The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstru...The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstructure,fracture surfaces,and crack growth paths were analyzed before and after CHT.Results indicate that in the stable crack growth region,the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^(−8)(ΔK)^(3.2271)and da/dN=1.4112×10^(−8)(ΔK)^(3.1125),respectively.Compared with that at the as-deposited state,the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-sphericalαandβ-transformed matrix phases.The cyclic process also disrupts the continuity of the grain boundaryα(αGB)at the primaryβ-phase grain boundary.The coarsening of primaryαand the disruption ofαGB continuity are the primary factors to release stress concentration and promote crack deflection,thereby decreasing the fatigue crack growth rate.Additionally,the increased occurrence of crack branching,secondary cracking,and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.展开更多
Biopolymeric nanocomposites have attracted considerable attention because of their biocompatibility,biodegradability,and unique physicochemical properties.It is essential to manufacture three-dimensional(3D)biocompati...Biopolymeric nanocomposites have attracted considerable attention because of their biocompatibility,biodegradability,and unique physicochemical properties.It is essential to manufacture three-dimensional(3D)biocompatible micro/nanostructures using biopolymeric nanocomposites.Herein,we demonstrate the high-fidelity fabrication of biocompatible 3D features with sub-50 nm resolution using femtosecond laser direct writing(FsLDW)of a biopolymeric nanocomposite composed of egg white and sulfonated graphene(S-graphene).The biopolymer nanocomposite acts as a negative photoresist suitable for water-based lithography.The introduction of S-graphene not only dramatically lowered the laser power threshold but also significantly modulated the morphology of the 3D features constructed by FsLDW.Microstructures with porous,rough,or smooth morphologies were obtained by optimizing the S-graphene concentration and laser scanning speed.The fabricated egg-white/S-graphene microstructures exhibited biocompatibility and environmental degradability.Egg white/S-graphene was also employed to fabricate diffractive gratings with superior optical quality.This study provides a promising method to manufacture biocompatible 3D features with controllable morphology,which has potential applications in biological and photonic fields.展开更多
The ultrasonic energy field(UEF)-induced grain refinement mechanisms in laser powder direct energy deposition-manufactured Ti5321G alloys were systematically investigated in this study.This study focused on the interp...The ultrasonic energy field(UEF)-induced grain refinement mechanisms in laser powder direct energy deposition-manufactured Ti5321G alloys were systematically investigated in this study.This study focused on the interplay between recrystallization in the high-temperature solid deposition layers and the ultrasonic cavitation-acoustic streaming effects during molten pool solidification.A novel experimental design was developed to decouple these mechanisms by creating four distinct UEF action zones(without UEF-N,withUEF-S,with UEF-L,and with UEF-S+L)within a single-pass multilayer sample.This approach enabled the dual effects of UEF(recrystallization in solidified layers and ultrasonic cavitation-acoustic streaming effects in liquid pools)to be directly compared.The UEF significantly refined the microstructures,reducing the average grain size by 64.2%(from(399.6±28.6)to(143.1±16.1)μm)in the with UEF-S+L zone,while promoting columnar-to-equiaxed transition,with the equiaxed grain probability increasing from 11.1%(without UEF) to 53.8%.The texture intensity was reduced by approximately 52.4%and the mechanical properties were enhanced,achieving a 6.2% increase in yield strength((702.0±10.6)MPa)and 31.7%improvement in elongation.Crucially,this study revealed the synergistic effect of the dual-action mechanisms of UEF,where recrystallization and cavitation-acoustic streaming collectively enabled non-linear grain refinement.This study provides a strategy for microstructural control in additive manufacturing,eliminating the need for complex post-processing and thereby advancing the industrial application of high-performance titanium components.展开更多
Able to precisely control and manipulate materials'states at micro/nano-scale level,femtosecond(fs)laser micro/nano processing technology has undergone tremendous development over the past three decades.Free-formi...Able to precisely control and manipulate materials'states at micro/nano-scale level,femtosecond(fs)laser micro/nano processing technology has undergone tremendous development over the past three decades.Free-forming three-dimensional(3D)microscale functional devices and inducing fascinating and unique physical or chemical phenomena have granted this technology powerful versatility that no other technology can match.As this technology advances rapidly in various fields of application,some key challenges have emerged and remain to be urgently addressed.This review firstly introduces the fundamental principles for understanding how fs laser pulses interact with materials and the associated unique phenomena in section 2.Then micro/nano-fabrication in transparent materials by fs laser processing is presented in section 3.Thereafter,several high efficiency/throughput fabrication methods as well as pulse-shaping techniques are listed in sections 4 and 5 reviews four-dimensional(4D)and nanoscale printing realized by fs laser processing technology.Special attention is paid to the heterogeneous integration(HI)of functional materials enabled by fs laser processing in section 6.Several intriguing examples of 3D functional micro-devices created by fs laser-based manufacturing methods such as microfluidics,lab-on-chip,micro-optics,micro-mechanics,micro-electronics,micro-bots and micro-biodevices are reviewed in section 7.Finally,a summary of the review and a perspective are proposed to explore the challenges and future opportunities for further betterment of fs laser micro/nano processing technology.展开更多
In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition...In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition(LDED).The effects of ultrasonic vibration(UV)and tempering treatment on microstructure evolution,microhardness distribution and mechanical properties of deposition layer were studied in detail.The microstructure of UV assisted LDED sample after tempering is mainly composed of tempered sorbite(TS).Due to the improvement of microstructure inhomogeneity and grains refinement,UV assisted LDED sample with tempering treatment obtains excellent mechanical properties.The ultimate tensile strength(UTS),yield strength(YS)and elongation after breaking(EL)reach 765 MPa,657 MPa and 19.5%,the increase ratios of UTS and YS are 14.5%and 33.8%while maintaining plasticity compared to original LDED sample,respectively.It is obvious that ultrasonic vibration combined with tempering is a potential and effective method to obtain uniform microstructure and excellent mechanical properties in metal laser directed energy deposition field.展开更多
Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in thi...Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in this study.The microstructure of the WE43 and CNTs/WE43 layers was systematically compared.The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment.The spot segregation composed of Mg_(24)Y_(5),CNTs,and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content.The grain growth of both types of layers underwent three stages:slow,rapid,and steady-state.The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature,resulting in a 47%increase at 510℃ and a 35%increase at 540℃ in the grain growth exponent compared to the WE43 layers at 510℃.During the subsequent aging treatment at 225℃,the precipitation sequences from plate-shaped β″to plate-shaped and globular β′ were observed in both types of layers.CNTs can facilitate an increase in the nucleation rate of precipitates,but without accelerating precipitation hardening rate.The long and short diameters of the precipitates in peak-aged state were decreased by 48.5%and 43.1%by addition of CNTs,respectively.The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment.The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.展开更多
Under the laser directed energy deposition(LDED)process,the rapid melting and solidification usually lead to the emergence of pores and coarse columnar dendrites,which in turn compromise the properties of the deposite...Under the laser directed energy deposition(LDED)process,the rapid melting and solidification usually lead to the emergence of pores and coarse columnar dendrites,which in turn compromise the properties of the deposited alloys.This study introduced in-situ ultrasonic rolling(UR)as an innovative method to enhance the corrosion resistance of LDED specimens,and the microstructural characteristics and their correlation with corrosion resistance were deeply investigated.The findings reveal that the LDED-UR specimen exhibits a reduction in both the fraction and size of pores.Under the influence of severe plastic deformation generated by LDED-UR process,fully equiaxed grains appear with a reduced average size of 28.61μm(compared to63.98μm for the LDED specimen with columnar grains).The electrochemical corrosion resistance of the LDED-UR specimen is significantly enhanced compared to the LDED specimen.This enhanced corrosion resistance can be attributed to the low fraction of small-sized pores,the fine and uniformly distributed Cr-enriched ferrite phase,and the formation of a compact and thick passive film due to dense grain boundaries.The insight of the correlation between microstructure and corrosion behavior opens up a new pathway to enhance the corrosion resistance of LDED specimens.展开更多
To address the issues of low accuracy,long time consumption,and high cost of the traditional temperature prediction methods for laser directed energy deposition(LDED),a machine learning model combined with numerical s...To address the issues of low accuracy,long time consumption,and high cost of the traditional temperature prediction methods for laser directed energy deposition(LDED),a machine learning model combined with numerical simulation was proposed to predict the temperature during LDED.A finite element(FE)thermal analysis model was established.The model's accuracy was verified through in-situ monitoring experiments,and a basic database for the predictive model was obtained based on FE simulations.Temperature prediction was performed using a generalized regression neural network(GRNN).To reduce dependence on human experience during GRNN parameter tuning and to enhance model prediction performance,an improved adaptive step-size fruit fly optimization algorithm(ASSFOA)was introduced.Finally,the prediction performance of ASSFOA-GRNN model was compared with that of back-propagation neural network model,GRNN model,and fruit fly optimization algorithm(FOA)-GRNN model.The evaluation metrics included the root mean square error(RMSE),mean absolute error(MAE),coefficient of determination(R^(2)),training time,and prediction time.Results show that the ASSFOA-GRNN model exhibits optimal performance regarding RMSE,MAE,and R^(2) indexes.Although its prediction efficiency is slightly lower than that of the FOA-GRNN model,its prediction accuracy is significantly better than that of the other models.This proposed method can be used for temperature prediction in LDED process and also provide a reference for similar methods.展开更多
Laser-directed energy deposition(LDED)technology has demonstrated great potential for the rapid and integrated fabrication of nickel-based superalloy components.The plastic deformation-assisted method is crucial for a...Laser-directed energy deposition(LDED)technology has demonstrated great potential for the rapid and integrated fabrication of nickel-based superalloy components.The plastic deformation-assisted method is crucial for achieving grain refinement and microstructural homogeneity in LDED-fabricated superalloys.However,existing methods suffer from uniformity constraints owing to their high deformation resistance,which significantly limits their application in load-bearing components.To address these issues,a synchronous-hot-forging-assisted(SHFA)LDED additive manufacturing method was proposed,and its effects on the macroscopic morphology,microstructure,and mechanical properties of GH4169 nickel-based alloy specimens were systematically compared.The results demonstrated up to 30.1%average plastic deformation in hot-forging components while maintaining good surface flatness.The synergistic effect of dislocation accumulation and dynamic recrystallization during hot forging enables dramatic grain refinement,reducing the average grain size by 89.1%(from 168.5μm to 18.4μm)while weakening texture intensity from 15.31 to 2.15,ultimately promoting equiaxed grain formation.The pores of hot-forging components changed from fine round to flat,the porosity decreased from 0.264%to 0.089%,and the densification level was significantly improved.With the increase in the synchronous hot-forging force,the average ultimate tensile strength of hot-forging components can reach 1175.1 MPa,while the anisotropy difference is gradually weakened.The SHFA-LDED process not only achieves excellent grain refinement and microstructure homogenization but also enhances mechanical properties,providing a new technical path for the additive manufacturing of high-performance nickel-based superalloy components.展开更多
High-density interconnect(HDI)soft electronics that can integrate multiple individual functions into one miniaturized monolithic system is promising for applications related to smart healthcare,soft robotics,and human...High-density interconnect(HDI)soft electronics that can integrate multiple individual functions into one miniaturized monolithic system is promising for applications related to smart healthcare,soft robotics,and human-machine interactions.However,despite the recent advances,the development of three-dimensional(3D)soft electronics with both high resolution and high integration is still challenging because of the lack of efficient manufacturing methods to guarantee interlayer alignment of the high-density vias and reliable interlayer electrical conductivity.Here,an advanced 3D laser printing pathway,based on femtosecond laser direct writing(FLDW),is demonstrated for preparing liquid metal(LM)-based any layer HDI soft electronics.FLDW technology,with the characteristics of high spatial resolution and high precision,allows the maskless fabrication of high-resolution embedded LM microchannels and high-density vertical interconnect accesses for 3D integrated circuits.High-aspect-ratio blind/through LM microstructures are formed inside the elastomer due to the supermetalphobicity induced during laser ablation.The LM-based HDI circuit featuring high resolution(~1.5μm)and high integration(10-layer electrical interconnection)is achieved for customized soft electronics,including various customized multilayer passive electric components,soft multilayer circuit,and cross-scale multimode sensors.The 3D laser printing method provides a versatile approach for developing chip-level soft electronics.展开更多
The fabrication of nanostructures beyond the diffraction limit has been the focus of nanotechnology research.Scanning probe microscopy(SPM)has attracted the attention of researchers for the detection and manufacture o...The fabrication of nanostructures beyond the diffraction limit has been the focus of nanotechnology research.Scanning probe microscopy(SPM)has attracted the attention of researchers for the detection and manufacture of nanostructures.Here,a nanosecond laser irradiated a cantilevered scanning nearfield optical microscopy(SNOM)tip and directly wrote subwavelength nanostructures on Au nano-film,without the assistance of a mask or vacuum atmosphere.This method was stable and reproducible for long-term use.The in situ morphology detection was conducted after the writing process by atomic force microscope(AFM).A feature linewidth of approximately 83.6 nm(<k/6)was confirmed using scanning electron microscopy(SEM).Linewidth of(167.8±6.6)nm was reproduced stably.Theoretical calculations revealed that the elliptical heat distribution under the SNOM tip generated different linewidths when the tip scanned vertically and horizontally.It also interpreted the influential mechanism of single-pulse energy.The simulated linewidths were consistent with the fabricated linewidths.According to the elemental analysis by energy dispersive spectrometer(EDS),the mechanism of this method can be interpreted asmelting of the Au nano-film instead of oxidation.Owing to its high positioning,machining accuracy,and instantaneous energy,this technology is considered convenient and economical for nanostructure fabrication and is proposed to be applied in nanolithography on multiple materials in the future.展开更多
Laser processing technologies enable the precise fabrication of arbitrary structures and devices with broad applications in micro-optics,micro-mechanics,and biomedicine.However,its adoption is limited by the large siz...Laser processing technologies enable the precise fabrication of arbitrary structures and devices with broad applications in micro-optics,micro-mechanics,and biomedicine.However,its adoption is limited by the large size,complexity,high cost,and low flexibility of optical systems.Metasurfaces enable precise multidimensional control of light fields,aligning well with the development trend toward compact,high-performance optical systems.Here,we review several recent studies on the application of metasurfaces in laser processing technologies,including 3D nanolithography,direct laser writing,and laser cutting.Metasurfaces provide an integrated operational platform with exceptional performance,poised to disrupt conventional laser processing workflows.This combination presents significant cost efficiency and substantial development potential,with promising applications in areas such as imaging,optical storage,advanced sensing,and space on-orbit manufacturing.展开更多
A mathematical model is developed for simulating the heat transferring behavior in a direct metal laser sintering process. The model considers the thermal phenomena involved in the process, including conduction, radia...A mathematical model is developed for simulating the heat transferring behavior in a direct metal laser sintering process. The model considers the thermal phenomena involved in the process, including conduction, radiation, and convection. A formula for the calculation of the heat conductivity of a sintering system containing solid phase, liquid phase, and gas phase is given. Due to the continuous movement of the laser beam, a local coordinate system centered on the laser beam is used to simplify the analytical calculation. Assuming that it is approximately a Gaussian laser beam, the heat conduction equation is resolved based on the assumption of the thermal insulating boundary conditions and the fixed thermal physical parameters. The FORTRAN language is employed to compile the program to simulate the temperature field in the direct copper powder sintering process. It shows a good agreement with the preliminary experimental results.[KH3/4D]展开更多
Microrobots play an essential role in early diagnosis and precision medicine with the increasing demands for controllability in bio-medicine and micromanipulation,which can complete the pre-designed behavior under ext...Microrobots play an essential role in early diagnosis and precision medicine with the increasing demands for controllability in bio-medicine and micromanipulation,which can complete the pre-designed behavior under external stimulation.However,most microrobots are currently made of a single material system and focus on fabricating a driving module as the main structure of microrobots.This hinders the integration of diverse functions in one microrobot to fulfill the complex application.Here,a multi-material and multi-module hand-microrobot based on femtosecond laser direct writing technology is proposed,which has a pH-responsive capturing module and a magnetic-responsive transportation module(MRTM).This microrobot can not only respond to pH for capturing and releasing objects,but also respond to magnetic fields for cargo delivery even with obstacles.The two responding modules of the hand-microrobot are fabricated independently,and can collaborate with each other to achieve the delivery of target objects like polystyrene(PS)microsphere(10µm)or 786-O cell by capturing,transporting,and spatial rolling.Besides,the MRTM can be locally fabricated on any prefabricated static structure,so that the whole microrobot can achieve controllable motion.This strategy is expected to be used to manipulate cells,deliver drugs for precise treatment,and environmental treatment.展开更多
With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must...With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must be performed in underwater environments.The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment.The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique.First,we elaborated recent advances and key issues of drainage nozzles all over the world.Next,we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials.Then,the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed.The differences between the convection,conduction,and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated.After that,several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed.Finally,suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided.The present review will not only enrich the knowledge in the underwater repair technology,but also provide important guidance for the potential applications of the technology on the marine engineering.展开更多
Stretchable electronic sensing devices are defining the path toward wearable electronics. High-performance flexible strain sensors attached on clothing or human skin are required for potential applications in the ente...Stretchable electronic sensing devices are defining the path toward wearable electronics. High-performance flexible strain sensors attached on clothing or human skin are required for potential applications in the entertainment,health monitoring, and medical care sectors. In this work,conducting copper electrodes were fabricated onpolydimethylsiloxane as sensitive stretchable microsensors by integrating laser direct writing and transfer printing approaches. The copper electrode was reduced from copper salt using laser writing rather than the general approach of printing with pre-synthesized copper or copper oxide nanoparticles. An electrical resistivity of 96 l X cm was achieved on 40-lm-thick Cu electrodes on flexible substrates. The motion sensing functionality successfully demonstrated a high sensitivity and mechanical robustness.This in situ fabrication method leads to a path toward electronic devices on flexible substrates.展开更多
Flexible and wearable humidity sensors play a vital role in daily point-of-care diagnosis and noncontact human-machine interactions.However,achieving a facile and high-speed fabrication approach to realizing flexible ...Flexible and wearable humidity sensors play a vital role in daily point-of-care diagnosis and noncontact human-machine interactions.However,achieving a facile and high-speed fabrication approach to realizing flexible humidity sensors remains a challenge.In this work,a wearable capacitive-type Ga_(2)O_(3)/liquid metal-based humidity sensor is demonstrated by a one-step laser direct writing technique.Owing to the photothermal effect of laser,the Ga_(2)O_(3)-wrapped liquid metal particles can be selectively sintered and converted from insulative to conductive traces with a resistivity of 0.19Ω·cm,while the untreated regions serve as active sensing layers in response to moisture changes.Under 95%relative humidity,the humidity sensor displays a highly stable performance along with rapid response and recover time.Utilizing these superior properties,the Ga_(2)O_(3)/liquid metal-based humidity sensor is able to monitor human respiration rate,as well as skin moisture of the palm under different physiological states for healthcare monitoring.展开更多
To improve the mechanical properties of the parts fabricated by Laser Direct Metal Shaping(LDMS),it is of great significance to understand the distribution regularities of transient temperature field during LDMS proce...To improve the mechanical properties of the parts fabricated by Laser Direct Metal Shaping(LDMS),it is of great significance to understand the distribution regularities of transient temperature field during LDMS process.Based on the“el-ement birth and death”technique of finite element method,a three-dimensional multi-track and multi-layer model for the transient temperature field analysis of LDMS is developed by ANSYS Parametric Design Language(APDL)for the first time.In the fab-ricated modal,X-direction parallel reciprocating scanning paths is introduced.Using the same process parameters,the simulation results show good agreement with the microstructure features of samples which fabricated by LDMS.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
The present work aims to investigate the fatigue behavior of Direct Laser Deposition(DLD) Ti-6.5 Al-2 Zr-1 Mo-1 V titanium alloy under constant amplitude stress. 22 pieces of DLD Ti-6.5 Al-2 Zr-1 Mo-1 V titanium alloy...The present work aims to investigate the fatigue behavior of Direct Laser Deposition(DLD) Ti-6.5 Al-2 Zr-1 Mo-1 V titanium alloy under constant amplitude stress. 22 pieces of DLD Ti-6.5 Al-2 Zr-1 Mo-1 V titanium alloy standard cylinder specimens were tested under a stress level of 800 MPa with a stress ratio of 0.06. Fatigue fractography and fatigue life data were obtained.Through the fracture surface analysis, the specimens were divided into two categories in accordance with the location of crack initiation and defect types. Comparison of fatigue life and behavior between two specimen types was given, which was followed by a discussion about the impact of defect type, size and position on the fatigue life of the specimen. The fatigue test results also show a large variation of fatigue life. To illustrate the statistical characteristics of the fatigue life, probabilistic analysis was performed, and a novel bimodal lognormal model was established. The model has a good fit with the experimental data and can reduce the scatter of the fatigue life significantly.展开更多
基金National Key Research and Development Program of China(2024YFB4610803)。
文摘The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstructure,fracture surfaces,and crack growth paths were analyzed before and after CHT.Results indicate that in the stable crack growth region,the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^(−8)(ΔK)^(3.2271)and da/dN=1.4112×10^(−8)(ΔK)^(3.1125),respectively.Compared with that at the as-deposited state,the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-sphericalαandβ-transformed matrix phases.The cyclic process also disrupts the continuity of the grain boundaryα(αGB)at the primaryβ-phase grain boundary.The coarsening of primaryαand the disruption ofαGB continuity are the primary factors to release stress concentration and promote crack deflection,thereby decreasing the fatigue crack growth rate.Additionally,the increased occurrence of crack branching,secondary cracking,and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.
基金financially supported by the National Key Research and Development Program of China(Nos.2024YFB4607402 and 2016YFC1100502)the National Natural Science Foundation of China(Nos.51673208 and 61975213)。
文摘Biopolymeric nanocomposites have attracted considerable attention because of their biocompatibility,biodegradability,and unique physicochemical properties.It is essential to manufacture three-dimensional(3D)biocompatible micro/nanostructures using biopolymeric nanocomposites.Herein,we demonstrate the high-fidelity fabrication of biocompatible 3D features with sub-50 nm resolution using femtosecond laser direct writing(FsLDW)of a biopolymeric nanocomposite composed of egg white and sulfonated graphene(S-graphene).The biopolymer nanocomposite acts as a negative photoresist suitable for water-based lithography.The introduction of S-graphene not only dramatically lowered the laser power threshold but also significantly modulated the morphology of the 3D features constructed by FsLDW.Microstructures with porous,rough,or smooth morphologies were obtained by optimizing the S-graphene concentration and laser scanning speed.The fabricated egg-white/S-graphene microstructures exhibited biocompatibility and environmental degradability.Egg white/S-graphene was also employed to fabricate diffractive gratings with superior optical quality.This study provides a promising method to manufacture biocompatible 3D features with controllable morphology,which has potential applications in biological and photonic fields.
基金supported by the National Key Researchand Development Program of China(No.2021YFC2801904)the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai,China(No.AMGM2024F11).
文摘The ultrasonic energy field(UEF)-induced grain refinement mechanisms in laser powder direct energy deposition-manufactured Ti5321G alloys were systematically investigated in this study.This study focused on the interplay between recrystallization in the high-temperature solid deposition layers and the ultrasonic cavitation-acoustic streaming effects during molten pool solidification.A novel experimental design was developed to decouple these mechanisms by creating four distinct UEF action zones(without UEF-N,withUEF-S,with UEF-L,and with UEF-S+L)within a single-pass multilayer sample.This approach enabled the dual effects of UEF(recrystallization in solidified layers and ultrasonic cavitation-acoustic streaming effects in liquid pools)to be directly compared.The UEF significantly refined the microstructures,reducing the average grain size by 64.2%(from(399.6±28.6)to(143.1±16.1)μm)in the with UEF-S+L zone,while promoting columnar-to-equiaxed transition,with the equiaxed grain probability increasing from 11.1%(without UEF) to 53.8%.The texture intensity was reduced by approximately 52.4%and the mechanical properties were enhanced,achieving a 6.2% increase in yield strength((702.0±10.6)MPa)and 31.7%improvement in elongation.Crucially,this study revealed the synergistic effect of the dual-action mechanisms of UEF,where recrystallization and cavitation-acoustic streaming collectively enabled non-linear grain refinement.This study provides a strategy for microstructural control in additive manufacturing,eliminating the need for complex post-processing and thereby advancing the industrial application of high-performance titanium components.
基金supported by National Key R&D Program of China(Grant Nos.2021YFB2802000 and 2022YFB2804300)Science and Technology Commission of Shanghai Municipality(Grant No.21DZ1100500)+3 种基金Shanghai Municipal Science and Technology Major Projectthe Shanghai Frontiers Science Center Program(2021-2025 No.20)National Natural Science Foundation of China(Grant No.61975123)Shanghai Scienceand Technology Innovation Action Plan(Grant No.23JC1403100)。
文摘Able to precisely control and manipulate materials'states at micro/nano-scale level,femtosecond(fs)laser micro/nano processing technology has undergone tremendous development over the past three decades.Free-forming three-dimensional(3D)microscale functional devices and inducing fascinating and unique physical or chemical phenomena have granted this technology powerful versatility that no other technology can match.As this technology advances rapidly in various fields of application,some key challenges have emerged and remain to be urgently addressed.This review firstly introduces the fundamental principles for understanding how fs laser pulses interact with materials and the associated unique phenomena in section 2.Then micro/nano-fabrication in transparent materials by fs laser processing is presented in section 3.Thereafter,several high efficiency/throughput fabrication methods as well as pulse-shaping techniques are listed in sections 4 and 5 reviews four-dimensional(4D)and nanoscale printing realized by fs laser processing technology.Special attention is paid to the heterogeneous integration(HI)of functional materials enabled by fs laser processing in section 6.Several intriguing examples of 3D functional micro-devices created by fs laser-based manufacturing methods such as microfluidics,lab-on-chip,micro-optics,micro-mechanics,micro-electronics,micro-bots and micro-biodevices are reviewed in section 7.Finally,a summary of the review and a perspective are proposed to explore the challenges and future opportunities for further betterment of fs laser micro/nano processing technology.
基金Project(2021YFC2801904) supported by the National Key R&D Program of ChinaProject(KY10100230067) supported by the Basic Product Innovation Research Project,China+3 种基金Projects(52271130,52305344) supported by the National Natural Science Foundation of ChinaProject(ZR2022QE073) supported by the Natural Science Foundation of Shandong Province,ChinaProject(AMGM2021F01) supported by the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai,ChinaProject(KY90200210015) supported by Leading Scientific Research Project of CNNC,China。
文摘In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition(LDED).The effects of ultrasonic vibration(UV)and tempering treatment on microstructure evolution,microhardness distribution and mechanical properties of deposition layer were studied in detail.The microstructure of UV assisted LDED sample after tempering is mainly composed of tempered sorbite(TS).Due to the improvement of microstructure inhomogeneity and grains refinement,UV assisted LDED sample with tempering treatment obtains excellent mechanical properties.The ultimate tensile strength(UTS),yield strength(YS)and elongation after breaking(EL)reach 765 MPa,657 MPa and 19.5%,the increase ratios of UTS and YS are 14.5%and 33.8%while maintaining plasticity compared to original LDED sample,respectively.It is obvious that ultrasonic vibration combined with tempering is a potential and effective method to obtain uniform microstructure and excellent mechanical properties in metal laser directed energy deposition field.
基金supported by the National Natural Science Foundation of China(52005264).
文摘Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in this study.The microstructure of the WE43 and CNTs/WE43 layers was systematically compared.The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment.The spot segregation composed of Mg_(24)Y_(5),CNTs,and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content.The grain growth of both types of layers underwent three stages:slow,rapid,and steady-state.The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature,resulting in a 47%increase at 510℃ and a 35%increase at 540℃ in the grain growth exponent compared to the WE43 layers at 510℃.During the subsequent aging treatment at 225℃,the precipitation sequences from plate-shaped β″to plate-shaped and globular β′ were observed in both types of layers.CNTs can facilitate an increase in the nucleation rate of precipitates,but without accelerating precipitation hardening rate.The long and short diameters of the precipitates in peak-aged state were decreased by 48.5%and 43.1%by addition of CNTs,respectively.The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment.The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.
基金financial supports from the National Natural Science Foundation of China (No.52305440)the Natural Science Foundation of Changsha City (Nos.kq2208272,kq2208274)+1 种基金the Tribology Science Fund of the State Key Laboratory of Tribology in Advanced Equipment (SKLTKF22B09)the National Key Research and Development Program of China (2022YFB3706902)。
文摘Under the laser directed energy deposition(LDED)process,the rapid melting and solidification usually lead to the emergence of pores and coarse columnar dendrites,which in turn compromise the properties of the deposited alloys.This study introduced in-situ ultrasonic rolling(UR)as an innovative method to enhance the corrosion resistance of LDED specimens,and the microstructural characteristics and their correlation with corrosion resistance were deeply investigated.The findings reveal that the LDED-UR specimen exhibits a reduction in both the fraction and size of pores.Under the influence of severe plastic deformation generated by LDED-UR process,fully equiaxed grains appear with a reduced average size of 28.61μm(compared to63.98μm for the LDED specimen with columnar grains).The electrochemical corrosion resistance of the LDED-UR specimen is significantly enhanced compared to the LDED specimen.This enhanced corrosion resistance can be attributed to the low fraction of small-sized pores,the fine and uniformly distributed Cr-enriched ferrite phase,and the formation of a compact and thick passive film due to dense grain boundaries.The insight of the correlation between microstructure and corrosion behavior opens up a new pathway to enhance the corrosion resistance of LDED specimens.
基金National Key Research and Development Program of China(2022YFB4602200)。
文摘To address the issues of low accuracy,long time consumption,and high cost of the traditional temperature prediction methods for laser directed energy deposition(LDED),a machine learning model combined with numerical simulation was proposed to predict the temperature during LDED.A finite element(FE)thermal analysis model was established.The model's accuracy was verified through in-situ monitoring experiments,and a basic database for the predictive model was obtained based on FE simulations.Temperature prediction was performed using a generalized regression neural network(GRNN).To reduce dependence on human experience during GRNN parameter tuning and to enhance model prediction performance,an improved adaptive step-size fruit fly optimization algorithm(ASSFOA)was introduced.Finally,the prediction performance of ASSFOA-GRNN model was compared with that of back-propagation neural network model,GRNN model,and fruit fly optimization algorithm(FOA)-GRNN model.The evaluation metrics included the root mean square error(RMSE),mean absolute error(MAE),coefficient of determination(R^(2)),training time,and prediction time.Results show that the ASSFOA-GRNN model exhibits optimal performance regarding RMSE,MAE,and R^(2) indexes.Although its prediction efficiency is slightly lower than that of the FOA-GRNN model,its prediction accuracy is significantly better than that of the other models.This proposed method can be used for temperature prediction in LDED process and also provide a reference for similar methods.
基金supported by National Natural Science Foundation of China(Grant No.52375312)National Key Research and Development Program of China(Grant No.2023YFB4605900)+3 种基金Liaoning Province Science and Technology Plan Joint Program(Grant No.2023JH2/101700299)Open Research Fund of Key Laboratory of Precision Special Machining and Micromanufacturing Technology of Ministry of Education for Dalian University of Technology(Grant No.B202305)Shenzhen National Major Science and Technology Projects(Grant No.CJGJZD20240729113704006)Shenzhen Key Technology R&D Programs(Grant No.JSGG20210420091802007).
文摘Laser-directed energy deposition(LDED)technology has demonstrated great potential for the rapid and integrated fabrication of nickel-based superalloy components.The plastic deformation-assisted method is crucial for achieving grain refinement and microstructural homogeneity in LDED-fabricated superalloys.However,existing methods suffer from uniformity constraints owing to their high deformation resistance,which significantly limits their application in load-bearing components.To address these issues,a synchronous-hot-forging-assisted(SHFA)LDED additive manufacturing method was proposed,and its effects on the macroscopic morphology,microstructure,and mechanical properties of GH4169 nickel-based alloy specimens were systematically compared.The results demonstrated up to 30.1%average plastic deformation in hot-forging components while maintaining good surface flatness.The synergistic effect of dislocation accumulation and dynamic recrystallization during hot forging enables dramatic grain refinement,reducing the average grain size by 89.1%(from 168.5μm to 18.4μm)while weakening texture intensity from 15.31 to 2.15,ultimately promoting equiaxed grain formation.The pores of hot-forging components changed from fine round to flat,the porosity decreased from 0.264%to 0.089%,and the densification level was significantly improved.With the increase in the synchronous hot-forging force,the average ultimate tensile strength of hot-forging components can reach 1175.1 MPa,while the anisotropy difference is gradually weakened.The SHFA-LDED process not only achieves excellent grain refinement and microstructure homogenization but also enhances mechanical properties,providing a new technical path for the additive manufacturing of high-performance nickel-based superalloy components.
基金supported by the National Science Foundation of China under the Grant Nos.12127806 and 62175195the International Joint Research Laboratory for Micro/Nano Manufacturing and Measurement Technologies。
文摘High-density interconnect(HDI)soft electronics that can integrate multiple individual functions into one miniaturized monolithic system is promising for applications related to smart healthcare,soft robotics,and human-machine interactions.However,despite the recent advances,the development of three-dimensional(3D)soft electronics with both high resolution and high integration is still challenging because of the lack of efficient manufacturing methods to guarantee interlayer alignment of the high-density vias and reliable interlayer electrical conductivity.Here,an advanced 3D laser printing pathway,based on femtosecond laser direct writing(FLDW),is demonstrated for preparing liquid metal(LM)-based any layer HDI soft electronics.FLDW technology,with the characteristics of high spatial resolution and high precision,allows the maskless fabrication of high-resolution embedded LM microchannels and high-density vertical interconnect accesses for 3D integrated circuits.High-aspect-ratio blind/through LM microstructures are formed inside the elastomer due to the supermetalphobicity induced during laser ablation.The LM-based HDI circuit featuring high resolution(~1.5μm)and high integration(10-layer electrical interconnection)is achieved for customized soft electronics,including various customized multilayer passive electric components,soft multilayer circuit,and cross-scale multimode sensors.The 3D laser printing method provides a versatile approach for developing chip-level soft electronics.
基金supported by the National Key Research and Development Program of China(2023YFB4605100)the Shaanxi Provincial Key Research and Development Program(2019ZDLGY01-09 and 2021ZDLGY10-02)the State Key Laboratory of Solidification Processing(SKLSP202203).
文摘The fabrication of nanostructures beyond the diffraction limit has been the focus of nanotechnology research.Scanning probe microscopy(SPM)has attracted the attention of researchers for the detection and manufacture of nanostructures.Here,a nanosecond laser irradiated a cantilevered scanning nearfield optical microscopy(SNOM)tip and directly wrote subwavelength nanostructures on Au nano-film,without the assistance of a mask or vacuum atmosphere.This method was stable and reproducible for long-term use.The in situ morphology detection was conducted after the writing process by atomic force microscope(AFM).A feature linewidth of approximately 83.6 nm(<k/6)was confirmed using scanning electron microscopy(SEM).Linewidth of(167.8±6.6)nm was reproduced stably.Theoretical calculations revealed that the elliptical heat distribution under the SNOM tip generated different linewidths when the tip scanned vertically and horizontally.It also interpreted the influential mechanism of single-pulse energy.The simulated linewidths were consistent with the fabricated linewidths.According to the elemental analysis by energy dispersive spectrometer(EDS),the mechanism of this method can be interpreted asmelting of the Au nano-film instead of oxidation.Owing to its high positioning,machining accuracy,and instantaneous energy,this technology is considered convenient and economical for nanostructure fabrication and is proposed to be applied in nanolithography on multiple materials in the future.
文摘Laser processing technologies enable the precise fabrication of arbitrary structures and devices with broad applications in micro-optics,micro-mechanics,and biomedicine.However,its adoption is limited by the large size,complexity,high cost,and low flexibility of optical systems.Metasurfaces enable precise multidimensional control of light fields,aligning well with the development trend toward compact,high-performance optical systems.Here,we review several recent studies on the application of metasurfaces in laser processing technologies,including 3D nanolithography,direct laser writing,and laser cutting.Metasurfaces provide an integrated operational platform with exceptional performance,poised to disrupt conventional laser processing workflows.This combination presents significant cost efficiency and substantial development potential,with promising applications in areas such as imaging,optical storage,advanced sensing,and space on-orbit manufacturing.
文摘A mathematical model is developed for simulating the heat transferring behavior in a direct metal laser sintering process. The model considers the thermal phenomena involved in the process, including conduction, radiation, and convection. A formula for the calculation of the heat conductivity of a sintering system containing solid phase, liquid phase, and gas phase is given. Due to the continuous movement of the laser beam, a local coordinate system centered on the laser beam is used to simplify the analytical calculation. Assuming that it is approximately a Gaussian laser beam, the heat conduction equation is resolved based on the assumption of the thermal insulating boundary conditions and the fixed thermal physical parameters. The FORTRAN language is employed to compile the program to simulate the temperature field in the direct copper powder sintering process. It shows a good agreement with the preliminary experimental results.[KH3/4D]
基金financial support of the National Key R&D Program of China(Grant Nos.2024YFB4607402 and 2016YFA0200500)National Natural Science Foundation of China(NSFC,Grant Nos.61975213,61475164 and 61205194)International Partnership Program of Chinese Academy of Sciences(GJHZ2021130)。
文摘Microrobots play an essential role in early diagnosis and precision medicine with the increasing demands for controllability in bio-medicine and micromanipulation,which can complete the pre-designed behavior under external stimulation.However,most microrobots are currently made of a single material system and focus on fabricating a driving module as the main structure of microrobots.This hinders the integration of diverse functions in one microrobot to fulfill the complex application.Here,a multi-material and multi-module hand-microrobot based on femtosecond laser direct writing technology is proposed,which has a pH-responsive capturing module and a magnetic-responsive transportation module(MRTM).This microrobot can not only respond to pH for capturing and releasing objects,but also respond to magnetic fields for cargo delivery even with obstacles.The two responding modules of the hand-microrobot are fabricated independently,and can collaborate with each other to achieve the delivery of target objects like polystyrene(PS)microsphere(10µm)or 786-O cell by capturing,transporting,and spatial rolling.Besides,the MRTM can be locally fabricated on any prefabricated static structure,so that the whole microrobot can achieve controllable motion.This strategy is expected to be used to manipulate cells,deliver drugs for precise treatment,and environmental treatment.
基金Supported by National Basic Scientific Research Project(Grant No.JCKY2017110B001)Jiangsu Provincial Postgraduate Research&Practice Innovation Program of China(Grant No.KYCX20_0080)。
文摘With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must be performed in underwater environments.The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment.The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique.First,we elaborated recent advances and key issues of drainage nozzles all over the world.Next,we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials.Then,the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed.The differences between the convection,conduction,and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated.After that,several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed.Finally,suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided.The present review will not only enrich the knowledge in the underwater repair technology,but also provide important guidance for the potential applications of the technology on the marine engineering.
基金supported by National Natural Science Foundation of China (51575016)the Beijing Oversea High-Level Talent Project+1 种基金strategic research Grant (KZ20141000500, B-type) of Beijing Natural Science Foundation P.R. Chinathe support by the China Scholarship Council (20160654015) for his research stay at the Institute of Physical and Chemical Research,Wako, Japan
文摘Stretchable electronic sensing devices are defining the path toward wearable electronics. High-performance flexible strain sensors attached on clothing or human skin are required for potential applications in the entertainment,health monitoring, and medical care sectors. In this work,conducting copper electrodes were fabricated onpolydimethylsiloxane as sensitive stretchable microsensors by integrating laser direct writing and transfer printing approaches. The copper electrode was reduced from copper salt using laser writing rather than the general approach of printing with pre-synthesized copper or copper oxide nanoparticles. An electrical resistivity of 96 l X cm was achieved on 40-lm-thick Cu electrodes on flexible substrates. The motion sensing functionality successfully demonstrated a high sensitivity and mechanical robustness.This in situ fabrication method leads to a path toward electronic devices on flexible substrates.
基金This study was supported by the National Natural Science Foundation of China (52105593 and 62271439)STI 2030 —Major Projects(2022ZD0208601)the “Pioneer” and “Leading Goose” R&D Program of Zhejiang (2023C01051)。
文摘Flexible and wearable humidity sensors play a vital role in daily point-of-care diagnosis and noncontact human-machine interactions.However,achieving a facile and high-speed fabrication approach to realizing flexible humidity sensors remains a challenge.In this work,a wearable capacitive-type Ga_(2)O_(3)/liquid metal-based humidity sensor is demonstrated by a one-step laser direct writing technique.Owing to the photothermal effect of laser,the Ga_(2)O_(3)-wrapped liquid metal particles can be selectively sintered and converted from insulative to conductive traces with a resistivity of 0.19Ω·cm,while the untreated regions serve as active sensing layers in response to moisture changes.Under 95%relative humidity,the humidity sensor displays a highly stable performance along with rapid response and recover time.Utilizing these superior properties,the Ga_(2)O_(3)/liquid metal-based humidity sensor is able to monitor human respiration rate,as well as skin moisture of the palm under different physiological states for healthcare monitoring.
文摘To improve the mechanical properties of the parts fabricated by Laser Direct Metal Shaping(LDMS),it is of great significance to understand the distribution regularities of transient temperature field during LDMS process.Based on the“el-ement birth and death”technique of finite element method,a three-dimensional multi-track and multi-layer model for the transient temperature field analysis of LDMS is developed by ANSYS Parametric Design Language(APDL)for the first time.In the fab-ricated modal,X-direction parallel reciprocating scanning paths is introduced.Using the same process parameters,the simulation results show good agreement with the microstructure features of samples which fabricated by LDMS.
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 support from the National Key Research and Development Program of China (No. 2017YFB1104003)the National Natural Science Foundation of China (No. 11772027)Aeronautical Science Foundation of China (No. 28163701002)
文摘The present work aims to investigate the fatigue behavior of Direct Laser Deposition(DLD) Ti-6.5 Al-2 Zr-1 Mo-1 V titanium alloy under constant amplitude stress. 22 pieces of DLD Ti-6.5 Al-2 Zr-1 Mo-1 V titanium alloy standard cylinder specimens were tested under a stress level of 800 MPa with a stress ratio of 0.06. Fatigue fractography and fatigue life data were obtained.Through the fracture surface analysis, the specimens were divided into two categories in accordance with the location of crack initiation and defect types. Comparison of fatigue life and behavior between two specimen types was given, which was followed by a discussion about the impact of defect type, size and position on the fatigue life of the specimen. The fatigue test results also show a large variation of fatigue life. To illustrate the statistical characteristics of the fatigue life, probabilistic analysis was performed, and a novel bimodal lognormal model was established. The model has a good fit with the experimental data and can reduce the scatter of the fatigue life significantly.
