Investigation on the Electrical Properties of Vacuum Cold Sprayed SiC-MoSi2 Coatings at Elevated Temperatures

SiC-MoSi₂ composite powders was prepared by wet milling with MoSi₂ powders and SiC loose grinding ball in alcohol solution. Vacuum cold spray (VCS) process was used to deposit SiC-MoSi₂ electric conducting composite coatings. The microstructure of the VCS SiC-MoSi₂ composite coatings were characterized by scanning electron microscopy. The electrical resistance of the coatings was measured using a four-point probe method. The effects of the deposition parameters on the electrical resistivity of the composite coatings were investigated. The electrical properties of the coatings at elevated temperatures in air and Ar gas atmospheres were also explored. The results show that the electrical resistivity of SiC-MoSi₂ coatings decreases with increasing He gas flow rates ranged from 3 to 6 L/min. The electrical resistivity increases with the increase in heat treatment temperature due to “pesting” behavior of MoSi_2. The electric conductive property of the VCS SiC-MoSi₂ coating is significantly improved after heat treatment at 1000 °C for 3 h in Ar protective atmosphere without oxidation. A minimum resistivity of the heat treated coating is 0.16 Ω · cm.     

Effect of Microstructure on the Electrical Properties of Nano-Structured TiN Coatings Deposited by Vacuum Cold Spray

TiN coatings on Al₂O₃ substrates were fabricated by vacuum cold spray (VCS) process using ultrafine starting ceramic powders of 20 nm in size at room temperature (RT). Microstructure analysis of the samples was carried out by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Sheet resistance of the VCS TiN coatings was measured with a four-point probe. The effects of microstructure on the electrical properties of the coatings were investigated. It was found that the sheet resistance and electrical resistivity of TiN coatings were significantly associating with the spray distance, nozzle traversal speed, and deposition chamber pressure. A minimum sheet resistance of 127 Ω was achieved. The microstructural changes can be correlated to the electrical resistivity of TiN coatings.     

Effects of processing parameters on the properties of tantalum nitride thin films deposited by reactive sputtering

The effects of processing parameters on the properties of tantalum nitride thin films deposited by radio frequency reactive sputtering have been investigated. The influence of the N₂ partial and (Ar + N₂) total gas pressures as well as the sputtering power on the microstructure and electrical properties is reported. Rising the N₂ partial pressure, from 2 to 10.7%, induces a change in the composition of the δ-TaN phase, from TaN to TaN_1.13. This composition change is associated with a drastic increase of the electrical resistivity over a 7.3% N₂ partial pressure. The total gas pressure is revealed to strongly affect the film microstructure since a variation in both composition and grain size is observed when the gas pressure rises from 6.8 to 24.6 Pa. When the sputtering power varied between 50 and 110 W, an increase of the grain size related to a decrease of the electrical resistivity is observed.     

Al_2O_3含量对等离子喷涂TiO_2-Al_2O_3陶瓷涂层组织性能的影响

采用大气等离子喷涂方法制备TiO2–Al2O3陶瓷涂层,利用SEM和XRD分析了涂层的显微组织和相结构,并研究了涂层的电阻率随温度变化的规律。研究结果表明:TiO2–Al2O3陶瓷涂层主要由金红石型TiO2、锐钛矿型TiO2、Magneli相、α–Al2O3及γ–Al2O3组成。涂层的显微硬度和电阻率随Al2O3含量的增加而增加,在通电升温条件下涂层的电阻率随温度升高而降低。     

电弧喷涂制备铁基耐磨陶瓷涂层的工艺优化

采用电弧喷涂方法在Q235钢基体上喷涂铁基涂层,并用正交设计的方法对工艺参数进行了优化。确定优化后的工艺参数为:喷涂电流180A,喷涂电压32V,雾化空气压力0.6MPa,喷涂距离100mm。试验结果表明:采用优化后的最优工艺参数进行喷涂,所得涂层的耐磨性为Q235钢的13.7倍。     

Effects of deposition parameters on characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition

The effects of deposition parameters on characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition are investigated. The deposition parameters are selected as follows. The CH₄/(CH₄ + N₂) ratio is in the range between 20% and 100%; the temperature is set from 1173 to 1248 K; the working pressure is arranged between 50 and 100 kPa, and the residence time is ranging from 1.47 to 7.37 s. The deposition rate, microstructure, and electrical resistivity of carbon coatings are measured. The low-temperature surface morphology of carbon-coated optical fibers is elucidated. Experimental results indicate that the deposition rate increases with increasing the CH₄/(CH₄ + N₂) ratio, deposition temperature, working pressure, and residence time. The activation energy (= 456 kJ/mol) of carbon deposition from methane was shown to correlate to the activation energy of methane dissociation. The deposition rate is proportional to about first-order of partial pressure of methane, and thus, the deposition process is mainly controlled by the process to create mono-carbon species in the carbon film. As the deposition rate increases, the size and number of particles on the carbon coating surface and electrical resistivity of carbon coatings increase, while the ordered degree, nano-crystallite size, and sp² carbon atoms of the carbon coatings decrease. Additionally, the low-temperature surface morphology of carbon coatings shows that as the carbon coating thickness is large enough to sustain the thermal loading, decreasing the deposition rate is good for producing hermetic optical fiber coatings.     

Zinc oxide targets for magnetron sputtering PVD prepared by plasma spray

TCO (Transparent Conductive Oxides) is a class of thin coatings which industrial importance is dramatically increasing. Their applications span from solar cells up to touch screen devices. Among them, ZnO has interesting electromagnetic properties, jointly to a price of raw materials significantly lower with respect to the Indium oxide based coatings, which are the most commonly used.TCO are usually produced by magnetron sputtering PVD, starting from a ceramic target, and plasma spraying technology is in some cases used to prepare targets. In the present work the preparation of ZnO targets by means of plasma spray is investigated, focussing on the effect of plasma spray process on the electromagnetic properties of the final thin film deposited using the obtained targets.As a first step, the effect of deposition parameters on the micro structural properties of the ZnO plasma sprayed coatings has been assessed. Coatings were characterised by means of SEM, EDS, and XRD. It was observed that coatings deposited under inert atmosphere contained a small amount of metallic Zn.Two targets for a magnetron sputtering PVD equipment were prepared depositing by plasma spraying ZnO layers onto metallic substrates. The two targets differed for the deposition atmosphere: air for the first target, Ar for the second one. Thin PVD coatings, deposited starting from the above mentioned targets, were analysed by means of SEM, XRD, XPS, and Hall effect, in order to correlate their characteristics with the target preparation process parameters.PVD coatings obtained by the target prepared in air presented a high value of resistivity. Coatings deposited using the target prepared under inert atmosphere had a high value of electrical conductivity. No metallic Zn was detected in the PVD coatings.     

Development of the Process Index for NiCrAlY Coatings with the Mettech Axial III™ System

NiCrAlY coatings were deposited using the Mettech Axial III? plasma spray system. The microstructural features of the coatings, such as the porosity, crack, un-melted particle, and oxide content, were analyzed to investigate the effects of the spray process parameters on these features. Two Taguchi arrays were used to examine the effects of the spray process parameters such as powder size, ratio of (H₂ + N₂) gas flow over total gas flow, current, spray-gun nozzle size, and spray distance, on the microstructural features of the coatings. The results from statistical analysis are used to create regression equations to predict the microstructural features of the coatings. In the regression equations, a process index (PI) is used as a complex variable incorporating a number of process parameters. The results from an additional set of experiments are used to verify the validity of the regression equations. It has been demonstrated that the equations correlate well with the results from the subsequent set of experiments. It is concluded from this study that the PI can be used to categorize coating qualities with respect to the extent of crack, porosity, unmelted particle, and oxide content in the coating. These equations can also serve as an initial step in developing process parameters by means of the Mettech Axial III? System.     

Thermal stability of Ta-Si-N nanocomposite thin films at different nitrogen flow ratios

Ta-Si-N thin films were applied as diffusion barriers for Cu interconnections or hard coatings in mechanical application. The resistivity, hardness and thermal stability were the important issues in the interconnections and hard coatings, respectively. In this paper, we investigated the relationship between the microstructures, resistivity, nanohardness and thermal stability of the Ta-Si-N thin films at different nitrogen flow ratios of 0-30% (N₂% = N₂ / (Ar + N₂) × 100%) by magnetron reactive co-sputtering. The Ta-Si-N films were annealed at 600, 750 and 900 °C at about 6 × 10⁻³ Pa for 1 h, respectively, to examine their thermal stability. The microstructures of Ta-Si-N films at low N₂% of 2-10% still retained the amorphous-like phase with nanocrystalline grains in an amorphous matrix at annealing of 600-900 °C. The nanohardness of amorphous-like Ta-Si-N film at N₂% of 3% was measured to be 15.2 GPa much higher than that of polycrystalline film of 10.1 GPa at N₂% of 20%. The average nanohardness of both films is stable up to 900 °C and varied in the range of 0.43-0.83 GPa. The resistivity of the as-deposited Ta-Si-N films increase with increasing N₂ flow rate. It is small around 220-540 μΩ cm for low N₂% of 2-10% while it increases abruptly to about 7700-43,000 μΩ cm at high N₂% of 20-30%. The best thermal stability of resistivity of Ta-Si-N film occurs at the N₂% of 2% in the range of 220 to 250 μΩ cm from RT to 900 °C.     

Phase decomposition of the γ phase in a Mn–30 at.% Cu alloy during aging

The phase decomposition process of γ phase in a Mn–30 at.% Cu alloy, when aged at 723 K from 2 to 50 h, is investigated with electrical resistivity and magnetic susceptibility measurement. In conjunction with the antiferro-magnetic transition of the Mn-rich regions during cooling to room temperature from the aging temperature, the temperature coefficient of electrical resistivity shows a continuous increase in a certain temperature range. The temperature where the coefficient has the maximum increasing rate is defined as the T_N temperature of the Mn-rich regions. It was found that the T_N temperature was 20–30 K higher than the concomitant f.c.c.–f.c.t. transformation temperature T_t, determined with the minima of Young’s modulus in the aged samples. The increment of temperature coefficient of electrical resistivity involved in the magnetic transition is used to estimate the changes of volume fraction for Mn-rich regions vs aging time. At the same time, the paramagnetic feature above the spin-freezing transition temperature for quenched Cu-rich alloys is summarized, and the Mn concentration in Cu-rich regions of aged samples is calculated. It should be noted that Mn and Cu-rich regions had already formed in the 2 h-aged Mn–30 at.% Cu sample, and longer aging further enriched Mn or Cu, while the volume fraction of Mn-rich regions decreased slightly with aging time. Electrical resistivity measurement sensitive to Mn-rich regions and the magnetic susceptibility measurement for Cu-rich regions have shown the compositional heterogeneity in decomposed phases. TEM observation confirms the interconnectivity of the two regions in the aged microstructure. All the results support the hypothesis that the decomposition of γ phase in Mn–Cu alloys proceeds in the spinodal manner.     

N2对Sn-Ag-Cu钎料与元器件引线无铅镀层润湿性的影响

以Sn-3．5Ag-0．5Cu钎料主要研究对象，配合免清洗助焊剂，基于润湿平衡原理测量了钎料对Sn、Sn—Cu、Sn—Bi三种镀层的润湿特性，研究了五种温度、三种镀层、两种气氛条件对润湿行为的影响。结果表明，空气气氛下，温度较低时Sn-Bi镀层的润湿性能相对较好，温度较高时三种镀层的润湿性相当；采用氮气保护后可明显改善钎料润湿性，润湿时间缩短22％-40％，同一温度下的三种镀层的润湿性能相当。     

Comparison of the Microstructural Characteristics and Electrical Properties of Thermally Sprayed Al2O3 Coatings from Aqueous Suspensions and Feedstock Powders

In this work the microstructural characteristics and electrical insulating properties of thermally sprayed alumina coatings produced by suspension-HVOF (S-HVOF) and conventional HVOF spray processes are presented. The electrical resistance at different relative air humidity (RH) levels (from 6 to 97% RH) and values of dielectric strength were investigated by direct current electrical resistance measurements, electrochemical impedance spectroscopy, and dielectric breakdown tests. Relationships between electrical properties and coating characteristics are discussed. At low humidity levels (up to 40% RH) the electrical resistivities of S-HVOF and HVOF coatings were on the same order of magnitude (10¹¹???·m). At a very high humidity level (97% RH) the electrical resistivity values for the S-HVOF coatings were in the range 10⁷-10¹¹???·m, up to five orders of magnitude higher than those recorded for the HVOF coating (orders of magnitude of 10⁶???·m). The better electrical resistance stability of the suspension-sprayed Al₂O₃ coatings can be explained by their specific microstructure and retention of a higher content of ??-Al₂O₃. The dielectric strength E _d of suspension-sprayed coatings was found to be 19.5-26.8?kV·mm^?1 for coating thicknesses ranging from 60 to 200???m. These values were slightly lower than those obtained for conventional HVOF coatings (up to 32?kV·mm^?1). However, it seemed that the dielectric strength of conventionally sprayed coatings was more sensitive to the coating thickness (when compared with the values of E _d determined for S-HVOF coatings) and varied to a greater extent (up to 10?kV·mm^?1) when the coating thickness varied in the range 100-200???m.     

High-rate deposition of amorphous and nanocomposite Ti-Si-C multifunctional coatings

Amorphous (a) and nanocomposite Ti-Si-C coatings were deposited at rates up to 16 μm/h by direct current magnetron sputtering from a Ti₃SiC₂ compound target, using an industrial pilot-plant system, onto high-speed steel, Si, and SiO₂ substrates as well as Ni-plated Cu cylinders, kept at a temperature of 200 or 270 °C. Electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analyses showed that TiC/a-C/a-SiC nanocomposites were formed consisting of textured TiC nanocrystallites (nc) embedded in a matrix of a-C and a-SiC. Elastic recoil detection analysis showed that coatings deposited at a target-to-substrate distance of 2 cm and an Ar pressure of 10 mTorr have a composition close to that of the Ti₃SiC₂ compound target, as explained by ballistic transport of the species. Increased target-to-substrate distance from 2 cm to 8 cm resulted in a higher carbon-to-titanium ratio in the coatings than for the Ti₃SiC₂ compound target, due to different gas-phase scattering properties between the sputtered species. The coating microstructure could be modified from nanocrystalline to predominantly amorphous by changing the pressure and target-to-substrate conditions to 4 mTorr and 2 cm, respectively. A decreased pressure from 10 mTorr to 4 or 2 mTorr at a target-to-substrate distance of 2 cm decreased the deposition rate up to a factor of ~ 7 as explained by resputtering and an increase in the plasma sheath thickness. The coatings exhibited electrical resistivity in the range 160-800 μΩ cm, contact resistance down to 0.8 mΩ at a contact force of 40 N, and nanoindentation hardness in the range of 6-38 GPa.     

Coatings to reduce hydrogen environment embrittlement of 304 austenitic stainless steel

Electroplated Zn, Ni, Cu, Al, PVD-Ti-DLC and electroless NiP coatings as well as carbon, nitrogen and oxygen diffusion layers were investigated for their suitability to reduce hydrogen environment embrittlement (HEE) of 304 austenitic stainless steel. The mechanical stability of the coatings was evaluated by interrupted slow strain rate tensile testing. The Zn, Ni, Ti-DLC and NiP coatings as well as the oxygen diffusion layer cracked or delaminated at very low strains. The Cu coating was too thin and showed poorly coated areas. HEE of the underlying bulk material was not improved by any of these coatings because embrittlement always started at such coating imperfections. Al coatings showed a high ductility but could not reduce HEE of the underlying material due to a columnar structure at which the H₂ gas could get in direct contact to the substrate material. The carbon and nitrogen diffusion layers could not eliminate HEE of the 304 steel entirely but crack propagation was reduced in these layers.     

Cubic Aluminum Nitride Coating Through Atmospheric Reactive Plasma Nitriding

Aluminum nitride is a promising material for structural and functional applications. Cubic AlN (c-AlN) is expected to have higher thermal conductivity due to their high symmetry; however, its fabrication is difficult. In this study, c-AlN was synthesized by atmospheric plasma spray process through the reaction between Al feedstock powder and nitrogen plasma. Al powders were supplied to the plasma stream by Ar carrier gas and reacted with surrounding N₂ plasma, then deposit onto substrate. The obtained coatings were c-AlN/Al mixture at 150 mm of spray distance, and the nitride content was improved by increasing the spray distance. The coatings almost consist of c-AlN at 300 mm of spray distance. The coatings thickness decreased from 100 to 10 μm with increasing spray distance from 150 to 300 mm. Using carrier gas, N₂ enable to fabricate thick c-AlN coating with hardness 1020 Hv.     

Comparative Study of the Electrical Properties and Characteristics of Thermally Sprayed Alumina and Spinel Coatings

In this study, APS and HVOF processes have been used to prepare alumina (Al₂O₃) and magnesium spinel (MgAl₂O₄) coatings designed for insulating applications. The electrical characteristics, i.e., dielectric strength and electrical resistance (electrical resistivity) were investigated using different methods: dielectric breakdown test, direct current (DC) measurements, and electrochemical impedance spectroscopy (EIS). The electrical resistance was measured at room temperature at different relative humidity (RH) levels (from 6% RH to 95% RH) as well as at 200 °C. The coating microstructure, phase composition, and water vapor sorption were studied. Differences in the electrical insulating properties due to the different coating system characteristics are discussed. Of the coatings and conditions investigated in this study, the HVOF spinel coatings showed superior dielectric breakdown strength and electrical resistance stability at high humidity levels.     

Effect of Nano-Sized TiN Additions on the Electrical Properties of Vacuum Cold Sprayed SiC Coatings

Three different contents of nano-sized TiN powers of 20 nm in size were added to nano-sized SiC powders of 40 nm. Vacuum cold spray (VCS) process was used to deposit SiC-TiN composite coatings on Al₂O₃ substrates. Microstructure and phase structure analysis of the samples was performed by scanning electron microscopy (SEM) and x-ray diffraction (XRD). Sheet resistance of the VCS coatings was measured using a four-point probe method. The influences of TiN additions on the electrical resistivity of SiC-TiN composite coatings and the conductive mechanisms were investigated. The electrical resistivity of SiC-TiN coatings decreases with increasing TiN contents, reaching a minimum of 1.82 Ω m with 50 mol% TiN.     

高速电弧喷涂雾化熔滴传热过程数值分析Ⅱ.工艺参数对熔滴传热过程的影响

在高速电弧喷涂雾化熔滴传热过程数学模型的基础上，用Fe-Al合金进行了数值计算，分析了工艺参数对熔滴传热过程的影响。结果表明，熔滴尺寸越小，在一定喷涂距离上的对流换热系数则越大、熔滴温度越高、固相分数越小、冷却速度越大；雾化气流压力和喷涂电流越大，在一定的喷涂距离上熔滴温度也就越高，熔滴中的固相分数越低，且其凝固过程也越长；熔滴的冷却速度对熔滴尺寸和喷涂距离的变化十分敏感，而对雾化气流压力和喷涂电流的变化不太敏感；Fe-Al合金熔滴的液态冷却速度达10^5～10^7K／s数量级，预示涂层将具有快速凝固组织特征。     

High Pressure Cold Sprayed (HPCS) and Low Pressure Cold Sprayed (LPCS) Coatings Prepared from OFHC Cu Feedstock: Overview from Powder Characteristics to Coating Properties

Cold spraying enables high quality Cu coatings to be deposited for applications where high electrical and/or thermal conductivity is needed. Fully dense Cu coatings can provide an effective corrosion barrier in specific environments. The structure of cold-sprayed Cu coatings is characterized by high deformation which imparts excellent properties. Coating properties depend on powder, the cold spray process and post treatments. First of all, powder characteristics have a strong influence on the formation of pure coatings. Secondly, cold spraying provides dense, adherent, and conductive coatings by using HPCS and LPCS. Furthermore, an addition of Al₂O₃ particles to the Cu powder in LPCS process significantly improves coating properties. Also, heat treatments improve electrical conductivity. This study summarizes optimal characteristics of Cu powder optimized for cold spraying, achieving high coating quality and compares properties of HPCS Cu, LPCS Cu and Cu+Al₂O₃ coatings prepared from the same batch of OFHC Cu powder.     

冷喷涂制备CuZn35涂层结构及耐摩擦磨损性能

目的 采用高压冷喷涂技术制备低氧化、致密、耐摩擦磨损的CuZn35涂层,并探究加速气体温度对CuZn35涂层性能的影响。方法 利用高压冷喷涂技术在铝板上沉积CuZn35涂层,探究加速气体温度对冷喷涂CuZn35涂层微观结构及耐摩擦磨损性能的影响。在载荷为2 N时,在旋转式摩擦磨损试验仪上进行试验,对比铸态CuZn35材料的耐磨性能,评估在压力为5 MPa,加速气体温度为400、600、800℃条件下冷喷涂制备的CuZn35涂层的耐磨性能。通过光学显微镜(OM)、扫描电镜(SEM)、三维轮廓仪(3D Profiler)对涂层的微观结构和磨损表面形貌进行分析。结果 当冷喷涂加速气体温度从400℃升至800℃时,CuZn35涂层内部颗粒的变形量不断增大,颗粒之间形成了较好的结合,孔隙率从2.67%降至0.5%以下,硬度从200HV0.3升至242HV0.3,涂层磨损率从3.67 mm³/(N·mm)降至1.80 mm³/(N·mm)。在温度为800℃条件下制备的CuZn35涂层表现出最优的耐摩擦磨损性能,在磨损过程中涂层材料未发生明显的块状脱落现象...