Predicted interfacial thermal conductance and thermal conductivity of diamond/Al composites with various interfacial coatings

The interfacial thermal conductance （ITC） and thermal conductivity （TC） of diamond/Al composites with various coatings were theoretically studied and discussed. A series of predictions and numerical analyses were performed to investigate the effect of thickness, sound velocity, and other parameters of coating layers on the ITC and TC. It is found that both the ITC and TC decline with increasing coating thickness, especially for the coatings with relatively low thermal conductivity. Nevertheless, if the coating thickness is close to zero, or quite a small value, the ITC and TC are mainly determined by the constants of the coating material. Under this condition, coatings such as Ni, TiC, Mo 2 C, SiC, and Si can significantly improve the ITC and TC of diamond/Al composites. By contrast, coatings like Ag will exert the negative effect. Taking the optimization of interfacial bonding into account, conductive carbides such as TiC or Mo 2 C with low thickness can be the most suitable coatings for diamond/Al composites.

Nickel and nickel-phosphorous matrix composite electrocoatings

Nickel and nickel-phosphorous matrix composite coatings reinforced by TiO2,SiC and WC particles were produced under direct and pulse current conditions from an additive-free Watts' type bath.The influence of the variable electrolysis parameters(type of current,frequency of current pulses and current density) and the reinforcing particles properties(type,size and concentration in the bath) on the surface morphology and the structure of the deposits was examined.It is demonstrated that the embedding of ceramic particles modifies in various ways the nickel electrocrystallisation process.On the other hand,Ni-P amorphous matrix is not affected by the occlusion of the particles.Overall,the imposition of pulse current conditions leads to composite coatings with increased embedded percentage and more homogenous distribution of particles in the matrix than coatings produced under direct current regime.

ELECTROLESS PLATING COMPOSITE COATINGS OF Ni-Ti-Re ON THE SURFACE OF DIAMOND

The coating of Ni W P was deposited as base layer, and then the composite coating of Ni Ti(particles) Re(rare earth) was deposited subsequently on the surface of diamond using electroless plating by adding 2～3 μm Ti particles and trace rare earth salt to bath solution. Ti particles deposited on the surface of diamond were found by SEM and formation of TiC was verified by X ray diffraction analysis after heat treatment of the coatings in vacuum at 900 ℃. The binding strength between the coated diamond and the metal matrix was improved effectively in the diamond composite based on metal cement.

Wear Behaviour of Electroless Ni-P-Diamond Composite Coatings

The wear behaviour of composite coatings is related to the nature of embedded particles.The effects of particle size on the wear behaviour of composite coatings are analyzed.Electroless nickel composite coatings containing diamond particles with the sizes in the range of 0—0.5,0.5—1,1—2μm are prepared.The surface morphology of diamond particles and composite coatings are observed by scanning electron microscopy(SEM).The wear tests of composite coatings are comparatively evaluated by sliding against a cemented tungsten carbide ball.The 3D morphology of worn scar is evaluated by using a 3Dprofiler.The results show that the hardness and wear resistance of composite coatings can increase with the increase of particle sizes.The mixture mechanism of adhesive wear and abrasive wear turn into single abrasive wear with the increase of particle sizes as well.The transformation of wear behaviour is mainly attributed to particle roles during wear process.

Application of ultra-smooth composite diamond film coated WC-Co drawing dies under water-lubricating conditions

A specific revised HFCVD apparatus and a novel process combining HFCVD and polishing technique were presented to deposit the micro-and nano-crystalline multilayered ultra-smooth diamond（USCD） film on the interior-hole surface of WC-Co drawing dies with aperture ranging from d1.0 mm to 60 mm.Characterization results indicate that the surface roughness values（Ra） in the entry zone,drawing zone and bearing zone of as-fabricated USCD coated drawing die were measured as low as 25.7,23.3 and 25.5 nm,respectively.Furthermore,the friction properties of USCD films were examined in both dry sliding and water-lubricating conditions,and the results show that the USCD film presents much superior friction properties.Its friction coefficients against ball-bearing steel,copper and silicon nitride balls（d4 mm）,is always lower than that of microcrystalline diamond（MCD） or WC-Co sample,regardless of the lubricating condition.Meanwhile,it still presents competitive wear resistance with the MCD films.Finally,the working lifetime and performance of as-fabricated USCD coated drawing dies were examined under producing low-carbon steel pipes in dry-sliding and water-lubricating conditions.Under the water-lubricating drawing condition,its production significantly increases by about 20 times compared with the conventional WC-Co drawing dies.

Composite Ni-Nanodiamond Coating Deposited by Electroless Method

The work in this study is focused on investigation of composite nickel coatings. The coatings were deposited on ductile cast iron samples of different composition by electroless method EFTTOM NICKEL with addition of strengthening nanodiamond particles （2-4 nm）, The samples were prepared by casting and austempering. The microstructure, microhardness and wear resistance of the coatings were investigated. The thickness of the coatings was also determined （8-10μm）. Metallographic analyses, SEM （scanning electron microscopic） investigation, microhardness measurements by knoop method, wear resistance tests were carried out. The coatings with and without heat treatment at 290℃, 6 h were tested. Duplication of microhardness value and improvement of the coating＇s properties of heat treated coatings were observed.

Preparation and tribological performance of electrodeposited Ni-TiB_2-Dy_2O_3 composite coatings

TiB2 and Dy2O3 were used as codeposited particles in the preparation of Ni-TiB2-Dy2O3 composite coatings to improve its performance. Ni-TiB2-Dy2O3 composite coatings were prepared by electrodeposition method with a nickel cetyltrimethylammonium bromide and hexadecylpyridinium bromide solution containing TiB2 and Dy2O3 particles. The content of codeposited TiB2 and Dy2O3 in the composite coatings was controlled by adding TiB2 and Dy2O3 particles of different concentrations into the solution, respectively. The effects of TiB2 and Dy2O3 content on microhardness, wear mass loss and friction coefficients of composite coatings were investigated. The composite coatings were characterized by X-ray diffraction （XRD）, inductively coupled plasma-atomic emission spectrometer （ICP-AES） and scanning electron microscopy （SEM） techniques. Ni-TiBE-Dy2O3 composite coatings showed higher microhardness, lower wear mass loss and friction coefficient compared with those of the pure Ni coating and Ni-TiB2 composite coatings. The wear mass loss of Ni-TiB2-Dy2O3 composite coatings was 9 and 1.57 times lower than that of the pure Ni coating and Ni-TiB2 composite coatings, respectively. The friction coefficient of pure Ni coating, Ni-TiB2 and Ni-TiB2-Dy2O3 composite coatings were 0.723, 0.815 and 0.619, respectively. Ni-TiBE-Dy2O3 composite coatings displayed the least friction coefficient among the three coatings. Dy2O3 particles in composite coatings might serve as a solid lubricant between contact surfaces to decrease the friction coefficient and abate the wear of the composite coatings. The loading-bearing capacity and the wear-reducing effect of the Dy2O3 particles were closely related to the content of Dy2O3 particles in the composite coatings.

Preparation and thermal conductivity of tungsten coated diamond/copper composites

Tungsten was plated on the surface of diamond by using thermal diffusion method.Different process parameters were employed to prepare the composites with tungsten,diamond and copper.The micro morphology of different samples was observed,and the thermal conductivity of samples was measured by laser flash method.The optimal process parameters for preparing diamond/copper composites with high thermal conductivity were investigated.The results indicated that plating tungsten on diamond could modify the interface bonding.When the diamond was plated for 60 min,the coating appeared intact,uniform and flat,and the thermal conductivity of the sample could reach as high as 486 W/(m·K).The integrity and uniformity were more important than thickness for the coating.When the tungsten-plated diamond was further annealed,the metallurgical bonding between the coating and the diamond was enhanced,and the thermal conductivity rose to 559 W/(m·K).

Characterization and optimization of pulse electrodeposition of Ni/nano-Al_2O_3 composite coatings

Nickel/nano-A1203 composite coatings produced by the pulse electrodeposition method and the influence of pulse parameters, i.e., pulse frequency, duty cycle, and current density on the microstructure, hardness, and corrosion resistance, were critically investigated on an AISI 1018 mild steel specimen electroplated in a Watt＇s type bath. The experiments were carried out with different combinations of pulse parameters using Taguchi＇s L27 orthogonal array, and 27 trials were conducted to study the effect of pulse parameters in view to maximize the hardness of the specimen. The assessment results clearly reveal that the specimen exhibits the maximum hardness at the pulse frequency of 20 Hz, duty cycle of 30%, and peak current density of 0.4 A/cm2, which are designated as the optimal parameters herein. Furthermore, the influences of those optimized pulse parameters over the microstructure and corrosion resistance were investigated, and some conclusions were drawn. Also, from the ANOVA examination, it is clear that duty cycle is predominant in affecting the hardness, while current density has relatively low impact.

Effect of sodium lauryl sulphate on microstructure, corrosion resistance and microhardness of electrodeposition of Ni-Co3O4 composite coatings

Ni?Co3O4 composite coatings were electrodeposited on mild steel surface from a Watts-type bath in the presence of sodium lauryl sulfate(SLS).The dispersed Co3O4 particles in the presence of SLS have a greater tendency to move towards cathode and get incorporated in the coating.SLS modifies chemical composition,surface morphology and microstructure of the Ni?Co3O4 composite coating.The developed composite coating exhibits higher corrosion resistance and microhardness than the pure nickel coating.The loadings of bath solution with different concentrations of Co3O4 particles in the presence of SLS provide hydrophobic nature to the coating surface,which is much effective in enhancing the corrosion resistance of Ni?Co3O4 composite coating.The agglomeration of Co3O4 particles(>3 g/L)under high bath load condition develops defects and dislocation on the coating surface,which results in lower corrosion resistance of the deposit.The mechanical properties of the hydrophobic coatings were assessed by the linear abrasion test.

Microstructure and thermal expansion of Ti coated diamond/Al composites

A titanium coating fabricated via vacuum vapor deposition for diamond/Al composites was used to improve the interfacial bonding strength between diamond particles and Al matrix,and the Ti coated diamond particles reinforced Al matrix composites were prepared by gas pressure infiltration for electronic packaging.The surface structure of the Ti coated diamond particles was investigated by XRD and SEM.The interfacial characteristics and fracture surfaces were observed by SEM and EDS.The coefficient of thermal expansion(CTE)of 50%(volume fraction)Ti coated diamond particles reinforced Al matrix composites was measured. The Ti coating on diamond before infiltration consists of inner TiC layer and outer TiO2 layer,and the inner TiC layer is very stable and cannot be removed during infiltration process.Fractographs of the composites illustrate that aluminum matrix fracture is the dominant fracture mechanism,and the stepped breakage of a diamond particle indicates strong interfacial bonding between the Ti coated diamond particles and the Al matrix.The measured low CTEs(5.07×10-6-9.27×10 -6K -1)of the composites also show the strong interfacial bonding between the Ti coated diamond particles and the Al matrix.

Studies on electroless Ni-P-Cr_2O_3 and Ni-P-SiO_2 composite coatings

本文对化学镀镍及化学镀镍磷基质中SiO2与Cr2O3的共沉积进行了研究。微粒在不断生长的膜层中共沉积引起了新的化学复合镀层的出现,这些复合镀层许多都具有优异的耐磨及耐蚀性能。通过选取镀层合金/复合微粒/金属基体的组分可改进镀层,获得所需的性能,以满足特别的需求。在对这些复合镀层的应用需求正在迫近与增长的同时,其市场正在迅速扩张。本文开发出了一种合适的复合化学镀镍液,并通过维氏硬度法对化学复合镀镍层进行了表征。采用动电位极化及交流阻抗法测定了镀层的Taber耐磨性能及耐蚀性能。采用SEM及XRD对复合镀层的表面形貌进行了分析。

Formation mechanism of electroless plating nickel-based composite coating on highly active rare earth magnesium alloys and its corrosion resistance and adhesion performance

The process of preparing anodic oxide film containing active sites and electroless nickel plating on highly active rare earth magnesium alloy was developed.The formation mechanism of electroless nickel plating on active anodic oxide film and the structure and properties of the composite coating were studied by several surface and electrochemical techniques.The results showed that Ag nanograins with an average size of 10 nm were embedded into the anodic oxide film with pores of 0.1−2μm.Ag nanoparticles provided a catalytic site for the deposition of Ni-B alloy,and the Ni crystal nucleus was first grown in horizontal mode and then in cylindrical mode.The corrosion potential of the composite coating increased by 1.37 V and the corrosion current reduced two orders of magnitude due to the subsequent deposition of Ni-P alloy.The high corrosion resistance was attributed to the misaligning of these micro defects in the three different layers and the amorphous structure of the Ni-P alloy in the outer layer.These findings provide a new idea for electroless nickel plating on anodic oxide film.

Antistatic coating material consisting of poly (butylacrylate-co-styrene) core-nickel shell particle

A transparent and antistatic coating material consisting of polymer core-metal shell particle was prepared. As a polymer core, poly(butylacrylate-co-styrene)s ([P(BA-co-sty)s]) with various compositions of butylacrylate and styrene were synthesized by emulsion polymerization. And the effect of comonomer composition on the thermal property of polymer core particle was investigated. By electroless plating method, the nickel particles were formed and deposited on the surface of P(BA-co-Sty) particles to form P(BA-co-Sty) core-nickel shell composite particles. SEM observation confirms that the nickel particles with size of 15 nm are distributed on the surface of the polymer core particles. The surface resistance of P(BA-co-Sty) core-nickel shell composite is 0.8×108Ω/cm2, enough to act as antistatic coating material.

Efect of Nanometer WC Coating on Thermal Conductivity of Diamond/6061 Composites

Diamond has poor interface tolerance with Al.To enhance interface bonding,in this study,tungsten carbide(WC)nanocoatings on the surface of diamond particles were prepared using sol–gel and in-situ reaction methods.WO_(3) sol–gel with two concentrations,0.2 mol/L,and 0.5 mol/L,was,respectively,coated on diamond particles,then sintered at 1250℃for 2 h to produce WC nanocoatings.The concentration of 0.2 mol/L WO_(3) sol–gel was not enough to cover the surface of the diamond completely,while 0.5 mol/L WO_(3) sol–gel could fully cover it.Moreover,WO_(3) was preferentially deposited on{100}planes of the diamond.WO_(3) converted to WC in-situ nanocoatings after sintering due to the in-situ reaction of WO_(3) and diamond.The diamond-reinforced Al composites with and without WC coating were fabricated by powder metallurgy.The diamond/Al composite without coating has a thermal conductivity of 584.7 W/mK,while the composite with a coating formed by 0.2 mol/L and 0.5 mol/L WO_(3) sol–gel showed thermal conductivities of 626.1 W/mK and 584.2 W/mK,respectively.The moderate thickness of nanocoatings formed by 0.2 mol/L WO_(3) sol–gel could enhance interface bonding,therefore improving thermal conductivity.The nanocoating produced by 0.5 mol/L WO_(3) sol–gel cracked during the fabrication of the composite,leading to Al12W formation and a decrease in thermal conductivity.

The Uniformal Metallization of the AlSiC Metal Matrix Composite Material Surface

The surface of the AlSiC composite material consists of aluminum and silicon carbide areas. The uniformal metallization by nickel is necessary in order to provide solderability and high thermal conductivity of the surface. The process of chemical deposition of nickel coatings elaborated in the research center VIAM yields the uniformal highly adhesive metallization. The kinetics of the deposition process has been studied and the estimation of the coatings quality has been made in comparison with commercially available samples produced elsewhere.

Novel Pretreatment of Hard Metal Substrate for Better Performance of Diamond Coated Cutting Tools

A surface engineering approach for a novel pre-treatment of hard metal tool substrate for optimum adhesion of diamond coatings is presented. Firsfly, an alkaline solution was used to etch the WC grains to generate a rough surface for better mechanical interlocking. Subsequently, surface Co was removed by etching in acid solution. Then the hard metal substrate was boronized to form a compound interlayer which acted as an efficient diffusion barrier to prevent the outward diffusion of Co. Novel nano-microcrystalline composite diamond film coatings with a very smooth surface was deposited on the surface engineering pre-treated hard metal surface. Promising results of measurement in adhesion strength as well as field cutting tests have been obtained.

WC含量对WC增强镍基复合涂层界面组织的影响

WC(碳化钨)增强镍基复合涂层具有高耐磨、耐腐蚀、高硬度特点,在盾构部件、旋耕刀具、石油钻探等领域广泛应用.为提高水力机械过流部件服役寿命,以WC颗粒和镍基粉状钎料为涂层材料,采用真空炉中热辐射钎涂方法在奥氏体不锈钢表面成功制备WC增强镍基复合钎涂层,借助扫描电镜、X射线衍射仪等对钎涂层显微组织和界面行为进行系统分析.结果表明,硬质相WC与镍基钎料界面结合存在机械咬合与冶金结合双重作用;钎涂层与钢基体之间存在一定程度的成分扩散,其较狭窄扩散区宽度约100μm;当WC含量低于25%时,复合钎涂层对不锈钢基体润湿性较好,可制备出最低孔隙率1.08%的复合钎涂层.

单脉冲电沉积Ni-纳米TiC-氧化石墨烯复合镀层结构及磨损性能

本研究利用单脉冲电沉积技术在Q235钢表面制备了一种新型的Ni基减摩耐磨三元复合镀层,首先通过研究氧化石墨烯(GO)浓度对Ni-纳米TiC基复合镀层形貌、镀速及硬度的影响确定了最佳的GO添加量,然后利用X射线衍射仪(XRD)、拉曼光谱仪(Raman)和X射线光电子能谱仪(XPS)等设备对三元复合镀层的结构进行了表征。最后与Ni-纳米TiC复合镀层等进行了对比,研究了三元复合镀层的硬度及耐磨损性能。结果表明:镀液中GO的最佳质量浓度为200 mg/L。此时,Ni-纳米TiC-GO复合镀层的表面均匀致密,粗糙度值Ra=3.087μm。XRD和拉曼光谱等分析结果表明纳米TiC和GO成功复合到Ni基镀层之中。Ni-纳米TiC-GO复合镀层的硬度为726.3HV,约是Ni-纳米TiC复合镀层(463.8HV)的1.5倍。Ni-纳米TiC-GO复合镀层的平均摩擦系数为0.108,相比于Ni-纳米TiC复合镀层(0.285),其具备更好的减摩耐磨性能。

纳米TiC浓度对双脉冲电沉积Ni-TiC复合镀层结构及性能的影响

研究了镀液中纳米TiC的添加量对双脉冲电沉积Ni-TiC复合镀层结构及性能的影响。通过扫描电镜(SEM)和X射线衍射(XRD)对镀层的表面形貌和物相进行了表征,并研究了镀层的表面粗糙度、显微硬度、耐磨性能和耐腐蚀性能。结果表明:当镀液中TiC浓度较低时,复合镀层表现为类似于纯Ni镀层的胞状沉积结构。当镀液中TiC浓度较高时,复合镀层表现为菜花状沉积结构。当纳米TiC浓度为8 g/L时,镀层表面致密性相对较高,Ni的衍射峰有明显的宽化现象。随着镀液中纳米TiC浓度的升高,复合镀层的磨损质量损失比表现为先下降后上升的趋势,当TiC浓度为8 g/L时,磨损质量损失比最小,为5.436%。当镀液中纳米TiC浓度为8 g/L时,镀层的自腐蚀电流密度最小,极化电阻值最大。结果表明双向脉冲电沉积制备Ni-TiC复合镀层镀液中最佳纳米TiC浓度为8 g/L。