The laser beam welding of BT20 titanium alloy was conducted to investigate the weld shape, microstructures and properties. The full penetration weld characteristics produced by CO_2 laser and by YAG laser were compare...The laser beam welding of BT20 titanium alloy was conducted to investigate the weld shape, microstructures and properties. The full penetration weld characteristics produced by CO_2 laser and by YAG laser were compared. The results show that the full penetration weld of YAG laser welding closes to “X” shape, and weld of CO_2 laser welding is “nail-head” shape. Those result from special heating mode of laser deep penetration welding. The tension strength of CO_2 laser and YAG laser joints equal to that of the base metal, but the former has better ductility. All welds consist mainly of the acicular α phase and a few β phase in microstructure. The dendritic crystal of CO_2 laser weld is a little finer than YAG laser weld. According the research CO_2 laser is better than YAG laser for welding of BT20 titanium alloy.展开更多
We numerically investigate the formation and interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by contro...We numerically investigate the formation and interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the intercavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, a stronger gain saturation energy will result in a higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compared to conventional solitons.展开更多
The Nd : YAG laser welding was used to join the TiNi shape memory alloy and AISI304 stainless steel wires. The microstructural features of the dissimilar material joint were analyzed. The tensile and hardness tests w...The Nd : YAG laser welding was used to join the TiNi shape memory alloy and AISI304 stainless steel wires. The microstructural features of the dissimilar material joint were analyzed. The tensile and hardness tests were carried out to examine the mechanical properties and microhardness distribution of the welded joint. The results show that the joint has the non-homogeneous microstructure and element distribution. The brittle phases such as Fe2 Ti , Fe Ti , Cr2 Ti , Ti3 Ni4, Feo 2 Ni4.s Ti5 and TiN mainly segregate in rich Ti region of fusion zone. The laser-welded joint has the tensile strength of 298 MPa with the elongation of 3.72 % and exhibits the brittle fracture features on the fracture surfaces. The reasons for low joint strength were discussed in this investigation.展开更多
The effect of the laser processing parameters on the composition uniformity and shape coefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloy steel has been studied.It was found that...The effect of the laser processing parameters on the composition uniformity and shape coefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloy steel has been studied.It was found that the composition uniformity depends on the shape coefficient of fusion zone,and the later is a function of both power density and interaction time.If the power density is fixed to a certain value,the shape coefficient is directly,propor- tional to the interaction time.A completely,uniform molten pool can be obtained,when the shape coefficient is between 1.6 and 3.0.展开更多
Electrochemical behaviors of laser-welded Ti-50.6%Ni(mole fraction) shape memory alloy and the base metal in 0.9% NaCl solution were investigated by electrochemical techniques as corrosion potential measurement, linea...Electrochemical behaviors of laser-welded Ti-50.6%Ni(mole fraction) shape memory alloy and the base metal in 0.9% NaCl solution were investigated by electrochemical techniques as corrosion potential measurement, linear and potentiodynamic polarization. The results indicate that the laser-welded NiTi alloy is less susceptible to pitting and crevice corrosion than the base metal, which is demonstrated by the increase in polarization resistance(Rp) and pitting potential(φpit) and decrease in corrosion current density(Jcorr) and mean difference between φpit and φprot values. It is confirmed by scanning electron microscope micrographs that pits could be observed on the surface of base metal but not on the surface of laser-welded alloy after potentiodynamic tests. An improvement of corrosion resistance of laser-welded NiTi alloy could be attributed to almost complete dissolution of inclusions upon laser welding.展开更多
Recent experimental data for anomalous magnetic moments strongly indicates the existence of new physics beyond the Standard Model.Energetic μ^(+) bunches are relevant to μ^(+) rare decay,spin rotation,resonance and ...Recent experimental data for anomalous magnetic moments strongly indicates the existence of new physics beyond the Standard Model.Energetic μ^(+) bunches are relevant to μ^(+) rare decay,spin rotation,resonance and relaxation(μSR)technology,future muon colliders,and neutrino factories.In this paper,we propose prompt μ^(+) acceleration in a nonlinear toroidal wakefield driven by a shaped steep-rising-front Laguerre–Gaussian(LG)laser pulse.An analytical model is described,which shows that a μ^(+) beam can be focused by an electron cylinder at the centerline of a toroidal bubble and accelerated by the front part of the longitudinal wakefield.A shaped LG laser with a short rise time can push plasma electrons,generating a higher-density electron sheath at the front of the bubble,which can enhance the acceleration field.The acceleration field driven by the shaped steep-rising-front LG laser pulse is about four times greater than that driven by a normal LG laser pulse.Our simulation results show that a 300 MeV μ^(+) bunch can be accelerated to 2 GeV and its transverse size is focused from an initial value of w_(0)=5μm to w=2μm in the toroidal bubble driven by the shaped steep-rising-front LG laser pulse with a normalized amplitude of a=22.展开更多
We perform a theoretical investigation on the control over the atomic excitation of Rydberg states with shaped intense ultrashort laser pulses.By numerically solving the time-dependent Schrodinger equation(TDSE),we sy...We perform a theoretical investigation on the control over the atomic excitation of Rydberg states with shaped intense ultrashort laser pulses.By numerically solving the time-dependent Schrodinger equation(TDSE),we systematically study the dependence of the population of the Rydberg states on theπphase step position in the frequency spectra of the laser pulse for different intensities,central wavelengths and pulse durations.Our results show that the Rydberg excitation process can be effectively modulated using shaped intense laser pulses with the laser intensity as high as 1×10^14 W/cm^2.Our work also have benefit to the future investigation to find out the dominant mechanism behind the excitation of Rydberg states in strong laser fields.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
The surface of Ti-50.8Ni at% shape memory alloy was melted by an Nd-YAG laser. The Ti/Ni and Ti4+/Ti atomic concentration ratios at the surface were changed significantly. The Ni ion release rate of the laser melted s...The surface of Ti-50.8Ni at% shape memory alloy was melted by an Nd-YAG laser. The Ti/Ni and Ti4+/Ti atomic concentration ratios at the surface were changed significantly. The Ni ion release rate of the laser melted surface was much lower than that of the mechanical polished samples. A calcium-phosphorous layer with high Ca/P ratio was detected after immersion in Hanks’ solution.展开更多
The quality assessment and prediction becomes one of the most critical requirements for improving reliability, efficiency and safety of laser welding. Accurate and efficient model to perform non-destructive quality es...The quality assessment and prediction becomes one of the most critical requirements for improving reliability, efficiency and safety of laser welding. Accurate and efficient model to perform non-destructive quality estimation is an essential part of this assessment. This paper presents a structured and comprehensive approach developed to design an effective artificial neural network based model for weld bead geometry prediction and control in laser welding of galvanized steel in butt joint configurations. The proposed approach examines laser welding parameters and conditions known to have an influence on geometric characteristics of the welds and builds a weld quality prediction model step by step. The modelling procedure begins by examining, through structured experimental investigations and exhaustive 3D modelling and simulation efforts, the direct and the interaction effects of laser welding parameters such as laser power, welding speed, fibre diameter and gap, on the weld bead geometry (i.e. depth of penetration and bead width). Using these results and various statistical tools, various neural network based prediction models are developed and evaluated. The results demonstrate that the proposed approach can effectively lead to a consistent model able to accurately and reliably provide an appropriate prediction of weld bead geometry under variable welding conditions.展开更多
This paper presents an experimentally validated weld joint shape and dimensions predictive 3D modeling for low carbon galvanized steel in butt-joint configurations. The proposed modelling approach is based on metallur...This paper presents an experimentally validated weld joint shape and dimensions predictive 3D modeling for low carbon galvanized steel in butt-joint configurations. The proposed modelling approach is based on metallurgical transformations using temperature dependent material properties and the enthalpy method. Conduction and keyhole modes welding are investigated using surface and volumetric heat sources, respectively. Transition between the heat sources is carried out according to the power density and interaction time. Simulations are carried out using 3D finite element model on commercial software. The simulation results of the weld shape and dimensions are validated using a structured experimental investigation based on Taguchi method. Experimental validation conducted on a 3 kW Nd: YAG laser source reveals that the modelling approach can provide not only a consistent and accurate prediction of the weld characteristics under variable welding parameters and conditions but also a comprehensive and quantitative analysis of process parameters effects. The results show great concordance between predicted and measured values for the weld joint shape and dimensions.展开更多
文摘The laser beam welding of BT20 titanium alloy was conducted to investigate the weld shape, microstructures and properties. The full penetration weld characteristics produced by CO_2 laser and by YAG laser were compared. The results show that the full penetration weld of YAG laser welding closes to “X” shape, and weld of CO_2 laser welding is “nail-head” shape. Those result from special heating mode of laser deep penetration welding. The tension strength of CO_2 laser and YAG laser joints equal to that of the base metal, but the former has better ductility. All welds consist mainly of the acicular α phase and a few β phase in microstructure. The dendritic crystal of CO_2 laser weld is a little finer than YAG laser weld. According the research CO_2 laser is better than YAG laser for welding of BT20 titanium alloy.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60372061)the Scientific Forefront and Interdisciplinary Innovation Project of Jilin University, China (Grant No. 200903296)
文摘We numerically investigate the formation and interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the intercavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, a stronger gain saturation energy will result in a higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compared to conventional solitons.
基金This research was supported by National Natural Science Foundation of China (No. 50975122).
文摘The Nd : YAG laser welding was used to join the TiNi shape memory alloy and AISI304 stainless steel wires. The microstructural features of the dissimilar material joint were analyzed. The tensile and hardness tests were carried out to examine the mechanical properties and microhardness distribution of the welded joint. The results show that the joint has the non-homogeneous microstructure and element distribution. The brittle phases such as Fe2 Ti , Fe Ti , Cr2 Ti , Ti3 Ni4, Feo 2 Ni4.s Ti5 and TiN mainly segregate in rich Ti region of fusion zone. The laser-welded joint has the tensile strength of 298 MPa with the elongation of 3.72 % and exhibits the brittle fracture features on the fracture surfaces. The reasons for low joint strength were discussed in this investigation.
文摘The effect of the laser processing parameters on the composition uniformity and shape coefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloy steel has been studied.It was found that the composition uniformity depends on the shape coefficient of fusion zone,and the later is a function of both power density and interaction time.If the power density is fixed to a certain value,the shape coefficient is directly,propor- tional to the interaction time.A completely,uniform molten pool can be obtained,when the shape coefficient is between 1.6 and 3.0.
基金Project(2002AA326010) supported by the Hi-tech Research and Development Program of China Project(50471066) supported by the National Natural Science Foundation of China
文摘Electrochemical behaviors of laser-welded Ti-50.6%Ni(mole fraction) shape memory alloy and the base metal in 0.9% NaCl solution were investigated by electrochemical techniques as corrosion potential measurement, linear and potentiodynamic polarization. The results indicate that the laser-welded NiTi alloy is less susceptible to pitting and crevice corrosion than the base metal, which is demonstrated by the increase in polarization resistance(Rp) and pitting potential(φpit) and decrease in corrosion current density(Jcorr) and mean difference between φpit and φprot values. It is confirmed by scanning electron microscope micrographs that pits could be observed on the surface of base metal but not on the surface of laser-welded alloy after potentiodynamic tests. An improvement of corrosion resistance of laser-welded NiTi alloy could be attributed to almost complete dissolution of inclusions upon laser welding.
基金supported in part by the National Key R&D Program of China(No.2018YFA0404802)National Natural Science Foundation of China(No.11875319)+2 种基金the Hunan Provincial Science and Technology Program(No.2020RC4020)Innovation Project of IHEP(Nos.542017IHEPZZBS11820,542018IHEPZZBS12427)the CAS Center for Excellence in Particle Physics(CCEPP),the Meritocracy Research Funds of China West Normal University(No.17YC504)。
文摘Recent experimental data for anomalous magnetic moments strongly indicates the existence of new physics beyond the Standard Model.Energetic μ^(+) bunches are relevant to μ^(+) rare decay,spin rotation,resonance and relaxation(μSR)technology,future muon colliders,and neutrino factories.In this paper,we propose prompt μ^(+) acceleration in a nonlinear toroidal wakefield driven by a shaped steep-rising-front Laguerre–Gaussian(LG)laser pulse.An analytical model is described,which shows that a μ^(+) beam can be focused by an electron cylinder at the centerline of a toroidal bubble and accelerated by the front part of the longitudinal wakefield.A shaped LG laser with a short rise time can push plasma electrons,generating a higher-density electron sheath at the front of the bubble,which can enhance the acceleration field.The acceleration field driven by the shaped steep-rising-front LG laser pulse is about four times greater than that driven by a normal LG laser pulse.Our simulation results show that a 300 MeV μ^(+) bunch can be accelerated to 2 GeV and its transverse size is focused from an initial value of w_(0)=5μm to w=2μm in the toroidal bubble driven by the shaped steep-rising-front LG laser pulse with a normalized amplitude of a=22.
基金Project supported by the National Natural Science Foundation of China(Grant No.11874246)
文摘We perform a theoretical investigation on the control over the atomic excitation of Rydberg states with shaped intense ultrashort laser pulses.By numerically solving the time-dependent Schrodinger equation(TDSE),we systematically study the dependence of the population of the Rydberg states on theπphase step position in the frequency spectra of the laser pulse for different intensities,central wavelengths and pulse durations.Our results show that the Rydberg excitation process can be effectively modulated using shaped intense laser pulses with the laser intensity as high as 1×10^14 W/cm^2.Our work also have benefit to the future investigation to find out the dominant mechanism behind the excitation of Rydberg states in strong laser fields.
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.
文摘The surface of Ti-50.8Ni at% shape memory alloy was melted by an Nd-YAG laser. The Ti/Ni and Ti4+/Ti atomic concentration ratios at the surface were changed significantly. The Ni ion release rate of the laser melted surface was much lower than that of the mechanical polished samples. A calcium-phosphorous layer with high Ca/P ratio was detected after immersion in Hanks’ solution.
文摘The quality assessment and prediction becomes one of the most critical requirements for improving reliability, efficiency and safety of laser welding. Accurate and efficient model to perform non-destructive quality estimation is an essential part of this assessment. This paper presents a structured and comprehensive approach developed to design an effective artificial neural network based model for weld bead geometry prediction and control in laser welding of galvanized steel in butt joint configurations. The proposed approach examines laser welding parameters and conditions known to have an influence on geometric characteristics of the welds and builds a weld quality prediction model step by step. The modelling procedure begins by examining, through structured experimental investigations and exhaustive 3D modelling and simulation efforts, the direct and the interaction effects of laser welding parameters such as laser power, welding speed, fibre diameter and gap, on the weld bead geometry (i.e. depth of penetration and bead width). Using these results and various statistical tools, various neural network based prediction models are developed and evaluated. The results demonstrate that the proposed approach can effectively lead to a consistent model able to accurately and reliably provide an appropriate prediction of weld bead geometry under variable welding conditions.
文摘This paper presents an experimentally validated weld joint shape and dimensions predictive 3D modeling for low carbon galvanized steel in butt-joint configurations. The proposed modelling approach is based on metallurgical transformations using temperature dependent material properties and the enthalpy method. Conduction and keyhole modes welding are investigated using surface and volumetric heat sources, respectively. Transition between the heat sources is carried out according to the power density and interaction time. Simulations are carried out using 3D finite element model on commercial software. The simulation results of the weld shape and dimensions are validated using a structured experimental investigation based on Taguchi method. Experimental validation conducted on a 3 kW Nd: YAG laser source reveals that the modelling approach can provide not only a consistent and accurate prediction of the weld characteristics under variable welding parameters and conditions but also a comprehensive and quantitative analysis of process parameters effects. The results show great concordance between predicted and measured values for the weld joint shape and dimensions.