The surface morphology of buffer layer yttrium-stabilized zirconia (YSZ) of YBa2CuaO7-σ (YBCO) high temperature superconducting films relies on a series of controllable experimental parameters. In this work, we f...The surface morphology of buffer layer yttrium-stabilized zirconia (YSZ) of YBa2CuaO7-σ (YBCO) high temperature superconducting films relies on a series of controllable experimental parameters. In this work, we focus on the influence of pulsed laser frequency and target crystalline type on surface morphology of YSZ films deposited by pulsed laser deposition (PLD) on rolling assisted biaxially textured substrate tapes. Usually two kinds of particles are observed in the YSZ layer: randomly distributed ones on the whole film and self-assembled ones along grain boundaries. SEM images are used to prove that particles can be partly removed when choosing dense targets of single crystalline. Lower frequency of pulsed laser also contributes to a smoother film surface. TEM images are used to view the crystalline structure of thin film. Thus we can obtain a basic understanding of how to prepare a particle-free YSZ buffer layer for YBCO in optimized conditions using PLD. The YBCO layer with nice structure and critical current density of around 5 MA/cm2 can be reached on smooth YSZ samples.展开更多
Laser surface alloying of γ TiAl alloy with nitrogen was studied under the constant protective nitrogen current (20l /min). The experimental results shown that the surface multi layers formed with experimental para...Laser surface alloying of γ TiAl alloy with nitrogen was studied under the constant protective nitrogen current (20l /min). The experimental results shown that the surface multi layers formed with experimental parameters could be up to 600μm depth; it consists of TiN,Ti 2AlN,α 2 and γ phases, without AlN, and the irregular coarse continuous “flow” line,dendrite,needle and granular nitrides disperse on the fine dendrite casting α 2 and γ phases substrate. The microstructure and compositions in the nitiding layer were determined and analyzed by SEM and EPMA and the mechanism for the formation of microstructure in the nitriding layer was also discussed.展开更多
The hydrodynamic effects of molten surface of titanium alloy on the morphology evolution by intense pulsed ion beam (IPIB) irradiation are studied. It is experimentally revealed that under irradiation of IPIB pulses...The hydrodynamic effects of molten surface of titanium alloy on the morphology evolution by intense pulsed ion beam (IPIB) irradiation are studied. It is experimentally revealed that under irradiation of IPIB pulses, the surface morphology of titanium alloy in a spatial scale of μm exhibits an obvious smoothening trend. The mechanism of this phenomenon is explained by the mass transfer caused by the surface tension of molten metal. Hydrodynamic simulation with a combination of the finite element method and the level set method reveals that the change in curvature on the molten surface leads to uneven distribution of surface tension. Mass transfer is caused by the relief of surface tension, and meanwhile a flattening trend in the surface morphology evolution is achieved.展开更多
For reducing the core loss of grain oriented silicon steel and improving its aging property, a new method, the LLSA by using Sb as the laser surface alloying element, was investigated, and at proper technique conditio...For reducing the core loss of grain oriented silicon steel and improving its aging property, a new method, the LLSA by using Sb as the laser surface alloying element, was investigated, and at proper technique conditions rather good result was obtained.展开更多
The LPE growth of quaternary InAs11-x-yPxSby with x = 0.2 and y = 0.09 on InAs substrate has been studied. This composition is very suitable for the laser and detector applications at about 2.5 μm. We show that in In...The LPE growth of quaternary InAs11-x-yPxSby with x = 0.2 and y = 0.09 on InAs substrate has been studied. This composition is very suitable for the laser and detector applications at about 2.5 μm. We show that in InAsPSb/InAs system there is a determinate relation between the surface morphology and the lattice mismatch of the epi-wafers, by which we can easily control the melt composition to grow high quality hetero-structures. The reason has been discussed. The p-n junctions with fairly good carrier profile have been prepared in this system.展开更多
Silicon was added to the surface of 304 stain- less steel by laser melting the sprayed preplaced Si powders.The optical microscopy,X-ray diffraction and EPMA were employed to investigate the microstructure and chemica...Silicon was added to the surface of 304 stain- less steel by laser melting the sprayed preplaced Si powders.The optical microscopy,X-ray diffraction and EPMA were employed to investigate the microstructure and chemical composition of the laser surface alloyed layer.The hardness of the al- loyed layer was measured by microhardness test and wear resistance was evaluated by scratch test. Corrosion resistance of laser alloyed sample was studied in 1N H_2SO_4+0.1N NaCl and 0.5N HCl+0.5N NaCl aqueous solutions.A microcrystalline intermetallic compound coating with smooth surface and good chemical homogeneity without porosity and crack is ob- tained.The hardness is about 720 HV.The wear re- sistance is 2 times better than that of the substrate. The corrosion resistance of the laser alloyed sample is much better than that of 304 stainless steel sample.展开更多
Laser surface alloying technique was applied to fabricate a metallic porous coating on a solid NiTi shape memory alloy. By laser surface alloying a 40%TiH2-60%NiTi powder mixture on the surface of NiTi alloy using opt...Laser surface alloying technique was applied to fabricate a metallic porous coating on a solid NiTi shape memory alloy. By laser surface alloying a 40%TiH2-60%NiTi powder mixture on the surface of NiTi alloy using optimized laser process parameters, a porous but crack-free NiTi layer can be fabricated on the NiTi substrate. The porous coating is metallurgically bonded to the substrate NiTi alloy. The pores are uniformly distributed and are interconnected with each other in the coating. An average pore size of less than 10 μm is achieved. The Ni content of the porous layer is much less than that of the original NiTi surface. The existence of the porous coating on the NiTi alloy causes a 37% reduction of the tensile strength and 55% reduction of the strain as compared with the NiTi alloy. Possible biomedical or other applications for this porous surface with good mechanical strength provided by the substrate are prospective.展开更多
Biodegradable implants from magnesium(Mg)alloys have emerged in the biomedical field especially in the orthopedic and cardiovascular stent applications owing to their low density,high specific strength,excellent machi...Biodegradable implants from magnesium(Mg)alloys have emerged in the biomedical field especially in the orthopedic and cardiovascular stent applications owing to their low density,high specific strength,excellent machinability,good biocompatibility,and biodegradability.The primary shortcoming of Mg-based implants is their low corrosion resistance in the physiological environment,which results in premature mechanical integrity loss before adequate healing and the production of excessive hydrogen gas,which is harmful to the body tissues and negatively affects the biocompatibility of the implant.Laser surface modification has recently received attention because it can improve the surface properties such as surface chemistry,roughness,topography,corrosion resistance,wear resistance,hydrophilicity,and thus cell response to the surface of the material.The composition and microstructures including textures and phases of laser-treated surfaces depend largely on the laser processing parameters(input laser power,laser scan velocity,frequency,pulse duration,pressure,gas circulation,working time,spot size,beam focal position,and laser track overlap)and the thermophysical properties of the substrate(solubility,melting point,and boiling point).This review investigates the impacts of various laser surface modification techniques including laser surface melting,laser surface alloying,laser cladding,laser surface texturing,and laser shock peening,and highlights their significance in improving the surface properties of biodegradable Mg alloys for implant applications.Additionally,we explore how different laser process parameters affect its composition,microstructure,and surface properties in each laser surface modification technique.展开更多
Rotation angle of the laser scan direction between two adjacent layers is a key controlling parameter during the high-power (≥ 1 kW) laser powder bed fusion (HP-LPBF) process. This study investigates the influen...Rotation angle of the laser scan direction between two adjacent layers is a key controlling parameter during the high-power (≥ 1 kW) laser powder bed fusion (HP-LPBF) process. This study investigates the influences of rotation angles (θ = 0°, 45°, 90°, 105°) on the surface morphology, microstructure, and mechanical properties of Inconel 718 (IN718) alloy produced by HP-LPBF. Results show that adopting low rotation angles (e.g., 0° and 45°) is prone to relatively poor surface finish and lack-of-fusion defects, whereas adopting high rotation angles (e.g., 90° and 105°) induces smaller surface roughness and better relative density. Each case reveals a noticeable edge effect but the maximal heights witness a downward trend with the increase of rotation angle. There are some minor differences in the primary dendrite arm spacing and grain morphology by varying the rotation angles. Moreover, the tensile property is slightly enhanced as the rotation angle increases. The present work suggests that high rotation angles like 90° and 105° would probably be more favorable for the 1 kW HP-LPBF process than rotation angles with relatively low values.展开更多
This work focuses on the structure and magnetic properties of Fe-50wt% Ni permalloy manufactured from the pre-alloyed powder by selective laser melting (SLM). The selective laser melted (SLMed) alloys were characteriz...This work focuses on the structure and magnetic properties of Fe-50wt% Ni permalloy manufactured from the pre-alloyed powder by selective laser melting (SLM). The selective laser melted (SLMed) alloys were characterized by a 3D profilometer,optical microscope, scanning electron microscope, X-ray diffraction, etc. The effects of the volume energy density of laser(LVED) on structure, and magnetic properties with coercivity ( H), remanence ( B), and power losses ( P), were evaluated and discussed systematically. The results show that the relative porosity rate and the surface roughness of the SLMed specimens decreased with the increase in LVED. Only the γ-(FeNi) phase was detected in the X-ray diffraction patterns of the SLMed permalloys fabricated from the different LVEDs. Statistical analysis of optical microscopy images indicated that the grain coarsened at higher LVED. Furthermore, the microstructure of the SLMed parts was a typical columnar structure with an oriented growth of building direction. The highest microhardness reached 198 HV. Besides, the magnetic properties including B, H, and Pof SLMed samples decreased when the LVED ranged from 33.3 to 60.0 J/mm ~3 firstly and then increased while LVED further up to 93.3 J/mm, which is related to the decrease in porosity and the increase in grain size, while the higher residual stress and microcracks presented in the samples manufactured using very high LVED. The observed evolution of magnetic properties and LVED provides a good compromise in terms of reduced porosity and crack formation for the fabrication of SLMed Fe-50 wt% Ni permalloy. The theoretical mechanism in this study can offer guidance to further investigate SLMed soft magnetic alloys.展开更多
The effect of material surface morphology on the periodic subwavelength of nano-structures induced by a femtosecond(fs) laser was investigated systematically from the initial surface roughness, the different scratch...The effect of material surface morphology on the periodic subwavelength of nano-structures induced by a femtosecond(fs) laser was investigated systematically from the initial surface roughness, the different scratches, the pre-formed ripples, and the "layer-carving" technology experiments. The results of the comparative experiments indicate that the initial surface conditions of the target surface have no obvious effects on the spatial structured periods(SSPs) and the ripple orientation of the periodic nano-structures induced by a fs laser, which agreed well with the foretold present surface two-plasmon resonance(STPR) model. Furthermore, different shapes of nanogrids with high regularity and uniformity were obtained by fs-laser fabrication.展开更多
The tungsten thin wall parts which were used as high-performance collimator devices were fabricated by optimizing selective laser melting laser parameters.The effect of laser power and scan rate on wall thickness and ...The tungsten thin wall parts which were used as high-performance collimator devices were fabricated by optimizing selective laser melting laser parameters.The effect of laser power and scan rate on wall thickness and surface morphology of tungsten山in wall parts was investigated,respectively.The results indicated that the wall thickness increased with the enhancemem in laser power as a linear relationship.On the contrary,the wall thickness decayed exponentially with the acceleration in laser sean rate.Meanwhile,the wall thickness of the parts fabricated by laser double-pass melting was ihinner than that fabricated by laser single-pass melting.In addition,mathematic models for selecting suitable laser power and laser sean rate to fabricate specified tungsten thin wall parts were proposed.Furthermore,the effects of laser parameters on the top surface roughness,adhesive parts and hot cracks were also discussed.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
The Al0. 5CoCrCuFeNi high-entropy alloy powders with simple face-centered-cubic (FCC) solid solution structure were introduced into the surface layer of a low carbon steel during laser surface alloying. A high perfo...The Al0. 5CoCrCuFeNi high-entropy alloy powders with simple face-centered-cubic (FCC) solid solution structure were introduced into the surface layer of a low carbon steel during laser surface alloying. A high performance surface layer with extremely fine martensite as the dominant phase was obtained, resulting in a great improvement in microhardness, wear resistance, and corrosion resistance. The great enhancement of microhardness and wear resistance of the laser alloyed layer is mainly due to the formation of extremely fine martensite hard phase, the solid solution strengthening of the alloying e!.ements in supersaturated a-Fe solid solution, and the existence of size effect and strain effect under rapid solidification. The enhancement of corrosion resistance is due to the alloying of Al, Co, Ni, Cr and Cu in the laser alloyed layer.展开更多
The unsatisfactory corrosion properties of Mg-based alloys pose a significant obstacle to their widespread application. Plasma electrolytic oxidation(PEO) is a prevalent and effective coating method that produces a ce...The unsatisfactory corrosion properties of Mg-based alloys pose a significant obstacle to their widespread application. Plasma electrolytic oxidation(PEO) is a prevalent and effective coating method that produces a ceramic-like oxide coating on the surface of Mg-based alloys,enhancing their resistance to corrosion. Research has demonstrated that PEO treatment can substantially improve the corrosion performance of alloys based on magnesium in the short term. In an effort to enhance the corrosion resistance of PEO coatings over an extended period of time, researchers have turned their attention to the use of laser processes as both pre-and post-treatments in conjunction with the PEO process. Various laser processes, such as laser shock melting(LSM), laser shock adhesion(LSA), laser shock texturing(LST), and laser shock peening(LSP), have been investigated for their potential to improve PEO coatings on Mg substrates and their alloys. These laser melting processes can homogenize and alter the microstructure of Mg-based alloys while leaving the bulk material unchanged, thereby modifying the substrate surface. However, the porous and rough structure of PEO coatings, with their open and interconnected pore structure, can reduce their long-term corrosion resistance. As such, various laser processes are well-suited for surface modification of these coatings. This study will first examine the PEO process and the various types of laser processes used in this process, before investigating the corrosion behavior of PEO coatings in conjunction with laser pre-and post-treatment processes.展开更多
TiB2/TiB/TiNx(x=1,0.3)/Ti composite coating was prepared on pure Ti by laser surface alloying by using powders of boron as starting materials.The composite coating was examined by X-ray diffraction(XRD),high-resolutio...TiB2/TiB/TiNx(x=1,0.3)/Ti composite coating was prepared on pure Ti by laser surface alloying by using powders of boron as starting materials.The composite coating was examined by X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM)and scanning electron microscopy(SEM).The friction and wear properties of the composite coating were examined using a pin-on-disk tester under dry sliding wear condition.The results showed that the top surface of the composite coating was mainly composed of TiB2,TiB,TiN0.3,TiN and Ti phases,while the interface of the composite coating was composed of TiB and Ti phases.The composite coating showed sticklike structure near the top surface,and dendrites structure near the interface.The friction and wear test showed that the composite coating had better wear resistance than pure Ti due to their higher microhardness than that of pure Ti substrate.展开更多
The cooperative effect of laser surface texturing(LST) and double glow plasma surface alloying on tribological performance of lubricated sliding contacts was investigated.A Nd:YAG laser was used to generate microdimpl...The cooperative effect of laser surface texturing(LST) and double glow plasma surface alloying on tribological performance of lubricated sliding contacts was investigated.A Nd:YAG laser was used to generate microdimples on steel surfaces. Dimples with the diameter of 150μm and the depth of 30-35μm distributed circumferentially on the disc surface.The alloying element Cr was sputtered to the laser texturing steel surface by double glow plasma technique.A deep diffusion layer with a thickness of 30μm and a high hardness of HV900 was formed in this alloy.Tribological experiments of three types of samples(smooth,texturing and texturing+alloying) were conducted with a ring-on-disc tribometer to simulate the face seal.It is found that,in comparison with smooth steel surfaces,the laser texturing samples significantly reduce the friction coefficient.Moreover,the lower wear rate of the sample treated with the two surface techniques is observed.展开更多
To strengthen the wear resistance of AISI321 stainless steel, the TiC carbide-reinforced composite coating was produced by laser surface alloying. The microstructure, microhardness, and wear resistance of the composit...To strengthen the wear resistance of AISI321 stainless steel, the TiC carbide-reinforced composite coating was produced by laser surface alloying. The microstructure, microhardness, and wear resistance of the composite coatings were investigated using optical microscopy, X-ray diffraction (XRD) meter, scanning electron microscopy (SEM), microhardness tester, and sliding wear tester. The results show that the composite coating is metallurgically bonded to the substrate and the microstructure is fine and uniform. The hardness of the composite coating is up to 400 HV, which is 2.5 times that of the substrate. Under room temperature and oil lubrication condition, the sliding wear tests indicate the friction coefficient and weight loss of the composite coating are smaller than those of substrate. The worn surface of the composite coatings is much smoother than that of the substrate, without grooves and crater. The wear resistance of the material has been greatly improved by laser surface alloying.展开更多
Laser Surface alloying is a process, in which a high-power laser beam is used to scan across the surface of a material, thus forming a melting zone, and then some alloying elements are spread into the melting pool to ...Laser Surface alloying is a process, in which a high-power laser beam is used to scan across the surface of a material, thus forming a melting zone, and then some alloying elements are spread into the melting pool to yield an alloying layer with characteristic properties on the surface of this material. We have studied the laser surface alloying technique and the properties of the alloying layer for 45 carbon steel with the elements Cr and Mo and obtained some useful data.展开更多
基金Supported by the ITER Project of the Ministry of Science and Technology of China under Grant No 2011GB113004the Shanghai Commission of Science and Technology under Grant No 11DZ1100402the Youth Fund of the National Natural Science Foundation of China under Grant No 11204174
文摘The surface morphology of buffer layer yttrium-stabilized zirconia (YSZ) of YBa2CuaO7-σ (YBCO) high temperature superconducting films relies on a series of controllable experimental parameters. In this work, we focus on the influence of pulsed laser frequency and target crystalline type on surface morphology of YSZ films deposited by pulsed laser deposition (PLD) on rolling assisted biaxially textured substrate tapes. Usually two kinds of particles are observed in the YSZ layer: randomly distributed ones on the whole film and self-assembled ones along grain boundaries. SEM images are used to prove that particles can be partly removed when choosing dense targets of single crystalline. Lower frequency of pulsed laser also contributes to a smoother film surface. TEM images are used to view the crystalline structure of thin film. Thus we can obtain a basic understanding of how to prepare a particle-free YSZ buffer layer for YBCO in optimized conditions using PLD. The YBCO layer with nice structure and critical current density of around 5 MA/cm2 can be reached on smooth YSZ samples.
文摘Laser surface alloying of γ TiAl alloy with nitrogen was studied under the constant protective nitrogen current (20l /min). The experimental results shown that the surface multi layers formed with experimental parameters could be up to 600μm depth; it consists of TiN,Ti 2AlN,α 2 and γ phases, without AlN, and the irregular coarse continuous “flow” line,dendrite,needle and granular nitrides disperse on the fine dendrite casting α 2 and γ phases substrate. The microstructure and compositions in the nitiding layer were determined and analyzed by SEM and EPMA and the mechanism for the formation of microstructure in the nitriding layer was also discussed.
基金Supported by the National Natural Science Foundation of China under Grant No 1175012the China Postdoctoral Science Foundation under Grant No 2016M600897the National Science and Technology Major Project of the Ministry of Science and Technology of China under Grant No 2013ZX04001-071
文摘The hydrodynamic effects of molten surface of titanium alloy on the morphology evolution by intense pulsed ion beam (IPIB) irradiation are studied. It is experimentally revealed that under irradiation of IPIB pulses, the surface morphology of titanium alloy in a spatial scale of μm exhibits an obvious smoothening trend. The mechanism of this phenomenon is explained by the mass transfer caused by the surface tension of molten metal. Hydrodynamic simulation with a combination of the finite element method and the level set method reveals that the change in curvature on the molten surface leads to uneven distribution of surface tension. Mass transfer is caused by the relief of surface tension, and meanwhile a flattening trend in the surface morphology evolution is achieved.
基金National Natural Science FOundation of China! (No. 59974010).
文摘For reducing the core loss of grain oriented silicon steel and improving its aging property, a new method, the LLSA by using Sb as the laser surface alloying element, was investigated, and at proper technique conditions rather good result was obtained.
文摘The LPE growth of quaternary InAs11-x-yPxSby with x = 0.2 and y = 0.09 on InAs substrate has been studied. This composition is very suitable for the laser and detector applications at about 2.5 μm. We show that in InAsPSb/InAs system there is a determinate relation between the surface morphology and the lattice mismatch of the epi-wafers, by which we can easily control the melt composition to grow high quality hetero-structures. The reason has been discussed. The p-n junctions with fairly good carrier profile have been prepared in this system.
文摘Silicon was added to the surface of 304 stain- less steel by laser melting the sprayed preplaced Si powders.The optical microscopy,X-ray diffraction and EPMA were employed to investigate the microstructure and chemical composition of the laser surface alloyed layer.The hardness of the al- loyed layer was measured by microhardness test and wear resistance was evaluated by scratch test. Corrosion resistance of laser alloyed sample was studied in 1N H_2SO_4+0.1N NaCl and 0.5N HCl+0.5N NaCl aqueous solutions.A microcrystalline intermetallic compound coating with smooth surface and good chemical homogeneity without porosity and crack is ob- tained.The hardness is about 720 HV.The wear re- sistance is 2 times better than that of the substrate. The corrosion resistance of the laser alloyed sample is much better than that of 304 stainless steel sample.
基金Project(20060400957) supported by the Postdoctoral Science Foundation of ChinaProject(20031024) supported by the Liaoning Scientific and Technological Development Foundation of ChinaProjects(2004D011, 05L301) supported by the Liaoning Educational Committee Research Plan of China
文摘Laser surface alloying technique was applied to fabricate a metallic porous coating on a solid NiTi shape memory alloy. By laser surface alloying a 40%TiH2-60%NiTi powder mixture on the surface of NiTi alloy using optimized laser process parameters, a porous but crack-free NiTi layer can be fabricated on the NiTi substrate. The porous coating is metallurgically bonded to the substrate NiTi alloy. The pores are uniformly distributed and are interconnected with each other in the coating. An average pore size of less than 10 μm is achieved. The Ni content of the porous layer is much less than that of the original NiTi surface. The existence of the porous coating on the NiTi alloy causes a 37% reduction of the tensile strength and 55% reduction of the strain as compared with the NiTi alloy. Possible biomedical or other applications for this porous surface with good mechanical strength provided by the substrate are prospective.
基金the Australian Research Council(ARC)through the discovery grant DP210101862。
文摘Biodegradable implants from magnesium(Mg)alloys have emerged in the biomedical field especially in the orthopedic and cardiovascular stent applications owing to their low density,high specific strength,excellent machinability,good biocompatibility,and biodegradability.The primary shortcoming of Mg-based implants is their low corrosion resistance in the physiological environment,which results in premature mechanical integrity loss before adequate healing and the production of excessive hydrogen gas,which is harmful to the body tissues and negatively affects the biocompatibility of the implant.Laser surface modification has recently received attention because it can improve the surface properties such as surface chemistry,roughness,topography,corrosion resistance,wear resistance,hydrophilicity,and thus cell response to the surface of the material.The composition and microstructures including textures and phases of laser-treated surfaces depend largely on the laser processing parameters(input laser power,laser scan velocity,frequency,pulse duration,pressure,gas circulation,working time,spot size,beam focal position,and laser track overlap)and the thermophysical properties of the substrate(solubility,melting point,and boiling point).This review investigates the impacts of various laser surface modification techniques including laser surface melting,laser surface alloying,laser cladding,laser surface texturing,and laser shock peening,and highlights their significance in improving the surface properties of biodegradable Mg alloys for implant applications.Additionally,we explore how different laser process parameters affect its composition,microstructure,and surface properties in each laser surface modification technique.
文摘Rotation angle of the laser scan direction between two adjacent layers is a key controlling parameter during the high-power (≥ 1 kW) laser powder bed fusion (HP-LPBF) process. This study investigates the influences of rotation angles (θ = 0°, 45°, 90°, 105°) on the surface morphology, microstructure, and mechanical properties of Inconel 718 (IN718) alloy produced by HP-LPBF. Results show that adopting low rotation angles (e.g., 0° and 45°) is prone to relatively poor surface finish and lack-of-fusion defects, whereas adopting high rotation angles (e.g., 90° and 105°) induces smaller surface roughness and better relative density. Each case reveals a noticeable edge effect but the maximal heights witness a downward trend with the increase of rotation angle. There are some minor differences in the primary dendrite arm spacing and grain morphology by varying the rotation angles. Moreover, the tensile property is slightly enhanced as the rotation angle increases. The present work suggests that high rotation angles like 90° and 105° would probably be more favorable for the 1 kW HP-LPBF process than rotation angles with relatively low values.
基金financially supported by the Sciences Platform Environment and Capacity Building Projects of GDAS(No.2021GDASYL-20210102005)the Guangdong Special Support Program(No.2019BT02C629)+2 种基金the GuangDong Basic and Applied Basic Research Foundation(Nos.2020A1515111031 and 2021A515010939)the Guangzhou Major Projects of Industry University-Research(IUR)Collaborative Innovation“Surface Treatment and Repair for Key Components of Industrial Gas Turbine(IGT).”support from the program of CSC(No.201801810066)support from the program of CSC(No.201801810106)。
文摘This work focuses on the structure and magnetic properties of Fe-50wt% Ni permalloy manufactured from the pre-alloyed powder by selective laser melting (SLM). The selective laser melted (SLMed) alloys were characterized by a 3D profilometer,optical microscope, scanning electron microscope, X-ray diffraction, etc. The effects of the volume energy density of laser(LVED) on structure, and magnetic properties with coercivity ( H), remanence ( B), and power losses ( P), were evaluated and discussed systematically. The results show that the relative porosity rate and the surface roughness of the SLMed specimens decreased with the increase in LVED. Only the γ-(FeNi) phase was detected in the X-ray diffraction patterns of the SLMed permalloys fabricated from the different LVEDs. Statistical analysis of optical microscopy images indicated that the grain coarsened at higher LVED. Furthermore, the microstructure of the SLMed parts was a typical columnar structure with an oriented growth of building direction. The highest microhardness reached 198 HV. Besides, the magnetic properties including B, H, and Pof SLMed samples decreased when the LVED ranged from 33.3 to 60.0 J/mm ~3 firstly and then increased while LVED further up to 93.3 J/mm, which is related to the decrease in porosity and the increase in grain size, while the higher residual stress and microcracks presented in the samples manufactured using very high LVED. The observed evolution of magnetic properties and LVED provides a good compromise in terms of reduced porosity and crack formation for the fabrication of SLMed Fe-50 wt% Ni permalloy. The theoretical mechanism in this study can offer guidance to further investigate SLMed soft magnetic alloys.
基金supported by the National Natural Science Foundation of China(No.51705009)
文摘The effect of material surface morphology on the periodic subwavelength of nano-structures induced by a femtosecond(fs) laser was investigated systematically from the initial surface roughness, the different scratches, the pre-formed ripples, and the "layer-carving" technology experiments. The results of the comparative experiments indicate that the initial surface conditions of the target surface have no obvious effects on the spatial structured periods(SSPs) and the ripple orientation of the periodic nano-structures induced by a fs laser, which agreed well with the foretold present surface two-plasmon resonance(STPR) model. Furthermore, different shapes of nanogrids with high regularity and uniformity were obtained by fs-laser fabrication.
文摘The tungsten thin wall parts which were used as high-performance collimator devices were fabricated by optimizing selective laser melting laser parameters.The effect of laser power and scan rate on wall thickness and surface morphology of tungsten山in wall parts was investigated,respectively.The results indicated that the wall thickness increased with the enhancemem in laser power as a linear relationship.On the contrary,the wall thickness decayed exponentially with the acceleration in laser sean rate.Meanwhile,the wall thickness of the parts fabricated by laser double-pass melting was ihinner than that fabricated by laser single-pass melting.In addition,mathematic models for selecting suitable laser power and laser sean rate to fabricate specified tungsten thin wall parts were proposed.Furthermore,the effects of laser parameters on the top surface roughness,adhesive parts and hot cracks were also discussed.
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Item Sponsored by National Natural Science Foundation of China(50401006)Fundamental Research Funds for Central Universities of China(N120409003)
文摘The Al0. 5CoCrCuFeNi high-entropy alloy powders with simple face-centered-cubic (FCC) solid solution structure were introduced into the surface layer of a low carbon steel during laser surface alloying. A high performance surface layer with extremely fine martensite as the dominant phase was obtained, resulting in a great improvement in microhardness, wear resistance, and corrosion resistance. The great enhancement of microhardness and wear resistance of the laser alloyed layer is mainly due to the formation of extremely fine martensite hard phase, the solid solution strengthening of the alloying e!.ements in supersaturated a-Fe solid solution, and the existence of size effect and strain effect under rapid solidification. The enhancement of corrosion resistance is due to the alloying of Al, Co, Ni, Cr and Cu in the laser alloyed layer.
文摘The unsatisfactory corrosion properties of Mg-based alloys pose a significant obstacle to their widespread application. Plasma electrolytic oxidation(PEO) is a prevalent and effective coating method that produces a ceramic-like oxide coating on the surface of Mg-based alloys,enhancing their resistance to corrosion. Research has demonstrated that PEO treatment can substantially improve the corrosion performance of alloys based on magnesium in the short term. In an effort to enhance the corrosion resistance of PEO coatings over an extended period of time, researchers have turned their attention to the use of laser processes as both pre-and post-treatments in conjunction with the PEO process. Various laser processes, such as laser shock melting(LSM), laser shock adhesion(LSA), laser shock texturing(LST), and laser shock peening(LSP), have been investigated for their potential to improve PEO coatings on Mg substrates and their alloys. These laser melting processes can homogenize and alter the microstructure of Mg-based alloys while leaving the bulk material unchanged, thereby modifying the substrate surface. However, the porous and rough structure of PEO coatings, with their open and interconnected pore structure, can reduce their long-term corrosion resistance. As such, various laser processes are well-suited for surface modification of these coatings. This study will first examine the PEO process and the various types of laser processes used in this process, before investigating the corrosion behavior of PEO coatings in conjunction with laser pre-and post-treatment processes.
基金National Natural Science Foundations of China(51045004)
文摘TiB2/TiB/TiNx(x=1,0.3)/Ti composite coating was prepared on pure Ti by laser surface alloying by using powders of boron as starting materials.The composite coating was examined by X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM)and scanning electron microscopy(SEM).The friction and wear properties of the composite coating were examined using a pin-on-disk tester under dry sliding wear condition.The results showed that the top surface of the composite coating was mainly composed of TiB2,TiB,TiN0.3,TiN and Ti phases,while the interface of the composite coating was composed of TiB and Ti phases.The composite coating showed sticklike structure near the top surface,and dendrites structure near the interface.The friction and wear test showed that the composite coating had better wear resistance than pure Ti due to their higher microhardness than that of pure Ti substrate.
基金Project(2007046) supported by High Technology Research Project of Jiangsu Province,China
文摘The cooperative effect of laser surface texturing(LST) and double glow plasma surface alloying on tribological performance of lubricated sliding contacts was investigated.A Nd:YAG laser was used to generate microdimples on steel surfaces. Dimples with the diameter of 150μm and the depth of 30-35μm distributed circumferentially on the disc surface.The alloying element Cr was sputtered to the laser texturing steel surface by double glow plasma technique.A deep diffusion layer with a thickness of 30μm and a high hardness of HV900 was formed in this alloy.Tribological experiments of three types of samples(smooth,texturing and texturing+alloying) were conducted with a ring-on-disc tribometer to simulate the face seal.It is found that,in comparison with smooth steel surfaces,the laser texturing samples significantly reduce the friction coefficient.Moreover,the lower wear rate of the sample treated with the two surface techniques is observed.
文摘To strengthen the wear resistance of AISI321 stainless steel, the TiC carbide-reinforced composite coating was produced by laser surface alloying. The microstructure, microhardness, and wear resistance of the composite coatings were investigated using optical microscopy, X-ray diffraction (XRD) meter, scanning electron microscopy (SEM), microhardness tester, and sliding wear tester. The results show that the composite coating is metallurgically bonded to the substrate and the microstructure is fine and uniform. The hardness of the composite coating is up to 400 HV, which is 2.5 times that of the substrate. Under room temperature and oil lubrication condition, the sliding wear tests indicate the friction coefficient and weight loss of the composite coating are smaller than those of substrate. The worn surface of the composite coatings is much smoother than that of the substrate, without grooves and crater. The wear resistance of the material has been greatly improved by laser surface alloying.
文摘Laser Surface alloying is a process, in which a high-power laser beam is used to scan across the surface of a material, thus forming a melting zone, and then some alloying elements are spread into the melting pool to yield an alloying layer with characteristic properties on the surface of this material. We have studied the laser surface alloying technique and the properties of the alloying layer for 45 carbon steel with the elements Cr and Mo and obtained some useful data.