YAG laser welding with surface activating flux

YAG laser welding with surface activating flux has been investigated, and the influencing factors and mechanism are discussed. The results show that both surface activating flux and surface active element S have fantastic effects on the YAG laser weld shape, that is to obviously increase the weld penetration and D/W ratio in various welding conditions. The mechanism is thought to be the change of weld pool surface tension temperature coefficient, thus, the change of fluid flow pattern in weld pool due to the flux.

Activating Flux Design for Laser Weldingof Ferritic Stainless Steel

The behaviors of YAG laser welding process of ferritic stainless steel with activating fluxes were investigatedin this study. Some conventional oxides, halides and carbonates were applied in laser welding. The resultsshowed that the effect of oxides on the penetration depth was more remarkable. Most activating fluxes improved thepenetration more effectively at low power than that at high power. The uniform design was adopted to arrange theformula of multicomponent activating fluxes, showing that the optimal formula can make the penetration depth up to2.23 times as large as that without flux, including 50% ZrO2, 12.09% CaCO3, 10.43% CaO and 27.48% MgO. Throughthe high-speed photographs of welding process, CaF2 can minimize the plasma volume but slightly improve the penetrationcapability.

Microstructure,properties and first principles calculation of titanium alloy/steel by Nd: YAG laser self-fluxing welding

The experiment of Nd： YAG pulsed laser self-fluxing welding for 304 stainless steel/Ti6Al4V titanium alloy dissimilar metal was carried out. The microstructure properties of welded joint were analyzed by SEM, EDS and XRD. The equilibrium lattice constants, enthalpies of formation, cohesive energies, mechanical properties, Debye temperatures and valence electron structures of Ti-Fe intermetallic compounds （IMCs） were calculated by the first principle pseudopotential plane wave method based on density functional theory （DFT）. According to the thermodynamic data of Ti-Fe-Cr compounds, the Gibbs free energy per mole of compound at different temperatures was calculated and their thermal stability was compared. The results show that there are no macroscopic cracks in the welded joints, and the IMCs distributed evenly along the welding interface exhibits 3 distinct layers of microstructure with different colors. The welds interface generates IMCs of TiFe, TiFe 2 and a small amount of Ti 5Cr 7Fe 17 IMCs. Ti-Fe IMCs with high thermodynamic stability and easy alloying formation. The results of Gibbs free energies show that the sequence of precipitates in the interface is Ti 5Cr 7Fe 17 , TiFe 2 and TiFe in high temperature during the metallurgical reaction. The G/B values of Ti-Fe IMCs are greater than the critical value of 0.5, indicating that it is an intrinsic brittleness.

Laser stealth absorbent of samarium oxysulfide prepared by flux method

A novel 1064 tun laser stealth absorbent of SmzO2S was prepared by flux method. The effects of different calcining temperatures and fluxes on the reflective property of Sm2O2S were investigated. The phase composition, morphology, and reflectivity of the powders were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and ultraviolet-visible spectrophotometer （UVPC）. The results showed that pure phase of Sm202S could be obtained with Na2CO3 as flux above 950~C, and the reflectivity decreased with the calcination temperature increasing. Compared with other samarium compounds, the reflectivity at 1064 nm of Sm2O2S was the lowest. Different fluxes had great impact on the phase composition, particle morphology, and reflectivity of the products. In short, Sm2O2S was suitable as a kind of absorbent against 1064 nm laser.

Effects of activating flux on CO_2 laser welding process of 6013 Al alloy

In order to increase the absorption of laser energy and improve the weld appearance in laser welding of Al alloy, 1.8 mm- 6013 Al alloy plate was welded by activating flux CO2 laser welding. Activating flux includes oxide and fluoride, which was coated on the workpiece surface before welding. The experimental results show that the activating flux can effectively improve the absorption of CO2 laser energy and increase the amount of the molten base metal. The improvement on the absorption of laser energy by oxide activating flux is greater than that by fluoride activating flux or two-component activating flux, but the slag detachability made from both the single activating flux and two-activating flux is poor. The gas pore sensitivity with oxide activating flux is much higher than that with fluoride activating flux in CO2 laser welding of 6013 Al alloy.

Eruption of the Continental Flood Basalts at -259 Ma in the Emeishan Large Igneous Province, SW China: Evidence from Laser Microprobe ^(40)Ar/^(39)Ar Dating

A suite of continental flood basalts sampled over a vast exposure and stratigraphic thickness in the Emeishan large igneous province （LIP）, SW China was investigated for laser microprobe ^40Ar/^39Ar dating. There are two ^40Ar/^39Ar age groups for these basalts, corresponding to 259-246 Ma and 177-137 Ma, respectively. A well-defined isochron gives an eruption age of huge quantities of mafic magmas at 258.9±3.4 Ma, which is identical to previous dating and paleontological data. Much younger ^40Ar/^39Ar ages for some basalts with Iow-greenschist metamorphic facies probably recorded a late thermo-tectonic event caused by collision between the Yangtze and Qiangtang continental blocks during the Mesozoic, which resulted in the reset of argon isotope system. The ^40Ar/^39Ar age data, we present here, combined with previous dating and paleontological data, suggest relatively short duration （about 3 Ma） of mafic volcanism, which have important implication on mantle plume genesis of the Emeishan continental flood basalts in the LIP.

Sediment flux and source in northern Yellow Sea by ^(210)Pb technique

Sedimentation of fine-grained deposits on coastal zones and continental shelves are important because of the association with chemical pollutants, and the implication to the impact on biological processes, the stratigraphic correlations, and changes in sedimentary environments. The Yellow Sea continental shelf receives large quantities of sediment from the Huanghe （Yellow） River. Unfortunately, little attention has been yet paid to the sedimentation on the shallow shelf and its features, and the vertical sediment flux in the area is poorly understood. In this study, nine cores were collected in northern Yellow Sea by the R/V Science 1 in September, 1998 and 1999 to examine the sedimentation rate, sediment flux and the provenance with ^210Pb analysis. The 2^210Pb activity profiles showed that the vertical sediment flux ranged from 0.06 to 1.18 g/cm^2·a in the region. In central part of the area, there was a patch of fine-grained mud, with the flux below 0.33 g/cm^2·a. Most profiles were featured in two-segment model. Differences in the profiles reflected spatial and temporal variations in hydrodynamic and sedimentary processes. In order to determine the provenance and sedimentary setting in the area, the geochemistry of Ca, Fe, Sr, Cu, Ti and Rb in 11 surficial sediment samples were studied, which showed that in the central northern Yellow Sea, the mud deposit was from multi-source but mainly from the Huanghe River.

Research progress of laser cladding self-fluxing alloy coatings on titanium alloys

Laser cladding is a new surface modification technology, and is widely used for fabricating wear and corrosion resistant composites coatings. Self-fluxing alloys have many advantages, such as excellent properties of deoxidizing and slagging, high wear resistance, low melting point and easy cladding, and are often used in laser cladding to improve wear and corrosion resistance of titanium and its alloys. In this paper, the recent development of Ni-based and Co-based self-fluxing alloy coatings which includes the influenee of rare earth and ceramic particles in coatings are summarized. Besides, the effects of processing parameters, such as laser power and scanning speed, on coatings are reviewed. Finally, the trend of development in the future is forecasted.

Development of the active flux in superalloy laser welding and the effect on the weld formation

In this study,adopting uniform design method established a mathematical model to prepare multi-element active flux. GH4169 superalloy plates were welded by the Nd: YAG laser equipment with the prepared active flux. The results show all kinds of fluxes increase the depth to width ratio and the multi-component systems are more significant. The largest increment of the weld depth to width ratio is 159%,obtained by using of the F12 series flux. It is proved that by using of the active flux to increase the depth to width ratio of micro laser welding is feasible.

Applicability of an eddy covariance system based on a close-path quantum cascade laser spectrometer for measuring nitrous oxide fluxes from subtropical vegetable fields

The soil of subtropical vegetable fields is an important source of the atmospheric greenhouse gas nitrous oxide（N2O）. In a field study in subtropical China, the authors used an eddy covariance（EC）system based on a close-path quantum cascade laser（QCL） spectrometer to measure N2O fluxes from a vegetable field. During the experimental period from 9 October 2014 to 18 February 2015,the observed half-hourly N2O fluxes ranged from.10.7 to 1077.4 μg N m^-2h^-1, with a mean value of99.3 μg N m^-2h^-1. The detection limit（95% confidence level） of the EC system for half-hourly fluxes was estimated at 18.5 μg N m^-2h^-1, i.e. smaller than 97.5% of all measured fluxes, and within the range of the lower limit of reported N2O emissions from subtropical vegetable fields. The random uncertainties in the half-hourly fluxes were estimated at 60% on average, of which 62% was due to stochastic variations caused by turbulence and 38% by instrumental noise. The flux systematic uncertainties were estimated at.18% on average, mainly due to the spectral attenuation; however,this negative bias had already been corrected for by calculating half-hourly fluxes. In conclusion,the close-path QCL-based EC technique is capable of measuring the N2O fluxes from the subtropical vegetable fields of China with high reliability and accuracy.

High Heat Flux Testing of B_4C/Cu and SiC/Cu Functionally Graded Materials Simulated by Laser and Electron Beam

B4C, SiC and C, Cu functionally graded-materials (FGMs) have been developed by plasma spraying and hot pressing. Their high-heat flux properties have been investigated by high energy laser and electron beam for the simulation of plasma disruption process of the future fusion reactors, And a study on eroded products of B4C/Cu FGM under transient thermal load of electron beam was performed. In the experiment, SEM and EDS analysis indicated that B4C and SiC were decomposed, carbon was preferentially evaporated under high thermal load, and a part of Si and Cu were melted, in addition, the splash of melted metal and the particle emission of brittle destruction were also found. Different erosive behaviors of carbon-based materials (CBMs) caused by laser and electron beam were also discussed.

Particulate organic carbon export fluxes on Chukchi Shelf,western Arctic Ocean,derived from ^(210)Po/^(210)Pb disequilibrium

Fluxes of particulate organic carbon （POC） were derived from ^210Po/^210Pb disequilibrium during the 4th Chinese National Arctic Research Expedition （CHINARE-4） from July 1 to September 28, 2010. Average residence times of particulate ^210Po in the euphotic zone were -16.00 a to 1.54 a, which are higher than those of dissolved ^210^Po （-6.89 a to -0.70 a）. Great excesses of dissolved ^210Po were observed at all stations, with an average 210^Po/^210^Pb ratio of 1.91±0.20, resulting from 210^Pb atmospheric deposition after sea ice melt. POC fluxes from the euphoric zone were estimated by two methods （E and B） in the irreversible scavenging model. Estimated POC fluxes were 945-126 mmol C/（m^2·a）and 1 848-109 mmol C/（m^2·a） by methods E and B, respectively, both decreasing from low to high latitude. The results are comparable to previous works for the same region, indicating efficient biological pumping in the Chukchi Sea. The results can improve understanding of the carbon cycle in the western Arctic Ocean.

Vertical flux of particulate organic carbon in the central South China Sea estimated from ^(234)Th-^(238)U disequilibria

^(234)Th-^(238)U disequilibria were applied to examine the particle dynamics in the euphotic zone of the central South China Sea during the spring 2002 cruise.The particulate organic carbon (POC),^(234)Th (including both dissolved and particulate) and ^(238)U in the water column at three stations were determined. The profiles of ^(234)Th/^(238)U activity ratio at the three stations all showed consistent ^(234)Th deficit as compared to ^(238)U in the upper 100 m water column.Based on the profiles of the dissolved and particulate ^(234)Th and a steady state box model,the dissolved ^(234)Th scavenging rates,the particulate ^(234)Th removal rates and their resident times were quantified.It was found that the POC downward export fluxes out of the upper 100 m euphotic zone ranged from 9.40 to 14.78 mmol·m^(-2)·d^(-1).The results from this study provide new information for our understanding of carbon biogeochemical cycle in the South China Sea.

Influence of Flux and Sulfur on YAG Laser Welding

The influence of flux and sulfur content on YAG laser welding has been investigated, and the influencing factors and mechanism were discussed. The results show that both surface activating flux and surface active element S have fantastic effects on the YAG laser weld shape, that is to obviously increase the weld penetration and D/W ratio in various welding conditions. The mechanism is thought to be the change of surface tension temperature coefficient in weld pool, thus, the change of fluid flow paten in weld pool due to the flux and sulfur.

High-flux electron beams from laser wakefield accelerators driven by petawatt lasers

Laser wakefield accelerators （LWFAs） are considered to be one of the most compeuuve next- generation accelerator candidates. In this paper, we will study the potential high-flux electron beam production of an LWFA driven by petawatt-level laser pulses. In our three-dimensional particle-in-cell simulations, an optimal set of parameters gives -40 nC of charge with 2 PW laser power, thus -400 kA of instantaneous current if we assume the electron beam duration is 100 fs. This high flux and its secondary radiation are widely applicable in nuclear and QED physics, industrial imaging, medical and biological studies.

Tracing surface seawater mixing and nutrient transport by^(222)Rn on the northern coast of Beibu Gulf,China

The transport and diffusion of substances in seawater are limited by the mixing motion of water bodies,while the main forms of mixing in offshore water bodies are advection and eddy diffusion.The eddy diffusion process of water indicates the possible transport direction of dissolved substances.However,the complex environment in the coastal zone makes it difficult to quantitatively assess the water diffusion process.^(222)Rn is a useful tool to trace the diffusion process of water bodies.However,studies on the^(222)Rn distribution and its behavior in the Beibu Gulf are scarce.In this study,the activity distribution characteristics of^(222)Rn in surface seawater of the Guangxi shelf area of the Beibu Gulf were measured.Based on the one-dimensional,steady-state model,the vorticity diffusion coefficient of^(222)Rn in the horizontal direction was calculated as(0.42−2.13)×10^(8) m^(2)/d,and the offshore fluxes of^(222)Rn under the influence of water mixing were calculated as 2.00×10^(12) Bq/d.Correspondingly,the horizontal transport fluxes of silicate,phosphate,nitrite and nitrate were 6.28×10^(−3)mol/(m^(2)·d),0.10×10^(−3)mol/(m^(2)·d),0.20×10^(−3)mol/(m^(2)·d)and 4.15×10^(−3)mol/(m^(2)·d),respectively.These results indicate that the study of eddy current diffusion in offshore marine water facilitates a deeper understanding of the water mixing process and nutrient transport and migration.

An injection-locking diode laser at 671 nm with a wide tuning range up to 6 GHz

We present a compact injection-locking diode laser module to generate 671 nm laser light with a high output power up to 150 m W.The module adopts a master-slave injection-locking scheme,and the injection-locking state is monitored using the transmission spectrum from a Fabry-Perot interferometer.Beat frequency spectrum measurement shows that the injection-locked slave laser has no other frequency components within the 150-MHz detection bandwidth.It is found that without additional electronic feedback,the slave laser can follow the master laser over a wide range of 6 GHz.All the elements of the module are commercially available,which favors fast construction of a complete 671-nm laser system for the preparation of cold^(6)Li atoms with only one research-grade diode laser as the seeding source.

热流密度对高速钢刀具多道熔覆WC/Co陶瓷层组织与性能的影响

目的研究高速钢刀具表面激光多道熔覆WC/Co陶瓷层时,热流密度对熔覆层道次间的影响规律,以及多道熔覆层制备时的参数选择。方法建立多道单层激光熔覆理论模型,并利用模拟仿真和实验的方法,以热流密度作为评价指标,对激光热源的不同参数和熔覆层组织与性能进行耦合分析。结果当热流密度小于24.06×10^(6) W/m^(2)时,熔覆层内形成细长的枝状晶。当热流密度在36.09×10^(6)~39.82×10^(6) W/m^(2)变化时,熔覆层内形成以胞状、枝状为主要强化相的多晶体混合组织。当热流密度大于44.11×10^(6) W/m^(2)时,熔覆层组织形成稳态的块状结构。不同热流密度下,熔覆层的物相组织均由Fe_(3)W_(3)C、Co_(3)W_(3)C、Mo_(3)Co_(3)C、W_(2)C、WC、Cr_(3)Mo、(Cr,Fe)_(7)C_(3)和多种间隙化合物组成。结论当第n道熔覆层制备完成后,受到后续第n+1道熔覆层制备时热流密度的影响较大,而此后道次的影响较小。熔覆层内部组织形态随着热流密度的增加从细长的枝状晶向胞状晶转变,再逐渐形成稳态块状晶。熔覆层内各位置的显微硬度值随着热流密度的增加而先增大,随后逐渐减小。较大的热流密度会导致基材参与熔覆的质量增加,但降低了基材的抗弯曲强度,加大了熔覆层及基材断裂的可能性。当热流密度为36.09×10^(6) W/m^(2)时,是一组较为理想的工艺参数选择。

基于激光法的圆箔式热流传感器动态特性研究

为使圆箔式热通量传感器满足不断发展的高超声速风洞等极端环境中动态热通量监测需求,采用了大功率半导体激光器作为热通量源,搭建了热流动态标定平台,并对系统产生的激光束能量进行了测量分析,确保了后续实验的科学性与合理性。系统产生热流密度达每平方米兆瓦级别,脉冲激励宽度为毫秒级别。通过动态响应实验,研究了戈登计动态响应时间与激励激光参数的关系。结果表明,在一定范围内,时间常数与激光功率、脉冲宽度为负相关关系。当激光脉冲宽度小于传感器时间常数一个数量级附近时,可以被视为理想脉冲激励。同时还得到了激光参数与产生热通量的线性关系,证明了采用激光法进行测试标定的可行性。

Nd^(3+):KGd(WO_4)_2激光晶体的研究

合成了一系列不同Nd3+ 浓度掺杂的Nd3+ :KGd(WO4 ) 2 粉末样品 ,进行了荧光光谱测试 ,初步确定了Nd3+ 的最佳掺杂浓度 ;测定了Nd3+ :KGd(WO4 ) 2 K2 WO4 生长体系的生长温度曲线 ,生长出尺寸达 50mm的Nd3+ :KGd(WO4 ) 2 优质激光晶体 ,切割出尺寸为 5mm× 5mm× 6mm的优质激光器件 ,采用钛宝石模拟LD泵浦 ,在 1.0 6 μm处得到 2 6 0mW的激光输出 ,斜率效率达到 6 6 % ;在 1.0 3μm处得到 135mW激光输出 ,斜率效率达到 34.3%。