Hybrid Laser Technology for Creation of Doped Biomedical Layers

Hybrid laser technologies for deposition of thin films and basic schemes of combination of pulsed laser deposition (PLD) with magnetron sputtering and RF discharges or two lasers or three laser deposition systems are presented. Experiences with deposition of chromium doped diamond-like carbon (DLC) films for coating of prostheses are described. Layers of different chromium concentrations were prepared using hybrid systems (PLD + magnetron sputtering or by double PLD). Results of physical and mechanical characterization of film properties and biomedical tests of trivalent and toxic hexavalent chromium are given. Experiences with double laser deposition of DLC layers doped with silver are also mentioned.

Hybrid laser/arc welding of thick high-strength steel in different configurations

In this investigation, hybrid laser/arc welding （HLAW） was employed to join 8-mm-thick high-strength quenched and tempered steel （HSQTS） plates in the butt- and T-joint configurations. The influences of welding parame- ters, such as laser power, welding speed, stand-off distance （SD） between the arc of gas metal arc welding, and the laser heat source on the weld quality and mechanical properties of joints, were studied to obtain non-porous and crack-free fully-penetrated welds. The weld microstructure, cross- section, and mechanical properties were evaluated by an optical microscope, and microhardness and tensile tests. In addition, a finite element model was developed to investigate the thermal history and molten pool geometry of the HLAW process to join the HSQTS. The numerical study demon- strated that the SD had a paramount role in good synergy between the heat sources and the stability of the keyhole. For the butt-joint configuration, the results showed that, at a higher welding speed （35 mm/s） and optimum SD between the arc and laser, a fully-penetrated sound weld could be achieved. A non-porous weld in the T-joint configuration was obtained at a lower welding speed （10 mm/s）. Microstructural evaluations indicated that the formation of residual austenite and the continuous network of martensitic structure along the grain boundary through the heat affected zone were the primary reasons of the softening behavior of this area. This was confirmed by the sharp hardness reduction and failure behavior of the tensile coupons in this area.

Joining mechanism of Mg alloy/steel butt joints with Cu-Zn interlayer by hybrid laser-TIG welding source

Hybrid laser-TIG （tungsten inert gas） welding technology was used to join the Mg to steel with Cu-Zn interlayer. The effect of Al content in Mg alloy on the interface bonding of AZ31BMg/Q235 steel dissimilar butt joints was investigated. For comparison, ZK60 Mg alloy with no Al addition and AZ31 Mg alloy were utilized. The results showed that AZ31/Q235 butt joints with Cu-Zn interlayer, of which the fractures occurred in the Mg weld seam, showed quite sound and reliable interface bonding. The obvious concentration of element Al occurred along the Mg/steel interface. The results indicated that the addition of Cu-Zn interlayer, especially Zn, could significantly decrease the reaction temperature of Fe-Al at the Mg/ steel interface and promote the formation of reaction layer along the interface. The diffusion of Al element on the Mg-Fe interface was increased by the Cu-Zn interlayer. For ZK60 Mg alloy, Mg and Zn approaching the Mg-Fe interface were evaporated. The intense vaporizing could inhibit the direct contact between steel and Mg weld pool, even destroying the possible formation of reaction layer. The intimate interface bonding of AZ31/Q235 butt joints was attributed to the synergistic effect of element AI and Cu.

Temperature field simulation of laser-TIG hybrid welding

The three dimensional transient temperature distribution of laser TIG hybrid welding was analyzed and simulated numerically. Calculations were based on a finite element model, in which the physical process of hybrid welding was studied and the coupling effect of the laser and arc in the hybrid process was fully considered. The temperature fields and weld cross sections of the typical welding parameters are obtained using present model. The calculation results show that the model can indicate the relationship of energy match between laser and arc to joints cross sections objectively, and the simulation results are well agreed with the experimental results.

Droplet-targeting laser hybrid indirect arc for additive manufacturing technology-A preliminary study

The contradiction between manufacturing accuracy and manufacturing efficiency is discussed in this paper.In order to solve this problem,a novel droplet-targeting laser hybrid indirect arc for additive manufacturing technology is proposed in which a couple of wires are melted using the alternating current with interwire indirect arc to achieve high deposition rate.On the other hand,droplets actively target the laser beam and detach from wire tip under the recoil pressure subjected to pulsed laser irradiating at desired position and with controlled mass for a precise bead forming.The process of alternative droplet growing at desired position are mathematically analyzed and then preliminary verified by experiment.By precisely controlling the wire feed speed and current frequency,the melting process at desired position and mass of wire is successfully obtained which is the fundamental for next-step for the droplet actively targeting laser.

Three thermal analysis models for laser, GMAW-P and Iaser＋GMAW-P hybrid welding

The temperature fields and the weld pool geometries for laser ＋ GMAW-P hybrid welding, laser welding and pulsed gas metal arc welding （GMAW-P） are numerically simulated in quasi-steady state by using the developed heat source models, respectively. The calculated weld cross-sectious of the three types of welding processes agree well with their respective measured results. Through comparison, it is found that the temperature distribution of laser＋GMAW-P hybrid welding possesses the advantages of those in both laser and GMAW-P welding processes so that the improvement of welding productivity and weld quality are ensured.

Effect of laser-wire distance on temperature distribution in laser ＋ GMAW-P hybrid welding

The temperature fields in laser ＋ GMAW-P hybrid welding for different laser-wire distances in quasi-steady state were calculated using an developed combined heat source model, and the influence of laser-wire distance on them was analyzed. The results show tbat, at a low level of arc power, the temperature profiles caused by laser and arc energy respecively cannot couple well when the laser-wire distance reaches 4 mm, a trend of separation between them beginning to take place. In the case of high arc power, both the critical laser-wire distance and HAZ width increase.

Research on laser-arc hybrid welding technology for long-distance pipeline construction

In recent years, the research on pipeline laser-arc hybrid welding technology has been the important and difficult in the field of welding all over the world. China Petroleum Pipeline Research Institute Co. Ltd. has firstly developed pipeline laser-arc hybrid welding system in China, and executed the welding tests based on X70/X80 steel. Preliminary experiment results showed that hybrid welding could meet the requirements of related standards such as API1104,ASME,etc., the mechanical properties of girth seam are qualified in the case that there were no internal defects. With the development of high-power fiber laser and the continuous improvement of welding equipment, laser-arc hybrid welding technology for pipeline field welding will be available soon.

Laser-pulsed MIG hybrid welding technology of A6N01S aluminum alloy

Welding research of A6N01S-T5 aluminum alloy profile for high-speed train was done by using laser-MIG hybrid welding and MIG welding individually. And the weld appearance,welding distortion,mechanical properties of the joints and microstructures were analyzed. The test results demonstrated that high-efficient welding for the profile can be achieved by using laser-MIG hybrid welding,the speed of which can be over 3. 0 m/min. The processing had a good gap bridging ability,even if the gap of the butt joint was up to 2. 0 mm,a good weld appearance can also be got. While the hybrid welding speed was greater than 2. 5 m/min,the welding distortion of the laser-tandem MIG hybrid joints was just about 33% of that of the MIG joints,but the welding efficiency was over 3 times of MIG welding. And tensile strength of the hybrid joints was 85% of that of A6N01S-T5 base metal,9% higher than that of the MIG joints. Fatigue properties was tested individually with pulsed tensile fatigue method in the condition of 1 × 10~7 lifetime. The test results demonstrated that the fatigue strength of the joints was a little lower than that of base material,which could be up to 115 MPa. But the fatigue strength of hybrid welding joints was 107. 5 MPa,which was 23% higher than 87 MPa of MIG welding joints.

Effect of Fe content on microstructure and mechanical properties of Cu-Fe-based composite coatings by laser induction hybrid rapid cladding

To select the proper composition and obtain an overall material?microstructure?property relationship for Cu?Fe alloy, theeffect of Fe content on microstructure and properties of Cu?Fe-based composite coatings by laser induction hybrid rapid claddingwas investigated. Microstructure characterization of the composite coatings was tested utilizing SEM, XRD and EDS. Microhardnessmeasurement was executed to evaluate the mechanical properties of the composite coatings. The results show that for low Fe content,the composite coating presents a feature that Fe-rich equiaxed dendrites are embedded in the Cu-rich matrix. With increasing Fecontent, the Fe-rich particles are dispersed in the Cu-rich matrix. With further increasing Fe content, large amounts of Cu-richparticles are homogeneously dispersed in the interdendrite of the Fe-rich matrix. Correspondingly, the average microhardness of thecomposite coatings increases gradually with the increase of Fe content and the microhardness of Cu14.5Fe83Si2C0.5 coating is muchtwice higher than that of the substrate.

Surface effects of hybrid vibration-assisted femtosecond laser system for micro-hole drilling of copper substrate

The ultrafast laser based hybrid machining system was studied and a novel approach was demonstrated to improve laser machining quality on metals by vibrating the optical objective lens with a low frequency (500 Hz) and various displacements (0-16.5 μm) during a femtosecond laser machining process.The laser used in this experiment is an amplified Ti:sapphire femtosecond (10-15 s) laser system that generates 100 femtosecond pulses having an energy of 3.5 mJ/pulse with a 5 kHz repetition rate at a central wavelength of 790 nm.It is found that both the wall surface finish of the machined structures and the aspect ratio obtained using the frequency vibration assisted laser machining are improved compared with those derived via laser machining without vibration assistance.

Microstructure and mechanical properties of wrought magnesium alloy AZ31B welded by laser-TIG hybrid

The laser-TIG hybrid welding was mainly used to weld the wrought magnesium alloy AZ31B. The technical characteristics of laser-TIG hybrid welding process was investigated and the interactional mechanism between laser and arc was discussed, at the same time the microstructure and mechanical properties of the wrought magnesium alloy AZ31B using laser-TIG hybrid welding were analyzed by optical microscope, EPMA, SEM, tensile machine, hardness machine. The experimental results show that the presence of laser beam boosts up the stability of the arc during high speed welding and augments the penetration of weld; the crystal grains of magnesium alloy weld are fine without porosity and cracks in the best welding criterion and the microstructure of HAZ does not become coarse obviously. The elements profile analysis reveals that Mg content in the weld is lower than that of the base metal, but Al content is higher slightly. Under this experimental condition, the wrought magnesium alloy AZ31B joint can be achieved using laser-TIG hybrid process and the tensile strength of the joint is equivalent to that of the base metal.

Welding characteristics in different laser-TIG hybrid manners

An experiment for determining the laser-TIG hybrid welding characteristics was carried out in three kinds of hybrid methods: CO_2 laser-TIG coaxial hybrid, CO_2 laser-TIG paraxial hybrid and Nd: YAG laser-TIG paraxial hybrid. The experimental results indicate that hybrid welding has two welding mechanisms in CO_2 laser-TIG hybrid welding: deep penetration welding and heat conduction welding. As the effect of the laser-induced keyhole, the arc root is condensed, the current density and penetration depth increase significantly, the welding characteristic is apt to deep penetration welding. When current increases to some degree, the keyhole induced by laser disappears, which produces a shallow penetration and wide bead. The weld exhibits heat conduction welding characteristics. Furthermore, the arc images and weld bead cross-sections of three kinds of hybrid manners were also compared and analyzed at different welding currents, which established the foundation for understanding the welding characteristics of laser-TIG hybrid welding comprehensively.

The numerical simulation of laser-MIG hybrid welding for Invar alloy

Composites are widely applied to the manufacturing of aircraft in aviation. Forming of large-scale composite component in aircraft requires the corresponding mold with precise size. The laser-MIG hybrid welding has a significant advantage in the manufacturing of Invar mold for aircraft composites. This paper mainly introduces the application of the laser-MIG hybrid welding,and the distribution of thermal field and flow field on the Invar alloy laser-MIG hybrid three-layer welding is analyzed and discussed specifically.

CHARACTERISTICS OF DROPLET TRANSFER IN CO_2 LASER-MIG HYBRID WELDING WITH SHORTCIRCUITING MODE

LF6 aluminum alloy plates with 4.5 mm thickness are welded in this experiment. Welding is carried out by using the CO2 laser-MIG paraxial hybrid welding in fiat position. The experimental results indicate that the inherent droplet transfer cycle time of conventional MIG arc is changed due to the interaction between CO2 laser beam and MIG arc in the short-circuiting mode of laser-MIG hybrid welding. Because of the preheating action of CO2 laser to electrode and base material, the droplet transfer frequency of MIG arc is increased in the hybrid welding process. When laser power is increased to a certain degree, the droplet transfer frequency is decreased due to the effect of laser-induced keyhole. Furthermore, through analyzing the MIG welding current and arc voltage waveforms and the characteristics of droplet transfer in the hybrid welding process, the effect of laser energy and the action point between laser beam and arc on the frequency of droplet transfer and weld appearance is investigated in details.

Low fabrication cost wavelength tunable WG-FP hybrid-cavity laser working over 1.7μm

A wide wavelength tuning range and single-mode hybrid cavity laser consists of a square Whispering-Gallery(WG)microcavity and a Fabry–Pérot(FP)was introduced and demonstrated.A wavelength tuning range over 12.5 nm from 1760.87 to 1773.39 nm which was single-mode emitting was obtained with the side-mode suppression ratio over 30 dB.The hybrid cavity laser does not need grating etching and special epitaxial structure,which reduces the fabrication difficulty and cost,and shows the potential for gas sensing with absorption lines in this range.

MODEL OF LASER-TIG HYBRID WELDING HEAT SOURCE

The welding mechanism of laser-TIG hybrid welding process is analyzed. Withthe variation of arc current, the welding process is divided into two patterns: deep-penetrationwelding and heat conductive welding. The heat flow model of hybrid welding is presented. As todeep-penetration welding, the heat source includes a surface heat flux and a volume heat flux. Theheat source of heat conductive welding is composed of two Gaussian distribute surface heat sources.With this heat source model, a temperature field is calculated. The finite element code MARC isemployed for this purpose. The calculation results show a good agreement with the experimental data.

Hybrid Laser-GMAW Welding of High Strength Quenched-Tempered Steels

High-strength quenched and tempered (HSQT) steels have been widely used in structural applications where light weight is of primary design interest.Gas metal arc welding is a common way to join QT steels.When GMAW is used to join the HSQT steel,multi-pass is usually required to achieve full penetration.In addition,weld crack is often observed because of HSQT steel's high susceptibility to hydrogen embrittlement.In addition,due to the large amount of heat input from the arc,the heat affected zone is often softened.This reduces the ductility and strength of welds and makes the weld weaker than the base metal.In this study,a hybrid laser/GMAW process is proposed to produce butt joint for 6.5mm thick HSQT A514 steel plate.Hydrogen diffusion mechanism is first discusses for GMAW and hybrid laser-GMAW welding processes.Metal transfer mode during the hybrid laser/GMAW welding process is also analyzed.A high speed CCD camera with 4000 frame/second is used to monitor the welding process in real time.Welds obtained by GMAW and hybrid laser/GMAW techniques are compared and tested by static lap shear and dynamic impact.Effects of gap between two metal plates and laser beam/GMAW torch spacing on weld property are studied.By appropriately choosing these two parameters,crack-free butt joints with full penetration can be successfully obtained by the hybrid laser/GMAW welding process for HSQT A514 steel plate.

Low-power YAG laser/arc hybrid welding of AZ-based Mg alloy

The results of recent researches on the weldability of laser/arc hybrid welding of AZ-based Mg alloy was presented.Experiments were conducted with a low-power(500 W) Nd:YAG laser and a TIG arc.The synergic effects and mechanical properties of the Mg joints by laser/arc hybrid welding were investigated,and the interaction mechanism of laser to arc was also discussed.The results show that Mg alloys can be easily welded in similar and dissimilar joints by laser/arc hybrid welding technique.With the arc power increasing,a higher weld depth is obtained,and the weld depths for laser and arc acting in combination(laser/arc) are two times higher than that of the total of laser and arc acting separately(laser+arc) in optimal conditions.The tensile strength and fatigue strength of the AZ31B joints welded by laser/arc hybrid process are equivalent to that of the based metal.Besides,the laser-induced plume/plasma images captured by high speed camera were used to study the interaction between laser beam and arc.

High-speed butt welding of magnesium alloy using pulsed laser-arc hybrid heat source

Laser-arc hybrid welding at a speed of 6 000 mm/min is carried out on 2 mm thick magnesium alloy AZ61 plateand completely-penetrated butt joints are obtained, lnvestigations of the influence of parameters on weld formation show that Ihe addition of pulsed laser can effctively enhance tlle heat penetrability attd directivity nf the hybrid heat source. Measurements on microstructures and mechanical properties the joint indicate that grain in the.fhsion zone is refined and the grain size is sensitive to the arc current ; the fitsioa zone exhibits the highest hardaess; the tensile strength of the joint reaches 93% of base metal; there is the brittle fracture along the grain bozmdaries in the fusion zone. High-speed camera images exhibit that although the two adjacent laser pulses can not overlap, the recorery relaxation of the concentrated electric arc after laser intlse action can still maintain the continuous welding process.