激光熔覆MoSi_(2)颗粒增强Co基涂层的耐磨性能研究

奥氏体不锈钢因低硬度和较差耐磨性限制了其应用,故改善不锈钢表面性能对于促进其应用有重要的工程意义。利用激光熔覆技术制备了不同质量分数(0,20%,40%)的MoSi_(2)增强Co基合金的复合涂层。采用扫描电镜(SEM)、X射线衍射仪(XRD)、电子探针显微分析仪(EPMA)等方法研究了MoSi_(2)的添加量对复合涂层的显微组织、相组成、硬度和摩擦磨损性能的影响。结果表明:MoSi_(2)的加入使复合涂层显微组织柱状晶向等轴晶和平面树枝晶转变,且具有细化组织的效果;随着MoSi_(2)含量的增加,Co基复合涂层的显微硬度和耐磨性能也随着提高。当MoSi_(2)的含量为40%时,MoSi_(2)/Co基复合涂层的显微硬度高达1455HV_(0.2),磨损率为6.9×10^(-5) mm^(3)/(N·m);在凝固过程中形成的硬质相(Cr_(5)Si_(3)、MoSi_(2)、Mo_(5)Si_(3)和Co_(2)Mo_(3))和(Fe、Cr、Co)Si_(2)新型固溶体显著提高复合涂层的耐磨性能;MoSi_(2)增强Co基合金涂层的磨损机制随着MoSi_(2)含量的增加发生转变,即由磨粒磨损、黏着磨损和塑性变形的协同作用转变为黏着磨损、脆性微断裂和氧化磨损。

激光熔覆Co-2%Ti_(3)SiC_(2)复合涂层在不同温度及载荷下的摩擦学性能

为了提高304不锈钢的耐磨减摩性能,采用激光熔覆技术在其表面制备了Co-2%Ti_(3)SiC_(2)复合涂层。通过扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)对Co-2%Ti_(3)SiC_(2)复合涂层的微观结构进行表征,并分析了304不锈钢基体与Co-2%Ti_(3)SiC_(2)复合涂层在等温摩擦实验(25和600℃)中不同载荷(2、5和8 N)下的摩擦学性能和磨损机理。结果表明:Co-2%Ti_(3)SiC_(2)复合涂层主要由γ-Co固溶体,硬质相Fe_(2)C、Cr_(7)C_(3)和TiC及润滑相Ti_(3)SiC_(2)组成。Co-2%Ti_(3)SiC_(2)复合涂层的平均显微硬度为358.61 HV0.5,约是304不锈钢基体(239.32 HV0.5)的1.5倍。在等温摩擦实验中,Co-2%Ti_(3)SiC_(2)复合涂层的磨损率均随着载荷的增加而减少,而摩擦系数在室温下随载荷的增加先增大后减小,在高温(600℃)下随载荷的增加而减小。在不同温度及载荷下,Co-2%Ti_(3)SiC_(2)复合涂层的磨损机理略有不同。

CO_2 laser-micro plasma arc hybrid welding for galvanized steel sheets

A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal, which is steel. In the autogenous laser welding, the zinc vapor generates from the lapped surfaces expels the molten pool and the expulsion causes numerous weld defects, such as spatters and blow holes on the weld surface and porosity inside the welds. The laser-arc hybrid welding was suggested as an alternative method for the laser lap welding because the arc can preheat or post-beat the weldment according to the arrangement of the laser beam and the arc. CO2 laser-micro plasma hybrid welding was applied to the lap welding of zinc-coated steel with zero-gap. The relationships among the weld quality and process parameters of the laser-arc arrangement, and the laser-arc interspacing distance and arc current were investigated using a full-factorial experimental design. The effect of laser-arc arrangement is dominant because the leading plasma arc partially melts the upper steel sheets and vaporizes or oxidizes the coated zinc on the lapped surfaces. Compared with the result from the laser-TIG hybrid welding, the heat input from arc can be reduced by 40%.

A study on the porosity of CO_2 laser welding of titanium alloy

The CO2 laser welding of BT20 titanium alloy and Ti-23Al-17Nb titanium aluminide was conducted to investigate into the porosity in titanium alloy weld. The results show that there are two sorts of porosities observed in welds of titanium alloy laser welding based on the microscopic characteristics of the porosities. One is the metallurgical porosity with round and smooth inner wall, which results from the surface contamination. The other is the processing porosity with irregular and rough inner wall that displays the trace of the pool flowing, which results from the ruffle on the keyhole wall gathering together locally and closing down the gas in the keyhole into bubbles because of the keyhole fluctuating. The CO2 laser welding could break down easily the surface oxide film and produce little metallurgical porosity, but produces easily processing porosity when partial penetration or unstable-full penetration laser welding is conducted, which always occurs in the center of weld.

Behavior of vapor/plasma within the keyhole and above the workpiece during CO_2 laser penetration welding

In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma show that two characteristic frequency bands exist, 100 -500 Hz and 1 500 -3 500 Hz. At the same time, the changing images of vapor/ plasma and bottom pool also confirm that there are two different fluctuation frequency bands. One of the frequency bands represents the characteristic of vapor/plasma within the keyhole, and it is within 167 -500 Hz. Another frequency band is within 1 500 - 3 500 Hz, and it obviously derives from the shielding gas. Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma. One of them is that the vapor/plasma pressure within the keyhole will increase slowly.

Macrostructural and microstructural features of 1000 MPa grade TRIP steel joint by CO_2 laser welding

Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.

Irradiation effects of CO_2 laser parameters on surface morphology of fused silica

To understand the surface morphology evolution of fused silica induced by 10.6μm CO2 laser irradiation at different parameters, this paper reports that optical microscopy, profilometry, and hydrophilicity tests are utilized to characterize the surface structure and roughness of the laser irradiated area. The results show that three typical surface morphologies and two typical hydrophilicity test images are observed at different laser powers and pulse durations. The correlations between surface temperature and surface morphology as well as hydrophilicity behaviours are presented. The different hydrophilicity behaviours are related to surface structures of the laser-induced crater and thermal diffusion area. The thermal diffusion length monotonously increases with increasing laser power and pulse duration. The crater width is almost determined by the laser beam size. The crater depth is more sensitive to the laser power and pulse duration than the crater width.

Multipass welding of thick section steels using autogenous CO2 laser welding and CO2 laser-MIG hybrid welding

Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavior using high speed photographic equipment. A stable autogenous CO2 laser welding process and greater penetration are generated at the root pass because of strong reduction of the plasma volume. According to the waveforms of welding current and arc voltage, and the interaction between the arc and the laser induced plasma, a suitable groove angle is obtained. Laser-double MIG hybrid welding process is studied and the optimum distances between the laser and two arcs are determined. By using autogenous CO2 laser welding, CO2 laser-MIG hybrid welding and laser-double MIG hybrid welding, 28 mm thick steel plates are welded with four passes. The welds produced are assessed by X-ray. No crack is found and there is only a small amount of pores. The experimental results show that the multipuss welding procedures proposed can realize the joining of thick section steels with high efficiency and good quality.

CO_2 Laser Collective Thomson Scattering Diagnostics on the HT-7 Tokamak

A CW CO2 laser collective Thomson scattering diagnostics was developed to measure plasma density fluctuations on the HT-7 tokamak. The design and construction of CO2 laser scattering apparatus is described. The laser source is a continuous-wave CO2 laser with a cavity length of 1.9 m and a power output of about 10 W at 10.6 μm. The k-resolution of the system is △k ≈ 3.2 cm-1. The preliminary data from the diagnostic is presented.

IR Spectra Analysis of SiO_2-TiO_2-GeO_2 Gel Glass of CO_2 Laser Transmitting Hollow Waveguide

Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO 2 laser.It is indicated by IR absorption spectra that as the content of SiO 2 decreases in this glass system TiO 2 and GeO 2 tends to exist in their own phases.As for the gel glass with a composition of 40SiO 2·30TiO 2·30GeO 2,when the temperature is below 600℃,germanium atoms exist mainly in Ge-O-Ge bonds.With the temperature increasing from 800℃ to 1000℃, titanium atoms in Si-O-Ti bonds almost transform into Ti-O-Ti bonds.Furthermore,a large number of Si-O-Ti and Si-O-Ge bonds formed when the temperature approaches 800℃,which makes a notable IR absorption band round the wavelength of CO 2 laser.Therefore, sol-gel based SiO 2-TiO 2-GeO 2 gel glass is a candidate material for CO 2 laser hollow waveguide.

Spectral Efficiency of Extreme Ultraviolet Emission from CO_2 Laser-Produced Tin Plasma Using a Grazing Incidence Flat-Field Spectrograph

A grazing incidence flat-field spectrograph using a concave grating was constructed to measure extreme ultraviolet （EUV） emission from a CO 2 laser-produced tin plasma throughout the wavelength region of 5 nm to 20 nm for lithography. Spectral efficiency of the EUV emission around 13.5 nm from plate, cavity, and thin foil tin targets was studied. By translating the focusing lens along the laser axis, the dependence of EUV spectra on the amount of defocus was investigated. The results showed that the spectral efficiency was higher for the cavity target in comparison to the plate or foil target, while it decreased with an increase in the defocus distance. The source＇s spectra and the EUV emission intensity normalized to the incident pulse energy at 45 from the target normal were characterized for the in-band （2% of bandwidth） region as a function of laser energy spanning from 46 mJ to 600 mJ for the pure tin plate target. The energy normalized EUV emission was found to increase with the increasing incident pulse energy. It reached the optimum value for the laser energy of around 343 mJ, after which it dropped rapidly.

Effect of CO_2 laser sclerectomy with iridectomy on ocular hypertension in rabbits

AIM:To evaluate the efficiency and safety of an optimized CO2 Laser glaucoma surgery system for laser sclerectomy with iridectomy.METHODS:Rabbit trials were performed to evaluate the efficiency and safety.RESULTS:IOP was significantly decreased in laser group compared with trabeculectomy group(P<0.05) from 7th postoperative day to 60th day.Compared with trabeculectomy group,histopathology studies confirmed fewer complications and better effects were found in laser group.CONCLUSION:CO2 laser sclerectomy with iridectomy is effective and safe in terms of IOP lowering.

Output mode characteristics of an in-phase locked gain waveguide array CO_2 laser

In this paper, experimental and theoretical studies of the output mode characteristics of an in-phase locked gain waveguide array CO2 laser are reported. The experimental results of the optical oscillation mode frequency, the far-field intensity distribution and the burnt pattern of the sliced waveguide array laser are obtained. A revised mode expression of the rectangle waveguide, which is suited for this waveguide array CO2 laser, is proposed. The theoretical simulation results based on the revised mode expression are shown to be in good agreement with the experimental results.

Mathematical modeling of output power in RF-excited CO_2 waveguide lasers

Theoretical analysis model has been established for CO 2 laser to describe the process of dynamic emission in the electrooptically Q switched laser .The electron excitation and the energy transfer of vibration level and the rotational relaxation of rotational levels are described. The comparison between this model and a set of coupled rat equations model are discussed.

CALCULATION OF INFRARED OPTICAL CONSTANTS FOR CO_2 LASER HOLLOW WAVEGUIDE MATERIALS

A simple method was deduced for calculat-ing optical constant, optical loss and transmittance per meter of hollow-core optical fiber using data analysis method, ge-ometerical optical and electromagnetic theory. The method was used to study the Na2O-ZnO-GeO2-SiO2-PbO and Sb2O3 sysem. The glasses have nr<1 region. When the core diameter ao is 0. 5mm, the hollow waveguides of the Sb2O3-containing . glass is predicted with minimum loss of 0. 8 dB/m at 940cm-1

Tunable RF excited waveguide CO-2 laser with two unequal long channels

Presents a waveguide CO 2 laser with two unequal long channels excited by radio frequency (RF) which has more than 30 laser lines from a long channel of 400 mm with grating, and 3 laser lines from a short channel of 200 mm by PZT.

THE SUPPORTED GOLD CATALYSTS FOR CLOSED CYCLE CO_2 LASER

Sealed-off carbon dioxide lasers encounter problem of dissociation of CO2, Which causes the output power to fall. Reformation of CO2 is therefore essential for long life CO2 lasers. Au/Fe2O3 and Au/NiFe2O4 are promising candidates for this application.

Effects of RFTVR and CO2 laser on symptoms improvement, QOL and vas of patients with early laryngeal cancer

Objective: To study the effect of RFTVR and CO2 laser on the improvement of symptoms, QOL and vas of patients with early laryngeal cancer. Methods: In this study, 120 patients with laryngeal cancer diagnosed and treated from January 2015 to December 2016 were taken as research objects. All patients were randomly divided into observation group and control group, 60 patients in each group. Patients in observation group were treated with RFTVR, and patients in control group were treated with new-type fiber-optic CO2 laser. The patients in the two groups were treated with cisplatin injection. The differences of perioperative indexes, swallowing function, pronunciation function, survival period, QOL score and VAS score between the two groups were compared. Results: There was no significant difference in the amount of intraoperative bleeding, operation time and hospitalization time between the two groups (P > 0.05);the correct swallowing of the observation group was significantly higher than that of the control group. After treatment, jitter, shimmer and HNR of the two groups were significantly improved, and jitter and shimmer of the observation group were significantly lower than that of the control group, and HNR was significantly higher than that of the control group (P < 0.05) The QOL score and VAS score of the two groups were significantly improved, and the QOL score of the observation group was significantly higher than that of the control group and the VAS score was significantly lower than that of the control group (P < 0.05);the total survival period and tumor free survival period of the observation group were significantly higher than that of the control group. Conclusion: Compared with CO2 laser treatment, the swallowing function and voice function of patients treated by low temperature plasma radiofrequency ablation were significantly improved, and the life quality of patients was significantly improved by prolonging the survival period of patients..

Effects of CO_2 laser on chromosomal aberration in the root tip cells of rice

Seeds of japonica rice cv.Zhenuo 2 with twodifferent physiological states(dry seeds withwater content 13% and wet seeds soaked in thewater for 36 h)were irradiated by COlaser infour different power-densities and durations re-spectively.The treatment irradiated with 200GY ofCo γ-rays was considered as control.The flesh root tips were cut and fixed inCarnoy’s fluid for cytological examination.

Observation on clinical effect of botulinum toxin type A injection combined with low-energy CO2 fractional laser periocular rejuvenation treatment

Objective To investigate the clinical effect of botulinum toxin type A injection combined with low-energy CO2 fractional laser periocular rejuvenation treatment.Methods The clinical effect of botulinum type A injection alone and botulinum type A injection combined with low-energy CO2 fractional laser was compared in 96 patients who needed to receive periocular rejuvenation treatment from April 2018 to April 2019.Results After the combined low-energy CO2 fractional laser treatment was given on the basis of botulinum toxin type A injection,the follow-up global aesthetic improvement scale(GAIS)scores of the observation group were 86.78±4.67,80.31±3.66,76.94±4.03 and 40.59±4.78.The global aesthetic improvement of the dynamic and static wrinkles was obvious.The total effective rate was 93.7%.The total satisfaction rate of the patients was 95.8%,which was higher than that of the control group(P<0.05).The clinical efficacy was significant.Conclusion The application of the combined periocular rejuvenation treatment can improve the dynamic and static wrinkles simultaneously with remarkable rejuvenation effect,increase the effective rate of treatment and enhance the patients'satisfaction.