Electrospark WC–Co coatings with different iron concentration

The effect of the iron concentration in WC–Co electrode materials on the structure and properties of coatings produced by electrospark alloying (ESA) on low-carbon steel is investigated. The effect of the iron concentration on the mass transfer and thickness of the deposited coatings is described. The phase composition, surface roughness and wear resistance of the coatings in dry and microabrasive friction are investigated. It is shown that the rate of decarbidization of tungsten carbide in ESA with a higher iron concentration of the electrode materials increases.     

脉冲放电熔涂Cr2B表面强化工艺及强化层组织性能研究

本文采用新型脉冲放电电火花表面强化设备,以Ｃｒ２Ｂ作为电极材料,研究了热作模具钢电火花表面强化工艺及强化层质量,分析了强化层组织结构的特点及强化层性能。研究结果表明,Ｃｒ２Ｂ电极强化层具有表面质量好、强化层厚和硬度高等特点,是一种高性能的表面强化涂层     

Investigation of WC-Co Electrospark Coatings with Various Carbon Contents

Electrospark deposition was employed to clad WC-10%Co, W/C1.6-10%Co, and W/C0.5-10%Co hard alloys on steel 1035, and the tribological properties of the coatings obtained were examined. The influence of the W/C ratio in the electrode materials on the decarburization of tungsten carbide was studied. It is shown that the degree of tungsten carbide degradation can be reduced by increasing the concentration of carbon in the WC-Co electrode materials, and also that the WC decarburization reaction is reversible on annealing. Coatings deposited using new electrode materials with an excess of carbon (W/C0.5) and/or tungsten (W/C1.6) have increased microhardness and improved frictional characteristics compared with the conventional coating.     

电火花沉积Ni基涂层的质量过渡及电极损失

采用逐层沉积的方法,在基材表面获得了1-8层Ni基电火花涂层,探讨了电火花沉积过程中Ni基电极的质量过渡规律及电极材料的流失形式。结果表明:Ni基电极向基材的平均质量过渡系数为0.76;电极的损失有气化、液态溅射和氧化三种形式;氩气保护在沉积过程中起重要作用;随着沉积层厚度的增加,基材对涂层的稀释越来越小。     

电火花涂层的特性和耐磨性研究

采用电火花表面强化设备，以YS2硬质合金作为强化电极在45钢表面涂覆形成一层合金强化涂层。用扫描电镜、X射线衍射仪和显微硬度计分析了电火花表面强化层形貌、性能和组织结构。在磨损试验机上对其耐磨性进行测试，同时利用扫描电镜对试样的磨损形貌进行观察分析。结果表明，获得了冶金结合的强化层，显著提高了基体的硬度和耐磨性。     

Investigation of coatings produced by the electrospark machining method of steel 45 with electrodes based on carbides of tungsten and titanium

The article is devoted to the development and investigation of tungsten-containing and tungstenless electrode materials for electrospark alloying using additives of boron-containing minerals, as well as aluminum-oxide nanopowder. The kinetics of the mass transfer process with the electrospark alloying of coatings was investigated. The phase composition, roughness, and kinetics of high-temperature oxidation of coatings were studied. The anticorrosive properties of obtained coatings were studied in 3% NaCl solution by the method of impedance spectroscopy. An improvement of the barrier properties of TiC–Ni–Mo coatings with increasing datolite concentrate was revealed.     

Effect of Heat Treatment on the Wear Resistance of Parts with Hard-Alloy Coatings

The phase composition, structure, and abrasive resistance of hard-alloy coatings on parts obtained by cavityless casting and coated on the surface with sormite PG-S27 powder luting with an additive of 2 – 6% B₄C are investigated. The results of the evaluation of the structure and wear resistance of the hard-alloy coating are analyzed in the initial condition and after standard and double heat treatment. An optimum mode of double heat treatment providing a highly wear-resistant structure is suggested.     

Materials for the electrospark strengthening and reconditioning of worn metal surfaces

The aim of this work is the development of technology for obtaining electrode materials from Colmonoy-WC alloys and hard alloys containing TiC, WC, Mo₂C, Tin, Co, Cr, Ni, and Al. The phase composition and structure are studied along with the kinetics of mass transfer, hardness, and wear resistance of electrospark coatings made of the manufactured alloys. The methods used were metallography and electron microscopy and X-ray phase and durometric analyses. It was shown that the alloys Colmonoy (Ni-Ni₃B–Si–Cu), Colmonoy-10% WC, and Colmonoy-25% WC have a eutectic structure. With an increase in the WC content in the alloys, the structure is found to be an aggregation of the phases of a hard solution based on nickel and tungsten carboborosilicide. At the pulse energy of 7.5 J, the thickness of the coatings formed was 3–4 mm. The wear resistance of the coatings increased with the growth of the WC content in the coatings from 64.5 μm/km for Colmonoy to 18.5 μm/km for the alloy with 70% WC, and the steel wear resistance under those conditions was 160 μm/km. It was established that the structure and composition of the manufactured electrode materials from the hard alloys based on TiC and WC carbides make it possible to produce electrospark coatings with a thickness up to 100 μm and hardness up to 20–24 GPa. The developed materials can be used to harden/recondition worn workpieces made of constructional steels by the electrospark method.     

Electrospark alloying for deposition on aluminum surface of Al-Sn coatings and their wear resistance under dry friction

Some aspects of coating deposition on aluminum substrate by electrospark alloying with toolelectrode from Al-Sn alloy stimulating the SnO₂ nanofibers formation in coatings have been studied. Wear resistance of such coatings, under dry friction conditions, in conjunction with a counterbody from hardened steel has been investigated. The conditions under which the coatings thus obtained manifest the of effect of the maximal wear excess of the counterbody compared to the wear of the coatings containing SnO₂ nanofibers have been specified. The effect reaches its maximum value under the dry friction after the treatment of the surface in the mode of “sparking” at a constant energy supply in the spark gap: at high rates of the tool electrode movement with respect to the specimen and at relatively large times of the electrospark effect on the treated surface.     

石墨-磷酸铝铬润滑涂层的制备及其摩擦学性能

以磷酸H3PO4、氢氧化铝Al(OH)3和氧化铬CrO3为原料合成了磷酸铝铬胶黏剂(ACP),并制备了以该磷酸铝铬为胶黏剂,胶体石墨为固体润滑剂的粘结固体润滑涂层。研究了石墨与磷酸铝铬胶黏剂的质量比、磷酸铝铬胶黏剂中金属离子与磷酸根的比值、铬含量以及磷酸铝铬的合成温度对润滑涂层摩擦磨损性能的影响。结果表明:磷酸铝铬胶黏剂的耐温性能优良,以磷酸铝铬为胶黏剂的石墨固体润滑涂层具有优异的减摩抗磨性能;磷酸铝铬胶黏剂的组成、分子结构对固体润滑涂层的摩擦磨损性能有较大影响,其中当磷酸铝铬胶黏剂中金属离子与磷酸根的比值(M∶P)为1∶3,铬铝比(Cr∶Al)为1∶3,合成温度为100~110℃时,石墨-磷酸铝铬润滑涂层的摩擦磨损性能最好。     

Development of electrode materials for electrospark hardening and reconditioning of worn-out surfaces: The structure and properties of the coatings

The relations between the erosion properties of the developed electrode materials (the alloys of the systems Ni-Cr-Al, Fe-Cr-Al, Fe-Cr-Ni, and AlN-MoSi₂) and the phase structure and manufacturing conditions are studied. The regularities of the formation of the protective coatings and their structure and properties are established, which makes it possible to develop new highly efficient electrode materials. The composition of the electrode materials and the manufacturing processes have been optimized considering the rate of the mass transfer in the course of the electrospark hardening and the main properties (wear resistance and heat resistance). The developed materials are used to increase the service life of various parts.     

氧化物颗粒增强 Ni-W-P / Nb2 O5 复合镀层制备及其耐腐蚀性能

目的对NdFeB磁性材料进行表面防护处理,改善其耐腐蚀性能。方法利用化学镀方法,在NdFeB基体材料表面制备氧化物颗粒增强的晶态和非晶态Ni-W-P/Nb2O5复合镀层,对镀层的组织形貌、元素组成分布及物相进行分析,并通过化学腐蚀失重法对耐腐蚀性能进行测试。结果当镀液中的次亚磷酸钠含量为20 g/L时,形成了晶态镀层;为35 g/L时,形成了非晶态镀层。晶态和非晶态Ni-W-P/Nb2O5镀层均由胞状突起组成,其中弥散分布着共沉积的Nb2O5颗粒。镀层样品的XRD图谱中没有出现与钕铁硼相关的衍射峰。对于制备的晶态和非晶态复合镀层,镀液中Nb2O5质量浓度由5 g/L增加到15 g/L时,化学腐蚀速率明显下降;Nb2O5质量浓度由15 g/L增加到20 g/L时,化学腐蚀速率的下降变得缓慢。结论利用化学镀可以在NdFeB磁性材料表面制备致密的Nb2O5增强Ni-W-P复合镀层,且随着Nb2O5含量的增加,复合镀层的耐腐蚀性能提高。     

45钢表面高能微弧火花数控化沉积AlCoCrFeNi高熵合金

采用参数化等间距点焊式沉积策略,以高能微弧火花数控化沉积工艺在45钢上制备出了AlCoCrFeNi高熵合金多层涂层.通过SEM和XRD研究了AlCoCrFeNi高熵合金涂层表面形貌及相组成.以层数为变量,研究了电极长度消耗规律和电极/工件质量过渡规律,并通过Bézier曲线拟合出电极长度消耗曲线、阳极质量损失曲线、和阴极质量增加曲线.电极长度消耗规律和质量过渡规律为实现多层连续不间断沉积和涂层显微结构的精确控制奠定基础.高能微弧火花数控化沉积工艺为功能涂层的制备提供了新方法.     

电火花沉积层质量的影响因素研究

研究了电极材料、润湿角、工艺参数、电火花沉积设备及后处理工艺等因素对实现提高沉积层耐磨性和耐腐蚀性等目的的影响,有助于提高电火花沉积层的沉积质量,为电火花沉积实验的制定和生产提供一定的参考,有利于电火花沉积工艺的改进与推广。分析表明:用短脉冲小功率沉积和较小的润湿角电极,相关联时序控制开关电源能有效提高沉积层的质量。     

Electrospark coatings produced by ceramic nanostructured SHS electrode materials

The paper considers the possibility to expand the number of materials used for electrospark alloying. Ceramic nanostructured TiB₂–TiC–Al₂O₃–ZrO₂-based materials produced by means of SHS extrusion are used as electrodes. The regularities of the alloyed layer formation with electrospark alloying (ESA) are studied. Three different modes of anode erosion and cathode gain are observed for single pulse energies ranging from 0.05 to 2.5 J. The microstructure of the coatings is studied. It is shown that, in the case of ESA by ceramic SHS electrodes, nanosized crystallites are formed. The microhardness of the alloyed layer is 1250 HV. The tribological tests of the protective coatings demonstrate a high wear resistance (10^–5 mm³/N/m) and low friction coefficient (0.2).     

Disperse-strengthening by nanoparticles advanced tribological coatings and electrode materials for their deposition

Two types of electrode materials were developed using self-propagating high-temperature synthesis (SHS) and powder metallurgy: 1- composite with nanosized additives; 2- nanostructured cemented carbide WC-Co. Electrospark deposition (ESD) was applied to produce tribological coatings which were disperse-strengthened by incorporation of nanosized particles. Nanostructured electrodes of cemented carbides WC-8% Co provide increasing density, thickness, hardness, Young's modulus, and wear resistance of ESD-coatings. Positive effects of nanostructural state of the electrodes on the deposition process and structure/properties of the coatings are discussed. In that case the tungsten carbide phase becomes predominant in the coatings. A mechanism of the dissolution reaction of WC in Ni at the contact surface of the electrode was proposed. It was shown that formation of the coating structure is initiated on the electrode and accomplished on the substrate.     

The modification effect of different compounds for protection of magnesium against corrosion

A protective layers were prepared on a magnesium electrode by treatment in different solutions and times after modification in 0.15 M HCl for 20 seconds. The corrosion of magnesium coated protective layer with different compounds was studied by using potential-time, current-potential curves and AC impedance spectra. The coatings morphology depends on the treating bath compositions and immersion times. The protective efficiencies of the surface layers were calculated by using corrosion rates obtained by extrapolation of Tafel zones of current-potential curves to the corrosion potential and by using Stern-Geary equation with polarization resistance from impedance spectra.     

Development of electrodes for welding transmission pipelines and marine equipment made of high-strength low-alloy cold-resistant steels

The problems of production of welding electrodes with basic coatings in Russia is associated with the changes in the raw materials base used as components for electrode coatings, in particular, the electrodes of the UONII-13 series used extensively in industry in welding important structures made of cold-resistant low-alloy steels of different strength categories are examined. A promising composition of the electrode coating with a new deoxidation alloying system is proposed. The system results in high welding and technological characteristics of the electrodes and stable mechanical properties of the metal of welded joints in low-alloy steels with a strength of up to 560 MPa. The high-quality parameters are achieved as a result of using Minal (mineral alloy) in the electrode coating for adding through this coating the mineral and rare-earth components. The compositions of the coatings of the developed electrodes are calculated using the phase equilibrium diagrams of non-metallic systems.     

Study of the HVOF Ni-Based Coatings’ Corrosion Resistance Applied on Municipal Solid-Waste Incinerators

Oxidation of exchanger steel tubes causes important problems in Municipal Solid-Waste Incinerator (MSWI) plants. The present paper shows a possible solution for this problem through High-Velocity Oxygen Fuel (HVOF) thermal spray coatings. A comparative study was carried out between powder and wire Ni-based thermal spray coatings (with the same composition). These optimized coatings were compared based on their microstructure, wear properties (ASTM G99-90, ASTM G65-91), and erosion-corrosion (E-C) resistance. An E-C test designed in the Thermal Spray Centre was performed to reproduce the mechanisms that take place in a boiler. Studying the results of this test, the wire HVT Inconel coating sprayed by propylene appears to be the best alternative. A commercial bulk material with a composition similar to Ni-based coatings was tested to find the products of the oxidation reactions. The protective mechanisms of these materials were assessed after studying the results obtained for HVOF coatings and the bulk material where the presence of nickel and chromium oxides as a corrosion product can be seen. Kinetic evolution of the Ni-based coatings can be studied by thermogravimetric analysis. The protection that Inconel coatings give to the tube through the difference of the gain mass can be seen. Ni-based HVOF coatings by both spray conditions are a promising alternative to MSWI protection against chlorine environments, and their structures have a very important role.     

Improved wear performance by the incorporation of solid lubricants during thermal spraying

For components that are required to function in sliding or rubbing contact with other parts, degradation often occurs through wear due to friction between the two contacting surfaces. Depending on the nature of the materials being used, the addition of water as a lubricant may introduce corrosion and accelerate the degradation process. To improve the performance and increase the life of these components, coatings may be applied to the regions subject to the greatest wear. These coatings may be engineered to provide internal pockets of solid lubricant in order to improve the tribological performance. In the present study, coatings containing a solid lubricant were produced by thermal spraying feedstock powders consisting of a blend of tungsten carbide-metal and a fluorinated ethylene-propylene (FEP) copolymer-based material. The volume content of this teflon-based material in the feedstock ranged from 3.5 to 36%. These feedstocks were deposited using a high velocity oxy-fuel (HVOF) system to produce coatings having a level of porosity below 2%. Sliding wear tests in which coated rotors were tested in contact with stationary carbon-graphite disks identified an optimum level of teflon-based material in the feedstock formulation required to produce coatings exhibiting minimum wear. This optimum level was in the range of 7 to 17% by volume and depended on the composition of the cermet constituent. Reductions in mass loss for the couples on the order of 50% (an improvement in performance by a factor of approximately 2) were obtained for the best performing compositions, as compared to couples in which the coating contained no solid lubricant.