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Effects of groove constraint space on plasma characteristics during Laser-MIG hybrid welding of Titanium alloy
摘要： Laser-MIG hybrid welding with groove shows great potential in thick plate joining. However, the plasma behaviors in?uenced by the groove space are not well understood. In this paper, special stair-stepping plates with groove were designed to form di?erent groove con?gurations, and the e?ects of groove depth on the plasma characteristics were investigated systematically. The results showed that the plasma temperature decreased from 10,589 K to 8,527 K and the electron density increased from 1.30 × 1016 cm?3 to 1.44 × 1016 cm?3 when the groove depth increased from 0 to 20 mm. The reason may be that more laser-induced metal vapor, cooler than arc plasma, cannot leave the deeper groove space in time. The heat convection and radiation between the vapor and plasma resulted in the temperature decrease. Besides, as the groove constraint space increased, the plasma pro?le, frequency of droplet-transfer and weld width decreased, while the penetration depth increased to some extent. This research results would be inspirational and meaningful to the laser-arc hybrid welding of medium and thick plate.
关键词： Plasma,Titanium alloy thick plate,Laser-MIG hybrid welding,Groove constraint space
更新于2025-09-16 10:30:52
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Microstructure and fatigue behavior of a laser additive manufactured 12CrNi2 low alloy steel
摘要： In this research, 12CrNi2 low alloy steel was successfully prepared by laser melting deposition (LMD). The mechanisms driving high cycle fatigue fracture of the as-built LMD 12CrNi2 low alloy steel were investigated and a concurrent process-microstructure-property relationship was established through microstructural analysis. The results showed that the crystal structures of the as-built LMD 12CrNi2 steel mainly consisted of the ferrite and a small amount of Cr23C6 carbides. No preferred texture was observed as a result of the complicated heat flux direction during fabrication. Based on the examination of the fracture surface, fatigue cracks of the as-built LMD 12CrNi2 steel initiated from subsurface defects for all the cases. Crack propagation zones showed a mixed mode of transgranular and intergranular fracture in a brittle manner, whereas the final fracture zones displayed dimples typical of ductile fracture. The kernel average misorientation (KAM) map indicated that the strain localization predominantly occurred at the grain boundaries and slightly appeared at the interior of the ferrite grains. Schmid factor distribution results implied that fatigue cracks originated from grains with {123}<111> slip system due to the prior activation of {123}<111> slip system.
关键词： Fractography,High cycle fatigue,Microstructure,12CrNi2 low alloy steel,Laser additive manufacturing
更新于2025-09-16 10:30:52
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Modeling of thermal behavior and microstructure evolution during laser cladding of AlSi10Mg alloys
摘要： An improved three-dimensional finite element model has been proposed for studying the thermal behavior and microstructure evolution during laser cladding of AlSi10Mg alloys. Different material properties between AlSi10Mg powders and AlSi10Mg alloys are distinguished from the experiment and theoretical calculation to provide more reliable material parameters for simulation. In order to investigate the melting and solidification process during the formation of cladding layers, a temperature selection judgment mechanism is established to simulate the evolution of AlSi10Mg powders from the powder state to melting state and alloy state. In addition, to simulate the complex thermal behavior associated with powder particles and the voids between particles, a simplified exponential attenuation model is used for correcting the heat source. A complex asymmetric heat source considering about the different material properties and laser absorptivity on both sides of the remelting zone is used for multi-track cladding process. By simulating the temperature distribution of molten pool, the improved FEM could be used to predict the geometric shape of cladding layers (ignoring the effect of melting flow) and the temperature history. The simulation results show that the heat tends to diffuse to the unmelted powder owing to the asymmetric heat source during multi-track cladding, which leads to the asymmetry of cladding layers along the width direction. Based on the results of the temperature field simulations and the solidification characteristics of AlSi10Mg powders, the temperature gradient (G), solidification growth rate (R), cooling rate (G*R) and G/R are investigated to predict the morphology and size of the solidification microstructure under different laser scanning parameters. The scanning speed mainly determines the cooling rate during the laser cladding process, which results in different microstructures. Higher scanning speed leads to higher cooling rate, corresponding to a finer microstructure. Coarse dendrites are generated at the bottom of the molten pool, while finer dendrites are formed at the top.
关键词： Simulation,Microstructure evolution,AlSi10Mg alloy,Laser cladding,Thermal behavior
更新于2025-09-16 10:30:52
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Functionalized PdAu Alloy on Nanocones Fabricated on Optical Fibers for Hydrogen Sensing
摘要： This paper reports the development of fiber optical hydrogen sensors using palladium and gold alloy nanostructures as sensor materials for hydrogen measurements using a D-shaped fiber as a platform. Using a maskless reactive ion etching technique, silica nanocone structures were formed on the surface of the D-shaped fiber. Palladium and gold alloys were deposited on the surface of nanostructured D-shaped fiber to form a nano-alloy sensor film. Evanescent interaction between guided light propagated in the fiber core and nano-alloy enabled highly sensitive hydrogen detection from concentrations that ranged from 0.25% to 10% in atmosphere pressure. The formation of nanostructured alloy enabled by the nanocone surface led to more than 3 times faster in sensor response time and significant improvements in sensor sensitivity and reversibility. The work presented here demonstrates that highly controllable VLSI microfabrication schemes can be applied to produce nanostructured sensor films on optical fibers for high-sensitivity chemical sensing.
关键词： palladium-gold alloy,D-shaped fiber,nanocones,Hydrogen sensor
更新于2025-09-16 10:30:52
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Distribution of Al Element of Ti–6Al–4V Joints by Fiber Laser Welding
摘要： In the process of laser welding, the uneven distribution of solute elements caused by element burning loss and ?ow of molten pool a?ects the quality of joints. In this paper, butt welding experiments were conducted on the 3 mm thick Ti–6Al–4V specimens with di?erent preset ratios of Al and Si powders by using 4 kW ?ber laser. The distribution of Al solute element and its in?uence on the microstructure and mechanical properties of the ?nal weld joint were investigated. The results showed that the self-di?usion of Al element and the ?ow of molten pool a?ects the alloy elements distribution in laser welding. And the microhardness of the welded joint with Ti–6Al–4V and 90% Al + 10% Si powders was signi?cantly higher than that with only Ti–6Al–4V, with the di?erence of about 130HV. At the same time, in the joint with 90% Al and 10% Si powders, the acicular α’ size was ?ner, and basketweave microstructure was present as well. This research is helpful to better understand the distribution of Al solute element and its in?uence on the joint quality during laser welding of Ti–6Al–4V alloy, which provides a certain reference for improving the weld or surface properties of Ti–6Al–4V alloy during laser processing.
关键词： Ti–6Al–4V alloy,structure morphology,laser welding,elements distribution,microhardness
更新于2025-09-16 10:30:52
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Surface modification of aluminum alloys with carbon nanotubes by laser surface melting
摘要： Carbon nanotubes (CNTs) could be an excellent reinforcement for metal matrix composites, specifically for composites with aluminum or aluminum alloy matrix. Surface modification to improve hardness and other material properties has been performed by laser surface melting (LSM) process, where the laser beam melts the substrate together with alloying elements or reinforcing phase additives. In this work, Multiwalled CNTs (MWCNTs) were mixed by the electrostatic adsorption process with aluminum powder and the resulting mixed powder was laser melted on the surface of a 6061-aluminum alloy substrate. As a result, a modified substrate surface has been obtained from the Al/MWCNT – substrate co-melting, dilution and re-solidification processes. This modified layer was obtained by different LSM parameters and were characterized by Optical (OM) and Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Field Emission Gun Scanning Electron Microscopy (FEG-SEM), X-Ray Diffraction (XRD) and Raman Spectroscopy (RS). The resulting mechanical behavior was evaluated by Vickers microhardness tests. The results showed that the presence of MWCNT in the aluminum powder improves the laser energy absorption, leading to the formation of a deeper modified layer, with segregation of Si particles homogeneously dispersed and improving the hardness. The formation of Al4C3 was not observed, evidencing that the MWCNTs did not react with the molten Al matrix during the LSM process.
关键词： Laser surface melting,MWCNT,Aluminum alloy
更新于2025-09-16 10:30:52
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Numerical Study on Thermodynamic Behavior during Selective Laser Melting of 24CrNiMo Alloy Steel
摘要： In this paper, a multi-layer and multi-track ?nite element model of 24CrNiMo alloy steel by selective laser melting (SLM) is established by using the ABAQUS software. The distribution and evolution of temperature ?eld and stress ?eld and the in?uence of process parameters on them are systematically studied. The results show that the peak temperature increases from 2153 C and the residual stress increases from 335 MPa to 364 MPa with increasing laser power from 200 W to 300 W; the peak temperature decreases from 2905 C and the residual stress increases from 327 MPa to 363 MPa with increasing scanning speed from 150 mm/s to 250 mm/s; the peak C and the residual stress decreases from 354 MPa to 300 temperature increases from 2621 MPa with increasing preheating temperature from 25 C. Far away from scanning area, far away from starting point, and the adjacent areas with vertical scanning direction, resulting in a uniform temperature distribution, help to reduce the residual stress. Due to the remelting e?ect, the interlayer scanning angle changing helps to release the residual stress of the former layer causing a smaller residual stress after redistribution.
关键词： substrate preheating,?nite element analysis,thermodynamic behavior,selective laser melting,scanning strategy,24CrNiMo alloy steel
更新于2025-09-16 10:30:52
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[Laser Institute of America ICALEO? 2016: 35th International Congress on Applications of Lasers & Electro-Optics - San Diego, California, USA (October 16–20, 2016)] International Congress on Applications of Lasers & Electro-Optics - Fibre laser trepanning drilling of metals and alloys
摘要： Laser drilling of metals and alloys is extensively used in modern manufacturing industries to produce holes of various sizes and shapes. Currently, most aerospace laser drilling is performed using Nd:YAG laser and over the years many attempts have been made to increase the productivity of Nd:YAG lasers drilling process, but with little success. This paper investigates the use of recently developed millisecond-pulsed-Quasi-CW-fibre-laser for trepanning drilling of aerospace grade nickel super-alloy. The main investigation concentrates on understanding the effects of Quasi-CW-fibre-laser parameters on trepanning laser drilled hole quality. The principal findings are based on reducing the recast and oxide layer. Results show that the high average power of the Quasi-CW-fibre-lasers can be effectively used to achieve increased trepanning drilling speed without undermining the drilling quality, which is not feasible with a free-space Nd:YAG laser. Low peak power and high average power can be effectively used to produce better laser drilled hole than the high peak power and low frequency, which is observed with the traditional millisecond Nd:YAG drilling process.
关键词： alloys,Fibre laser,nickel super-alloy,trepanning drilling,oxide layer,aerospace,recast layer,metals
更新于2025-09-16 10:30:52
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The New Heat Source Model of AZ31B Magnesium Alloy Laser-TIG Hybrid Welding
摘要： A new heat source model consisted of inverted conical heat source and rotary Gauss body heat source is established using the CAE software for the keyhole effect of laser-TIG hybrid welding. The inverted conical heat source is used for analyzing the wide upper part of weld pool due to the rapid heat up by the laser and arc. The rotary Gauss body heat source model is used for analyzing the long and narrow lower part of weld pool formed by the laser. The result showed that, compared with other single source mode, this new heat source model may get a better simulation of the weld pool morphology, especially the inflection point near the keyhole. It provides a new method to predict the morphology and size of the weld pool of magnesium alloy laser-TIG welding.
关键词： shape of weld molten,keyhole effect,magnesium alloy,laser-TIG hybrid welding
更新于2025-09-16 10:30:52
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Obtaining Spherical Powders of Grade 5 Alloy for Application in Selective Laser Melting Technology
摘要： In this paper, the process of obtaining a spherical powder of titanium alloy of the grade 5 brand using inductively coupled argon-helium plasma has been studied. The structure of titanium alloy was studied before and after the spheroidization process. The results of particle size and X-ray fluorescent analysis were also obtained. As a result of the analysis of the structure, it was concluded that the crystallite sizes and microstress values change.
关键词： plasmachemical synthesis,additive technology,titanium alloy,spheroidization,grade 5
更新于2025-09-16 10:30:52