Superior mechanical and tribological properties governed by optimized modulation ratio in WC/a-C nano-multilayers

WC/a-C nano-multilayers with different modulation ratio (WC:a-C) ranging from 1:10 to 1.5:1 were deposited by fixing a-C individual layer thickness and tailoring WC individual layer thickness. The effect of modulation ratio on mechanical and tribological performance of WC/a-C nano-multilayers were investigated. Superior mechanical and tribological properties were simultaneously achieved at modulation ratio of 1:1.2. In addition to the improvement of mechanical properties, the improved tribological properties should also be attributed to the friction-induced formation of a WO₃-rich transfer film under an appropriate WC individual layer thickness, which combing the graphitized worn film surface constructed an intrinsically weak-interacting sliding interface (WO₃/C interface). Also, graphitized carbon is an essential coadjutant for the formation of WO₃-rich transfer film.     

A comparative investigation on microstructure evolution and wear resistance of in situ synthesized NbC,WC, TaC reinforced Mo2FeB2 coatings by laser cladding

To improve the microhardness and wear resistance of Mo₂FeB₂ coatings, composite coatings were prepared by laser cladding using in situ synthesized NbC, WC, and TaC. The influence of different carbides on the morphology, microstructure, microhardness, residual stress, and tribological properties of the composite coatings was investigated. The results showed various microstructural morphologies in different composite coatings. Apparent herringbone structures were observed in most coatings except for the Mo₂FeB₂/TaC composite coating and a eutectic structure was formed in the Mo₂FeB₂/WC composite coating. In addition, the heat-affected zone was typically composed of acicular martensite and lath martensite. The microhardness of the Mo₂FeB₂/WC composite coating increased to 1543.6 HV_0.5 compared with 985.7 HV_0.5 observed for the Mo₂FeB₂ coating. Tensile stress existed in the coating, bonding zone, and heat-affected zone, whereas the substrate exhibited compressive stress. The Mo₂FeB₂/WC composite coating exhibited the lowest tensile stress (298 MPa). The Mo₂FeB₂/WC composite coating containing WC and the W₂C phase had the lowest coefficient of friction (0.38) and wear rate (3.90 × 10^?5 mm³/Nm), indicating its excellent tribological properties. Moreover, the wear mechanism of the Mo₂FeB₂ coating is severe adhesive and abrasive wear. The adhesive wear mechanism was mitigated by the formation of in situ synthesized NbC, WC, and TaC. The wear mechanism of the Mo₂FeB₂/WC composite coating was only a slight abrasive wear.     

等离子喷涂Ni包WC陶瓷涂层激光重熔研究

利用X射线衍射、金相显微镜及显微硬度计研究了等离子喷涂Ni包WC陶瓷涂层激光重熔后的组织结构和硬度变化特征。结果表明:利用激光重熔Ni包WC陶瓷涂层,能够有效提高涂层的致密度,减少孔隙率,XRD显示WC相在激光重熔后分解为W2C相,而显微硬度稍有提高。     

Effect of MoS2/PTFE coatings on performance of Si3N4/TiC ceramics in dry sliding against WC/Co

To enhance the tribological performance of Si₃N₄/TiC ceramics, MoS₂/PTFE composite coatings were deposited on the ceramic substrate through spraying method. The micrographs and basic properties of the MoS₂/PTFE coated samples were investigated. Dry sliding friction experiments against WC/Co ball were performed with the coated ceramics and traditional ones. These results showed that the composite coatings could significantly reduce the friction coefficient of ceramics, and protect the substrate from adhesion wear. The primary tribological mechanisms of the coated ceramics were abrasive wear, coating spalling and delamination, and the tribological property was transited from slight wear to serious wear with the increase of load because of the lower surface hardness and shear strength. The possible mechanisms for the effects of MoS₂/PTFE composite coatings on the friction performance of ceramics were discussed.     

Effects of WC particles on microstructure and mechanical properties of 316L steel obtained by laser melting deposition

Stainless steel has many excellent characteristics such as high strength, weldability, corrosion resistance, easy processing and surface gloss. It has been widely applied in many industrial and architectural decoration aspects such as aerospace, chemical, and automotive. However, 316L material manufactured by Laser melting deposition has poor wear resistance and tensile strength. In this paper, WC particles are used as a strengthening phase to make up for these deficiencies of 316L. In order to comprehensively evaluate the effect of WC particles on the mechanical properties of 316L formed by laser melting deposition, 316L samples with different proportions of WC particles and different fabricating directions were prepared. The microstructure of samples was observed, and the phase composition, Vickers hardness, friction and wear properties, tensile properties were analyzed. The mechanism of the influence of WC particles on the structure and the mechanism of friction, wear and tensile fracture were studied. The results show that most of the WC particles are evenly distributed in the coating. The microhardness and wear resistance of the 316L/WC composite coating have been significantly improved with the increase in the proportion of WC. The tensile strength and elongation are the best when the WC mass fraction is 6%.     

Microstructure and properties of Ni-WC gradient composite coating prepared by laser cladding

In this study, an Ni-based gradient composite coating reinforced with WC was prepared on a Q345R steel substrate by laser cladding. The Ni-WC composite coating was designed as a multilayer structure with gradient composition. The coating started with a layer of C276 alloy with 10 wt% WC on the substrate, and the subsequent layers were composed of Ni60 alloy with different WC contents (10, 30, and 50 wt% WC). The overall morphology, phase composition, and microstructure of the coatings were investigated. The microhardness and the wear properties of each layer of the coatings were also evaluated. The results showed that the gradient composition design was beneficial for reducing the cracking tendency. The coating was composed of an Ni-based matrix, WC, and multiple carbides and borides hard phases. With increasing WC content in the layers, the hard phases exhibited regional distribution characteristics. The WC reinforcement particles underwent different types of dissolution during the cladding process. From the surface to the substrate, the average microhardness of the coating was 1053.5 HV_0.2, 963.4 HV_0.2, 859.0 HV_0.2, 441.7 HV_0.2, and 260.5 HV_0.2. The wear tests revealed that the coefficient of friction and the wear loss values of the four layers were all lower than those of the substrate, demonstrating enhanced wear resistance.     

活性炭载碳化钨复合材料的制备及其对对硝基苯酚的电催化性能

以浓度为10%的偏钨酸铵溶液为前驱体、CH4/H2为还原碳化气氛,采用表面修饰技术和还原碳化技术制备了碳化钨(WC)/活性炭(C)复合材料。通过FT-IR、XRD、SEM等对制备的WC/C材料进行表征,结果表明,酸处理后的活性炭外表面大幅度增加了羟基和羰基,WC/C复合材料是由WC、W2C和C三相组成,碳化钨均匀地分散于活性炭表面,粒径约50～100nm。采用循环伏安法研究了碱性介质中WC/C-PME对对硝基苯酚的电还原行为,结果表明,该材料对对硝基苯酚的电催化活性优于WC和C,且WC/C材料在对硝基苯酚电还原过程中保持良好的化学稳定性。     

Ni-纳米WC复合镀层结构与性能研究

通过恒流电沉积制备Ni镀层和Ni-纳米WC复合镀层,利用扫描电镜和X射线衍射仪,并通过浸泡腐蚀实验和高温氧化实验,研究纳米WC颗粒对Ni镀层的微观形貌、物相结构、耐蚀性能和抗高温氧化性能的影响。结果表明,纳米WC颗粒使Ni镀层表面平整性明显改善,组织结构趋于完整且致密,镀层的耐蚀性能和抗高温氧化性能得到了提高;与Ni镀层相比,Ni-纳米WC复合镀层表面平整、结构致密,同等条件下的腐蚀速率和氧化增量均较低,表现出良好的耐蚀性能和抗高温氧化性能。     

WC/MMT纳米复合材料制备及其对PNP的电催化活性

以剥离后的蒙脱石(MMT)为载体,将浸渍法与原位还原技术相结合制备了碳化钨/蒙脱石(WC/MMT)纳米复合材料。采用X射线衍射、扫描电子显微镜和透射电子显微镜等手段对样品进行了表征。结果表明,剥离后蒙脱石的片层厚度为10～15 nm,层间距增大,边缘发生卷曲;复合材料由碳化钨(WC)、碳化二钨(W₂C)和蒙脱石组成,碳化钨颗粒均匀地分布于蒙脱石外表面。采用循环伏安法测试了样品对对硝基苯酚(PNP)的电化学还原性能,结果表明,WC/MMT纳米复合材料对对硝基苯酚具有良好的电催化活性,且具有较好的稳定性。蒙脱石是碳化钨基复合电催化材料良好的载体。     

Effects of tailored nitriding layers on comprehensive properties of duplex plasma-treated AlTiN coatings

Duplex-treated AlTiN coatings were deposited by advanced plasma assisted arc (APA-Arc) technology on pre-plasma nitrided AISI-H13 steel substrates using different N₂/H₂ flow ratios. The microstructures and properties of the AlTiN coatings were comprehensively characterized and analyzed. The results show that the N₂/H₂ flow ratios can tailor the thickness of compound layer during plasma nitriding process and the bright nitriding layer without compound layer is achieved. The properties of duplex-treated AlTiN coatings are well improved compared with monolayer AlTiN coating. The adhesion of the AlTiN coating is well enhanced by duplex treatment process, and adhesion grade increases from HF3-4 for monolayer AlTiN coating to HF1 for composite coatings. Moreover, the composite coatings with various thickness compound layers show different load-bearing capacities, and the interfacial adhesion force of the composite coating without compound layer reaches 61 N. The hardness of AlTiN coating is also enhanced by duplex treatment with the highest hardness of 2935 HV_0.05. Meanwhile, tribological properties of AlTiN coatings are also slightly improved by duplex treatments.     

Fabrication of WC-Co cemented carbides with gradient distribution of WC grain size and Co composition by lamination pressing and microwave sintering

WC-Co composite powders with different particle sizes and Co contents were prepared by ball milling WC and Co powder mixtures for different durations. Functionally graded WC-Co cemented carbides with both Co content and WC grain size gradient were prepared by lamination pressing different WC-xCo (x?=?10, 15, 20) powder mixtures and microwave sintering the layered compacts. The WC-xCo powder mixtures were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), and the phase composition and microstructure of the functionally graded cemented carbides (FGCCs) were investigated by XRD, and FE-SEM coupled with energy dispersive spectroscopy (EDS). Mechanical behaviors of the layered WC-Co materials were measured and compared with those of WC-Co cemented carbides with single composition. The results showed that increasing the milling time from 6 to 24?h, results in the decrease of the particle size of WC-Co composite powders from 0.31 to 0.11?µm. After lamination pressing and microwave sintering, the WC-Co samples show nearly complete densification with a relative density higher than 99.7% and no ?-phase was detected in the FGCCs. The Co content and WC grain size in FGCCs decrease from the core to the surface. Homogenization of Co has hardly occurred and no cracks have formed between the layers in the sintered samples. In the inner layer, the mean WC grain size is 529?nm, while in the outer layer it is only 274?nm. Because of the difference in Co content and WC grain size, FGCCs have a Rockwell hardness of 90.75 HRA at the surface, which decreases to 86.75 HRA in the core. However the fracture toughness increases from 11.53 at the surface to 18.12?MPa?m^?1/2 in the core. The present results show that FGCCs with high outer layer hardness and high inner layer toughness were successfully prepared.     

Preparation of WC/Co composite powders by electroless plating

Ultra-fine WC/Co composite powders were prepared by electroless plating in this study. The Co layers with an average thickness of 50–100 nm were uniformly and completely covered on raw WC particles with a diameter of 0.3–0.5 µm. The influences of electroless plating conditions on the composites were investigated. The Co layer covering on WC particles was controlled by the content of CoSO₄·7H₂O, pH value and bath temperature. With increasing the content of CoSO₄·7H₂O up to 25 g/L, both the weight gain and the plating rate markedly increased. However, when the content of CoSO₄·7H₂O further increased to 30 g/L, while the weight gain displayed a slight decrease, the plating rate continued to increase moderately. Moreover, with the increase of pH value from 9.5 to 11, both the weight gain and the reaction time decreased. Furthermore, the plating rate exhibited an exponential relationship with the bath temperature. When the pH value, bath temperature and the concentration of CoSO₄·7H₂O are 10, 80 °C and 25 g/L respectively, the weight gain of Co-coated WC composite powders is 185.1 mg/g.     

材料转移层对Al2O3基自润滑陶瓷/铸铁摩擦副摩擦的影响研究

在MG－200磨损试验机上采用销－盘对磨方式，研究了分别含有固态润滑组元石墨，BN的Al2O3基自润滑陶瓷／HT20－40灰铸铁摩擦副的特性，并以Al2O3陶瓷／HT20－40铸铁摩擦画作对比。通过扫苗电镜对陶瓷磨损表面材料转移物的形貌进行了观察与对比，分析了材料转移层对摩擦副在自身固态润滑条件下其摩擦性能的影响作用。结果表明：陶瓷靡抽上金属转移层的数量和形貌对摩擦副的摩擦特性（自润滑特性）具有决定性的影响作用，当陶瓷磨损面上形成了大面积，致密的金属转移层时，由于固态润滑作用的衰退以及金属相之间严重的粘着倾向使得摩擦系数大幅度上升，而金属偶件其相对低的高温机械性能是金属材料转移层大面积形成的原因。     

Fretting wear and electrochemical corrosion of well-adhered CVD diamond films deposited on steel substrates with a WC–Co interlayer

Diamond films have been grown on carbon steel substrates by hot-filament chemical vapour deposition methods. A Co-containing tungsten-carbide (WC–Co) coating prepared by high velocity oxy-fuel spraying was used as an intermediate layer on the steel substrates to minimize the early formation of graphite (and thus growth of low quality diamond films) and to enhance the diamond film adhesion. The effects of the WC–Co interlayer on nucleation, quality, adhesion, tribological behaviour and electrochemical corrosion of the diamond film were investigated. The diamond films exhibit excellent adhesion under Rockwell indentation testing (1500 N load) and when subjected to high-speed, high-load, long-time reciprocating dry sliding ball-on-flat wear tests against a Si₃N₄ counterface in ambient air (500 rpm, 200 N, 300,000 cycles). A WC–Co interlayer with appropriate chemical pretreatment is shown to play an important role in improving the nucleation, quality and adhesion of the diamond film, relative to that shown by substrates without such pretreatment.     

碳化钨对激光熔覆层组织和耐磨性的影响

采用激光熔覆的方法在Q235钢板表面得到熔覆层,研究了激光熔覆后显微组织的变化、表层显微硬度的变化趋势及其原因及熔覆层抗磨损性能提高的幅度。结果表明：添加WC,可使熔覆层组织细化,硬度和抗磨损性能得到不同程度的提高。     

Ultrafine porous boron nitride nanofiber-toughened WC composites

Porous fibers are widely used in catalysis chemistry and hydrogen storage but are rarely used in structural ceramics. In this study, spark plasma sintering was used to prepare an ultrafine porous boron nitride nanofiber-toughened WC composite for the first time. The obtained WC-0.05 wt% ultrafine porous boron nitride nanofiber composites exhibited better properties (ie, a 2.3% increase in hardness and a 19.6% increase in fracture toughness) compared to those of the pure WC specimen. The fiber porosity improved the second phase-WC matrix microstructural combination. The described approach is a novel preparation method for the WC composites. Furthermore, a new toughening mechanism, which is based on “pinning and stretching”, was determined. These findings suggest that porous boron nitride fibers can be considered to be second phases for toughening the WC composites.     

WC的质量浓度对Ni-WC纳米复合镀层耐蚀性及硬度的影响

采用脉冲电沉积方法在304不锈钢基体上制备出Ni-WC纳米复合镀层。研究了WC的质量浓度对Ni-WC纳米复合镀层性能的影响。结果表明:随着WC的质量浓度的增加,Ni-WC纳米复合镀层的耐蚀性先增强后减弱,硬度先增大后减小;当WC的质量浓度为30g/L时,Ni-WC纳米复合镀层的耐蚀性最好,硬度最大。     

激光熔覆Ni包WC复合涂层的组织、耐磨和耐蚀性分析及应用

对45钢基体进行激光熔覆Ni包WC金属陶瓷涂层强化处理,通过X射线衍射(XRD)、扫描电子显微镜-能谱分析(SEM-EDX)和透射电子显微镜(TEM),研究了激光熔履Ni包WC涂层的显微组织和物相组成,并采用摩擦磨损试验和电化学测试系统研究了Ni包WC涂层的摩擦磨损性能和耐蚀性能.结果表明,在激光熔覆Ni包WC金属陶瓷...     

Surface science and electrochemical studies of WC and W2C PVD films as potential electrocatalysts

The stability of WC and W₂C in an electrochemical environment has been examined using an electrochemical half-cell in combination with X-ray photoelectron spectroscopy (XPS) to monitor changes in surface composition. The W₂C film is not stable in the electrochemical environment, immediately oxidizing to form surface W_xO_y species. In contrast, the WC film is stable at the anode potential below 0.6 V, demonstrating the potential to be used as an electrocatalyst. In order to determine the feasibility of using WC as an electrocatalyst for direct methanol fuel cells (DMFC), the reaction of methanol on the PVD WC film has been studied using ultrahigh vacuum (UHV) surface techniques, including high-resolution electron energy loss spectroscopy (HREELS) and Auger electron spectroscopy (AES). Methanol dissociates on the WC film to produce the methoxy intermediate (CH₃O), which is stable on the WC surface to 500 K. The reaction of methanol has also been investigated on WC films modified by low coverages of Pt, which shows a promoting effect of Pt for the dissociation of methoxy in the temperature range of 400–500 K. The surface science results suggest a synergistic effect for supporting low coverages of Pt on WC films for the potential application as electrocatalysts.     

Anisotropic tribological behavior of LSI based 2.5D needle-punched carbon fiber reinforced Cf/C–SiC composites

C_f/C–SiC composites were fabricated via liquid silicon infiltration with 2.5D needle-punched carbon fiber reinforced C_f/C composites. The effect of surface topography and carbon content of the C_f/C–SiC composites on the tribological properties was researched by the ball-on-disk reciprocating tribometer. The results indicate that different fiber layers and cross-section of the composites have various surface topography and show significant differences in the friction and wear properties. By the wear morphology and model analyses, the reason for the tribological anisotropy of the composites is that the distribution of carbon and SiC phases in the composites are inhomogeneous caused by the difference of the carbon fiber orientation and the relative content in each layer. Moreover, the wear rate of the short-cut fiber web layer was the lowest and there is an obvious linear decrease in coefficient of friction with increase of carbon content. The present work explains why the tribological properties of the composites are inconsistent and provides a way to adjust the friction properties of composite materials by optimizing the friction surface.