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%.

Study on Effect of Welding Speed on Micro Structure and Mechanical Properties of Pulsed Current Micro Plasma Arc Welded Inconel 625 Sheets

Nickel alloys had gathered wide acceptance in the fabrication of components which require high temperature resistance and corrosion resistance, such as metallic bellows used in expansion joints used in aircraft, aerospace and petroleum industry. Micro Plasma Arc Welding (MPAW) is one of the important arc welding processes commonly using in fabric- cation of Nickel alloys. In the present paper welding of Inconel 625 sheets using pulsed current micro plasma arc weld- ing was discussed. The paper mainly focuses on studying the weld quality characteristics like weld pool geometry pa- rameters, microstructure, grain size, hardness and tensile properties of Pulsed Current Micro Plasma Arc Welded In- conel 625 sheets at different welding speeds. Results reveals that at a welding speed of 260 mm/minute better weld quality characteristics can be obtained.

Study on Weld Quality Characteristics of Pulsed Current Micro Plasma Arc Welding of Inconel625 Sheets

Nickel alloys had gathered wide acceptance in the fabrication of components which require high temperature resistance and corrosion resistance, such as metallic bellows used in expansion joints used in aircraft, aerospace and petroleum industry. In the present paper an attempt is made to study various weld quality characteristics like weld bead geometry dimensions, micro hardness, microstructure, grain size and tensile properties of Pulsed Current Micro Plasma Welding of Inconel625sheets. Weld joint was prepared by fusing the two parent metals of Inconel625 sheets. Square butt joint is used and welding was carried out using Pulsed DCEN, without filler wire. Peak current, back current, pulse and pulse width are considered as the main influential input variables during the welding.

Effects of cathodic component of current on porosity and hardness characteristics of micro plasma oxidation(MPO) coatings on aluminum alloy

Micro plasma oxidation(MPO) has recently been investigated as a novel, rapid and effective means to provide modified surfaces with improved properties of load bearing and wear resistance on light alloys particularly aluminum alloys. MPO is a multifactor-controlled process, these factors must be controlled to produce high quality coatings. The main research emphasis in MPO coating development over the past years seems to be the attainment of higher hardness levels and thick coatings. The porosity of MPO coating is the most complex phenomenon affecting the distribution, levels and the measurements of the hardness; and it is controlled by suitable selection of important parameters such as the electrical conditions. Ceramics coatings were synthesized on Al substrate by MPO to examine the effects of adding a cathodic phase alternated with anodic-cathodic current on the porosity and hardness characteristics of coatings by X-ray diffraction(XRD), scanning electron microscopy(SEM), and microhardness tester. The coatings produced by the combined mode are more dense and less porous than that by the anodic-cathodic mode. (Microhardness) test shows that the coatings produced by the combined mode exhibit both the highest hardness, and less reduction percentage in hardness with increasing the coatings thickness. These improvements become more significant for the polished and thicker coatings.

Application of Hooke &Jeeves Algorithm in Optimizing Fusion Zone Grain Size and Hardness of Pulsed Current Micro Plasma Arc Welded AISI 304L Sheets

AISI 304L is an austenitic Chromium-Nickel stainless steel offering the optimum combination of corrosion resistance, strength and ductility. These attributes make it a favorite for many mechanical components. The paper focuses on developing mathematical models to predict grain size and hardness of pulsed current micro plasma arc welded AISI 304L joints. Four factors, five level, central composite rotatable design matrix is used to optimize the number of experiments. The mathematical models have been developed by Response Surface Method (RSM) and its adequacy is checked by Analysis of Variance (ANOVA) technique. By using the developed mathematical models, grain size and hardness of the weld joints can be predicted with 99% confidence level. The developed mathematical models have been optimized using Hooke and Jeeves algorithm to minimize grain size and maximize the hardness.

Study on Factors Effecting Weld Pool Geometry of Pulsed Current Micro Plasma Arc Welded AISI 304L Austenitic Stainless Steel Sheets Using Statistical Approach

Pulsed current Micro Plasma Arc Welding is used to joint thin sheets of AISI 304L sheets, which are used in manufacturing of metallic bellows and diaphragms. In this article the effects of pulsing current parameters on weld pool geometry namely front width, back width, front height and back height of pulsed current micro plasma arc welded AISI 304L stainless steel sheets was analyzed. Four factors, five levels, central composite design was used to develop mathematical models, incorporating pulsed current parameters and weld pool geometry. The mathematical models have been developed by Response Surface Method. The adequacy of the models was checked by ANOVA technique. Variation of output responses with input process variables are discussed. By using the developed mathematical models, weld pool geometry parameters can be predicted.

Effect of pulsed current micro plasma arc welding process parameters on fusion zone grain size and ultimate tensile strength of Inconel 625 sheets

The paper focuses on developing mathematical models to predict grain size and ul- timate tensile strength of pulsed current micro plasma arc welded Inconel 625 nickel alloy. Four factors, five levels, central composite rotatable design matrix is used to op- timize the number of experiments. The mathematical models have been developed by response surface method. The adequacy of the models is checked by analysis of vari- ance technique. By using the developed mathematical models, grain size and ultimate tensile strength of the joints can be predicted with 99% confidence level. Contour plots are drawn to study the interaction effect of pulsed current micro plasma arc welding parameters on fusion zone grain size and ultimate tensile strength of Inconel 625 weld joints.

Green hydrogen from bio-ethanol reforming using micro plasma

Hydrogen is a kind of energy source with a characteristic of high calorific value and plasma is regarded as a good method of hydrogen production.Hydrogen produced from ethanol reforming using micro plasma can be utilized for portable applications.The study introduces water/carbon ratio,residence time,and ethanol mass flow rate as the parameters of experimental conditions,and makes ethanol conversion,gas production rate,gas product selectivity,energy consumption,and efficiency of hydrogen production per unit as the evaluation parameters of ethanol reforming reaction.The experimental results showed that(1)in the argon micro plasma:the maximum ethanol conversion of 25.3%was obtained at residence time=2.1 ms,ethanol mass flow rate=0.01 g/s and S/C=1.0,and the peak value of hydrogen production of 18.7μmol/s was achieved at residence time=2.1 ms,ethanol mass flow rate=0.05 g/s and S/C=1.0;(2)in the air micro plasma:the maximum ethanol conversion of 37.4%was obtained at residence time=2.1 ms,ethanol mass flow rate=0.01 g/s and S/C=1.0,and the peak value of hydrogen production of 36.8μmol/s was achieved at residence time=2.1 ms,ethanol mass flow rate=0.03 g/s and S/C=3.0.These experimental results showed that the microreactor can substantially reduce the volume of the device while producing a large amount of output.

Micro-Plasma闪耀离子束治疗40例萎缩性痤疮瘢痕疗效观察

[背景]观察Micro-Plasma闪耀离子束治疗面部皮肤痤疮萎缩性瘢痕的临床疗效.[病例报告]给40例萎缩性痤疮瘢痕患者行Micro-Plasma闪耀离子束治疗,分别记录术前、第1,2,3次治疗后患者术后评价、术后皮肤反应、医师综合评测、不良反应等情况,并进行对比分析.均按照5级评分标准对疗效及患者满意度加以评估.结果见,利用Micro-Plasma闪耀离子束治疗痤疮萎缩性瘢痕疗效满意率为82.6%.[讨论]Micro-Plasma闪耀离子束治疗痤疮萎缩性瘢痕安全、有效.

Salt spray corrosion test of micro-plasma oxidation ceramic coatings on Ti alloy

Ceramic coatings were prepared on Ti-6Al-4V alloy in NaAlO2 solution by micro-plasma oxidation （MPO）. The salt spray tests of the coated samples and the substrates were carded out in a salt spray test machine. The phase composition and surface morphology of the coatings were investigated by XRD and SEAM. Severe corrosion occurred on the substrate surface, while there were no obvious corrosion phenomena on the coated samples. The coatings were composed of Al2TiO5 and a little α-Al2O3 and mille TiO2, and the salt spray test did not change the composition of the coatings. The weight loss rate of the coatings decreased with increasing MPO time because of the increase in density and thickness of the coatings. The surface morphology of the coatings was influenced by salt spray corrosion test. Among the coated samples, the coating prepared for 2 h has the best corrosion resistance under salt spray test.

Study of Multi-Function Micro-Plasma Spraying Technology

A multi-functional micro-arc plasma spraying system was developed according to aerodynamics and plasma spray theory. The soft switch IGBT （Insulated Gate Bipolar Transistor） invert technique, micro-computer control technique, convergent-divergent nozzle structure and axial powder feeding techniques have been adopted in the design of the micro-arc plasma spraying system. It is not only characterized by a small volume, a light weight, highly accurate control, high deposition efficiency and high reliability, but also has multi-functions in plasma spraying, welding and quenching. The experimental results showed that the system can produce a supersonic flame at a low power, spray Al2O3 particles at an average speed up to 430 m/s, and make nanostructured AT13 coatings with an average bonding strength of 42.7 MPa. Compared to conventional 9M plasma spraying with a higher power, the coatings with almost the same properties as those by conventional plasma spray can be deposited by multi-functional micro-arc plasma spraying with a lower power plasma arc due to an improved power supply design, spray gun structure and powder feeding method. Moreover, this system is suitable for working with thin parts and undertaking on site repairs, and as a result, the application of plasma spraying will be greatly extended.

Methane conversion into higher hydrocarbons with dielectric barrier discharge micro-plasma reactor

We reported a coaxial,micro-dielectric barrier discharge(micro-DBD)reactor and a conventional DBD reactor for the direct conversion of methane into higher hydrocarbons at atmospheric pressure.The effects of input power,residence time,discharge gap and external electrode length were investigated for methane conversion and product selectivity.We found the conversion of methane in a micro-DBD reactor was higher than that in a conventional DBD reactor.And at an input power of 25.0 W,the conversion of methane and the total C2+C3 selectivity reached 25.10% and 80.27%,respectively,with a micro-DBD reactor of 0.4 mm discharge gap.Finally,a nonlinear multiple regression model was used to study the correlations between both methane conversion and product selectivity and various system variables.The calculated data were obtained using SPSS 12.0 software.The regression analysis illustrated the correlations between system variables and both methane conversion and product selectivity.

Compounded Surface Modification of ZK60 Mg Alloy by High Current Pulsed Electron Beam+Micro-plasma Oxidation

In this study, compounded surface modification technology-high current pulsed electron beam （HCPEB） ＋ micro-plasma oxidation （MPO） was applied to treat ZK60 Mg alloys. The characteristics of the microstructure of ZK60 Mg alloy after single MPO and HCPEB＋MPO compounded treatment were investigated by SEM. The results showed that the density of the ceramic layer of HCPEB＋MPO-treated ZK60 Mg alloy was improved and defects were reduced compared to that under MPO treatment alone. Surface modified layer of ZK60 Mg alloys treated by HCPEB＋MPO was divided into three zones, namely the top loose ceramic zone, middle compact zone and inside HCPEB-induced melted zone. Corrosion resistance of ZK60 Mg alloy before and after the compounded surface modification was measured in a solution of 3.5% NaCl by potentiodynamic polarization curves. It was found that the corrosion current density of ZK60 Mg alloys could be reduced by about three orders of magnitude, from 311μA/cm^2 of the original sample to 0.2μA/cm^2 of the HCPEB＋MPO-treated sample. This indicates the great application potential of the HCPEB＋MPO compounded surface modification technology in improving the corrosion resistance of ZK60 Mg alloys in the future.

Treatment of Invasive Marine Species on Board by Using Micro-gap Discharge Plasma

A pilot-scale experiment of 20t/h for the treatment of ship＇s ballast water is reported in this paper. When the concentration of the dissolved OH. was 0.68 mg/L during the experiment, the rate of destroying bacteria, mono-algae, protozoan reached 100% within 2.67 s. The effect of hydroxyl radicals on biochemical processes was also studied. The attenuation rate of photosynthesis pigment was 100%. And the main reason for the cells＇ death was the strong destruction of the monose, amylose, protein, DNA and RNA in the cells. As an advanced oxidation method, the procedure can destroy invasive marine species when a ship is in the process of discharging its ballast water.

Compound Ceramic Coatings on Ti-6Al-4V by Micro-Plasma Oxidation in NaAlO_2 Solution

Micro-plasma oxidation (MPO) technique is a new technique by which compound ceramic coating can be grown in situ on Al, Ti, Mg and many other valve-metals. Compound ceramic coatings on Ti-6Al-4V alloy were prepared for different time by pulsed bi-polar MPO in NaAlO2 solution. The phase composition, morphology and the element distribution of the coatings were studied by XRD, SEM and JEOL SUPERPROBE 733 electric probe, respectively. Electrochemical Impedance Spectra (EIS) of the coatings were measured to study the structure character of the coatings. Through the proper EIS interpreting software, the "equivalent circuit" of the coatings was established, and the fitting values of equivalent element were calculated. The coating is mainly composed of Al2TiO5, a-A12O3 and rutile TiO2. The content of Ti element in the coating is less than that of substrate; its distribution is relatively uniform, and Ti in the outer layer is less than that in the inner layer. The content of Al in the coating is more than that of substrate, and its distribution is not even: Al in the middle part is more than that on both sides of the coating; And the EIS analysis has illustrated the double-layer structure of the coatings, and the outside layer is loosen and the inner layer compact; with the increase of the oxidizing time, the surface roughness of the coatings, and the porosity of the outer layer of the coating are increased while the compactness of the inner layer of the coatings are improved.

Effect of Spraying Parameters on the Microstructure and Mechanical Properties of Micro-Plasma Sprayed Alumina-Titania Coatings

Electrical property of a micro-plasma spray system with different working-gas feed- ing schemes was tested to optimize the plasma spray process. The arc voltage with an integrated gas injection mode is higher than that with radial injection or axial injection modes. Thus, an integrated gas injection mode with an excellent electrical characteristic was adopted to deposit alumina-titania coating. The microstructure, bonding strength and hardness of the plasma sprayed alumina-titania coating, as a function of the spraying parameters, e.g., plasma current, gas flow rate and gas pressure, were studied. It was shown that the spraying parameters affected remarkably on the microstructure of the coating. Different tendencies in bonding strength and hardness were also shown for different spraying parameters. At an arc current of 250 A, a gas flow rate of 20 L/min and a gas pressure of 0.5 MPa, the bonding strength and micro-hardness of the coatings reach 40.6 MPa and HV1406.1, respectively.

Compound Ceramic Coatings Grown by Micro-plasma Oxidation on Ti-6Al-4V Alloy

Compound ceramics coatings on the Ti-6Al-4V alloy were prepared by the direct current micro-plasma oxidation （MPO） in NaAlO2 solution. The composition and morphology of the coatings were studied with the X-ray diffraction （XRD） and the scanning electron microscopy （SEM）, respectively. Inductively coupled plasma atomic emission spectrometer technique was used to analyze the solution features of Ti-6Al-4V alloy in the process of preparation. The results reveal that Al2TiO5 forms in the coatings at the initial stages of MPO reaction, and its content changes rapidly with the reaction continuing： after 20 min, the ceramics coatings are composed of α-Al2O3, 7-Al2O3 and Al2TiO5, but after 40 min, its main composition is of α-Al2O3. The content of Ti in the solution will increase when the MPO time extends, and as will Al in the anode area until, after 30 min, it reaches the maximum and keeps constant from then on. Both substrata of Ti and Al in the electrolyte join the MPO reaction at the initial stage, where the formation of Al2TiO5 happens; but as the MPO reaction prolongs, more and more Al in the electrolyte will take part in the reaction, leading to the appearance of a large amount ofAl2O3.

冷等离子体和微量润滑复合微铣削铝锂合金的表面性能研究

铝锂合金的延展性造成材料对刀具的粘附,会导致毛刺和积屑瘤等问题产生。为此,采用冷等离子体和微量润滑复合微铣削的方法加工铝锂合金,研究了工件的表面性能,并与单纯的干式、冷等离子体和微量润滑方法进行了对比。结果表明冷等离子体不仅改善了纳米流体在工件表面的浸润性,而且提高了材料的去除效率;相比于单纯的干式、冷等离子体和微量润滑方法,冷等离子体和微量润滑复合条件下的微铣削力分别降低了52.9%、42.9%和17.5%,而三维表面粗糙度Sa分别降低了67.3%、44.8%和33.3%。

新型KTN衬底上生长金刚石及其光催化性能研究

采用微波等离子体化学气相沉积技术,以钽铌酸钾(KTa1-xNbxO3,简称KTN)作为衬底,生长高质量金刚石薄膜。用X射线衍射仪、扫描电子显微镜和拉曼光谱仪观察并分析金刚石薄膜的表面形貌和微观结构,并研究样品的光催化性能。结果表明:金刚石生长过程中形成了碳化钽过渡层;随着生长时间延长金刚石质量不断提高;所有样品均表现出良好的降解罗丹明B的能力,其中生长时间为12 h的样品对罗丹明B的降解效率提高了0.29倍,与生长时间为3 h的样品相比其降解效率提高了1.6倍。本研究为生长多晶金刚石提供新型衬底,并探索金刚石在光催化方面的应用。

航空发动机叶片微束等离子堆焊转角焊缝模型研究

航空发动机叶片修复时,将受损部位切除后在新平面上进行多层多道焊接,在焊缝转角区域特别是转角点,因焊接工艺难以匹配导致过多熔滴进入熔池增加了焊缝熔高与熔宽,造成焊缝凸起,影响焊接质量。针对微束等离子焊接叶片转角区域焊缝的这种特征,建立了转角区域焊缝模型。首先利用抛物线曲线拟合建立了单道焊缝模型,并通过实验验证该模型能准确地表征单缝外形轮廓。然后提出了一种双焊缝转角重叠的焊缝成型模型。实验表明,采用该转角焊缝模型能够极大地降低转角区域焊缝的凸起,能满足航空发动机叶片修复精度的要求。