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

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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.

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.

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.

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。

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。

Tribological performance of novel nickel-based composite coatings with lubricant particles

The present study is focused on the evaluation of the tribological performance of novel Ni/h BN and Ni/WS_2 composite coatings electrodeposited from an additive-free Watts bath with the assistance of ultrasound. Lubricated and non-lubricated scratch tests were performed on both novel composite coatings and on standard Ni deposits used as a benchmark coating to have an initial idea of the effect of the presence of particles within the Ni matrix. Under lubricated conditions, the performance of the Ni/h BN composite coating was very similar to the benchmark Ni coating, whereas the Ni/WS_2 behaved quite differently, as the latter did not only show a lower coefficient of friction, but also prevented the occurrence of stick-slip motion that was clearly observed in the other coatings. Under non-lubricated conditions, whereas the tribological performance of the Ni/hBN composite coating was again very similar to that of the benchmark Ni coating, the Ni/WS_2 composite coatings again showed a remarkable enhancement, as the incorporation of the WS_2 particles into the Ni coating not only resulted in a lower coefficient of friction, but also in the prevention of coating failure.

Effect of activators on the properties of nickel coated diamond composite powders

Nickel coated diamond composite powders were fabricated via a newly developed direct electrodeposition technique. The effects of activators on the coating of diamond were firstly investigated and diamond grinding wheels were then prepared from Ni-coated diamond composite powders with different activators. The microstructural characterizations of this composite powders were finally conducted by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction, and the mechanical and tribological properties of as-prepared diamond grinding wheels were also measured. There are changes in microstructures and properties of the composite powders with activators. The activator concentration also has an influence on the morphologies and phase structures of the Ni coating on diamond particles.The composite powders with more compact coating of nickel can be prepared by adding 1 g dm^（-3） or more AgNO_3 as an activator to electrodeposit nickel on diamond. The mechanical and tribological properties of diamond grinding wheels were significantly improved when the coating phase structure of Ni crystal grew with（111） plane orientation on the surface of diamond particles. The wheels made from nickel coated diamond composite powders possessed the advantages of easy preparation and outstanding tribological properties. Therefore, Ni coated diamond composite powders exhibit a great potential to be extensively applied in diamond cutting and grinding tools.

电泳共沉积法制备金刚石/Al_(2)O_(3)/玻璃复合涂层的工艺

以304不锈钢为基体,采用电泳共沉积法制备复合涂层,并通过烧结方式实现涂层在基体的固化。研究电泳共沉积过程中不同悬浮液组成、沉积电压、沉积时间和Al^(3+)质量分数等因素对涂层性能的影响,对涂层进行微观结构表征和力学性能测试,并使用该工艺制备抛光盘,用于蓝宝石的抛光。结果表明:当沉积电压为50 V,沉积时间为6 min,添加质量分数为0.10%的Al^(3+)时,可获得光滑、均匀的金刚石/Al_(2)O_(3)/玻璃复合涂层;复合涂层经450℃烧结3 h后,表面致密均匀,硬度达521 HV,复合涂层的耐磨性、与基体的结合强度均良好;使用抛光盘对蓝宝石进行抛光,可将表面粗糙度降低90.2%。

真空蒸镀钨改性金刚石/铜硼复合材料导热性能

采用真空蒸镀法在平板金刚石衬底表面镀覆钨镀层,构建多层平板结构以研究热处理温度对金刚石表面钨界面层形貌结构、物相成分及其与金刚石基体间界面结合情况的影响,并为金刚石颗粒表面金属化改性提供实验指导。在此基础上,以相同真空蒸镀和热处理工艺制备的钨改性金刚石颗粒作为增强体,以铜硼合金作为基体,采用气体压力浸渗法制备相应的金刚石/铜硼复合材料,探究金刚石颗粒的热处理温度对复合材料导热性能的影响。结果表明:随着热处理温度的升高,复合材料热导率呈现先上升后下降的趋势,当热处理温度为1000℃时,复合材料界面结合明显改善,同时金刚石表面钨镀层依旧连续完整,此时,复合材料的热导率最高可达629 W/(m∙K)。