As a substitute for toxic cadmium coatings in the aerospace industry,zinc-nickel coatings have excellent application prospects,and their properties can be improved by adding molybdenum.In this study,laser-assisted ele...As a substitute for toxic cadmium coatings in the aerospace industry,zinc-nickel coatings have excellent application prospects,and their properties can be improved by adding molybdenum.In this study,laser-assisted electrodeposition is used to improve the surface quality and properties of Zn–Ni–Mo coatings,with investigation of how laser energy in the range of 0–21.1μJ affects their element content,surface morphology,crystal phase,microhardness,residual internal stress,and corrosion resistance.The laser irradiation accelerates the electrodeposition,refines the grain size,improves the hydrogen adsorption,and reduces the residual tensile stress,and a laser energy of 15.4μJ gives the highest Ni and Mo contents and the lowest Zn content,as well as the optimum surface morphology,microhardness,residual internal stress,and corrosion resistance of the coating.展开更多
(CoCrFeNi)95Nb5 high entropy alloy(HEA)coatings were successfully fabricated on a substrate of Q235 steel by laser cladding technology.These(CoCrFeNi)95Nb5 HEA coatings possess excellent properties,particularly corros...(CoCrFeNi)95Nb5 high entropy alloy(HEA)coatings were successfully fabricated on a substrate of Q235 steel by laser cladding technology.These(CoCrFeNi)95Nb5 HEA coatings possess excellent properties,particularly corrosion resistance,which is clearly superior to that of some typical bulk HEA and common engineering alloys.In order to obtain appropriate laser cladding preparation process parameters,the effects of laser energy density on the microstructure,microhardness,and corrosion resistance of(CoCrFeNi)95Nb5 HEA coating were closely studied.Results showed that as the laser energy density increases,precipitation of the Laves phase in(CoCrFeNi)95Nb5 HEA coating gradually decreases,and diffusion of the Fe element in the substrate intensifies,affecting the integrity of the(CoCrFeNi)95Nb5 HEA.This decreases the microhardness of(CoCrFeNi)95Nb5 HEA coatings.Moreover,the relative content of Cr2O3,Cr(OH)3,and Nb2O5 in the surface passive film of the coating decreases with increasing energy density,causing corrosion resistance to decrease.This study demonstrates the controllability of a high-performance HEA coating using laser cladding technology,which has significance for the laser cladding preparation of other CoCrFeNi-system HEA coatings.展开更多
This experiment obtained different laser energy density(LED) by changing SLM molding process parameters.The surface morphology, surface quality, and microstructure of as-fabricated samples were studied. The effects of...This experiment obtained different laser energy density(LED) by changing SLM molding process parameters.The surface morphology, surface quality, and microstructure of as-fabricated samples were studied. The effects of scanning speed, hatching space, and laser power on surface quality were analyzed, and the optimal LED range for surface quality was determined. The results show that pores and spherical particles appear on the sample’s surface when low LED is applied, while there are lamellar structures on the sides of the samples. Cracks appear on the sample’s surface,and the splash phenomenon increases when a high LED is taken. At the same time, a large amount of unmelted powder adhered to the side of the sample. The surface quality is the best when the LED is 150-170 J/mm^(3). The preferred hatch space is currently 0.05-0.09 mm, the laser power is 200-350 W, and the average surface roughness value is(15.1±3) μm.The average surface hardness reaches HV404±HV3, higher than the forging standard range of HV340-HV395.Increasing the LED within the experiment range can increase the surface hardness, yet an excessively high LED will not further increase the surface hardness. The microstructure is composed of needle-like α’-phases with a length of about 20μm, in a crisscross ‘N’ shape, when the LED is low. The β-phase grain boundary is not obvious, and the secondaryphase volume fraction is high;when the LED is high, the α’-phase of the microstructure is in the form of coarse slats, and the secondary-phase is composed of a small amount of secondary α’-phase, the tertiary α’-phase and the fourth α’-phase disappear, and the volume fraction of the secondary-phase becomes low.展开更多
Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstrea...Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.展开更多
Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheat...Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheating,and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal,a gradient distribution of Ni4Ti3 precipitates along the building direction,and preferential formation of Ni4Ti3 precipitates in the columnar zone.The austenite transformation finish temperature(Af)varies from-12.65℃(Z=33 mm)to 60.35℃(Z=10 mm),corresponding to tensile yield strength(σ0.2)changed from 120±30 MPa to 570±20 MPa,and functional properties changed from shape memory effect to superelasticity at room temperature.The sample in the Z=20.4 mm height has the best plasticity of 9.6%and the best recoverable strain of 4.2%.This work provided insights and guidelines for the spatial characterization of DEDed NiTi.展开更多
Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket...Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket engines giving fresh impetus to the birth of gas flow and chemical lasers,which finally turned megawatt lasers from dream into reality.Nowadays,the development of HELs has entered the age of electricity as well as the rocket engines.The properties of current electric rocket engines are highly consistent with HELs’goals,including electrical driving,effective heat dissipation,little medium consumption and extremely light weight and size,which inspired a second fusion of laser and aerospace and motivated the exploration for potential HELs.As an exploratory attempt,a new configuration of diode pumped metastable rare gas laser was demonstrated,with the gain generator resembling an electric rocket-engine for improved power scaling ability.展开更多
Three-dimensional parts of the 30 CrMnSiA steel were successfully fabricated using selective laser melting（SLM）. The microstructures and mechanical properties of the SLM-processed 30 CrMnSiA samples were investigate...Three-dimensional parts of the 30 CrMnSiA steel were successfully fabricated using selective laser melting（SLM）. The microstructures and mechanical properties of the SLM-processed 30 CrMnSiA samples were investigated by scanning electron microscope and transmission electron microscopy. The results indicate that the microstructures of the 30 CrMnSiA samples consist mainly of lath martensite and acicular martensite. The value of the surface roughness decreases with increasing laser energy density（LED） before it reaches a minimum and then increases with further increasing LED. The relative density, microhardness and ultimate tensile strength of the SLM-processed samples initially increase and then decrease with increasing LED. By taking the relative density, surface roughness, microhardness and ultimate tensile strength into account, the optimized LED should be in the range of 46.15–51.28 J mm^（-3） for the SLM-processed30 CrMnSiA alloys. In addition, the differences in the microstructures and mechanical properties between the conventionally wrought 30 CrMnSiA sample and SLM-processed 30 CrMnSiA samples were also studied.展开更多
Research interest has been growing in recent years in supersonic transport,particularly supersonic propulsion systems.A key component of a commonly studied propulsion system,ramjets,is the air intake.For supersonic pr...Research interest has been growing in recent years in supersonic transport,particularly supersonic propulsion systems.A key component of a commonly studied propulsion system,ramjets,is the air intake.For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery.This refers to the ratio of the average total pressure after the intake to that of the freestream.One phenomenon that can have a large effect on this performance index is flow separation at the inlet.The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet.This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel.Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ.Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance.Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone.Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake.At the optimal laser frequency,found for this Mach number to be 10 kHz,the pressure recovery is found to increase by up to 4.7%.When the laser power added to the system is considered,this results in an overall increase in propulsive power of 2.47%.展开更多
NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emph...NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emphasis on its phase composition,microstructure,mechanical property and deformation mechanism.The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%,respectively,which are remarkably different from DED result with 700 MPa and 2%.The load path of SLM sample presents shape memory effect,corresponding to martensite phase detected by XRD;while the load path of DED presents pseudo-elasticity with austenite phase.In SLM sample,fine grain and hole provide a uniform deformation during tensile test,resulting in a better elongation.Furthermore,the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods.Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample,which leads to similar grain morphologies because of similar G/R.While higher G×R of SLM leads to a finer grain size in SLM sample,providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.展开更多
Systematic experiments about the antitumor effects of low energy laser irradiation combined with the traditional antitumor medicine of cyclophosphamide were conducted using the experimental model of mouse S180 ascite...Systematic experiments about the antitumor effects of low energy laser irradiation combined with the traditional antitumor medicine of cyclophosphamide were conducted using the experimental model of mouse S180 ascites sarcoma.The three groups of tumor bearing mice were irradiated upon the inner corners with the dosages of 11 00,14 67 and 22 00 J·cm -2 LELI respectively,and injected with CYT intraperitoneally to observe the changes of the survival time,the ascites growth speed,and the kinetic changes of immune functions.The survival times of the three groups of CYT/LELI combination were obviously longer than those of the tumor and CYT control groups.Correspondingly,the amounts of ascites,tumor cells densities and total tumor cells in CYT/LELI groups decreased significantly,while the death ratio of the tumor cells increased.Comparatively,the group of 22 00 J·cm -2 LELI combined with CYT showed the most ideal antitumor effects,and the life prolongation ratio was up to 53 20%.展开更多
The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control...The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.展开更多
The spectral characteristic of laser-induced plasma in soil was studied in this work,laser-induced breakdown spectroscopy was used to analyze the spectral characteristic of plasma under the condition of different time...The spectral characteristic of laser-induced plasma in soil was studied in this work,laser-induced breakdown spectroscopy was used to analyze the spectral characteristic of plasma under the condition of different time delays and irradianccs.Moreover,the time evolution characteristics of plasma temperature and electron density were discussed.Within the time delay range of 0-5μs,the spectral intensity of the characteristic lines of Si I:288.158 nm,Ti I:336.126 nm.Al I:394.400 nm and Fe I:438.354 nm of the four main elements in two kinds of national standard soil decayed exponentially with time.The average lifetime of the spectral lines was nearly 1.56μs.Under the condition of different time delays,the spectral intensity of Pb I:405.78 nm in soil increased linearly with laser energy.However,the slope between the spectral intensity and laser energy decreased exponentially with the increase in time delay,from 4.91 to 0.99 during 0-5μs.The plasma temperature was calculated by the Boltzmann plot method and the electron density was obtained by inversion of the full width at half maximum of the spectrum.The plasma temperature decreased from 8900 K to 7800 K and the electron density decreased from 1.5 x 1Ol7cm-3 to 7.8 x lO16cm-3 in the range of 0-5μs.展开更多
We report a diode-pumped rod-type Yb:YAG laser amplifier operating at 1 kHz.Cryogenic cooling method was adopted to make the Yb:YAG crystal work with four-level behavior.A single-frequency fiber laser acts as the seed...We report a diode-pumped rod-type Yb:YAG laser amplifier operating at 1 kHz.Cryogenic cooling method was adopted to make the Yb:YAG crystal work with four-level behavior.A single-frequency fiber laser acts as the seed in an actively Q-switched Yb:YAG oscillator.The resonator delivers 5.75-mJ pulses at 1 kHz with a pulse duration of approximately 40 ns.The pulses were amplified to 61 mJ in a four-pass rod-type Yb:YAG amplifier with optical-to-optical efficiency of 24%in the main amplifier.The M^(2)parameter of the output laser is<1.4.展开更多
In the 1970s,scientists began experimenting with powerful laser beams to compress and heat the hydrogen isotopes to the point of fusion,a technique called ICF(Inertial Confinement Fusion).In the“direct drive”approac...In the 1970s,scientists began experimenting with powerful laser beams to compress and heat the hydrogen isotopes to the point of fusion,a technique called ICF(Inertial Confinement Fusion).In the“direct drive”approach to ICF,powerful beams of laser light are focused on a small spherical pellet containing micrograms of deuterium and tritium.The rapid heating caused by the laser“driver”makes the outer layer of the target explode.In keeping with Isaac Newton’s Third Law“For every action,there is an equal and opposite reaction”,the remaining portion of the target is driven inwards in a rocket-like implosion,causing compression of the fuel inside the capsule and the formation of a shock wave,which further heats the fuel in the very center and results in a self-sustaining burn.The fusion burn propagates outward through the cooler,outer regions of the capsule much more rapidly than the capsule can expand.Instead of magnetic fields,the plasma is confined by the inertia of its own mass—hence the term inertial confinement fusion.A similar process can be observed on an astrophysical scale in stars and the terrestrial uber world,that have exhausted their nuclear fuel,hence inertially or gravitationally collapsing and generating a supernova explosion,where the results can easily be converted to induction of energy in control forms for a peaceful purpose(i.e.,inertial fusion reaction)by means of thermal physics and statistical mechanics behavior of an ideal Fermi gas,utilizing Fermi-Degeneracy and Thomas-Fermi theory.The fundamental understanding of thermal physics and statistical mechanics enables us to have a better understanding of Fermi-Degeneracy as well as Thomas-Fermi theory of ideal gas,which results in laser compressing matter to a super high density for purpose of producing thermonuclear energy in way of controlled form for peaceful shape and form i.e.CTR(Controlled Thermonuclear Reaction).In this short review,we have concentrated on Fundamental of State Equations by driving them as it was evaluated in book Statistical Mechanics written by Mayer,J.and Mayer,M.in this article.展开更多
The application of titanium alloys in aerospace put forward the requirement for higher strength.Additive manu-facturing is a promising method for the efficient and economical processing of titanium alloys.However,rese...The application of titanium alloys in aerospace put forward the requirement for higher strength.Additive manu-facturing is a promising method for the efficient and economical processing of titanium alloys.However,research on the additive manufacturing of ultrahigh-strength titanium alloys is still limited.The mechanisms of microseg-regation for high alloying elements and poor plasticity are still not clear.In this study,an ultrahigh-strength titanium alloy Ti-4.5Al-5Mo-5V-6Cr-1Nb(TB18)was prepared using two methods:laser direct energy deposi-tion(LDED)and forging.The LDEDed alloy contains three zones with similar grain morphologies but different microstructure.The microsegregation of the alloy is limited due to the rapid solidification and almost eliminated after the thermal cycle and solution treatment.With stress relief treatment,the LDEDed alloy exhibits anisotropic mechanical properties.After solution and aging treatments,its ultimate strength is enhanced;however,its plas-ticity is relatively lower than that of the wrought alloy with equally high strength.The excellent balance of the strength and plasticity of the wrought alloy can be ascribed to the formation of𝛼WGB and multiscale𝛼laths,which provides enlightenment for optimizing the properties of the LDEDed alloy.展开更多
Inconel 718 is a nickel-based superalloy of high interest in high temperature applications such as turbine parts.To be used in such applications,heat treatments are commonly applied to dissolute Laves phase and to ach...Inconel 718 is a nickel-based superalloy of high interest in high temperature applications such as turbine parts.To be used in such applications,heat treatments are commonly applied to dissolute Laves phase and to achieve𝛾γ′phase.However,conventional heat treatment methods for wrought Inconel 718 may not be suitable for Inconel 718 fabricated by laser directed energy deposition(LDED)due to its unique microstructure formed during the rapid solidification process.There has been a lack of investigation in heat treatments for Inconel 718 fabricated by this process,specifically around the impact of aging parameters on this alloy.In this study,the effects of aging parameters were studied by performing seven different heat treatments,including solutionising and aging treatments.Our results indicate that for LDED Inconel 718,a high temperature solution treatment of 1100℃for 1 h followed by single aging at 650℃for 20 h achieved a tensile strength and elongation of 1247 MPa and 23%,respectively.Further,results indicated that even with a shorter aging time of 10 h,γ′phase was found to be of comparable size to the standard double aged treatment.展开更多
Oxide melt growth ceramics(OMGCs)exhibit excellent performance and microstructure stability near their melt-ing point and are expected to become a new structural material for long-term stable service in extremely high...Oxide melt growth ceramics(OMGCs)exhibit excellent performance and microstructure stability near their melt-ing point and are expected to become a new structural material for long-term stable service in extremely high-temperature water-oxygen environments.Owing to its unique advantages of high efficiency,flexible manufac-turing,and near-net shaping,laser directed energy deposition(LDED)has become a promising technology for the rapid preparation of high-performance OMGCs.However,owing to the limited understanding of the crack-ing mechanism,the severe cracking problem that hinders OMGCs-LDED towards engineering applications has not been resolved.Alumina/aluminum titanate(Al_(2)O_(3)/Al_(x)Ti_(y)O_(z),A/AT)ceramics are prepared using an LDED system and their cracking characteristics are investigated.Subsequently,numerical simulations are conducted to reveal the dominant factors and influencing mechanisms of the cracking behavior.The results demonstrate that the cracking nucleation process is mainly controlled by solidification defects,whereas the cracking propagation process is determined primarily by both the microstructure and stress level.This study provides a theoretical basis for the development of appropriate cracking suppression methods for OMGCs-LDED.展开更多
Energy field-assisted machining technology has the potential to overcome the limitations of machining difficult-to-machine metal materials,such as poor machinability,low cutting efficiency,and high energy consumption....Energy field-assisted machining technology has the potential to overcome the limitations of machining difficult-to-machine metal materials,such as poor machinability,low cutting efficiency,and high energy consumption.High-speed dry milling has emerged as a typical green processing technology due to its high processing efficiency and avoidance of cutting fluids.However,the lack of necessary cooling and lubrication in high-speed dry milling makes it difficult to meet the continuous milling requirements for difficult-to-machine metal materials.The introduction of advanced energy-field-assisted green processing technology can improve the machinability of such metallic materials and achieve efficient precision manufacturing,making it a focus of academic and industrial research.In this review,the characteristics and limitations of high-speed dry milling of difficult-to-machine metal materials,including titanium alloys,nickel-based alloys,and high-strength steel,are systematically explored.The laser energy field,ultrasonic energy field,and cryogenic minimum quantity lubrication energy fields are introduced.By analyzing the effects of changing the energy field and cutting parameters on tool wear,chip morphology,cutting force,temperature,and surface quality of the workpiece during milling,the superiority of energy-field-assisted milling of difficult-to-machine metal materials is demonstrated.Finally,the shortcomings and technical challenges of energy-field-assisted milling are summarized in detail,providing feasible ideas for realizing multi-energy field collaborative green machining of difficult-to-machine metal materials in the future.展开更多
Near-equiaxed β grain was achieved in the near-α Ti60(Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C) titanium alloy via laser directed energy deposition(LDED). The microstructural evolution along the building d...Near-equiaxed β grain was achieved in the near-α Ti60(Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C) titanium alloy via laser directed energy deposition(LDED). The microstructural evolution along the building direction and the room-temperature tensile properties along the horizontal and vertical directions(building direction) were systematically studied through SEM and OM. EBSD and XRD were utilized to accurately demonstrate the texture of the α and β phases. The results showed that the α phase presented a low texture intensity, which was ascribed to the weak textured β grain with near-equiaxed morphology, since there are Burgers orientation relationships during the β →α transition. In addition, numerical simulation, combined with the CET curve of Ti60 alloy considering the effect of multi-composition,was utilized to elucidate the formation mechanism of the near-equiaxed β grains. Furthermore, according to the solidification theory, we proposed that the solidification temperature range ΔTfwas more accurate than the growth restriction factor Q in predicting the formation tendency of equiaxed β grain in different titanium alloys. Tensile results showed that the horizontal and vertical samples had similar strength,while the former exhibited larger elongation than the latter. The effect of the near-equiaxed β grain and the internal α phase on mechanical properties were revealed at last.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51905226,52075227,and 52105449)the Natural Science Foundation of Jiangsu Province(Grant No.BK20210755)the Postdoctoral Foundation of Jiangsu Province(Grant No.2021K264B).
文摘As a substitute for toxic cadmium coatings in the aerospace industry,zinc-nickel coatings have excellent application prospects,and their properties can be improved by adding molybdenum.In this study,laser-assisted electrodeposition is used to improve the surface quality and properties of Zn–Ni–Mo coatings,with investigation of how laser energy in the range of 0–21.1μJ affects their element content,surface morphology,crystal phase,microhardness,residual internal stress,and corrosion resistance.The laser irradiation accelerates the electrodeposition,refines the grain size,improves the hydrogen adsorption,and reduces the residual tensile stress,and a laser energy of 15.4μJ gives the highest Ni and Mo contents and the lowest Zn content,as well as the optimum surface morphology,microhardness,residual internal stress,and corrosion resistance of the coating.
基金This work was financially supported by the National Key R&D Program of China(No.2018YFB0606104)the National Natural Science Foundation of China(No.51702332).
文摘(CoCrFeNi)95Nb5 high entropy alloy(HEA)coatings were successfully fabricated on a substrate of Q235 steel by laser cladding technology.These(CoCrFeNi)95Nb5 HEA coatings possess excellent properties,particularly corrosion resistance,which is clearly superior to that of some typical bulk HEA and common engineering alloys.In order to obtain appropriate laser cladding preparation process parameters,the effects of laser energy density on the microstructure,microhardness,and corrosion resistance of(CoCrFeNi)95Nb5 HEA coating were closely studied.Results showed that as the laser energy density increases,precipitation of the Laves phase in(CoCrFeNi)95Nb5 HEA coating gradually decreases,and diffusion of the Fe element in the substrate intensifies,affecting the integrity of the(CoCrFeNi)95Nb5 HEA.This decreases the microhardness of(CoCrFeNi)95Nb5 HEA coatings.Moreover,the relative content of Cr2O3,Cr(OH)3,and Nb2O5 in the surface passive film of the coating decreases with increasing energy density,causing corrosion resistance to decrease.This study demonstrates the controllability of a high-performance HEA coating using laser cladding technology,which has significance for the laser cladding preparation of other CoCrFeNi-system HEA coatings.
基金Projects(51975006, 51505006) supported by the National Natural Science Foundation of China。
文摘This experiment obtained different laser energy density(LED) by changing SLM molding process parameters.The surface morphology, surface quality, and microstructure of as-fabricated samples were studied. The effects of scanning speed, hatching space, and laser power on surface quality were analyzed, and the optimal LED range for surface quality was determined. The results show that pores and spherical particles appear on the sample’s surface when low LED is applied, while there are lamellar structures on the sides of the samples. Cracks appear on the sample’s surface,and the splash phenomenon increases when a high LED is taken. At the same time, a large amount of unmelted powder adhered to the side of the sample. The surface quality is the best when the LED is 150-170 J/mm^(3). The preferred hatch space is currently 0.05-0.09 mm, the laser power is 200-350 W, and the average surface roughness value is(15.1±3) μm.The average surface hardness reaches HV404±HV3, higher than the forging standard range of HV340-HV395.Increasing the LED within the experiment range can increase the surface hardness, yet an excessively high LED will not further increase the surface hardness. The microstructure is composed of needle-like α’-phases with a length of about 20μm, in a crisscross ‘N’ shape, when the LED is low. The β-phase grain boundary is not obvious, and the secondaryphase volume fraction is high;when the LED is high, the α’-phase of the microstructure is in the form of coarse slats, and the secondary-phase is composed of a small amount of secondary α’-phase, the tertiary α’-phase and the fourth α’-phase disappear, and the volume fraction of the secondary-phase becomes low.
基金supported by the 2022 MTC Young Individual Research Grants(Grant No.M22K3c0097)the Singapore Research,Innovation and Enterprise(RIE)2025 PlanSingapore Aerospace Programme Cycle 16(Grant No.M2215a0073)。
文摘Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.
基金the financial support of the Hunan Innovation Platform and Talent Plan(2022RC3033)Natural Science Foundation of Shandong Province(ZR2020ZD04)Ganzhou Science and Technology Planning Project(Grant No.Ganshikefa[2019]60)。
文摘Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheating,and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal,a gradient distribution of Ni4Ti3 precipitates along the building direction,and preferential formation of Ni4Ti3 precipitates in the columnar zone.The austenite transformation finish temperature(Af)varies from-12.65℃(Z=33 mm)to 60.35℃(Z=10 mm),corresponding to tensile yield strength(σ0.2)changed from 120±30 MPa to 570±20 MPa,and functional properties changed from shape memory effect to superelasticity at room temperature.The sample in the Z=20.4 mm height has the best plasticity of 9.6%and the best recoverable strain of 4.2%.This work provided insights and guidelines for the spatial characterization of DEDed NiTi.
文摘Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket engines giving fresh impetus to the birth of gas flow and chemical lasers,which finally turned megawatt lasers from dream into reality.Nowadays,the development of HELs has entered the age of electricity as well as the rocket engines.The properties of current electric rocket engines are highly consistent with HELs’goals,including electrical driving,effective heat dissipation,little medium consumption and extremely light weight and size,which inspired a second fusion of laser and aerospace and motivated the exploration for potential HELs.As an exploratory attempt,a new configuration of diode pumped metastable rare gas laser was demonstrated,with the gain generator resembling an electric rocket-engine for improved power scaling ability.
基金financially supported by the National Natural Science Foundation of China (Grant No. 51405467)the Strategic Industry Key Generic Technology Innovation Project of Chongqing (No. cstc2015zdcy-ztzx50005)+1 种基金the Entrepreneurship and Innovation Support Program for Chongqing Overseas Returned Scholars (No. cx2017040)financial support from the West Light Foundation of the Chinese Academy of Sciences
文摘Three-dimensional parts of the 30 CrMnSiA steel were successfully fabricated using selective laser melting（SLM）. The microstructures and mechanical properties of the SLM-processed 30 CrMnSiA samples were investigated by scanning electron microscope and transmission electron microscopy. The results indicate that the microstructures of the 30 CrMnSiA samples consist mainly of lath martensite and acicular martensite. The value of the surface roughness decreases with increasing laser energy density（LED） before it reaches a minimum and then increases with further increasing LED. The relative density, microhardness and ultimate tensile strength of the SLM-processed samples initially increase and then decrease with increasing LED. By taking the relative density, surface roughness, microhardness and ultimate tensile strength into account, the optimized LED should be in the range of 46.15–51.28 J mm^（-3） for the SLM-processed30 CrMnSiA alloys. In addition, the differences in the microstructures and mechanical properties between the conventionally wrought 30 CrMnSiA sample and SLM-processed 30 CrMnSiA samples were also studied.
文摘Research interest has been growing in recent years in supersonic transport,particularly supersonic propulsion systems.A key component of a commonly studied propulsion system,ramjets,is the air intake.For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery.This refers to the ratio of the average total pressure after the intake to that of the freestream.One phenomenon that can have a large effect on this performance index is flow separation at the inlet.The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet.This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel.Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ.Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance.Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone.Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake.At the optimal laser frequency,found for this Mach number to be 10 kHz,the pressure recovery is found to increase by up to 4.7%.When the laser power added to the system is considered,this results in an overall increase in propulsive power of 2.47%.
基金Project(2020JJ2046)supported by the Science Fund for Hunan Distinguished Young Scholars,ChinaProject(S2020GXKJGG0416)supported by the Special Project for Hunan Innovative Province Construction,China+1 种基金Project(2018RS3007)supported by the Huxiang Young Talents,ChinaProject(GuikeAB19050002)supported by the Science Project of Guangxi,China。
文摘NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emphasis on its phase composition,microstructure,mechanical property and deformation mechanism.The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%,respectively,which are remarkably different from DED result with 700 MPa and 2%.The load path of SLM sample presents shape memory effect,corresponding to martensite phase detected by XRD;while the load path of DED presents pseudo-elasticity with austenite phase.In SLM sample,fine grain and hole provide a uniform deformation during tensile test,resulting in a better elongation.Furthermore,the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods.Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample,which leads to similar grain morphologies because of similar G/R.While higher G×R of SLM leads to a finer grain size in SLM sample,providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.
文摘Systematic experiments about the antitumor effects of low energy laser irradiation combined with the traditional antitumor medicine of cyclophosphamide were conducted using the experimental model of mouse S180 ascites sarcoma.The three groups of tumor bearing mice were irradiated upon the inner corners with the dosages of 11 00,14 67 and 22 00 J·cm -2 LELI respectively,and injected with CYT intraperitoneally to observe the changes of the survival time,the ascites growth speed,and the kinetic changes of immune functions.The survival times of the three groups of CYT/LELI combination were obviously longer than those of the tumor and CYT control groups.Correspondingly,the amounts of ascites,tumor cells densities and total tumor cells in CYT/LELI groups decreased significantly,while the death ratio of the tumor cells increased.Comparatively,the group of 22 00 J·cm -2 LELI combined with CYT showed the most ideal antitumor effects,and the life prolongation ratio was up to 53 20%.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51132004,11474096 and 11604199the Science and Technology Commission of Shanghai Municipality under Grant No 14JC1401500the Higher Education Key Program of He'nan Province under Grant Nos 17A140025 and 16A140030
文摘The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.
文摘The spectral characteristic of laser-induced plasma in soil was studied in this work,laser-induced breakdown spectroscopy was used to analyze the spectral characteristic of plasma under the condition of different time delays and irradianccs.Moreover,the time evolution characteristics of plasma temperature and electron density were discussed.Within the time delay range of 0-5μs,the spectral intensity of the characteristic lines of Si I:288.158 nm,Ti I:336.126 nm.Al I:394.400 nm and Fe I:438.354 nm of the four main elements in two kinds of national standard soil decayed exponentially with time.The average lifetime of the spectral lines was nearly 1.56μs.Under the condition of different time delays,the spectral intensity of Pb I:405.78 nm in soil increased linearly with laser energy.However,the slope between the spectral intensity and laser energy decreased exponentially with the increase in time delay,from 4.91 to 0.99 during 0-5μs.The plasma temperature was calculated by the Boltzmann plot method and the electron density was obtained by inversion of the full width at half maximum of the spectrum.The plasma temperature decreased from 8900 K to 7800 K and the electron density decreased from 1.5 x 1Ol7cm-3 to 7.8 x lO16cm-3 in the range of 0-5μs.
基金Project supported by the National National Science Foundation of China(Grant Nos.12004262 and 62005184)the Natural Science Foundation of Top Talent of SZTU(Grant No.202024555101039)。
文摘We report a diode-pumped rod-type Yb:YAG laser amplifier operating at 1 kHz.Cryogenic cooling method was adopted to make the Yb:YAG crystal work with four-level behavior.A single-frequency fiber laser acts as the seed in an actively Q-switched Yb:YAG oscillator.The resonator delivers 5.75-mJ pulses at 1 kHz with a pulse duration of approximately 40 ns.The pulses were amplified to 61 mJ in a four-pass rod-type Yb:YAG amplifier with optical-to-optical efficiency of 24%in the main amplifier.The M^(2)parameter of the output laser is<1.4.
文摘In the 1970s,scientists began experimenting with powerful laser beams to compress and heat the hydrogen isotopes to the point of fusion,a technique called ICF(Inertial Confinement Fusion).In the“direct drive”approach to ICF,powerful beams of laser light are focused on a small spherical pellet containing micrograms of deuterium and tritium.The rapid heating caused by the laser“driver”makes the outer layer of the target explode.In keeping with Isaac Newton’s Third Law“For every action,there is an equal and opposite reaction”,the remaining portion of the target is driven inwards in a rocket-like implosion,causing compression of the fuel inside the capsule and the formation of a shock wave,which further heats the fuel in the very center and results in a self-sustaining burn.The fusion burn propagates outward through the cooler,outer regions of the capsule much more rapidly than the capsule can expand.Instead of magnetic fields,the plasma is confined by the inertia of its own mass—hence the term inertial confinement fusion.A similar process can be observed on an astrophysical scale in stars and the terrestrial uber world,that have exhausted their nuclear fuel,hence inertially or gravitationally collapsing and generating a supernova explosion,where the results can easily be converted to induction of energy in control forms for a peaceful purpose(i.e.,inertial fusion reaction)by means of thermal physics and statistical mechanics behavior of an ideal Fermi gas,utilizing Fermi-Degeneracy and Thomas-Fermi theory.The fundamental understanding of thermal physics and statistical mechanics enables us to have a better understanding of Fermi-Degeneracy as well as Thomas-Fermi theory of ideal gas,which results in laser compressing matter to a super high density for purpose of producing thermonuclear energy in way of controlled form for peaceful shape and form i.e.CTR(Controlled Thermonuclear Reaction).In this short review,we have concentrated on Fundamental of State Equations by driving them as it was evaluated in book Statistical Mechanics written by Mayer,J.and Mayer,M.in this article.
基金supported by National Natural Science Foundation of China(Grant No.52071005)National Science and Technology Sup-porting Project of China(Grant No.JPPT-135-GH-2-036)Funda-mental Research Funds for the Central Universities of China(Grant No.030810).
文摘The application of titanium alloys in aerospace put forward the requirement for higher strength.Additive manu-facturing is a promising method for the efficient and economical processing of titanium alloys.However,research on the additive manufacturing of ultrahigh-strength titanium alloys is still limited.The mechanisms of microseg-regation for high alloying elements and poor plasticity are still not clear.In this study,an ultrahigh-strength titanium alloy Ti-4.5Al-5Mo-5V-6Cr-1Nb(TB18)was prepared using two methods:laser direct energy deposi-tion(LDED)and forging.The LDEDed alloy contains three zones with similar grain morphologies but different microstructure.The microsegregation of the alloy is limited due to the rapid solidification and almost eliminated after the thermal cycle and solution treatment.With stress relief treatment,the LDEDed alloy exhibits anisotropic mechanical properties.After solution and aging treatments,its ultimate strength is enhanced;however,its plas-ticity is relatively lower than that of the wrought alloy with equally high strength.The excellent balance of the strength and plasticity of the wrought alloy can be ascribed to the formation of𝛼WGB and multiscale𝛼laths,which provides enlightenment for optimizing the properties of the LDEDed alloy.
文摘Inconel 718 is a nickel-based superalloy of high interest in high temperature applications such as turbine parts.To be used in such applications,heat treatments are commonly applied to dissolute Laves phase and to achieve𝛾γ′phase.However,conventional heat treatment methods for wrought Inconel 718 may not be suitable for Inconel 718 fabricated by laser directed energy deposition(LDED)due to its unique microstructure formed during the rapid solidification process.There has been a lack of investigation in heat treatments for Inconel 718 fabricated by this process,specifically around the impact of aging parameters on this alloy.In this study,the effects of aging parameters were studied by performing seven different heat treatments,including solutionising and aging treatments.Our results indicate that for LDED Inconel 718,a high temperature solution treatment of 1100℃for 1 h followed by single aging at 650℃for 20 h achieved a tensile strength and elongation of 1247 MPa and 23%,respectively.Further,results indicated that even with a shorter aging time of 10 h,γ′phase was found to be of comparable size to the standard double aged treatment.
基金supported by National Natural Science Founda-tion of China(Grant.Nos.51805070,51790172,52175291)Funda-mental Research Funds for the Central Universities of China(Grant.Nos.DUT22YG210,DUT22LAB117)+1 种基金Science Center for Gas Turbine Project of China(Grant.No.P2022-B-IV-012-001)Shenzhen Sci-ence and Technology Innovation Commission of China(Grant.No.JCYJ20210324115413036).
文摘Oxide melt growth ceramics(OMGCs)exhibit excellent performance and microstructure stability near their melt-ing point and are expected to become a new structural material for long-term stable service in extremely high-temperature water-oxygen environments.Owing to its unique advantages of high efficiency,flexible manufac-turing,and near-net shaping,laser directed energy deposition(LDED)has become a promising technology for the rapid preparation of high-performance OMGCs.However,owing to the limited understanding of the crack-ing mechanism,the severe cracking problem that hinders OMGCs-LDED towards engineering applications has not been resolved.Alumina/aluminum titanate(Al_(2)O_(3)/Al_(x)Ti_(y)O_(z),A/AT)ceramics are prepared using an LDED system and their cracking characteristics are investigated.Subsequently,numerical simulations are conducted to reveal the dominant factors and influencing mechanisms of the cracking behavior.The results demonstrate that the cracking nucleation process is mainly controlled by solidification defects,whereas the cracking propagation process is determined primarily by both the microstructure and stress level.This study provides a theoretical basis for the development of appropriate cracking suppression methods for OMGCs-LDED.
基金supported by the National Key R&D Program of China(Grant No.2020YFB2010500).
文摘Energy field-assisted machining technology has the potential to overcome the limitations of machining difficult-to-machine metal materials,such as poor machinability,low cutting efficiency,and high energy consumption.High-speed dry milling has emerged as a typical green processing technology due to its high processing efficiency and avoidance of cutting fluids.However,the lack of necessary cooling and lubrication in high-speed dry milling makes it difficult to meet the continuous milling requirements for difficult-to-machine metal materials.The introduction of advanced energy-field-assisted green processing technology can improve the machinability of such metallic materials and achieve efficient precision manufacturing,making it a focus of academic and industrial research.In this review,the characteristics and limitations of high-speed dry milling of difficult-to-machine metal materials,including titanium alloys,nickel-based alloys,and high-strength steel,are systematically explored.The laser energy field,ultrasonic energy field,and cryogenic minimum quantity lubrication energy fields are introduced.By analyzing the effects of changing the energy field and cutting parameters on tool wear,chip morphology,cutting force,temperature,and surface quality of the workpiece during milling,the superiority of energy-field-assisted milling of difficult-to-machine metal materials is demonstrated.Finally,the shortcomings and technical challenges of energy-field-assisted milling are summarized in detail,providing feasible ideas for realizing multi-energy field collaborative green machining of difficult-to-machine metal materials in the future.
基金supported by the National Key Technologies R&D Program (Nos. 2016YFB1100102, 2018YFB1106003).
文摘Near-equiaxed β grain was achieved in the near-α Ti60(Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C) titanium alloy via laser directed energy deposition(LDED). The microstructural evolution along the building direction and the room-temperature tensile properties along the horizontal and vertical directions(building direction) were systematically studied through SEM and OM. EBSD and XRD were utilized to accurately demonstrate the texture of the α and β phases. The results showed that the α phase presented a low texture intensity, which was ascribed to the weak textured β grain with near-equiaxed morphology, since there are Burgers orientation relationships during the β →α transition. In addition, numerical simulation, combined with the CET curve of Ti60 alloy considering the effect of multi-composition,was utilized to elucidate the formation mechanism of the near-equiaxed β grains. Furthermore, according to the solidification theory, we proposed that the solidification temperature range ΔTfwas more accurate than the growth restriction factor Q in predicting the formation tendency of equiaxed β grain in different titanium alloys. Tensile results showed that the horizontal and vertical samples had similar strength,while the former exhibited larger elongation than the latter. The effect of the near-equiaxed β grain and the internal α phase on mechanical properties were revealed at last.
