Morphology and tribological properties of Ni/n-SiO_2 composite coatings by pulse-reverse current brush-plating

1INTRODUCTION Pulse reversecurrent(RC)platingisanew technologycomingwithpulsecurrent(PC)andre versecurrent.Onthisaspect,earlierstudiesmani festedthat[16],intheconditionofRC,theeffectofelectricdoublelayerwasrestrained,thecontrol ofcrystallinegrowthwasenfor…     

Microstructure and properties of sputtered thermal barrier coatings

A 3 kW radio frequency (RF) magnetron-sputtering unit was used to produce zirconia ceramic coatings on hollow turbine blades and vanes, which had been deposited a NiCrAlY bond coat layer by cathodic arc deposition. The NiCrAlY coating surface was shot-peened, and the residual stress in the bond coat layer and the effects of heat treatment on the residual stress are presented. After shot peening porosities and microgaps disappear in the NiCrAlY bond coat, the whole depth profile is residual compressive stress. Coarseness tests show that the roughness value (Rz) decreases from 16.4 to 3.3 μm. The microstructure and phase composition of the coatings were investigated using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The results show that tho/NiCrAlY bond coat is composed of γ and Cr phases, and the Al2O3 scales are formed near the interface between the ZrO2 ceramic layer and the NiCrAlY bond coat. No degradation occurred to RF sputtered ceramic coatings after oxidating at 1150℃ for 100 h, heating at 1150℃ for 5 min and then air-cooling for 500 thermal cycles.     

Microstructures and mechanical properties of Mg-Ce-Zn-Zr wrought alloy

Microstructures and mechanical properties of Mg-2.0 ?-0.7 % Zn-0.7% Zr alloy were studied. The results of scanning electron microscopy show that Mg12 Ce phase mainly distributes at the grain boundaries. The fine Mg12 Ce phase can apparently elevate recrystallization temperature by preventing the grain boundary migration. No dynamic recrystallization occurs during the hot-extrusion. The mechanical properties of as extruded specimens are σb=278.5MPa, δ=12.0%, while those of the specimens annealed at 250℃ for 100 h are σb=272.6 MPa, δ=11.3%, which indicate that the alloy has good mechanical properties at room temperature.     

Microstructures of laser cladding of intermetallic-ceramic composite coatings

The microstructures of laser cladding of (Ni-24.5%(atom fraction)Al)+5O%(mass haction)WC coatingsbefore and after aging was comparetively studied by using SEM and TEM. It is shown that dissolving of WC and reprecipitating in the forms of WC and W,Coccurred during laser cladding, and intermetallic γ' (Ni3Al) orderly precipitatefrom metastable supersaturant Ni-matrix solid solution after heat treatment. The structures are favorable for coating'sproperties.     

Effects of particle size on the mechanical properties of particle-reinforced Sn-Ag composite solder joint

Particulate size has significant influenced on the mechanical properties of particle-reinforced composite solder joints. In this current research, Cu or Ni reinforcement particles were mechanically added to the Sn-3.5Ag eutectic solder, and the effects of the particle size on the mechanical properties of particle-reinforced composite solder joint were systematically studied. This investigation touched on how mechanical properties of the solder joints are affected by particles size. A quantitative formula was set up to correlate the mechanical property of the solder joint with particle size in different processing conditions. Besides, the fracture mechanism of the composite solder joint was analyzed.     

Preparation and properties of metal-PVA composite hydrophilic ultrafiltration membranes

1　INTRODUCTIONOrganicmembraneshavegoodflexibilityandse lectivitybutpoormechanicalstrength ,whileinorgan icmembraneshavegoodthermalandchemicalstabili ty ,andimmunetomicroorganism ,butpoorselectivi ty .Thus ,thecombinationofboththeirgoodproper tiesmaymakeanovelmembranewithexcellentprop erties .Metallicfibersinteredmembranehasthechar acteristicsofhighmechanicalstrength ,greatvoidfractionandlittleflowdragoffiltration ,soitiswide lyusedasfiltrationmedium ,butithastoobigholediameterandisdifficu…     

Preparation and mechanical properties of β-SiC nanoparticle reinforced aluminum matrix composite by a multi-step powder metallurgy process

β-SiC nanoparticle reinforced A1 matrix （nano-SiCp/A1） composite was prepared by a multi- step powder metallurgy strategy including presureless sintering, hot compacting process and hot extrusion. The microstructures of the as-prepared composites were observed by scanning electronic microscopy （SEM）, and the mechanical properties were characterized by tensile strength measurement and Brinell hardness test. The experimental results revealed that the tensile strength of the composite with the addition of 5wt%/3-SIC nanoprtieles could be increased to 215 MPa, increasing by 110% compared with pure A1 matrix. Comparative experiments reflected that theβ-SIC nanoprticles showed significant reinforcement effect than traditional a-SiC micro-sized particles. The preparation process and sintering procedure were investigated to develop a cost effective preparation strategy to fabricate nano-SiCp/A1 composite.     

Tribological properties of electroless Ni-P-SiC composite coatings in rolling/sliding contact under boundary lubrication

Ni-P-SiC composite coatings were prepared under a given bath composition and operation parameters of electroless plating. The tribological properties of the Ni-P-SiC composite coatings after annealing at 400℃ for 1 h were tested in rolling/sliding contact under boundary lubrication condition using a two-roller tribometer. The measurement contained friction coefficient, contact surface temperature, contact electrical resistance, and wear rate of the Ni-P-SiC composite coatings under various slide to roll ratios, loads, and rolling speeds. For the simultaneous examination of the effect of the chosen parameters on the tribological properties of the Ni-P-SiC composite coatings, an orthogonal regression experimental design method was used.     

Fabrication and properties of Al matrix composites strengthened by in situ alumina particulates

New aluminum matrix composites strengthened by Al2O3 particulates through stirring cast by adding NH4Al（SO4）2 to the molten aluminum have been fabricated. TEM observation shows that in-situ Al2O3 particulates are generally spherical and they are uniformly distributed in the Al matrix. Dry sliding wear test results show that the volume loss of the unreinforced Al matrix is about three times that of the Al2O3 reinforced metal matrix composite （MMC） and the volume loss of the MMC fabricated by adding Al2O3 is larger than that of the MMC by adding NH4Al（SO4）2. Lubricating sliding wear test results show that the volume loss of the MMCs increases more slowly than that of the matrix with the increasing of the load.     

Design and micro mechanical properties of nano-SiO2 strengthened composite coatings towards remanufacturing

Nano-SiO₂ particles strengthened Ni-based composite coating was designed and prepared on steel substrate. The structures and nanoparticle content of the nano-SiO₂/Ni composite coating were determined by SEM, EDS and TEM; and the micro mechanical properties were tested by nano-indentation technique. The results show that 56% of particles in the solution are dispersed in size of less than 100 nm, the content of nanoparticles co-deposited in the coating doubles and structure of the coating is more compact and uniform than that of Ni coating. Nano-SiO₂/Ni coating exhibits excellent micro mechanical properties, and the nanohardness and elastic modulus are 7.81 GPa and 198 GPa, respectively, which are attributed to finer crystal strengthening, dispersion strengthening and high-density dislocation strengthening of nano-SiO₂ particles to the composite coatings. Foundation item: Project (50235030) supported by the National Natural Science Foundation of China; Project (G1999065009) supported by the National Basic Research Program of China     

Comparison of tribological properties for graphite coatings used for remanufacturing

To improve the solid lubricity on the worn surface of frictional-pairs, a convenient and simple brush-painting technique was utilized to prepare the solid lubrication graphite coatings. The bonding between the coatings and substrate is good. To examine the influence of the different graphite contents on the tribological properties of the graphite coatings, the comparison experiments were carried out on the ring-on-block friction tester. The tribological results show a change law of saddle-shape between the tribological properties of graphite coatings and graphite content. When the amount of graphite is up to 28 g, the tribological properties of graphite coating are the best. The excellent anti-friction of the graphite coating is associated with the close-packed hexagonal crystal structure of graphite.     

Comparison of tribological properties for graphite coatings used for remanufacturing

To improve the solid lubricity on the worn surface of frictional-pairs, a convenient and simple brushpainting technique was utilized to prepare the solid lubrication graphite coatings. The bonding between the coatings and substrate is good. To examine the influence of the different graphite contents on the tribological properties of the graphite coatings, the comparison experiments were carried out on the ring-on-block friction tester. The tribological results show a change law of saddle-shape between the tribological properties of graphite coatings and graphite content. When the amount of graphite is up to 28 g, the tribological properties of graphite coating are the best.The excellent anti-friction of the graphite coating is associated with the close-packed hexagonal crystal structure of graphite.     

脉冲电沉积Ni-SiC复合镀层的组织形貌与性能研究

利用直流(DC)和脉冲(PRC)两种电沉积方法制备了Ni-SiC复合镀层.利用X射线衍射仪(XRD)检测了镀层的微观结构与性能,通过扫描电镜(SEM)观察了镀层的表面形貌.结果表明:脉冲方法得到的纯镍镀层和复合镀层结晶晶粒更细小均匀,表面更致密平整.当镀层中SiC含量约为10.6%时脉冲镀层的宏观残余应力较直流镀层降低19.5%,硬度提高6.6%.     

Morphology and tribological properties of Ni/n-SiO2 composite coatings by pulse-reverse current brush-plating

Ni/n-SiO₂ composite coating was electrodeposited by brush-plating with pulse-reverse current(RC). The morphology, hardness, and tribological properties of the coating were investigated and compared with those of Ni and composite coatings electrodeposited with direct current (DC). The results indicate that Ni/n-SiO₂ composite coating electrodeposited by RC, because of RC and the nano powders, has denser coating, finer crystal grains, higher hardness (HV650.0, nearly 1.5 times higher than that of Ni coating electrodeposited by DC) and lower friction coefficient (nearly 0.62), as a result, in the wearing experiment, the Ni/n-SiO₂ composite coating electrodeposited by RC has the least worn loss. So this kind of coating has better wear resistance. And RC electro brush-plating can be used as a new technology of brush-plating in the area of wear resistance. Foundation item: Project (50235030) supported by the National Natural Science Foundation of China; Project (51489020104JS9102) supported by the National Key Laboratory for Remanufacturing     

纳米SiO2的改性及其复合电解质的性能分析

锂离子电池具有高电压、高容量和高比能量等特点,是重要的储能器件。针对传统的液态锂离子电池容易发生电解液泄漏、燃烧爆炸和短路等问题,聚合物锂离子电池虽可以较好地解决安全问题,但仍存在电导率、离子迁移分数和力学性能较低等因素。以叔丁醇钾与纳米SiO2表面的羟基进行反应,再将1,3-丙磺酸内酯进行接枝反应,对纳米SiO2表面进行接枝改性;以改性和未改性的纳米 SiO2与苯乙烯、甲基丙烯酸甲酯进行聚合反应,制备SiO2/P（ MMA-S）复合聚合电解质。FT-IR和TGA研究结果表明,纳米SiO2表面含有丙磺酸锂基团。采用扫描电镜研究改性前后的纳米SiO2颗粒的形态,发现改性后纳米SiO2粒度分布均匀、团聚减弱。SiO2/P（ MMA-S）复合聚合物电解质的研究结果表明,含有质量比为6℅的改性纳米SiO2的复合电解质膜的吸液率可达310℅,经历15 d失重率不超过18℅,抗拉强度可达40.0 MPa以上,断裂伸长率也超过40℅,交流阻抗法测定其室温电导率可达3.98×10-3 S/cm。     

激光熔覆Fe基非晶／纳米晶复合涂层的组织与性能

对以激光熔覆方式在45钢基体上制备的FeNiSiBVRE非晶涂层进行激光晶化,制备非晶／纳米晶复合涂层.利用X射线衍射仪、透射电镜、扫描电镜和磨损试验机研究非晶／纳米晶复合涂层的组织与性能.研究结果表明,涂层存在着分层结构,组成相有晶化相、非晶相和纳米晶相;涂层底部和顶部的显微组织由大量的稀土树枝晶、板条状硼化物和粒状碳化物组成,涂层中部的显微组织是由大量的纳米晶相镶嵌在非晶基体上构成.与没有进行激光晶化的非晶涂层相比,涂层的耐磨损性能下降.其磨损机制以粘着磨损和剥层磨损为主.     

改进的组合式L形钢管混凝土柱力学性能试验

为研究改进的组合式L形钢管混凝土柱力学性能,对18个改进的组合式L形钢管混凝土柱进行了轴压试验,分析了钢管厚度、混凝土强度和长细比等参数对试件力学性能的影响,提出了改进的组合式L形钢管混凝土柱承载力计算公式.研究结果表明:试件最终破坏形态主要表现为腰鼓型破坏、局部鼓曲(或拉裂)型破坏和弯曲型破坏;钢管厚度、混凝土强度和长细比均是影响承载力的主要因素,但增加钢管厚度更有利于承载力的提高;含钢率α越大,钢管对核心混凝土的约束作用越强;承载力公式计算结果与试验结果吻合较好.     

Reactive processing and mechanical properties of Al/SiCP composite

The reactive process for Al/SiC_P composite was studied. SiC particles were in-situ coated by the exothermal reaction of SiC-Ti powder compact in Al melt bath, and easily incorporated into Al melt. The detailed study was carried out to understand the microstructures of the reacted SiC particles. During the reaction and consequent mixing, the successive processes include in-situ coating on the reacted SiC particles, coat dissolution and SiC_P splitting. The tensile mechanical properties of 6013Al/SiC_P composite processed by the present technology showed that the reacted SiC_P considerably reinforced the 6013 matrix. Foundation item: The Key Program of the 9th Five-year Plan of China(No. 95-YS-005) Biography of the first author: CHEN Kang-hua, professor, born on Aug. 30, 1962, received Ph. D degree in 1991, majoring in Al alloy, Al matrix composite and powder metallurgy.