Influence of high frequency pulse on electrode wear in micro-EDM

An electromagnetic coupling mathematical model is established by finite element method and is verified by the contrastive experiments of copper matrix Ni-TiN cylindrical coating electrode,copper electrode and Cu50 W electrode.The wear mechanism of Ni-TiN/Cu composite electrode in the case of high-frequency pulse current is studied,and the influence of the fluctuation frequency of discharge current on electrode wear in micro-EDM is found out.Compared with the electrode made from homogeneous material,the high frequency electromagnetic properties of Ni-TiN composite layer can be used effectively to inhibit the effect of high frequency pulse on the electrode and improve the distribution trend of current density.

Ni doped La_(0.6)Sr_(0.4)FeO_(3-δ) symmetrical electrode for solid oxide fuel cells

The conventional Ni cermet anode suffers from severe carbon deposition and sulfur poisoning when fossil fuels are used. Alternative anode materials are desired for high performance hydrocarbon fuel solid oxide fuel cells （SOFCs）. We report the rational design of a very active Ni doped La0.6Sr0.4FeO3‐δ（LSFN） electrode for hydrocarbon fuel SOFCs. Homogeneously dispersed Ni‐Fe alloy nanoparticles were in situ extruded onto the surface of the LSFN particles during the operation of the cell. Sym‐metric SOFC single cells were prepared by impregnating a LSFN precursor solution onto a YSZ （yt‐tria stabilized zirconia） monolithic cell with a subsequent heat treatment. The open circuit voltage of the LSFN symmetric cell reached 1.18 and 1.0 V in humidified C3H8 and CH4 at 750？？, respective‐ly. The peak power densities of the cells were 400 and 230 mW/cm2 in humidified C3H8 and CH4, respectively. The electrode showed good stability in long term testing, which revealed LSFN has good catalytic activity for hydrocarbon fuel oxidation.

Effect of electrode wear on weld nugget formation in resistance spot welding of magnesium alloy

The effect of electrode wear on the formation and growth of weld nugget in resistance spot welding of AZ31B Mg alloy was studied by an axisymmetric finite element model, employing a contact resistance model based on the micro-contact theory. The results show that electrode wear causes the growth of electrode tip diameter, which leads to the current density and temperature at the sheet/sheet interface reduced and diameter of nugget decreased, has been shown to be dominant in determining the deterioration in weld quality. Alloying and pitting at electrode surface decrease the electric conduction of electrode, resulting in non-uniform distribution of temperature and current density and contribution to the further damage, at the same time initiate expulsion and electrode sticking during welding process and worse the quality of weld.

Effect of Electrode Materials on Electric Discharge Machining of 316 L and 17 - 4 PH Stainless Steels

Electric Discharge Machining (EDM) is one of the most efficiently employed non-traditional machining processes for cutting hard-to-cut materials, to geometrically complex shapes that are difficult to machine by conventional machines. In the present work, an experimental investigation has been carried out to study the effect of pulsed current on material removal rate, electrode wear, surface roughness and diameteral overcut in corrosion resistant stainless steels viz., 316 L and 17-4 PH. The materials used for the work were machined with different electrode materials such as copper, copper-tungsten and graphite. It is observed that the output parameters such as material removal rate, electrode wear and surface roughness of EDM increase with increase in pulsed current. The results reveal that high material removal rate have been achieved with copper electrode whereas copper-tungsten yielded lower electrode wear, smooth surface finish and good dimensional accuracy.

La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3)-δ−Ce_(0.8)Gd_(0.2)O_(1.9) composite electrodes as anodes in LaGaO_(3)-based direct carbon solid oxide fuel cells

Direct carbon solid oxide fuel cells(DC-SOFCs)are promising,green,and efficient power-generating devices that are fueled by solid carbons and comprise all-solid-state structures.Developing suitable anode materials for DC-SOFCs is a substantial scientific challenge.Herein we investigated the use of La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3)-δ−Ce_(0.8)Gd_(0.2)O_(1.9)(LSCM−GDC)composite electrodes as anodes for La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3)-δelectrolyte-based DC-SOFCs,with Camellia oleifera shell char as the carbon fuel.The LSCM−GDC-anode DC-SOFC delivered a maximum power density of 221 mW/cm^(2) at 800℃ and it significantly improved to 425 mW/cm^(2) after Ni nanoparticles were introduced into the LSCM−GDC anode through wet impregnation.The microstructures of the prepared anodes were characterized,and the stability of the anode in a DC-SOFC and the influence of catalytic activity on open circuit voltage were studied.The above results indicate that LSCM–GDC anode is promising to be applied in DC-SOFCs.

Electrochemical Behavior and Its Electrocatalytic Activity of A P-Mo Heteropolyanion Modified ITO Electrode

s: A new method for the preparation of an organic-inorganic composite film of the heteropolyanion has been developed by modifying P(Mo2O7)6-7 to the indium tin oxide (ITO) electrode surface. The modified electrode displayed a strong catalytic activity towards the reduction of IO3-. In the range of 1.0?0-6~5?0-4mol/L, the catalytic current was linear proportional to the IO3- concentration.

Development of new type of wear and crack resistant hardfacing electrode

By using H08A bare electrode and the coating fluxes of ferrotitanium,rutile,gr aphite,calcium carbonate and calcium fluoride,a new type of wear and crack res istant hardfacing electrode was developed. The microstructure and wear propertie s of deposited layer were studied by means of scanning electron microscopy (SEM),transmission electron microscopy (TEM),X-ray diffractometry(XRD) and wear te st. The results indicate that TiC particles are produced by direct metallurgical reaction between ferrotitanium or rutile and graphite during welding process. T iC particles with sizes in the range of 35 μm are dispersed in the mat rix of lath martensite and retained austenite. The deposited layer of the new ty pe of hardfacing electrode possesses better wear and crack resistance than that of D618 and D667 hardfacing electrodes.

A novel scrape-applied method for the manufacture of the membrane-electrode assembly of the fuel-cell system

This study investigates the transfer of the scrape-applied method from the electrodes of a lithium battery to the membrane-electrode assembly of fuel cells, including Proton Exchange Membrane Fuel Cells and Direct Methanol Fuel Cell. Three methods are commonly used to manufacture lithium battery electrodes： the roller-applied method, the spraying-applied method, and the scrape-applied method. This study develops novel scrape-applied equip- ment for lithium battery electrodes. This method is novel and suitable for producing fuel cell, better than other tradi- tional methods. In this study, the stability of coating process was tested by measuring the weight and thickness of a dry electrode. The stability and reproducibility of electrode fab- rication were examined by systematic data analysis. Finally, the study used a specially designed single cell composed of 16 conductive segments, which are insulated locally. The current passing through each segment was measured using Hall Effect sensors connected to the segment compartments. Based on the measured distribution of the local current in a segmented single cell, the influence of flooding and stoi- chiometry variation of feed gas was discussed in terms of electrochemical reaction rate. The experimental results serve as an important basis for future research in this field, which hold potential benefits to the academia and the industry.

HIGH SPEED MILLING OF GRAPHITE ELECTRODE WITH ENDMILL OF SMALL DIAMETER

Graphite becomes the prevailing electrode material in electrical discharging machining （EDM）currently.Orthogonal cutting experiments are carried out to study the characteristics of graphite chip formation process.High speed milling experiments are conducted to study tool wear and cutting forces.The results show that depth of cut has great influence on graphite chip formation.The removal process of graphite in high speed milling is the mutual result of cutting and grinding process. Graphite is prone to cause severe abrasion wear to coated carbide endmills due to its high abrasiveness nature.The major patterns of tool wear are flank wear,rake wear,micro-chipping and breakage. Cutting forces can be reduced by adoption of higher cutting speed,moderate feed per tooth,smaller radial and axial depths of cut,and up cutting.

A micromechanical model for efective conductivity in granular electrode structures

Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells （SOFC） and lithium-ion batteries （LIB）. For this, the porous electrode structures of both SOFC and LIB are modeled as a binary mixture of electronic and ionic conducting particles to estimate effective transport properties. Particle packings of 10000 spherical, binary sized and randomly positioned particles are created numerically and densified considering the different manufacturing processes in SOFC and LIB： the sintering of SOFC electrodes is approximated geometrically, whereas the calendering process and volume change due to intercalation in LIB are modeled physically by a discrete el- ement approach. A combination of a tracking algorithm and a resistor network approach is developed to predict the con- nectivity and effective conductivity for the various densified structures. For SOFC, a systematic study of the influence of morphology on connectivity and conductivity is performed on a large number of assemblies with different compositions and particle size ratios between 1 and 10. In comparison to percolation theory, an enlarged percolation area is found, es- pecially for large size ratios. It is shown that in contrast to former studies the percolation threshold correlates to varying coordination numbers. The effective conductivity shows not only an increase with volume fraction as expected but also with size ratio. For LIB, a general increase of conductivity during the intercalation process was observed in correlation with increasing contact forces. The positive influence of cal- endering on the percolation threshold and the effective conductivity of carbon black is shown. The anisotropy caused by the calendering process does not influence the carbon black phase.

Evaluation of Microstructure and Wear Properties of Ti-6Al-4V Alloy Plasma Carbonized at Different Temperatures

Ti-6A1-4V （TC4） alloys were plasma carbonized at different temperatures （900, 950, and 1 000 ℃） for duration of 3 h. Graphite rod was employed as carbon supplier to avoid the hydrogen brittleness which is ubiquitous in traditional gas carbonizing process. Two distinguished structures including a thin compound layer （carbides layer） and a thick layer with the mixed microstructure of TiC and the a-Ti in carburing layer were formed during carburizing. Furthermore, it was found that the microstructure and the properties of TC4 alloy were significantly related to the carbonizing temperature. The specimen plasma carbonized at 950 ~2 obtained maximum value both in the hardness and wear resistance.

Store Environment:Its Importance and Consumers'Expectations on Casual-wear Chain Stores in Honk Kong

This study attempted to examine the importance of storeenvironment in affecting consumers’store choice deci-sion;the relative importance among the three environ-mental factors;and consumers’expectations on store en-vironment for the casual-wear chain stores in HongKong.Julie Baker’s Three-category framework onstore environments namely ambient,design and socialfactors was adopted for investigation.The results indi-cated that the store environment was important in affect-ing consumers’selection of store for shopping.It alsorevealed that social factor was perceived relatively im-portant than ambient and design factors.Nine store ex-pectation dimensions were categorised and the resultdemonstrated that most respondents were concerned onthe social aspect in their expectation of having a satisfy-ing store environment.

Al_(2)O_(3)-TiC陶瓷材料微细电火花加工试验研究

为研究电火花加工Al_(2)O_(3)-TiC陶瓷材料工艺参数对工艺性能的影响,设计了混合2-3水平正交试验方法。研究加工极性、极间电压、最大放电电流、增益、脉冲频率、脉宽、放电间隙与电极长度损耗、电极轮廓损耗、材料去除率之间的规律。通过极差分析,获得了工艺参数对工艺性能的影响趋势。结合方差分析,表明加工极性对电极损耗有显著影响,极间电压、最大放电电流显著影响材料去除率。综合三项工艺性能,最优的参数组合为负加工极性、130 V极间电压、50 A最大放电电流、45增益、150 Hz脉冲频率、1.0μs脉宽、放电间隙40μm。

Effect of Silicon Content on Wear Resistance of Al-Si Alloys

The sliding wear behavior of hypoeutectic, eutectic and hypereutectic Al - Si alloys under lubricating condition was investigated. The wear mechanism of three kinds of alloys was discussed and an effective way to improve the wear reslstance of Al - Si alloys was put forward, that is increasing the silicon content.

Microstructural Characteristics and Wear Performance of Plasma Sprayed Al_2O_3-13 wt. % TiO_2 Coating on the Surface of Extrusion Wheel

The conventional Al2O3-13 wt. % TiO2 composite ceramic coatings are fabricated by plasma spraying on the surface of extrusion wheel. The microstrueture, morphology and phase compositions of the substrate and coat- ing are investigated by using X-ray diffractometry （XRD） , scanning electron microsopy （SEM） and energy dis- persive spectroscopy （EDS）. Moreover, the microhardness of the substrate and the coating are investigated using Vickers mierohardness tester, the friction and wear behaviors of the substrate and the coating are investigated by using a block-on-ring tribometer under dry sliding conditions with the load of 245 N. The results show that both γ-Al2O3 and α-Al2O3 phases are observed in the as-sprayed coatings, the mian phase is γ-Al2O3. There are white particulates Al2O3 on its surface. The Al2O3-13 wt. % TiO2 coating possesses higher mierohardness which is about 1018HV and 1.6 times that of the substrate. The wear performance of coating is better than that of the substrate. In a practical application, the life of the extrusion wheel which is plasma sprayed Al2O3-13 wt. % TiO2 coating on the surface is 1.2 times that of the conventional extrusion wheel, and the life is about 330 h.

Ni-Mo-BN复合镀层热处理前后组织与力学性能的研究

通过直流电沉积的方式在铜片基体表面制备不同BN含量的Ni-Mo-BN复合镀层,研究了镀液中不同浓度的BN粉末(5、10、15、20 g/L)以及Ni-Mo-BN镀层在经退火热处理后BN对膜层微观组织及硬度的影响规律。结果表明:电流密度在2 A/dm^(2)、BN添加量为10 g/L、电镀15 min得到的镀层综合性能最优良。随着镀液中BN浓度的增加,所得镀层中BN含量先升高,后下降。当镀液中BN浓度为10 g/L时,能在基体表面沉积最多的BN,且此时的晶粒尺寸较小,对膜层的力学性能提升最为显著。膜层硬度与BN在膜层中的含量呈正相关,但当在镀液中添加的BN含量过高时,BN会产生团聚现象,不仅会让BN的沉积率降低,同时也会让晶粒尺寸增大,使膜层的力学性能下降。此外,通过对试样进行600℃退火热处理,可对镀层的硬度、耐磨性等性能的提升起到极大的促进作用。

Novel recovery of a low-concentration gold thiosulfate complex through electroreduction via a walnut shell charcoal electrode

Low-concentration Au(S_(2)O_(3))2^(3-)recovery is an urgent issue to facilitate the application of thiosulfate leaching instead of cyanide leaching in factories.Herein,this work presents a novel recovery of low-concentration Au(S_(2)O_(3))2^(3-) combining adsorption and electrodeposition(electroreduction)to realize high Au(S_(2)O_(3))2^(3-)recovery in the form of gold particles(Au^(0)).Walnut shells were used as the raw material for the successful preparation of charcoal with porous structure and rich oxygen-containing functional groups.Walnut shell charcoal(WSC)as the electrode achieved efficient recovery of low-concentration Au(S_(2)O_(3))2^(3-).The recovery under low-concentration conditions was higher than 90%,with the highest reduction of 46.97 mg·g^(-1).Applying a suitable low voltage(0.8 V)facilitated lowconcentration Au(S_(2)O_(3))2^(3-)recovery,which was immensely improved than that without voltage.Au(S_(2)O_(3))2^(3-)recovery performances under applied voltage via the WSC electrode were related to electrochemical abilities,including reaction intensity and charge transfer.More reactive sites containing suitable pores and oxygen functional groups were beneficial for the reduction reaction.This work offers a new way to recover low-concentration Au(S_(2)O_(3))2^(3-)via cheap charcoal electrodes from solutions for application in the cyanide-free leaching method in industry.

TiC-VC耐磨堆焊焊条

利用药皮中的石墨、钛铁、钒铁、金红石等组分 ,通过电弧冶金反应生成了具有高显微硬度的TiC、VC等碳化物 ,探讨了焊条药皮组分石墨、钛铁、钒铁等的含量对焊条工艺性、抗裂性及堆焊层硬度的影响 ,利用X射线衍射、扫描电镜 (SEM )和电子探针 (EMPA)对堆焊层显微组织 ,TiC、VC等碳化物的分布以及断口形貌进行了分析 .研究结果表明 ,堆焊层组织为低碳马氏体 +残余奥氏体 +碳化物 ,碳化物极弥散分布在低碳马氏体基体上 ,断口为准解理断裂 ;堆焊层具有较高塑韧性 ,焊前不预热 ,焊后不缓冷连续堆焊不产生裂纹 ;堆焊层硬度达到HRC5 5以上 ,具有高的耐磨性 ,相对耐磨性优于D6 6

Cu-SiC复合电极电火花加工烧结NdFeB永磁体的研究

将超声波和复合电沉积技术相结合制备了Cu-SiC复合电极材料,利用SiC颗粒高熔点、高导电性的特点探索对烧结NdFeB永磁体电火花的可加工性。研究了Cu-SiC电极对NdFeB永磁体加工效率、加工效果的影响规律。结果表明SiC颗粒在火花放电中使电场产生畸变,降低了击穿电压,火花痕迹大而浅,表面粗糙度降低;同时提高了加工效率,降低了电极损耗。

不锈钢衬底化学镀Ni-W-P三元合金组织及性能研究

采用复合络合剂,在2Cr12不锈钢上直接化学镀Ni-W-P,并对镀层的形貌、成分、组织结构及性能进行了检测和分析。结果表明:不锈钢经过合适的前处理后,得到的镀层光亮、均匀,表面呈胞状组织;在400℃热处理后,开始析出Ni3P相;镀态层的硬度HK值由8186MPa提高至11850MPa;结合力、耐磨性也有明显增强。