铜电极表面电火花沉积TiB_2/TiC复层涂层的微观结构及成因

采用电火花沉积工艺将烧结二硼化钛和碳化钛涂覆到铜电极表面形成TiB2/TiC复层涂层,通过扫描电镜(SEM)结合能谱分析研究涂层和界面的微观结构及成分。结果表明,涂层电极横截面分为多个区域,涂层内有裂纹,与基体无明显分层;基体热影响区出现细晶和柱状晶,主要化学成分为铜。细晶区的形成主要是电火花放电过程中快速冷凝时高的形核率所致,并可能与电火花放电的脉冲能量有关。柱状晶区主要是因单向散热引起晶体的定向生长而产生的。

Microstructures and mechanical properties of electroplated Cu-Bi coatings

Electroplating has been used to produce Cu-Bi coatings. The crystal structure and lattice parameters of Cu in Cu-Bi composite coating were measured and compared with Cu coating. The mechanical properties of the coatings were also studied. It was found that the deposition parameters have significant effect on the mechanical properties of the Cu-Bi coatings. The microhardness has been improved from HVso165 of Cu coating to HVs0 250 of Cu-Bi composite coating prepared at 50 mA/cm2 for 20 min. Correspondingly, wear resistance of the Cu-Bi composite coating has also been enhanced significantly.

CeO2/Zn NANOCOMPOSITE COATING BY ELECTRODEPOSITION

The nanocomposite coating is obtained by electrochemical deposition of the zinc plating solution with ceria nanoparticles (mean diameter 30 nm). The effect of ceria nanoparticles on the electrodeposited zinc coating is stu died by weight loss test, inductively copuled plasma quantometer (ICP), scanning electron microscopy (SEM) and X ray diffraction (XRD), respectively. It is found that under the same electrodeposition conditions, the corrosion resistance of the nanocomposite coating increases obviously while that of the micron composite coating only improves slightly; The ceria content of the nanocomposite coating is more than that of the micron composite coating. Ceria nanoparticles modify the surface morphology and crystal structure of the zinc matrix in correlation with the increase of corrosion resistance.

Effects of Cr interlayer on mechanical and tribological properties of Cr-Al-Si-N nanocomposite coating

Cr-A1-Si-N coatings were deposited on SUS 304 substrate by a hybrid coating system. A Cr interlayer was introduced between Cr-A1-Si-N coating and SUS 304 substrate to improve the coating adherence. The effects of Cr interlayer on the microhardness, adhesion, and tribological behavior of Cr-A1-Si-N coatings were systematically investigated. The results indicate that the microhardness of the Cr-A1-Si-N coatings gradually deceases with increasing thickness of Cr interlayers. The adhesion between Cr-A1-Si-N and SUS 304 substrate is improved by addition of the Cr interlayers. A peak critical load of-50 N is observed for the coating containing Cr interlayer of 60 nm as compared - 20 N for the coating without Cr interlayer. The thicker Cr interlayers result in reduced critical load values. Moreover, the wear resistance of the Cr-AI-Si-N coatings is greatly enhanced by introducing the Cr interlayer with thickness of 60 nm in spite of the decreased microhardness. The friction coefficient of the coating system is also moderately reduced.

Mechanical properties and friction-wear characteristics of VN/Ag multilayer coatings with heterogeneous and transition interfaces

The heterogeneous multilayer interface of VN/Ag coatings and transition multilayer interface of VN/Ag coatings were prepared on Inconel 781 and Si(100),and the microstructures,mechanical and tribological properties were investigated from 25 to 700℃.The results showed that the surface roughness and average grain size of VN/Ag coatings with transition multilayer interface are obviously larger than those of VN/Ag coatings with heterogeneous multilayer interface.The coatings with transition multilayer interface have higher adhesion force and hardness than the coatings with heterogeneous multilayer interface,and both coatings can effectively restrict the initiation and propagation of microcracks.Both coatings have excellent self-adaptive lubricating properties with a decrease of friction coefficient as the temperature increases,but their wear rates reveal a drastic increase.The phase composition of the worn area of both coatings was investigated,which indicates that a smooth Ag,Magnéli phase(V2O5)and bimetallic oxides(Ag3VO4 and AgVO3)can be responsible to the excellent lubricity of both coatings.To sum up,the coatings with transition multilayer interface have excellent adaptive lubricating properties and can properly control the diffusion rate and release rate of the lubricating phase,indicating that they have great potential in solving the problem of friction and wear of mechanical parts.

Influence of pH values on electroless Ni-P-SiC plating on AZ91D magnesium alloy

A novel Ni-P-SiC composite coating was prepared by electroless plating in order to improve the corrosion capacity and wear resistance of AZ91D magnesium alloy.The influence of pH values on deposition rates and properties of the coatings was studied.The microstructure and phase structure of the Ni-P-SiC coatings were analyzed by scanning electron microscopy(SEM)and X-ray diffractometry(XRD).The corrosion and wear resistance performances of the coatings were also investigated through electrochemical technique and pin-on-disk tribometer,respectively.The results indicate that the composite coating is composed of Ni, P and SiC.It exhibits an amorphous structure and good adhesion to the substrate.The coatings have higher open circuit potential than that of the substrate.The composite coating obtained at pH value of 5.2 possesses optimal integrated properties,which shows similar corrosion resistance and ascendant wear resistance properties to the substrate.

Catalytic graphitization of polyacrylonitrile(PAN)-based carbon fibers with Fe-Cr_2O_3 composite coating

The process of electrodepositing Fe-Cr2O3 composite coating on polyacrylonitrile （PAN）-based carbon fibers and its catalytic graphitization were studied. Carbon fibers with and without electrodeposited Fe-Cr2O3 composite coating were heat treated at different temperatures and the structural changes were characterized by XRD, Raman spectroscopy and SEM. The results indicate that Fe-Cr2O3 composite coating exhibits a significant catalytic effect on graphitization of carbon fibers at low temperatures. When the Fe-Cr2O3-coated carbon fibers were heat treated at 1 300℃ the interlayer spacing （doo2） and ratio of relative peak area （AD/AG） reach 3.364/k and 0.34, respectively. Whereas, the extent of graphitization of pristine carbon fibers is comparatively low even after heat treatment at 2 800℃ and the values of doo2 and AD/AG are 3.414 A and 0.68, respectively. The extent of graphitization of carbon fibers increases not only with the increase of the catalyst gross but also the Cr2O3 content in Fe-Cr2O3 coating. The catalytic effect of Fe-Cr2O3 composite coating accords with the dissolution-precipitation mechanism.

The influence of MoS_2 on tribology characteristic parameter of Ni60A/MoS_2 composite lubricating coating

The influence of MoS2 on the tribology characteristic parameter of Ni60A/MoS2 composite lubricating coating was researched on the UMT-2 fretting abrasion tester （USA） The result shows that with increasing content of MoS2, the hardness curve of the composite coating decreases and the trend accelerates. Under the same experimental conditions, the mass loss of plasma spray composite coating without adding MoS2 iS 1.27×10^-2 mg. When the amount of MoS2 reaches 35%, the mass loss is 0.96×10^-2 mg. It can be seen that adding MoS2 phase can improve the wear resistance, the amplitude of which is close to 30%. The friction coefficient of plasma spray composite coating without adding MoS2 is 0.23. Adding MoSz could decrease the friction coefficient of the coating and presents a downtrend. When the mass fraction is 35%, the friction coefficient is the smallest （0.13）, and the range is doubled.

Crystallization characteristics of Ni-W-P composite coatings reinforced by CeO_2 and SiO_2 nano-particles

Ni-W-P composite coatings reinforced by Ce O2 and Si O2 nano-particles on the surface of common carbon steels, were prepared by double pulse electrodeposition. The crystallization course was characterized by phase structures, crystallinity, grain sizes and microstructures. The results indicate that as-deposited composite coating is amorphous. Whereas it turns into the crystalline structure with 98.25% crystallinity, and Ni3 P, Ni2 P and Ni5P2 alloy phases precipitate from structures at 400 °C. Thereafter, Ni2 P and Ni5P2 metastable alloy phases turn into Ni3 P stable alloy phase at 500 °C. The crystallization course of the composite coating has finished when being heat-treated at 700 °C. The average sizes of Ni grains increase with the rise of heat treatment temperature from400 °C to 700 °C. Ce O2 and Si O2 nano-particles deposited into Ni-W-P alloys can delay the crystallization course and habit the growth of alloy phases.

Mechanical properties of AISI 1045 ceramic coated materials by nano indentation and crack opening displacement method

Abstract： An effective approach was conducted for estimating fracture toughness using the crack opening displacement （COD） method for plasma enhanced chemical vapor deposition （PECVD） coating materials. For this evaluation, an elastoplastic analysis was used to estimate critical COD values for single edge notched bending （SENB） specimens. The relationship between fracture toughness （Kic） and critical COD for SENB specimens was obtained. Microstructure of the interface between AleO3-TiO2 composite ceramic coatings and AISI 1045 steel substrates was studied by using scanning electron microscope （SEM）. Chemical compositions were clarified by energy-dispersive X-ray spectroscopy （EDS）. The results show that the interface between of Al203-TiO2 and substrate has mechanical combining. The nanohardness of the coatings can reach 1 200 GPa examined by nanoindentation. The Klc was calculated according to this relationship from critical COD. The bending process produces a significant relationship of COD independent of the axial force applied. Fractographic analysis was conducted to determine the crack length. From the physical analysis of nanoindentation curves, the elastic modulus of 1045/AI2O3-TiO2 is 180 GPa for the 50 μm film. The highest value of fracture toughness for 1045/A1203-TiO2-250 μm is 348 MPa·mv2.

Corrosion protection of composite coating combining ceramic layer,copper layer and benzotriazole layer on magnesium alloy

A novel composite coating was fabricated on AZ91 magnesium alloy by applying a composite surface treatment which combined the methods of plasma electrolytic oxidation(PEO)pre-treatment,electroless copper and benzotriazole(BTA)passivation. The cross-section microstructures and chemical compositions of coating were examined using scanning electron microscopy(SEM) equipped with energy dispersive analysis of X-rays(EDX).Potentiodynamic polarization curves and salt spray tests were employed to evaluate corrosion protection of the coating to substrate in 5%NaCl solution.It is indicated that electroless copper produces a rough interface between the electroless copper layer and the ceramic layer.The corrosion potential shifts to the positive direction significantly and the current density decreases by more than one order of magnitude.There is no visible galvanic corrosion pits on the surface of the composite coating combination of PEO and electroless copper after 168 h neutral salt spray testing.The color of copper after BTA immersion could be held more than 60 d.

Comparison in characterization of composite and sol-gel coating on AZ31 magnesium alloy

An Al2O3 protective coating on magnesium alloy AZ31 was prepared by a repeated direct sol-gel process annealing at 300℃and a composite coating was also deposited using Al2O3 particles dispersed sol followed by phosphating treatment and annealing at 300℃.The morphologies,structures and critical adhesive loads as well as corrosion properties of the coatings were comparatively investigated by scanning electron microscopy(SEM),X-ray diffractometry(XRD),nanoscratch test and electrochemical measurement.The results show that the composite coating has a more uniform,crack-free layer and improved adhesion to the substrate as compared with that of the repeated direct sol-gel coating owing to its lower heat strain.The main phases in both coatings consist ofγ-Al2O3 andδ-Al2O3 derived from annealed alumina sol,and the composite coating has an anticorrosion performance which is superior to that of the repeated direct sol-gel coating.

Research progress on silicon carbide and its modified coatings in C/SiC composites

Carbon fiber reinforced silicon carbide ceramic composite(C/SiC)has become a key structural material due to its excellent high temperature resistance,corrosion resistance and oxidation resistance.However,C/SiC composites are prone to oxidation under long-term high temperature loading conditions.In this work,the research progress of SiC coating and its modified coating on the surface of C/SiC composite is reviewed.The optimization of these coatings mainly involves two aspects:structure and composition.The focus of structural optimization is to improve the interphase structure by such as SiC nanowires,thereby improving the interfacial bonding strength between the coatings and between the coatings and the substrate.The focus of composition optimization is to improve the performance of the coatings under high temperature loads by rare earth silicates,etc.The modification strategies of various modified coatings are emphatically introduced,which is helpful to guide the preparation of high-performance C/SiC coating materials in the future.

Lubricating a bright future:Lubrication contribution to energy saving and low carbon emission

Both the academic society and the industry are hunting for new energy forms for the future.However,the world should not forget the conventional technologies that contribute to the sustainable society by technical innovations.Among them,lubrication plays a significant role in energy saving and in low CO2emission by increasing the fuel efficiency and by prolonging the service life of machines.With the advance of novel synthetic approaches,and nanoscience and technologies,novel lubrication oils and additives and their formulations are being developed to reduce friction and wear,and novel surface treatment routes and surface coatings are invented and provide more efficient lubrication.These technologies create tremendous chances for machines to work more efficiently with low energy consumption.Here we review the recent progresses and challenges associated with some novel lubrication techniques that include novel surface treatment(such as texturing,high-performance nanocomposite coatings,adapting coating),tribology design(solid and liquid lubrication),energy-conserving engine oil and novel lubricants and formula(such as ionic liquids,low S,P content additives)which are to be adopted to enhance the fuel efficiency to achieve energy saving and low carbon emission.There is increased demand to replace fossil lubricants by degradable green lubricants.Specially designed coatings can reduce drag significantly during navigation of both airplanes and ships.All these aspects will be also reviewed in the paper.