maintaining proper ferrite/austenite balance in both weld metal and HAZ in case of nitrogen shielding. As a conclusion, laser power, welding speed, defocusing distance and type of shielding gas combination have to be optimized for obtaining welded joints with acceptable profile as well as mechanical and corrosion properties.展开更多
Plasma-based optical elements can withstand laser intensities several orders of magnitude higher than traditional optical elements,making them highly promising for manipulating relativistic intensity laser pulses.In t...Plasma-based optical elements can withstand laser intensities several orders of magnitude higher than traditional optical elements,making them highly promising for manipulating relativistic intensity laser pulses.In this work,we propose and demonstrate a novel microstructured plasma target,inspired by the design of traditional Fresnel zone plates.The specific target structure causes diffraction of the input laser at each zone,resulting in constructive interference and facilitating effective focusing of the input laser pulse.Three-dimensional particle-in-cell simulation results show that the microstructured plasma target can focus Gaussian laser pulses with an intensity of the order of 10^(22) W/cm^(2)to an intensity exceeding 10^(24) W/cm^(2)with the laser focus spot size approaching the diffraction limit of-0.73μm and laser fluence enhancement by a factor of 46.It is also found that when the microstructured plasma target is modified into a reflective element,laser intensities up to 10^(25) W/cm^(2)may be achieved.This extremely high-intensity tightly focused laser pulse can trigger intense photon radiation when interacting with targets,(e.g.,wire plasma targets),with potential applications in laboratory astrophysics,as well as providing the opportunity to explore phenomena such as vacuum birefringence and quantum electrodynamical cascades.展开更多
Inertial confinement fusion(ICF)requires a constant search for the most effective materials to improve the efficiency of compression of the capsule and of laser-to-target energy transfer.Foams could provide a solution...Inertial confinement fusion(ICF)requires a constant search for the most effective materials to improve the efficiency of compression of the capsule and of laser-to-target energy transfer.Foams could provide a solution,but they require further experimental and theoretical investigation.The new 3D-printing technologies,such as two-photon polymerization,are opening a new era in the production of foams,allowing fine control of material morphology.Very few detailed studies of the interaction of foams with high-power lasers in regimes relevant for ICF have been described in the literature to date,and more investigation is needed.In this work,we present the results of an experimental campaign performed at the ABC laser facility at ENEA Centro Ricerche Frascati in which 3D-printed microstructured materials were irradiated at high power.3D simulations of the laser-target interaction performed with the FLASH code reveal that the laser is scattered by plasma density gradients and channeled into the structure when the center of the focal spot is on the through hole.The time required for the laser to completely ablate the structure given by the simulations is in good agreement with the experimental measurement.Measurements of the reflected and transmitted laser light indicate that scattering occurred during the irradiation,in accordance with the simulations.Two-plasmon decay has also been found to be active during irradiation.展开更多
Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel st...Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel steel. The results showed that although the roughness of the original specimen induced by mechanical processing would diminish to some extent in the experiment, the 0.5 - 1.5 μm thick layer of ultrafine microstructure on the original mechanically-processed specimen surface would still become micro-cracks and small spalling pits due to spalling, and would further evolve into fatigue crack source. Additionally, even under the impact of the load that was not adequate to make the material reach fatigue limit, the ferrite in the microstructure underwent plastic deformation, which led the refinement of proeutectoid ferrite grains. During the experiment, the hardening and the refinement caused by plastic deformation consisted with the theory that dislocation gave rise to plastic deformation and grain refinement. The distribution laws of hardness and ferrite grain sizes measured could be explained by the distribution law of the shearing stress in the subsurface.展开更多
Stress corrosion cracking(SCC) of an SA508-309 L/308 L–316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a...Stress corrosion cracking(SCC) of an SA508-309 L/308 L–316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a microstructure characterization. The 308 L weld metal shows a higher content of δ ferrite than the 309 L weld metal. In addition, no obvious Cr-depletion but carbides precipitation at δ phase boundaries was observed in both 308 L and 309 L weld metals. The slow strain rate tension tests showed that the SCC susceptibility of the base and weld metals of the dissimilar metal weld joint follows the order of SA508 < 308 L weld metal < the heat affected zone of 316 L base metal < 309 L weld metal.The higher SCC susceptibility of 309 L weld metal than that of 308 L weld metal is likely due to the lower content of δ ferrite. In addition, a preferential SCC initiation in the 309 L weld metal adjacent to 308 L weld metal is attributed to few carbides in this region.展开更多
Fiber-optic sensing technology has the advantages of passivity, anti-electromagnetic interference, longdistancemeasurement, high sensitivity and high accuracy, small size, and adaptability to harsh environments such a...Fiber-optic sensing technology has the advantages of passivity, anti-electromagnetic interference, longdistancemeasurement, high sensitivity and high accuracy, small size, and adaptability to harsh environments such ashigh-vacuum, high-pressure, and strong magnetic fields compared with the traditional electrical sensing technology.However, with the increasing application requirements, how to further improve the sensitivity of fiber-optic sensors,extend the detection limit and improve the maintenance-free capability has become one of the core issues of thecurrent research. This paper reviews the principle, preparation, and application of fiber-optic microstructured sensingbased on abrupt field type. It specifically outlines the development and applications of micro-nano optical fibers,photonic crystal optical fibers, optical fiber gratings and structured optical fibers, and lists the main preparationmethods of two types of micro-nano optical fibers from the basic theory of optical fiber microstructured sensordevices.展开更多
The optimization of microstructure represents a significant methodology for enhancing coercivity(Hcj).This paper concentrates on optimizing the microstructure of magnets through the manipulation of the composition of ...The optimization of microstructure represents a significant methodology for enhancing coercivity(Hcj).This paper concentrates on optimizing the microstructure of magnets through the manipulation of the composition of low-melting-point and high-melting-point elements,thereby achieving the objective of augmenting the comprehensive magnetic properties of magnets.The present study is concerned with the microstructure of magnets comprising three distinct Ga and B contents,and the associated changes in their magnetic properties.The findings indicate that when the Ga content is 0.5 wt%and the B content is 0.88 wt%,the coercivity of the magnets is markedly enhanced.This is evidenced by an increase in coercivity from 8.51 to 14.83 kOe,representing a 74.26%rise.Concurrently,the residual magnetization strength of the magnet remains unaltered.This finding provides a crucial foundation for optimizing the overall magnetic properties of the magnets.The microstructural analysis indicates that a reduction in B content coupled with an increase in Ga content leads to the melting of sharp angles on the surface of the main-phase grains,facilitated by low-melting-point rare-earth-rich phases.This process results in the migration of Fe from the grain boundaries(GBs)to the triple junction phases(TJPs),while Nd migrates from the TJPs to the GBs.This migration results in a reduction in the agglomeration of rare-earth-rich elements within the TJPs,thereby increasing the Nd content in the GBs.This increase enhances the wettability of the GBs,while the reduction of Fe content in this phase mitigates the exchange-coupling effect between the main-phase GBs.Consequently,the GBs become more smooth,more homogeneous and more continuous,which ultimately results in an enhancement of the coercivity of the magnets.展开更多
The Cu-12Fe alloy has attracted significant attention due to its excellent electrical conductivity and electromagnetic shielding capability,high strength,cost-effectiveness,and recyclability.In the present work,the Cu...The Cu-12Fe alloy has attracted significant attention due to its excellent electrical conductivity and electromagnetic shielding capability,high strength,cost-effectiveness,and recyclability.In the present work,the Cu-12Fe alloy strip with the thickness of 2.4 mm was successfully produced by twin-roll strip casting.The microstructure and properties of the Cu-12Fe alloy were tailored by cold rolling and aging treatment.The tensile strength of the as-cast strip is approximately 328 MPa and its elongation is 25%.The Fe phase randomly dispersed in the matrix,and the average size of Fe-rich phase is 2μm.Besides,enrichment of Fe phase is observed in the central layer of the strip,results in the formation of the“sandwich structure”.Moreover,the as-cast strip of Cu-12Fe was directly cold-rolled from 2.4 to 0.12 mm.The directly cold-rolled sample after aging at 450℃for 16 h(ProcessⅠ)shows excellent electrical conductivity of 69.5%IACS,the tensile strength and elongation are 513 MPa and 3.8%,the saturation magnetic flux density is 20.1 emu·g^(-1),and the coercive force is 25.2 Oe.In ProcessⅡ,the as-cast strip firstly cold-rolled to 1.2 mm,then aged at 500℃for 1.5 h,followed by cold rolling to 0.12 mm,finally aged at 450℃for 16 h.The sample after ProcessⅡshows the electrical conductivity of 66.3%IACS,the tensile strength of 533 MPa,an elongation of 3.5%,saturation magnetic flux density of 21.4 emu·g^(-1),and the coercive force of 22.3 Oe.展开更多
In two-scale topology optimization,enhancing the connectivity between adjacent microstructures is crucial for achieving the collaborative optimization of micro-scale performance and macro-scale manufacturability.This ...In two-scale topology optimization,enhancing the connectivity between adjacent microstructures is crucial for achieving the collaborative optimization of micro-scale performance and macro-scale manufacturability.This paper proposes a two-scale concurrent topology optimization strategy aimed at improving the interface connection strength.This method employs a parametric approach to explicitly divide the micro-design domain into a“boundary connection region”and a“free design domain”at the initial stage of optimization.The boundary connection region is used to generate a connection layer that enhances the interface strength,while the free design domain is not constrained by this layer,thus fully exploiting the design potential of the material layout.During the optimization process,the solid isotropic material with penalization(SIMP)method is first used to optimize the material distribution in the free design domain,and filtering and projection techniques are employed to alleviate numerical instability and obtain a clear topological structure.Subsequently,the effective performance of the microstructure is calculated through homogenization and transferred to the macro-scale for global response analysis.Throughout the iterative process,the geometry of the connection layer remains unchanged,and only the free design domain is optimized,thereby achieving a balance between high performance and good manufacturability.The effectiveness of the proposed method is verified through numerical examples.展开更多
5xxx Al alloys are widely used in additive manufacturing(AM)components across various industries due to their advantageous properties,including low density,high strength,and excellent corrosion resistance.However,conv...5xxx Al alloys are widely used in additive manufacturing(AM)components across various industries due to their advantageous properties,including low density,high strength,and excellent corrosion resistance.However,conventional melt-based AM methods often introduce defects such as pores,cracks and elemental evaporation.In the present study,a novel screw extrusion-plasticizing friction stir deposition(SEFSD)process,which enables the extrusion plasticization of 5183 particulate feedstocks via a three-stage tapered screw tool,was utilized to fabricate a 20-layer 5183 deposition wall through continuous linear reciprocating deposition in the solid state.The deposition wall exhibited a refined equiaxed microstructure.Due to the low stacking fault energy(SFE)of Al-Mg alloy,the influence of thermal cycles on microstructural evolution was minimal.Overall,the deposition wall demonstrated excellent mechanical properties,though strength and ductility in the deposition direction were reduced due to interlayer defects,which could be mitigated by incorporating stir pins or enhancing interlayer adhesive friction to intensify the material flow.This study confirms the applicability and significant potential of SEFSD for additive manufacturing 5xxx Al alloy components.展开更多
The strength-ductility synergy in heterogeneous materials offers significant advantages,though their scalable and controlled fabrication remains challenging.This study introduces an in situ fabrication strategy for he...The strength-ductility synergy in heterogeneous materials offers significant advantages,though their scalable and controlled fabrication remains challenging.This study introduces an in situ fabrication strategy for heterogeneous lamellar titanium(HLT)alloy via laser powder bed fusion of a powder mixture consisting of Ti6Al4V(TC4)and 3 wt%Fe.By periodically varying the scanning velocity between layers,a heterogeneous lamellar microstructure is achieved due to the unique Fe distribution originating from the various volumetric energy densities(VEDs).Consequently,the HLT achieves high yield strength(1036 MPa)and ultimate tensile strength(1419 MPa)without compromising uniform elongation(UE),surpassing most TC4 alloys.The high strength may be attributed to precipitation strengthening originating from the nano-sizedαandωprecipitates,while the high UE and work hardening arise from the strain-induced martensite(SIM)and strong hetero-deformation induced(HDI)stress.The denser dual-phase interfaces and smaller grains in the low VED layers contribute to the higher sensitivity to the SIM.A strain gradient between soft and hard layers evolves during loading,and it further enhances the HDI strengthening and SIM behavior.Through this work,the in situ fabrication method and the deformation mechanism of lamellar heterostructure could offer valuable reference for the optimization and application of heterogeneous materials.展开更多
Cold deformation treatment of Cu-bearing stainless steel through a cold rolling process combined with electric pulse treatment(EPT)can significantly improve the microstructure and formability of cold-rolled Cu-bearing...Cold deformation treatment of Cu-bearing stainless steel through a cold rolling process combined with electric pulse treatment(EPT)can significantly improve the microstructure and formability of cold-rolled Cu-bearing stainless steel.The microstructure after EPT was characterized by scanning electron microscopy,transmission electron microscopy,and in-situ tensile testing.It is found that compared with conventional heat treatment,EPT process can significantly promote the nucleation rate and mobility at grain boundaries of the deformed samples,greatly accelerating the recovery and static recrystallization of Cu-bearing stainless steel samples at lower temperatures and contributing to the recovery of anisotropy and the re-molding of deformed samples.Microstructural characterization and theoretical analyses show that the rapid recrystallization during EPT process is caused not only by Joule heating effects but also by non-thermal effects that accelerate grain boundary migration and dislocation destruction and regeneration.In addition,EPT process significantly accelerated the nucleation and precipitation growth of Cu-rich phase.The coarsening of Cu-rich phase during EPT process is due to not only the high vacancy diffusion coefficient under the action of the electric pulse but also the increase in the vacancy diffusion flux induced by the electromigration in the process of the electric pulse.展开更多
The impact of Mn addition on the microstructure,mechanical properties and corrosion behavior of T6-treated Al−Si−Mg−xMn(x=0.2−1.0 wt.%)alloys in a 3.5 wt.%NaCl solution was investigated.The results showed that adding ...The impact of Mn addition on the microstructure,mechanical properties and corrosion behavior of T6-treated Al−Si−Mg−xMn(x=0.2−1.0 wt.%)alloys in a 3.5 wt.%NaCl solution was investigated.The results showed that adding 0.2 wt.%Mn to T6-treated Al−Si−Mg alloys enhanced the corrosion resistance by promoting the formation ofα-AlFeMnSi phase,characterized by smaller absolute Volta potential values compared to eutectic Si,β-AlFeSi andπ-AlFeMgSi phases.However,the addition of 0.5 wt.%Mn and 1.0 wt.%Mn to the T6-treated Al−Si−Mg alloys increased the size of theα-AlFeMnSi phase.This decreased the properties of T6-treated Al−Si−Mg alloys.Therefore,the optimum Mn content was 0.2 wt.%,providing a novel approach for synergistically enhancing mechanical properties and corrosion resistance of Al−Si−Mg alloys.展开更多
The densification characterization,phase constitution,precipitation evolution and mechanical performance of Al−Mg−Sc−Zr alloy processed by laser powder bed fusion(LPBF)were systematically investigated.Moreover,the evo...The densification characterization,phase constitution,precipitation evolution and mechanical performance of Al−Mg−Sc−Zr alloy processed by laser powder bed fusion(LPBF)were systematically investigated.Moreover,the evolution of phase constitution and precipitation behavior after heat treatment were characterized by using X-ray diffraction(XRD)and transmission electron microscope(TEM)analysis.The ultimate tensile strength(UTS)of as-built samples ranged from 396.8 to 414.6 MPa as the scanning speed decreased from 1600 to 1000 mm/s.After post heat treatment,the yield strength(YS)increased to(513.1±1.3)MPa,while the UTS increased from(414.6±5.1)to(539.2±1.5)MPa.The significant improvement of mechanical performance was ascribed to the formation of secondary Al3(Sc,Zr)precipitates.展开更多
The creep response,mechanical properties,and microstructure evolution of the Al−Zn−Mg−Cu alloy were investigated under different initial heat treatment conditions.The results indicate that the density of geometrically...The creep response,mechanical properties,and microstructure evolution of the Al−Zn−Mg−Cu alloy were investigated under different initial heat treatment conditions.The results indicate that the density of geometrically necessary dislocations(GNDs)increases during the initial creep stage(<0.5 h)and undergoes dynamic changes in the stable creep stage.During creep aging,the dislocation distribution within the grains becomes more uniform,and additional subgrains are formed.The key factors influencing creep behavior are crystal orientation and the degree of initial precipitation.Grains oriented in the<001>and<101>directions are more susceptible to deformation during the creep process.Based on a strength model,the inhibitory effects of the η'phase in T6 specimens and the GP I zone in T4 specimens on dislocation motion were evaluated.This study demonstrates that selecting an appropriate initial precipitation state is an effective strategy to enhance the creep aging response and to produce high-performance components.展开更多
Incorporating ceramic particles into metal matrices is a proven strategy for boosting mechanical properties and wear resistance.The reinforcement potential of tungsten carbide(WC)particles in 316L stainless steel is r...Incorporating ceramic particles into metal matrices is a proven strategy for boosting mechanical properties and wear resistance.The reinforcement potential of tungsten carbide(WC)particles in 316L stainless steel is revealed,utilizing selective laser melting(SLM)to fabricate composites with 5 and 10 vol.%WC.The WC incorporation markedly alters the composite’s microstructure and mechanical attributes.Notably,5 vol.%WC-316L composite exhibits a refined submicron cellular structure,averaging 0.67μm in grain size.Elemental diffusion at WC-316L interface formed a 0.8μm gradient transition layer enriched with M_(2)C carbides(Fe,Cr,W),ensuring robust metallurgical bonding.Compared with unreinforced 316L,5%WC composite exhibits a 70%increase in tensile strength,reaching 1012.6 MPa,and a 25.3%rise in hardness,while maintaining acceptable ductility.10%WC composite achieves a 70.8%hardness enhancement,albeit with reduced elongation.Friction coefficient is reduced by up to 17.3%,and the wear mechanism shifts from adhesive to abrasive,significantly improving wear resistance.展开更多
A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysi...A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysis of typical slag rims for two highly crystalline powders revealed that their formation was primarily driven by the solidification of the liquid slag.Distinct differences were observed in the microstructures of slag rims from the two powders.Powder A(characterized by a higher breaking temperature and viscosity)displayed alternating lamellar microstructures of coarse and fine phases,with the coarse phases composed of akermanite-gehlenite transition phases.In contrast,powder B(with a lower breaking temperature and viscosity)predominantly comprised regular akermanite-gehlenite crystals interspersed with a certain amount of glassy phases.Numerical simulations of a three-phase fluid flow coupled with heat transfer indicate that slag rim formation correlates with mold oscillation.Solidification of the liquid slag at the slag rim front predominantly occurs during the negative stroke of the mold oscillation.The average heating rate during the ascending stage of the mold reaches approximately 100 K·s^(−1),whereas the average cooling rate during the descending stage attains 400 K·s^(−1).This temperature variation leads to the formation of lamellar microstructures,whereas the ascending stage promotes the formation of coarse structures and thicker slag rims.Based on the powder properties,two distinct formation pathways exist for highly crystalline mold powders.For the powders with a higher breaking temperature,higher viscosity,and narrower solidification range(powder A),coarse microstructures and thicker slag rims were preferentially formed.For powders with lower breaking temperature and viscosity and wider solidification ranges(powder B),the liquid slag resisted rapid solidification,and the extended mushy zone allowed the partial liquid slag to persist at the slag rim front,promoting the formation of a thin slag rim.This study enhances the understanding of slag rim formation in highly crystalline mold powders and provides critical insights into the control of longitudinal surface cracks in hypo-peritectic steel.展开更多
文摘High spatial frequency laser induced periodic surface structures(HSFLs)on silicon substrates are often developed on flat surfaces at low fluences near ablation threshold of 0.1 J/cm2,seldom on microstructures or microgrooves at relatively higher fluences above 1 J/cm^2.This work aims to enrich the variety of HSFLs-containing hierarchical microstructures,by femtosecond laser(pulse duration:457 fs,wavelength:1045 nm,and repetition rate:100 kHz)in liquids(water and acetone)at laser fluence of 1.7 J/cm^2.The period of Si-HSFLs in the range of 110–200 nm is independent of the scanning speeds(0.1,0.5,1 and 2 mm/s),line intervals(5,15 and 20μm)of scanning lines and scanning directions(perpendicular or parallel to light polarization direction).It is interestingly found that besides normal HSFLs whose orientations are perpendicular to the direction of light polarization,both clockwise or anticlockwise randomly tilted HSFLs with a maximal deviation angle of 50°as compared to those of normal HSFLSs are found on the microstructures with height gradients.Raman spectra and SEM characterization jointly clarify that surface melting and nanocapillary waves play important roles in the formation of Si-HSFLs.The fact that no HSFLs are produced by laser ablation in air indicates that moderate melting facilitated with ultrafast liquid cooling is beneficial for the formation of HSFLs by LALs.On the basis of our findings and previous reports,a synergistic formation mechanism for HSFLs at high fluence was proposed and discussed,including thermal melting with the concomitance of ultrafast cooling in liquids,transformation of the molten layers into ripples and nanotips by surface plasmon polaritons(SPP)and second-harmonic generation(SHG),and modulation of Si-HSFLs direction by both nanocapillary waves and the localized electric field coming from the excited large Si particles.
文摘A novel, Ti-6 Al-4 V(Ti64)/Hydroxyapatite(HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion(EPBF) additive manufacturing(AM): specifically, the commercial electron beam melting(EBM?) process. In addition to solid Ti64 and Ti64/5% HA samples, four different unit cell(model) open-cellular mesh structures for the Ti64/5% HA composite were fabricated having densities ranging from 0.68 to 1.12 g/cm^3, and corresponding Young's moduli ranging from 2.9 to 8.0 GPa, and compressive strengths ranging from ~3 to 11 MPa. The solid Ti64/5%HA composite exhibited an optimal tensile strength of 123 MPa, and elongation of 5.5% in contrast to a maximum compressive strength of 875 MPa. Both the solid composite and mesh samples deformed primarily by brittle deformation, with the mesh samples exhibiting erratic, brittle crushing. Solid, EPBF-fabricated Ti64 samples had a Vickers microindentation hardness of 4.1 GPa while the Ti64/5%HA solid composite exhibited a Vickers microindentation hardness of 6.8 GPa. The lowest density Ti64/5%HA composite mesh strut sections had a Vickers microindentation hardness of 7.1 GPa. Optical metallography(OM) and scanning electron microscopy(SEM) analysis showed the HA dispersoids to be highly segregated along domain or grain boundaries, but homogeneously distributed along alpha(hcp) platelet boundaries within these domains in the Ti64 matrix for both the solid and mesh composites. The alpha platelet width varied from ~5 μm in the EPBF-fabricated Ti64 to ~1.1 m for the Ti64/5%HA mesh strut. The precursor HA powder diameter averaged 5 μm, in contrast to the dispersed HA particle diameters in the Ti64/5%HA composite which averaged 0.5 m. This work highlights the use of EPBF AM as a novel process for fabrication of a true composite structure, consisting of a Ti64 matrix and interspersed and exposed HA domains, which to the authors' knowledge has not been reported before. The results also illustrate the prospects not only for fabricating specialized, novel composite bone replacement scaffolds and implants, through the combination of Ti64 and HA, but also prospects for producing a variety of related metal/ceramic composites using EPBF AM.
文摘The present study is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of duplex stainless steel welded joints. In this regard, influence of different laser welding parameters was clarified. Both bead-on-plate and autogenously butt welded joints were made using carbon dioxide laser with a maximum output of 9 kW in the continuous wave mode. Welded joints were subjected to visual, dye penetrant and radiography tests before sectioning it for different destructive tests. Accelerated corrosion test was carried out based on tafel plot technique. The results achieved in this investigation disclosed that welding parameters play an important role in obtaining satisfactory properties of welded joint. High laser power and/or high welding speed together with adjusting laser focused spot at specimen surface have produced welded joints with a remarkable decrease in fusion zone size and an acceptable weld profile with higher weld depth/width ratio. Besides, acceptable mechanical and corrosion properties were obtained. Using nitrogen as a shielding gas has resulted in improving mechanical and corrosion properties of welded joints in comparison with argon shielding. This is related to maintaining proper ferrite/austenite balance in both weld metal and HAZ in case of nitrogen shielding. As a conclusion, laser power, welding speed, defocusing distance and type of shielding gas combination have to be optimized for obtaining welded joints with acceptable profile as well as mechanical and corrosion properties.
基金supported by the National Natural Science Foundation of China(Grant Nos.12375244 and 12135009)the Natural Science Foundation of Hunan Province of China(Grant No.2025JJ30002).
文摘Plasma-based optical elements can withstand laser intensities several orders of magnitude higher than traditional optical elements,making them highly promising for manipulating relativistic intensity laser pulses.In this work,we propose and demonstrate a novel microstructured plasma target,inspired by the design of traditional Fresnel zone plates.The specific target structure causes diffraction of the input laser at each zone,resulting in constructive interference and facilitating effective focusing of the input laser pulse.Three-dimensional particle-in-cell simulation results show that the microstructured plasma target can focus Gaussian laser pulses with an intensity of the order of 10^(22) W/cm^(2)to an intensity exceeding 10^(24) W/cm^(2)with the laser focus spot size approaching the diffraction limit of-0.73μm and laser fluence enhancement by a factor of 46.It is also found that when the microstructured plasma target is modified into a reflective element,laser intensities up to 10^(25) W/cm^(2)may be achieved.This extremely high-intensity tightly focused laser pulse can trigger intense photon radiation when interacting with targets,(e.g.,wire plasma targets),with potential applications in laboratory astrophysics,as well as providing the opportunity to explore phenomena such as vacuum birefringence and quantum electrodynamical cascades.
基金framework of the EUROfusion Consortium,funded by the European Union via the Euratom Research and Training Programme(Grant Agreement No.101052200—EUROfusion)The CRESCO-ENEAGRID High Performance Computing infrastructure is funded by ENEA+3 种基金the Italian National Agency for New Technologies,Energy and Sustainable Economic Developmentby Italian and European research programmesthe framework of the“Universities’Excellence Initiative”programme by the Ministry of Education,Science and Sports of the Republic of Lithuania under an agreement with the Research Council of Lithuania(Project No.S-A-UEI-23-6)support was received through EU LASERLAB-EUROPE JRAextension(Grant Agreement No.871124,Horizon 2020 Research and Innovation Programme).
文摘Inertial confinement fusion(ICF)requires a constant search for the most effective materials to improve the efficiency of compression of the capsule and of laser-to-target energy transfer.Foams could provide a solution,but they require further experimental and theoretical investigation.The new 3D-printing technologies,such as two-photon polymerization,are opening a new era in the production of foams,allowing fine control of material morphology.Very few detailed studies of the interaction of foams with high-power lasers in regimes relevant for ICF have been described in the literature to date,and more investigation is needed.In this work,we present the results of an experimental campaign performed at the ABC laser facility at ENEA Centro Ricerche Frascati in which 3D-printed microstructured materials were irradiated at high power.3D simulations of the laser-target interaction performed with the FLASH code reveal that the laser is scattered by plasma density gradients and channeled into the structure when the center of the focal spot is on the through hole.The time required for the laser to completely ablate the structure given by the simulations is in good agreement with the experimental measurement.Measurements of the reflected and transmitted laser light indicate that scattering occurred during the irradiation,in accordance with the simulations.Two-plasmon decay has also been found to be active during irradiation.
文摘Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel steel. The results showed that although the roughness of the original specimen induced by mechanical processing would diminish to some extent in the experiment, the 0.5 - 1.5 μm thick layer of ultrafine microstructure on the original mechanically-processed specimen surface would still become micro-cracks and small spalling pits due to spalling, and would further evolve into fatigue crack source. Additionally, even under the impact of the load that was not adequate to make the material reach fatigue limit, the ferrite in the microstructure underwent plastic deformation, which led the refinement of proeutectoid ferrite grains. During the experiment, the hardening and the refinement caused by plastic deformation consisted with the theory that dislocation gave rise to plastic deformation and grain refinement. The distribution laws of hardness and ferrite grain sizes measured could be explained by the distribution law of the shearing stress in the subsurface.
基金supported by the National Natural Science Foundation of China(No.51571204)the support of the Youth Scientific and Innovation Research Team for Advanced Surface Functional Materials(Southwest Petroleum University,No.2018CXTD06)the Young Scholars Development Found of Southwest Petroleum University(No.201899010040).
文摘Stress corrosion cracking(SCC) of an SA508-309 L/308 L–316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a microstructure characterization. The 308 L weld metal shows a higher content of δ ferrite than the 309 L weld metal. In addition, no obvious Cr-depletion but carbides precipitation at δ phase boundaries was observed in both 308 L and 309 L weld metals. The slow strain rate tension tests showed that the SCC susceptibility of the base and weld metals of the dissimilar metal weld joint follows the order of SA508 < 308 L weld metal < the heat affected zone of 316 L base metal < 309 L weld metal.The higher SCC susceptibility of 309 L weld metal than that of 308 L weld metal is likely due to the lower content of δ ferrite. In addition, a preferential SCC initiation in the 309 L weld metal adjacent to 308 L weld metal is attributed to few carbides in this region.
基金financially supported by the High-Tech Research and Development Program of China(No.SS2013AA031305)the Key Technologies R&D Program of Tianjin(No.12ZCDGGX49100)
基金support by National Natural Science Foundation of China (Nos. 51606158, 12104402)
文摘Fiber-optic sensing technology has the advantages of passivity, anti-electromagnetic interference, longdistancemeasurement, high sensitivity and high accuracy, small size, and adaptability to harsh environments such ashigh-vacuum, high-pressure, and strong magnetic fields compared with the traditional electrical sensing technology.However, with the increasing application requirements, how to further improve the sensitivity of fiber-optic sensors,extend the detection limit and improve the maintenance-free capability has become one of the core issues of thecurrent research. This paper reviews the principle, preparation, and application of fiber-optic microstructured sensingbased on abrupt field type. It specifically outlines the development and applications of micro-nano optical fibers,photonic crystal optical fibers, optical fiber gratings and structured optical fibers, and lists the main preparationmethods of two types of micro-nano optical fibers from the basic theory of optical fiber microstructured sensordevices.
基金Project supported by the National Key Research and Development Program of China(2022YFB3503302)the Major Projects in Inner Mongolia Autonomous Region(20212D0035)the High-quality Development Special Funds Program Ministry of Industry Technology(TC220H06G)。
文摘The optimization of microstructure represents a significant methodology for enhancing coercivity(Hcj).This paper concentrates on optimizing the microstructure of magnets through the manipulation of the composition of low-melting-point and high-melting-point elements,thereby achieving the objective of augmenting the comprehensive magnetic properties of magnets.The present study is concerned with the microstructure of magnets comprising three distinct Ga and B contents,and the associated changes in their magnetic properties.The findings indicate that when the Ga content is 0.5 wt%and the B content is 0.88 wt%,the coercivity of the magnets is markedly enhanced.This is evidenced by an increase in coercivity from 8.51 to 14.83 kOe,representing a 74.26%rise.Concurrently,the residual magnetization strength of the magnet remains unaltered.This finding provides a crucial foundation for optimizing the overall magnetic properties of the magnets.The microstructural analysis indicates that a reduction in B content coupled with an increase in Ga content leads to the melting of sharp angles on the surface of the main-phase grains,facilitated by low-melting-point rare-earth-rich phases.This process results in the migration of Fe from the grain boundaries(GBs)to the triple junction phases(TJPs),while Nd migrates from the TJPs to the GBs.This migration results in a reduction in the agglomeration of rare-earth-rich elements within the TJPs,thereby increasing the Nd content in the GBs.This increase enhances the wettability of the GBs,while the reduction of Fe content in this phase mitigates the exchange-coupling effect between the main-phase GBs.Consequently,the GBs become more smooth,more homogeneous and more continuous,which ultimately results in an enhancement of the coercivity of the magnets.
基金financially supported by the Natural Science Foundation of Liaoning Province of China(2022-MS-109)the Key Research and Development Program of Liaoning Province(2023JH2/101800045)the Ministry of Science and Technology of the Peoples Republic of China(ZZ2021006).
文摘The Cu-12Fe alloy has attracted significant attention due to its excellent electrical conductivity and electromagnetic shielding capability,high strength,cost-effectiveness,and recyclability.In the present work,the Cu-12Fe alloy strip with the thickness of 2.4 mm was successfully produced by twin-roll strip casting.The microstructure and properties of the Cu-12Fe alloy were tailored by cold rolling and aging treatment.The tensile strength of the as-cast strip is approximately 328 MPa and its elongation is 25%.The Fe phase randomly dispersed in the matrix,and the average size of Fe-rich phase is 2μm.Besides,enrichment of Fe phase is observed in the central layer of the strip,results in the formation of the“sandwich structure”.Moreover,the as-cast strip of Cu-12Fe was directly cold-rolled from 2.4 to 0.12 mm.The directly cold-rolled sample after aging at 450℃for 16 h(ProcessⅠ)shows excellent electrical conductivity of 69.5%IACS,the tensile strength and elongation are 513 MPa and 3.8%,the saturation magnetic flux density is 20.1 emu·g^(-1),and the coercive force is 25.2 Oe.In ProcessⅡ,the as-cast strip firstly cold-rolled to 1.2 mm,then aged at 500℃for 1.5 h,followed by cold rolling to 0.12 mm,finally aged at 450℃for 16 h.The sample after ProcessⅡshows the electrical conductivity of 66.3%IACS,the tensile strength of 533 MPa,an elongation of 3.5%,saturation magnetic flux density of 21.4 emu·g^(-1),and the coercive force of 22.3 Oe.
基金supported by the Science and Technology Research Project of Henan Province(242102241055)the Industry-University-Research Collaborative Innovation Base on Automobile Lightweight of“Science and Technology Innovation in Central Plains”(2024KCZY315)the Opening Fund of State Key Laboratory of Structural Analysis,Optimization and CAE Software for Industrial Equipment(GZ2024A03-ZZU).
文摘In two-scale topology optimization,enhancing the connectivity between adjacent microstructures is crucial for achieving the collaborative optimization of micro-scale performance and macro-scale manufacturability.This paper proposes a two-scale concurrent topology optimization strategy aimed at improving the interface connection strength.This method employs a parametric approach to explicitly divide the micro-design domain into a“boundary connection region”and a“free design domain”at the initial stage of optimization.The boundary connection region is used to generate a connection layer that enhances the interface strength,while the free design domain is not constrained by this layer,thus fully exploiting the design potential of the material layout.During the optimization process,the solid isotropic material with penalization(SIMP)method is first used to optimize the material distribution in the free design domain,and filtering and projection techniques are employed to alleviate numerical instability and obtain a clear topological structure.Subsequently,the effective performance of the microstructure is calculated through homogenization and transferred to the macro-scale for global response analysis.Throughout the iterative process,the geometry of the connection layer remains unchanged,and only the free design domain is optimized,thereby achieving a balance between high performance and good manufacturability.The effectiveness of the proposed method is verified through numerical examples.
基金the support received from the National Key Research and Development Program of China(Grant No.2023YFB3407400)the National Natural Science Foundation of China(Grant No.52475386,Grant No.52025058).
文摘5xxx Al alloys are widely used in additive manufacturing(AM)components across various industries due to their advantageous properties,including low density,high strength,and excellent corrosion resistance.However,conventional melt-based AM methods often introduce defects such as pores,cracks and elemental evaporation.In the present study,a novel screw extrusion-plasticizing friction stir deposition(SEFSD)process,which enables the extrusion plasticization of 5183 particulate feedstocks via a three-stage tapered screw tool,was utilized to fabricate a 20-layer 5183 deposition wall through continuous linear reciprocating deposition in the solid state.The deposition wall exhibited a refined equiaxed microstructure.Due to the low stacking fault energy(SFE)of Al-Mg alloy,the influence of thermal cycles on microstructural evolution was minimal.Overall,the deposition wall demonstrated excellent mechanical properties,though strength and ductility in the deposition direction were reduced due to interlayer defects,which could be mitigated by incorporating stir pins or enhancing interlayer adhesive friction to intensify the material flow.This study confirms the applicability and significant potential of SEFSD for additive manufacturing 5xxx Al alloy components.
基金financially supported by the National Natural Science Foundation of China(No.52375347)Shanghai Pujiang Programme(No.8003PJD023)Natural Science Foundation of Ningbo(Grant No.2023J008)。
文摘The strength-ductility synergy in heterogeneous materials offers significant advantages,though their scalable and controlled fabrication remains challenging.This study introduces an in situ fabrication strategy for heterogeneous lamellar titanium(HLT)alloy via laser powder bed fusion of a powder mixture consisting of Ti6Al4V(TC4)and 3 wt%Fe.By periodically varying the scanning velocity between layers,a heterogeneous lamellar microstructure is achieved due to the unique Fe distribution originating from the various volumetric energy densities(VEDs).Consequently,the HLT achieves high yield strength(1036 MPa)and ultimate tensile strength(1419 MPa)without compromising uniform elongation(UE),surpassing most TC4 alloys.The high strength may be attributed to precipitation strengthening originating from the nano-sizedαandωprecipitates,while the high UE and work hardening arise from the strain-induced martensite(SIM)and strong hetero-deformation induced(HDI)stress.The denser dual-phase interfaces and smaller grains in the low VED layers contribute to the higher sensitivity to the SIM.A strain gradient between soft and hard layers evolves during loading,and it further enhances the HDI strengthening and SIM behavior.Through this work,the in situ fabrication method and the deformation mechanism of lamellar heterostructure could offer valuable reference for the optimization and application of heterogeneous materials.
基金supported by the National Natural Science Foundation of China(Nos.52305401 and 52475391)National Key Research and Development Program of China(2024YFB3714301)+1 种基金the Fundamental Research Program of Shanxi Province(202303011211004,TZLH20230818001)Engineering Research Center of the Ministry of Education.
文摘Cold deformation treatment of Cu-bearing stainless steel through a cold rolling process combined with electric pulse treatment(EPT)can significantly improve the microstructure and formability of cold-rolled Cu-bearing stainless steel.The microstructure after EPT was characterized by scanning electron microscopy,transmission electron microscopy,and in-situ tensile testing.It is found that compared with conventional heat treatment,EPT process can significantly promote the nucleation rate and mobility at grain boundaries of the deformed samples,greatly accelerating the recovery and static recrystallization of Cu-bearing stainless steel samples at lower temperatures and contributing to the recovery of anisotropy and the re-molding of deformed samples.Microstructural characterization and theoretical analyses show that the rapid recrystallization during EPT process is caused not only by Joule heating effects but also by non-thermal effects that accelerate grain boundary migration and dislocation destruction and regeneration.In addition,EPT process significantly accelerated the nucleation and precipitation growth of Cu-rich phase.The coarsening of Cu-rich phase during EPT process is due to not only the high vacancy diffusion coefficient under the action of the electric pulse but also the increase in the vacancy diffusion flux induced by the electromigration in the process of the electric pulse.
基金supported by the National Key Research and Development Program of China(No.2022YFB3404202)the National Natural Science Foundation of China(No.52271103)the Jilin Scientific and Technological Development Program,China(Nos.20220301026GX,20210301041GX)。
文摘The impact of Mn addition on the microstructure,mechanical properties and corrosion behavior of T6-treated Al−Si−Mg−xMn(x=0.2−1.0 wt.%)alloys in a 3.5 wt.%NaCl solution was investigated.The results showed that adding 0.2 wt.%Mn to T6-treated Al−Si−Mg alloys enhanced the corrosion resistance by promoting the formation ofα-AlFeMnSi phase,characterized by smaller absolute Volta potential values compared to eutectic Si,β-AlFeSi andπ-AlFeMgSi phases.However,the addition of 0.5 wt.%Mn and 1.0 wt.%Mn to the T6-treated Al−Si−Mg alloys increased the size of theα-AlFeMnSi phase.This decreased the properties of T6-treated Al−Si−Mg alloys.Therefore,the optimum Mn content was 0.2 wt.%,providing a novel approach for synergistically enhancing mechanical properties and corrosion resistance of Al−Si−Mg alloys.
基金support of the Research and Development Program in Key Areas of Guangdong Province,China(No.2019B090907001)the Science and Technology Program of Guangdong Province,China(No.2014B010129002)the National Key R&D Program of China(No.2017YFB0305800)。
文摘The densification characterization,phase constitution,precipitation evolution and mechanical performance of Al−Mg−Sc−Zr alloy processed by laser powder bed fusion(LPBF)were systematically investigated.Moreover,the evolution of phase constitution and precipitation behavior after heat treatment were characterized by using X-ray diffraction(XRD)and transmission electron microscope(TEM)analysis.The ultimate tensile strength(UTS)of as-built samples ranged from 396.8 to 414.6 MPa as the scanning speed decreased from 1600 to 1000 mm/s.After post heat treatment,the yield strength(YS)increased to(513.1±1.3)MPa,while the UTS increased from(414.6±5.1)to(539.2±1.5)MPa.The significant improvement of mechanical performance was ascribed to the formation of secondary Al3(Sc,Zr)precipitates.
基金support from the National Key Research and Development Program of China(No.2023YFB3710501)。
文摘The creep response,mechanical properties,and microstructure evolution of the Al−Zn−Mg−Cu alloy were investigated under different initial heat treatment conditions.The results indicate that the density of geometrically necessary dislocations(GNDs)increases during the initial creep stage(<0.5 h)and undergoes dynamic changes in the stable creep stage.During creep aging,the dislocation distribution within the grains becomes more uniform,and additional subgrains are formed.The key factors influencing creep behavior are crystal orientation and the degree of initial precipitation.Grains oriented in the<001>and<101>directions are more susceptible to deformation during the creep process.Based on a strength model,the inhibitory effects of the η'phase in T6 specimens and the GP I zone in T4 specimens on dislocation motion were evaluated.This study demonstrates that selecting an appropriate initial precipitation state is an effective strategy to enhance the creep aging response and to produce high-performance components.
基金supported by Opening funding of National Key Laboratory of Aerospace Liquid Propulsion(HTKJ2024KL011004)Aeronautical Science Fund of China(ASFC-20240042070001)+2 种基金Opening funding of State Key Laboratory of Metal Forming Technology and Heavy Equipment(B2408100.W05)National Key R&D Program of China(2022YFB4601804)National Natural Science Foundation of China(52250287,52275375).
文摘Incorporating ceramic particles into metal matrices is a proven strategy for boosting mechanical properties and wear resistance.The reinforcement potential of tungsten carbide(WC)particles in 316L stainless steel is revealed,utilizing selective laser melting(SLM)to fabricate composites with 5 and 10 vol.%WC.The WC incorporation markedly alters the composite’s microstructure and mechanical attributes.Notably,5 vol.%WC-316L composite exhibits a refined submicron cellular structure,averaging 0.67μm in grain size.Elemental diffusion at WC-316L interface formed a 0.8μm gradient transition layer enriched with M_(2)C carbides(Fe,Cr,W),ensuring robust metallurgical bonding.Compared with unreinforced 316L,5%WC composite exhibits a 70%increase in tensile strength,reaching 1012.6 MPa,and a 25.3%rise in hardness,while maintaining acceptable ductility.10%WC composite achieves a 70.8%hardness enhancement,albeit with reduced elongation.Friction coefficient is reduced by up to 17.3%,and the wear mechanism shifts from adhesive to abrasive,significantly improving wear resistance.
基金supported by the National Natural Science Foundation of China(No.52274318).
文摘A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysis of typical slag rims for two highly crystalline powders revealed that their formation was primarily driven by the solidification of the liquid slag.Distinct differences were observed in the microstructures of slag rims from the two powders.Powder A(characterized by a higher breaking temperature and viscosity)displayed alternating lamellar microstructures of coarse and fine phases,with the coarse phases composed of akermanite-gehlenite transition phases.In contrast,powder B(with a lower breaking temperature and viscosity)predominantly comprised regular akermanite-gehlenite crystals interspersed with a certain amount of glassy phases.Numerical simulations of a three-phase fluid flow coupled with heat transfer indicate that slag rim formation correlates with mold oscillation.Solidification of the liquid slag at the slag rim front predominantly occurs during the negative stroke of the mold oscillation.The average heating rate during the ascending stage of the mold reaches approximately 100 K·s^(−1),whereas the average cooling rate during the descending stage attains 400 K·s^(−1).This temperature variation leads to the formation of lamellar microstructures,whereas the ascending stage promotes the formation of coarse structures and thicker slag rims.Based on the powder properties,two distinct formation pathways exist for highly crystalline mold powders.For the powders with a higher breaking temperature,higher viscosity,and narrower solidification range(powder A),coarse microstructures and thicker slag rims were preferentially formed.For powders with lower breaking temperature and viscosity and wider solidification ranges(powder B),the liquid slag resisted rapid solidification,and the extended mushy zone allowed the partial liquid slag to persist at the slag rim front,promoting the formation of a thin slag rim.This study enhances the understanding of slag rim formation in highly crystalline mold powders and provides critical insights into the control of longitudinal surface cracks in hypo-peritectic steel.
