The original online version of this article was revised:Several errors occurred in the published version of the article.These have now been corrected as follows:Page 2,section"2.2 Laser Texturing Procedure of Sur...The original online version of this article was revised:Several errors occurred in the published version of the article.These have now been corrected as follows:Page 2,section"2.2 Laser Texturing Procedure of Surfaces",line 2:The device name was corrected from"YDFLP-E-50-M8"to"YDFLP-50-M8."Page 3,Section 2.4:The phrase"95%confidence interval"has been corrected to"95%confidence level."Page 3,Figure 1 caption:The phrase"fandg"has been corrected to"f and g."The order"C4 and C12"has been reversed to"C12 and C4,"in accordance with the display order in the figure.Page 4,Figure reference:The phrase"Figs.4c and d"has been corrected to"Figs.5b and c."Page 5,paragraph starting with"The ANOVA results are presented...":The phrase"95%confidence interval"has been corrected to"95%confidence level."展开更多
While laser surface texturing(LST)is a promising manufacturing technique for surface functionalization,simultaneously realizing high precision and high efficiency in the LST of complex curved surface is challenging,du...While laser surface texturing(LST)is a promising manufacturing technique for surface functionalization,simultaneously realizing high precision and high efficiency in the LST of complex curved surface is challenging,due to continuously varied geometries of laser-matter incidence.In the present work,we propose a novel manufacturing system of 7-axis on-the-fly LST for complex curved surface,based on the integrated synchronization of 5-axis linkage motion platform with 2-axis galvanometer.Specifically,the algorithm for decomposing spatial texture trajectory on curved surface into low-frequency and high-frequency parts is established,based on which the kinematic model of synchronized 7-axis system is developed to derive the motion of each axis in both 5-axis linkage motion platform and 2-axis galvanometer simultaneously.Subsequently,the synchronized 7-axis LST system is experimentally realized,including the setup of mechanical stages integrated with optical path,the configuration of numerical control unit,and the development of processing software.Finally,case study of 7-axis on-the-fly LST of freeform aluminum surface is performed,and the advantages in terms of processing efficiency and texturing accuracy over 5-axis linkage LST are demonstrated.The correlation of reduced following errors between mechanical stages with the promoted performance of curved surface texturing by the 7-axis on-the-fly LST is further analyzed.Current work provides a feasible solution for establishing the manufacturing system for high performance LST of complex curved surface.展开更多
Photonic crystal surface emitting lasers(PCSELs)utilize the Bragg diffraction of two-dimensional photonic crystals to achieve a single-mode output with a high power and a small divergence angle,and has recently attrac...Photonic crystal surface emitting lasers(PCSELs)utilize the Bragg diffraction of two-dimensional photonic crystals to achieve a single-mode output with a high power and a small divergence angle,and has recently attracted much attention^([1−3]).In 2023,Kyoto University reported GaAs-based 945 nm PCSELs with a continuous-wave(CW)single-mode output power of exceeding 50 W,and a narrow beam divergence angle of 0.05°,demonstrating a brightness of 1 GW·cm^(−2)·sr^(−1),which rivals those of the existing bulky lasers^([4]).展开更多
Silicon carbide(SiC)is a highly valued material for power semiconductor devices due to its wide bandgap,high thermal conductivity,and high breakdown electric field.However,its high hardness,brittleness,and chemical st...Silicon carbide(SiC)is a highly valued material for power semiconductor devices due to its wide bandgap,high thermal conductivity,and high breakdown electric field.However,its high hardness,brittleness,and chemical stability present substantial challenges for efficient and high-quality processing.This study investigated the effects of picosecond laser surface scanning on 4H-SiC to enhance the material removal performance.The research focused on surface morphology,phase transitions,subsurface/interface characteristics,and material removal mechanisms under varying laser parameters.The results demonstrate that the laser thermal effect decomposes 4H-SiC into amorphous silicon(a-Si),disordered carbon,and graphite,forming a resolidified layer containing Si-O and Si-C-O oxides.Crystalline silicon(c-Si)is produced under high fluences or extensive irradiations.The variation in the resolidified layer thickness with changing laser parameters is revealed.A detailed laser-induced subsurface damage model is developed,encompassing a resolidified layer that includes the above decomposition and oxidation products,and a deformed layer formed primarily under laser-induced stress.The presence of the resolidified layer and the deformed layer leads to a decreased elastic recovery rate and an increased scratching depth,exceeding 2.5 times that of the unmodified condition.Enhanced material removal performance is mainly driven by the resolidified layer at low fluence and by the deformed layer at high fluence.When aligning the total of the ablation depth and the resolidified layer thickness with the subsurface damage depth in the original material,excellent polishing performance is achieved.These findings provide critical insights for understanding the phase evolution,subsurface damage mechanisms,and material removal behavior of 4H-SiC,offering valuable guidance for optimizing the laser surface modification parameters to achieve high-efficiency processing.展开更多
Triply periodic minimal surface(TPMS)structures,characterized by special repeating 3D surface periodically with an average curvature of zero in threedimensional directions,have a wide range of applications.Laser powde...Triply periodic minimal surface(TPMS)structures,characterized by special repeating 3D surface periodically with an average curvature of zero in threedimensional directions,have a wide range of applications.Laser powder bed fusion(LPBF)technique,as a type of additive manufacturing techniques,provides the capability to fabricate such complex-shaped porous TPMS structures.In this study,Ti6Al4V G-sheet TPMS structures with various unit cell sizes were fabricated using LPBF to investigate the structural and material anisotropy and their effects on the anisotropy in energy absorption capacity by combining the finite element simulations and experimental analysis.The results showed that the TPMS structures can be successfully fabricated using LPBF,although the sheet thickness exceeds the designed values,with deviation decreasing as the unit cell size increases from 2 to 4 mm.The inherent anisotropy during the LPBF process results in variations in structural dimension,materials characteristics,and energy absorption capacity between directions parallel and perpendicular to the build direction.The anisotropic ratio of the LPBFed Ti6Al4V G-sheet TPMS structures increases from 1.5 to 2.2 in the structural dimension and from 2.8 to 3.3 in specific energy absorption per unit mass(SEA_(m))respectively with decreasing the unit cell size from 4 to 2 mm.The anisotropy of SEA_(m) primarily originates from the coupling effects of anisotropic dimensions and material properties in the LPBFed G-sheet TPMS structure.Among these factors,anisotropic material properties play a more significant role compared to dimensional anisotropy.展开更多
The recent progress in semiconductor processing technology has served as a major driving force behind the rapid development of nanophotonics research.Among the emerging applications,metasurfaces have attracted signifi...The recent progress in semiconductor processing technology has served as a major driving force behind the rapid development of nanophotonics research.Among the emerging applications,metasurfaces have attracted significant attention as saturable absorbers(SAs)for mode-locked laser systems that generate short pulses.In this study,we present the comprehensive design,fabrication,and experimental demonstration of a metasurface-based SA operating in the 1μm wavelength range,leveraging both the localized surface plasmon resonance(LSPR)phenomenon and the epsilon-near-zero(ENZ)effect of indium tin oxide.展开更多
A laser surface melting(LSM)technology was applied to enhancing the corrosion resistance of a Mg−Zn−Y alloy containing large and discontinuous long-period stacking-ordered(LPSO)phases.The microstructural evolution and...A laser surface melting(LSM)technology was applied to enhancing the corrosion resistance of a Mg−Zn−Y alloy containing large and discontinuous long-period stacking-ordered(LPSO)phases.The microstructural evolution and solidification behavior of this alloy during LSM were studied.It was demonstrated that the significantly reduced corrosion rate of the alloy after LSM,can be attributed to the disappearance of the original micron-sized LPSO phase and a decrease in the grain size from 300 to 15μm.The refined grains were composed of three adjacent zones,namely theβeutectic phase zone,the W phase zone,and the lamellar structures zone,which formed sequentially during the rapid cooling process.The dendritic lamellae grew along the basal plane of the magnesium matrix and were separated by supersaturatedα-Mg phases.Ultimately,the disappearance of large primary batteries and grain refinement improved the corrosion resistance of the Mg−Zn−Y alloy.展开更多
To solve the problems of deformation,micro-cracks,and residual tensile stress in laser cladding coatings,the technique of laser cladding with Fe-based memory alloy can be considered.However,the process of in-situ synt...To solve the problems of deformation,micro-cracks,and residual tensile stress in laser cladding coatings,the technique of laser cladding with Fe-based memory alloy can be considered.However,the process of in-situ synthesis of Fe-based memory alloy coatings is extremely complex.At present,there is no clear guidance scheme for its preparation process,which limits its promotion and application to some extent.Therefore,in this study,response surface methodology(RSM)was used to model the response surface between the target values and the cladding process parameters.The NSGA-2 algorithm was employed to optimize the process parameters.The results indicate that the composite optimization method consisting of RSM and the NSGA-2 algorithm can establish a more accurate model,with an error of less than 4.5%between the predicted and actual values.Based on this established model,the optimal scheme for process parameters corresponding to different target results can be rapidly obtained.The prepared coating exhibits a uniform structure,with no defects such as pores,cracks,and deformation.The surface roughness and microhardness of the coating are enhanced,the shaping quality of the coating is effectively improved,and the electrochemical corrosion performance of the coating in 3.5%NaCl solution is obviously better than that of the substrate,providing an important guide for engineering applications.展开更多
The lightweight refractory high-entropy alloys(LRHEAs)are considered as next-generation high-performance weaponry matrix material.In this work,we employ the laser surface melting(LSM)method to ulteriorly optimize surf...The lightweight refractory high-entropy alloys(LRHEAs)are considered as next-generation high-performance weaponry matrix material.In this work,we employ the laser surface melting(LSM)method to ulteriorly optimize surface mechanical properties of Al_(0.5)NbTi_(3)VZr_(0.5) matrix HEA,where the phase structures,mechanical properties and deformation mechanism of as-cast and LSM-treated HEAs have been investigated.The LSM process eliminates tanglesome intermetallic Zr_(5)Al_(3) structures and effectively improves the mechanical properties of as-cast HEA.The sample after 2000 W LSM treatment exhibits the superior comprehensive mechanical properties,its tensile elongation,microhardness of remelt zone and volume wear loss are 31.6%,HV 809.6 and 296.4×10^(−3) mm^(3),representing the advancement of 85.9%,180.1%and 64.6%compared to that of as-cast HEA sample,respectively.Additionally,the deformation behavior of the as-cast sample involves solid phase transformation,stacking faults and deformation twinnings.The deformation mechanism of as-cast Al_(0.5)NbTi_(3)VZr_(0.5) HEA is transformation-induced plasticity(TRIP)and twinning-induced plasticity(TWIP),the classical Burgers mechanism of BCC→HCP solid phase transformation is revealed,which obeys[111]_(BCC)∥[1120]_(HCP).As for the 2000 W treated sample,the deformation mechanism is mainly TWIP as the stacking fault energy enhancement evidenced by the presence of cross-slip dislocations after LSM process.展开更多
Fabrication of the surface micro-texture on the C-plane sapphire is undertaken by a355 nm Ultraviolet(UV)pulsed laser.The surface micro-textures of sapphire with different laser scanning line spacing ranging from 10 l...Fabrication of the surface micro-texture on the C-plane sapphire is undertaken by a355 nm Ultraviolet(UV)pulsed laser.The surface micro-textures of sapphire with different laser scanning line spacing ranging from 10 lm to 100 lm are obtained,where the selection range of scanning line spacing is controlled in the range of the groove width and plasma width to obtain a surface of high Peak-Valley(PV)value.A reasonable processing order is proposed to manufacture different types of surface micro-textures on sapphire by laser ablation trajectory regulation.In the multiple-passes laser ablation of sapphire by the UV nanosecond pulsed laser,the scanning lines in each direction is treated as once scanning.On this basis,the multiple processing can be carried out to avoid the influence of the subsequent scanning on the machined groove.In addition,the effect of different scanning line spacing on the PV value is quantified and different types of surface microtextures on sapphire,including the squares,the rhombuses and the hexagons,are successfully fabricated,which can be applied in the friction reduction or anti-reflection field.展开更多
Laser surface melting（LSM） is a high-energy surface treatment that allows modification of the microstructure and surface properties of Mg alloys. In the present work, an attempt of LSM on magnesium alloy with liquid...Laser surface melting（LSM） is a high-energy surface treatment that allows modification of the microstructure and surface properties of Mg alloys. In the present work, an attempt of LSM on magnesium alloy with liquid nitrogen-assisted cooling（LNSC） was carried out to get the higher cooling rate and improve the surface properties. The experimental results were compared with those of Ar gas protection at room temperature. The samples after LSM with LNSC resulted in a thinner melted layer, a highly homogeneous, refined melted microstructure and formed a lot of worm-like nanocrystals and local amorphous structures. Microhardness of the melted layer with LNAC was improved to HV 90-148 as compared to HV 65-105 of the samples with Ar gas protection. The corrosion resistance of the melted layer in a 3.5% Na Cl solution（mass fraction） was improved because of the grain refinement and redistribution of β-Mg17Al12 phases following rapid quenching associated with the process.展开更多
Lateral oxidation in vertical cavity surface emitting lasers （VCSELs） is described,and its characteristics are investigated.A linear growth law is found for stripe mesas. However, oxide growth （above 435℃ ） follo...Lateral oxidation in vertical cavity surface emitting lasers （VCSELs） is described,and its characteristics are investigated.A linear growth law is found for stripe mesas. However, oxide growth （above 435℃ ） follows a nonlinear law for the two geometry mesa structures which we employ in VCSEL. Theoretical analysis indicates that mesa structure geometry influences oxide growth rate at higher temperatures.展开更多
High slope efficiency and high power selected oxide-confined 850nm VCSELs grown by MOCVD are reported.The slope efficiency and the threshold current respectively are 0 82mW/mA and 2 59mA with a 9μm diameter oxidati...High slope efficiency and high power selected oxide-confined 850nm VCSELs grown by MOCVD are reported.The slope efficiency and the threshold current respectively are 0 82mW/mA and 2 59mA with a 9μm diameter oxidation aperture at 25℃.The maximum power of 16mW is obtained at 23mA current bias.The minimum threshold current can be as low as 570μA with a 5μm diameter oxidation aperture at 25℃.The maximum saturated power is 5 5mW.展开更多
Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is propo...Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is proposed as a substituting method.By absorbing high energy of the 1064 nm pulsed laser, the paint is vaporized quickly.The ablated debris is then collected by using a suction pump.Initial metal surface of the steel is exposed when laser beam irradiates perpendicularly and scans over it.The cleaned surface fulfills the requirements of surface preparation standards ISO 8501 of SA2.The adhesion is further characterized with pull-off test after carrying out painting with Jotamastic 87 aluminum paint.The repainting can be embedded onto the laser cleaned surface to bond much more tightly.The excellent adhesion strength of 20 MPa between repainted coating and the substrate is achieved, which is higher than what is required by shipyards applications.展开更多
In order to improve the performance of the metal rollers, Mo＋Y2O3 alloy powders were used to coat uniformly on the surface of 40Cr steel roller substrates for the laser surface alloying treatment by a CO2 laser, The ...In order to improve the performance of the metal rollers, Mo＋Y2O3 alloy powders were used to coat uniformly on the surface of 40Cr steel roller substrates for the laser surface alloying treatment by a CO2 laser, The results showed that many good consequences were ob- tained after adding the rare earth oxide Y2O3. The crystal grains of the alloy layer were significantly refined. The boundary of crystal grains was strengthened. The unifomaity and density of the microstructure were increased. The hardness and wearing resistance of the alloy layer were considerably improved. The valence electron structure analysis of the alloy layer was made by the empirical electron theory of solids and molecules （EET）. The calculated results demonstrated that Y should be mixed in the first stage and Fe should be in the eighteenth hybrid bands. The analyzed outcomes illustrated that the electron theory of the solid solution shows the strengthening effect on the alloying layer, which has enhanced bond and confirrned the experimental results.展开更多
In this investigation,a picosecond laser was employed to fabricate surface textures on a Stavax steel substrate,which is a key material for mold fabrication in the manufacturing of various polymer products.Three main ...In this investigation,a picosecond laser was employed to fabricate surface textures on a Stavax steel substrate,which is a key material for mold fabrication in the manufacturing of various polymer products.Three main types of surface textures were fabricated on a Stavax steel substrate:periodic ripples,a two-scale hierarchical two-dimensional array of micro-bumps,and a micro-pits array with nanoripples.The wettability of the laser-textured Stavax steel surface was converted from its original hydrophilicity into hydrophobicity and even super-hydrophobicity after exposure to air.The results clearly show that this super-hydrophobicity is mainly due to the surface textures.The ultrafast laserinduced catalytic effect may play a secondary role in modifying the surface chemistry so as to lower the surface energy.The laser-induced surface textures on the metal mold substrates were then replicated onto polypropylene substrates via the polymer injection molding process.The surface wettability of the molded polypropylene was found to be changed from the original hydrophilicity to superhydrophobicity.This developed process holds the potential to improve the performance of fabricated plastic products in terms of wettability control and easy cleaning.展开更多
YAG laser welding with surface activating flux has been investigated, and the influencing factors and mechanism are discussed. The results show that both surface activating flux and surface active element S have fanta...YAG laser welding with surface activating flux has been investigated, and the influencing factors and mechanism are discussed. The results show that both surface activating flux and surface active element S have fantastic effects on the YAG laser weld shape, that is to obviously increase the weld penetration and D/W ratio in various welding conditions. The mechanism is thought to be the change of weld pool surface tension temperature coefficient, thus, the change of fluid flow pattern in weld pool due to the flux.展开更多
This paper presents the results of a study concerned with the surface hardening of Fe-based alloys and WC-8Co cemented carbide by inte-grating laser cladding and the electrospark deposition processes.Specimens of low ...This paper presents the results of a study concerned with the surface hardening of Fe-based alloys and WC-8Co cemented carbide by inte-grating laser cladding and the electrospark deposition processes.Specimens of low carbon steel were processed firstly by laser cladding with Fe-based alloy powders and then by electrospark deposition with WC-SCo cemented carbide.It is shown that,for these two treatments,the electrospark coating possesses finer microstructure than the laser coating,and the thickness and surface hardness of the electrospark coating can be substantially increased.展开更多
The present work explored effects of laser surface melting on microstructure and surface topography evolution in AZ31B magnesium alloy.Thermokinetic effects experienced by the material during laser surface melting wer...The present work explored effects of laser surface melting on microstructure and surface topography evolution in AZ31B magnesium alloy.Thermokinetic effects experienced by the material during laser surface melting were simulated using a multiphysics finite element model.Microstructure and phase evolution were examined using scanning electron microscopy,X-ray diffraction,and electron back scatter diffraction.Surface topography was evaluated using white light interferometry.The interaction of surface melted samples with simulated body fluid was monitored by contact angle measurements and immersion studies up to 7 days.Laser surface melting led to formation of a refined microstructure with predominantly basal crystallographic texture.Concurrently,the amount ofβphase(Mg_(17)Al_(12))increased with an increase in the laser fluence.βphase preferentially decorated the cell boundaries.In terms of topography,the surface became progressively rougher with an increase in laser fluence.As a result,upon immersion in simulated body fluid,the laser surface melted samples showed an improved wettability,corrosion resistance,and precipitation of mineral having composition closer to the hydroxyapatite bone mineral compared to the untreated sample.展开更多
Based on the finite element method,the angled surface defects have been investigated by using the laser generated surface acoustic wave(SAW).The feature of laser generated SAW interaction with the angled defect is ana...Based on the finite element method,the angled surface defects have been investigated by using the laser generated surface acoustic wave(SAW).The feature of laser generated SAW interaction with the angled defect is analyzed in time and frequency domains.An increase in the amplitude of SAW at the edge of the defect is observed,and the spectral feature is angle dependent.With the angle decreasing from 120°to 30°,the maximum amplitude of frequency spectrum of SAW increases gradually.The corresponding experimental results verify the feasibility of numerical analyses and reach a good agreement with simulation results.展开更多
文摘The original online version of this article was revised:Several errors occurred in the published version of the article.These have now been corrected as follows:Page 2,section"2.2 Laser Texturing Procedure of Surfaces",line 2:The device name was corrected from"YDFLP-E-50-M8"to"YDFLP-50-M8."Page 3,Section 2.4:The phrase"95%confidence interval"has been corrected to"95%confidence level."Page 3,Figure 1 caption:The phrase"fandg"has been corrected to"f and g."The order"C4 and C12"has been reversed to"C12 and C4,"in accordance with the display order in the figure.Page 4,Figure reference:The phrase"Figs.4c and d"has been corrected to"Figs.5b and c."Page 5,paragraph starting with"The ANOVA results are presented...":The phrase"95%confidence interval"has been corrected to"95%confidence level."
基金the support by the Harbin Manufacturing Science and Technology Innovation Talent Project(No.2023CXRCGD035)the Open Research Foundation of State Key Laboratory of Digital Manufacturing Equipment and Technology in Huazhong University of Science and Technology,China(No.IMETKF2023012).
文摘While laser surface texturing(LST)is a promising manufacturing technique for surface functionalization,simultaneously realizing high precision and high efficiency in the LST of complex curved surface is challenging,due to continuously varied geometries of laser-matter incidence.In the present work,we propose a novel manufacturing system of 7-axis on-the-fly LST for complex curved surface,based on the integrated synchronization of 5-axis linkage motion platform with 2-axis galvanometer.Specifically,the algorithm for decomposing spatial texture trajectory on curved surface into low-frequency and high-frequency parts is established,based on which the kinematic model of synchronized 7-axis system is developed to derive the motion of each axis in both 5-axis linkage motion platform and 2-axis galvanometer simultaneously.Subsequently,the synchronized 7-axis LST system is experimentally realized,including the setup of mechanical stages integrated with optical path,the configuration of numerical control unit,and the development of processing software.Finally,case study of 7-axis on-the-fly LST of freeform aluminum surface is performed,and the advantages in terms of processing efficiency and texturing accuracy over 5-axis linkage LST are demonstrated.The correlation of reduced following errors between mechanical stages with the promoted performance of curved surface texturing by the 7-axis on-the-fly LST is further analyzed.Current work provides a feasible solution for establishing the manufacturing system for high performance LST of complex curved surface.
基金funded by National Key R&D Program of China(Grant Nos.2024YFB3612200,2023YFB3609601,2022YFB3604300,2022YFB2802801,2022YFB3604802)Natural Science Foundation of China(Grant Nos.U24A20300,62174174,62274177,62275263,62325406,62374172,62304242,62304240,62404241)+4 种基金Youth Innovation Promotion Association of CAS(Grant Nos.2022323 and 2022324)Key R&D Program of Jiangsu Province(Grant No.BE2023018-2)Basic Research Program of Jiangsu(Grant No.BK20240126)Suzhou Science and Technology Program(Grant Nos.SYC2022089,ZXL2024379,and ZXL2024376)Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2022A1515110482 and 2022A1515110004).
文摘Photonic crystal surface emitting lasers(PCSELs)utilize the Bragg diffraction of two-dimensional photonic crystals to achieve a single-mode output with a high power and a small divergence angle,and has recently attracted much attention^([1−3]).In 2023,Kyoto University reported GaAs-based 945 nm PCSELs with a continuous-wave(CW)single-mode output power of exceeding 50 W,and a narrow beam divergence angle of 0.05°,demonstrating a brightness of 1 GW·cm^(−2)·sr^(−1),which rivals those of the existing bulky lasers^([4]).
基金supported by the research studentship of The Hong Kong Polytechnic University(Project code:RMAN)the Research and Innovation Office of The Hong Kong Polytechnic University(Project codes:1-W308 and 1-BECE)+2 种基金the Research Grants Council of the Government of the Hong Kong Special Administrative Region(HKSAR),China(No.15205423)funding support from the Innovation and Technology Commission(ITC)of HKSAR,China(MHP/151/22)funding support from the State Key Laboratory of Ultra-precision Machining Technology(Project code:BBX5).
文摘Silicon carbide(SiC)is a highly valued material for power semiconductor devices due to its wide bandgap,high thermal conductivity,and high breakdown electric field.However,its high hardness,brittleness,and chemical stability present substantial challenges for efficient and high-quality processing.This study investigated the effects of picosecond laser surface scanning on 4H-SiC to enhance the material removal performance.The research focused on surface morphology,phase transitions,subsurface/interface characteristics,and material removal mechanisms under varying laser parameters.The results demonstrate that the laser thermal effect decomposes 4H-SiC into amorphous silicon(a-Si),disordered carbon,and graphite,forming a resolidified layer containing Si-O and Si-C-O oxides.Crystalline silicon(c-Si)is produced under high fluences or extensive irradiations.The variation in the resolidified layer thickness with changing laser parameters is revealed.A detailed laser-induced subsurface damage model is developed,encompassing a resolidified layer that includes the above decomposition and oxidation products,and a deformed layer formed primarily under laser-induced stress.The presence of the resolidified layer and the deformed layer leads to a decreased elastic recovery rate and an increased scratching depth,exceeding 2.5 times that of the unmodified condition.Enhanced material removal performance is mainly driven by the resolidified layer at low fluence and by the deformed layer at high fluence.When aligning the total of the ablation depth and the resolidified layer thickness with the subsurface damage depth in the original material,excellent polishing performance is achieved.These findings provide critical insights for understanding the phase evolution,subsurface damage mechanisms,and material removal behavior of 4H-SiC,offering valuable guidance for optimizing the laser surface modification parameters to achieve high-efficiency processing.
基金financially supported by the Open Project Program of Chinese Scholar Tree Ridge State Key Laboratory(No.AF20240023)
文摘Triply periodic minimal surface(TPMS)structures,characterized by special repeating 3D surface periodically with an average curvature of zero in threedimensional directions,have a wide range of applications.Laser powder bed fusion(LPBF)technique,as a type of additive manufacturing techniques,provides the capability to fabricate such complex-shaped porous TPMS structures.In this study,Ti6Al4V G-sheet TPMS structures with various unit cell sizes were fabricated using LPBF to investigate the structural and material anisotropy and their effects on the anisotropy in energy absorption capacity by combining the finite element simulations and experimental analysis.The results showed that the TPMS structures can be successfully fabricated using LPBF,although the sheet thickness exceeds the designed values,with deviation decreasing as the unit cell size increases from 2 to 4 mm.The inherent anisotropy during the LPBF process results in variations in structural dimension,materials characteristics,and energy absorption capacity between directions parallel and perpendicular to the build direction.The anisotropic ratio of the LPBFed Ti6Al4V G-sheet TPMS structures increases from 1.5 to 2.2 in the structural dimension and from 2.8 to 3.3 in specific energy absorption per unit mass(SEA_(m))respectively with decreasing the unit cell size from 4 to 2 mm.The anisotropy of SEA_(m) primarily originates from the coupling effects of anisotropic dimensions and material properties in the LPBFed G-sheet TPMS structure.Among these factors,anisotropic material properties play a more significant role compared to dimensional anisotropy.
基金National Research Foundation of Korea(RS-2020-NR049597,RS-2023-00256050)Korea Evaluation Institute of Industrial Technology(RS-2024-00432036)Korea Institute for Advancement of Technology(P0024164)。
文摘The recent progress in semiconductor processing technology has served as a major driving force behind the rapid development of nanophotonics research.Among the emerging applications,metasurfaces have attracted significant attention as saturable absorbers(SAs)for mode-locked laser systems that generate short pulses.In this study,we present the comprehensive design,fabrication,and experimental demonstration of a metasurface-based SA operating in the 1μm wavelength range,leveraging both the localized surface plasmon resonance(LSPR)phenomenon and the epsilon-near-zero(ENZ)effect of indium tin oxide.
基金supported by the National Natural Science Foundation of China(Nos.52101015,52171021)the National Key R&D Program of China(No.2021YFA1600704)+1 种基金the Science and Technology Research Project of Colleges and Universities in Hebei Province,China(No.BJK2022020)the Natural Science Foundation of Hebei Province,China(No.E2022208070).
文摘A laser surface melting(LSM)technology was applied to enhancing the corrosion resistance of a Mg−Zn−Y alloy containing large and discontinuous long-period stacking-ordered(LPSO)phases.The microstructural evolution and solidification behavior of this alloy during LSM were studied.It was demonstrated that the significantly reduced corrosion rate of the alloy after LSM,can be attributed to the disappearance of the original micron-sized LPSO phase and a decrease in the grain size from 300 to 15μm.The refined grains were composed of three adjacent zones,namely theβeutectic phase zone,the W phase zone,and the lamellar structures zone,which formed sequentially during the rapid cooling process.The dendritic lamellae grew along the basal plane of the magnesium matrix and were separated by supersaturatedα-Mg phases.Ultimately,the disappearance of large primary batteries and grain refinement improved the corrosion resistance of the Mg−Zn−Y alloy.
基金financial supports from the National Natural Science Foundation of China-Youth Project(51801076)the Provincial Colleges and Universities Natural Science Research Project of Jiangsu Province(18KJB430009)+1 种基金the Postdoctoral Research Support Project of Jiangsu Province(1601055C)the Senior Talents Research Startup of Jiangsu University(14JDG126)。
文摘To solve the problems of deformation,micro-cracks,and residual tensile stress in laser cladding coatings,the technique of laser cladding with Fe-based memory alloy can be considered.However,the process of in-situ synthesis of Fe-based memory alloy coatings is extremely complex.At present,there is no clear guidance scheme for its preparation process,which limits its promotion and application to some extent.Therefore,in this study,response surface methodology(RSM)was used to model the response surface between the target values and the cladding process parameters.The NSGA-2 algorithm was employed to optimize the process parameters.The results indicate that the composite optimization method consisting of RSM and the NSGA-2 algorithm can establish a more accurate model,with an error of less than 4.5%between the predicted and actual values.Based on this established model,the optimal scheme for process parameters corresponding to different target results can be rapidly obtained.The prepared coating exhibits a uniform structure,with no defects such as pores,cracks,and deformation.The surface roughness and microhardness of the coating are enhanced,the shaping quality of the coating is effectively improved,and the electrochemical corrosion performance of the coating in 3.5%NaCl solution is obviously better than that of the substrate,providing an important guide for engineering applications.
基金supported by the Science and Technology Innovation Fund Project of GRIMAT Engineering Institute Co.,Ltd.,China,the National Key R&D Program of China(No.2023YFB3710403).
文摘The lightweight refractory high-entropy alloys(LRHEAs)are considered as next-generation high-performance weaponry matrix material.In this work,we employ the laser surface melting(LSM)method to ulteriorly optimize surface mechanical properties of Al_(0.5)NbTi_(3)VZr_(0.5) matrix HEA,where the phase structures,mechanical properties and deformation mechanism of as-cast and LSM-treated HEAs have been investigated.The LSM process eliminates tanglesome intermetallic Zr_(5)Al_(3) structures and effectively improves the mechanical properties of as-cast HEA.The sample after 2000 W LSM treatment exhibits the superior comprehensive mechanical properties,its tensile elongation,microhardness of remelt zone and volume wear loss are 31.6%,HV 809.6 and 296.4×10^(−3) mm^(3),representing the advancement of 85.9%,180.1%and 64.6%compared to that of as-cast HEA sample,respectively.Additionally,the deformation behavior of the as-cast sample involves solid phase transformation,stacking faults and deformation twinnings.The deformation mechanism of as-cast Al_(0.5)NbTi_(3)VZr_(0.5) HEA is transformation-induced plasticity(TRIP)and twinning-induced plasticity(TWIP),the classical Burgers mechanism of BCC→HCP solid phase transformation is revealed,which obeys[111]_(BCC)∥[1120]_(HCP).As for the 2000 W treated sample,the deformation mechanism is mainly TWIP as the stacking fault energy enhancement evidenced by the presence of cross-slip dislocations after LSM process.
基金supported by the National Natural Science Foundation of China(No.51805257)the China Postdoctoral Science Foundation(No.2019TQ0151)+3 种基金the National Natural Science Foundation of China for Creative Research Groups(No.51921003)the Foundation of Graduate Innovation Center in NUAA,China(No.KFJJ20190502)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(No.KYCX19_0162)the Jiangsu Key Laboratory of Precision and Micro-Manufacturing Technology,China。
文摘Fabrication of the surface micro-texture on the C-plane sapphire is undertaken by a355 nm Ultraviolet(UV)pulsed laser.The surface micro-textures of sapphire with different laser scanning line spacing ranging from 10 lm to 100 lm are obtained,where the selection range of scanning line spacing is controlled in the range of the groove width and plasma width to obtain a surface of high Peak-Valley(PV)value.A reasonable processing order is proposed to manufacture different types of surface micro-textures on sapphire by laser ablation trajectory regulation.In the multiple-passes laser ablation of sapphire by the UV nanosecond pulsed laser,the scanning lines in each direction is treated as once scanning.On this basis,the multiple processing can be carried out to avoid the influence of the subsequent scanning on the machined groove.In addition,the effect of different scanning line spacing on the PV value is quantified and different types of surface microtextures on sapphire,including the squares,the rhombuses and the hexagons,are successfully fabricated,which can be applied in the friction reduction or anti-reflection field.
基金Project(51305292)supported by the National Natural Science Foundation of ChinaProject(2014-024)supported by Shanxi Scholarship Council of China
文摘Laser surface melting（LSM） is a high-energy surface treatment that allows modification of the microstructure and surface properties of Mg alloys. In the present work, an attempt of LSM on magnesium alloy with liquid nitrogen-assisted cooling（LNSC） was carried out to get the higher cooling rate and improve the surface properties. The experimental results were compared with those of Ar gas protection at room temperature. The samples after LSM with LNSC resulted in a thinner melted layer, a highly homogeneous, refined melted microstructure and formed a lot of worm-like nanocrystals and local amorphous structures. Microhardness of the melted layer with LNAC was improved to HV 90-148 as compared to HV 65-105 of the samples with Ar gas protection. The corrosion resistance of the melted layer in a 3.5% Na Cl solution（mass fraction） was improved because of the grain refinement and redistribution of β-Mg17Al12 phases following rapid quenching associated with the process.
文摘Lateral oxidation in vertical cavity surface emitting lasers （VCSELs） is described,and its characteristics are investigated.A linear growth law is found for stripe mesas. However, oxide growth （above 435℃ ） follows a nonlinear law for the two geometry mesa structures which we employ in VCSEL. Theoretical analysis indicates that mesa structure geometry influences oxide growth rate at higher temperatures.
文摘High slope efficiency and high power selected oxide-confined 850nm VCSELs grown by MOCVD are reported.The slope efficiency and the threshold current respectively are 0 82mW/mA and 2 59mA with a 9μm diameter oxidation aperture at 25℃.The maximum power of 16mW is obtained at 23mA current bias.The minimum threshold current can be as low as 570μA with a 5μm diameter oxidation aperture at 25℃.The maximum saturated power is 5 5mW.
基金supported by the National Natural Science Foundation of China (U1609209)National Natural Science Foundation of China (61605162)+2 种基金NSFC-Liaoning Province united foundation (U1608259)National Natural Science Foundation of China (51501219)the financial support from the China Scholarship Council
文摘Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is proposed as a substituting method.By absorbing high energy of the 1064 nm pulsed laser, the paint is vaporized quickly.The ablated debris is then collected by using a suction pump.Initial metal surface of the steel is exposed when laser beam irradiates perpendicularly and scans over it.The cleaned surface fulfills the requirements of surface preparation standards ISO 8501 of SA2.The adhesion is further characterized with pull-off test after carrying out painting with Jotamastic 87 aluminum paint.The repainting can be embedded onto the laser cleaned surface to bond much more tightly.The excellent adhesion strength of 20 MPa between repainted coating and the substrate is achieved, which is higher than what is required by shipyards applications.
基金supported by the High Technology Research Project of Science and Technology Department of Guizhou Province(GY[2008]3029,SY[2010]3037)
文摘In order to improve the performance of the metal rollers, Mo＋Y2O3 alloy powders were used to coat uniformly on the surface of 40Cr steel roller substrates for the laser surface alloying treatment by a CO2 laser, The results showed that many good consequences were ob- tained after adding the rare earth oxide Y2O3. The crystal grains of the alloy layer were significantly refined. The boundary of crystal grains was strengthened. The unifomaity and density of the microstructure were increased. The hardness and wearing resistance of the alloy layer were considerably improved. The valence electron structure analysis of the alloy layer was made by the empirical electron theory of solids and molecules （EET）. The calculated results demonstrated that Y should be mixed in the first stage and Fe should be in the eighteenth hybrid bands. The analyzed outcomes illustrated that the electron theory of the solid solution shows the strengthening effect on the alloying layer, which has enhanced bond and confirrned the experimental results.
基金the Agency for Science Technology and Research (A*STAR) of Singapore for financial support
文摘In this investigation,a picosecond laser was employed to fabricate surface textures on a Stavax steel substrate,which is a key material for mold fabrication in the manufacturing of various polymer products.Three main types of surface textures were fabricated on a Stavax steel substrate:periodic ripples,a two-scale hierarchical two-dimensional array of micro-bumps,and a micro-pits array with nanoripples.The wettability of the laser-textured Stavax steel surface was converted from its original hydrophilicity into hydrophobicity and even super-hydrophobicity after exposure to air.The results clearly show that this super-hydrophobicity is mainly due to the surface textures.The ultrafast laserinduced catalytic effect may play a secondary role in modifying the surface chemistry so as to lower the surface energy.The laser-induced surface textures on the metal mold substrates were then replicated onto polypropylene substrates via the polymer injection molding process.The surface wettability of the molded polypropylene was found to be changed from the original hydrophilicity to superhydrophobicity.This developed process holds the potential to improve the performance of fabricated plastic products in terms of wettability control and easy cleaning.
文摘YAG laser welding with surface activating flux has been investigated, and the influencing factors and mechanism are discussed. The results show that both surface activating flux and surface active element S have fantastic effects on the YAG laser weld shape, that is to obviously increase the weld penetration and D/W ratio in various welding conditions. The mechanism is thought to be the change of weld pool surface tension temperature coefficient, thus, the change of fluid flow pattern in weld pool due to the flux.
文摘This paper presents the results of a study concerned with the surface hardening of Fe-based alloys and WC-8Co cemented carbide by inte-grating laser cladding and the electrospark deposition processes.Specimens of low carbon steel were processed firstly by laser cladding with Fe-based alloy powders and then by electrospark deposition with WC-SCo cemented carbide.It is shown that,for these two treatments,the electrospark coating possesses finer microstructure than the laser coating,and the thickness and surface hardness of the electrospark coating can be substantially increased.
文摘The present work explored effects of laser surface melting on microstructure and surface topography evolution in AZ31B magnesium alloy.Thermokinetic effects experienced by the material during laser surface melting were simulated using a multiphysics finite element model.Microstructure and phase evolution were examined using scanning electron microscopy,X-ray diffraction,and electron back scatter diffraction.Surface topography was evaluated using white light interferometry.The interaction of surface melted samples with simulated body fluid was monitored by contact angle measurements and immersion studies up to 7 days.Laser surface melting led to formation of a refined microstructure with predominantly basal crystallographic texture.Concurrently,the amount ofβphase(Mg_(17)Al_(12))increased with an increase in the laser fluence.βphase preferentially decorated the cell boundaries.In terms of topography,the surface became progressively rougher with an increase in laser fluence.As a result,upon immersion in simulated body fluid,the laser surface melted samples showed an improved wettability,corrosion resistance,and precipitation of mineral having composition closer to the hydroxyapatite bone mineral compared to the untreated sample.
基金supported by the National Natural Science Foundation of China(No.51505220)
文摘Based on the finite element method,the angled surface defects have been investigated by using the laser generated surface acoustic wave(SAW).The feature of laser generated SAW interaction with the angled defect is analyzed in time and frequency domains.An increase in the amplitude of SAW at the edge of the defect is observed,and the spectral feature is angle dependent.With the angle decreasing from 120°to 30°,the maximum amplitude of frequency spectrum of SAW increases gradually.The corresponding experimental results verify the feasibility of numerical analyses and reach a good agreement with simulation results.
