金属材料表面爆炸喷涂WC-Co涂层的均匀性性能分析及数学描述

利用扫描电子显微镜和X射线衍射分析仪研究喷涂距离和氧燃率对爆炸喷涂WC-Co涂层性能的影响。结果表明,WC-Co涂层的最佳爆炸喷涂距离为110 mm,氧燃率为1.06。WC-Co涂层结构致密、耐磨性好,拥有近似各向同性的特征。     

石墨烯改性自润滑耐磨涂层的组织与耐磨机理研究

为了降低WC-Co涂层的摩擦系数,采用湿法球磨工艺实现了氧化石墨烯和WC-Co喷涂粉末的均匀混合,基于爆炸喷涂技术制备了氧化石墨烯改性WC-Co涂层。借助XRD、SEM、EDS等手段分析了涂层的氧化石墨烯存在、组织结构形貌、化学成分组成。采用显微硬度计、万能拉伸机及UMT-2摩擦磨损试验机等仪器研究了涂层的力学及摩擦磨损性能。结果表明：氧化石墨烯改性后涂层内均匀分布有片层状氧化石墨烯,涂层组织致密、均匀,结合强度约82MPa,显微硬度为1024HV0.3,氧化石墨烯改性后涂层相比WC-Co涂层摩擦系数降低了30%,氧化石墨烯的添加提高了WC-Co涂层的抗磨、减磨性能。     

氧气-空气混合助燃超音速火焰喷涂WC-Co涂层性能研究

采用液体燃料氧气-空气混合助燃超音速火焰喷涂(HVO/AF)工艺在45钢表面制备WC-Co涂层,采用扫描电镜(SEM)、X射线衍射(XRD)表征了涂层的微观结构及相组成,并对涂层的孔隙率、显微硬度和结合强度进行了分析.研究结果表明,采用液体燃料氧气-空气混合助燃超音速火焰喷涂制备的涂层均具有较好的性能,超音速火焰喷涂氧气与空气混合比例对涂层的性能影响较大,采用HVO/AF喷涂技术能有效地抑制WC的氧化和分解,降低了涂层的孔隙率,提高了WC-Co涂层的硬度和结合强度等性能.涂层质量要好于传统的氧气助燃超音速火焰喷涂.     

粉末结构对冷喷涂纳米结构WC-Co沉积行为的影响

纳米结构WC-Co具有比常规WC-Co更高的硬度,因此受到了广泛关注.冷喷涂制备纳米结构WC-Co涂层过程中,因粒子温度低于熔点,沉积过程需要依靠WC-Co粒子的塑性变形,然而WC-Co粒子变形能力有限,使得WC-Co涂层难以实现有效沉积.文中从粉末结构角度出发,选用3种不同孔隙结构的WC-12Co粉末,运用扫描电镜研究不同结构WC-12Co单个粒子在基体上的沉积行为,分析了3种粉末在相同喷涂工艺参数下沉积的涂层的组织结构.研究发现,定点喷涂容易实现,沉积的WC-12Co沉积层组织结构致密,硬度接近块材,为粉末的连续沉积制备涂层提供了可能.涂层的连续沉积需要粉末和基体材料均产生一定的变形,具有一定孔隙结构的纳米结构WC-Co粉末,因其多孔结构促进了粉末拟变形的发生,适合于冷喷涂制备纳米结构WC-Co涂层.     

氧化石墨烯改性自润滑耐磨涂层的组织与耐磨机理

为了降低WC-Co涂层的摩擦系数,采用湿法球磨工艺实现了氧化石墨烯(Graphene Oxide,GO)和WC-Co喷涂粉末的均匀混合,基于爆炸喷涂技术制备了氧化石墨烯改性WC-Co涂层。借助XRD、SEM、EDS等手段分析了涂层的氧化石墨烯存在、组织结构形貌、化学成分组成。采用显微硬度计、万能拉伸机及UMT-2摩擦磨损试验机等研究了涂层的力学及摩擦磨损性能。结果表明:氧化石墨烯改性后涂层内均匀分布有片层状氧化石墨烯,涂层组织致密、均匀,结合强度约82 MPa,显微硬度HV0。3为10062 MPa,氧化石墨烯改性后涂层相比WC-Co涂层摩擦系数降低了30%,氧化石墨烯的添加提高了WC-Co涂层的抗磨、减磨性能。     

超音速火焰喷涂碳钢表面制备Ni9Al/WC-Co复合涂层组织与性能研究

采用高速电弧喷涂工艺在20钢样品表面制备了Ni9Al涂层,以其作为超音速火焰喷涂WC-Co涂层的中间层.采用光学显微镜分析、场发射扫描电镜分析以及性能测试方法,研究Ni9Al中间层对涂WC-Co涂层组织结构及性能的影响.结果表明:Ni9Al中间层能提高WC-Co涂层与基体的结合强度;Ni9Al/WC-Co复合涂层试样的热震试验结果表明,Ni9Al中间层显著改善了涂层抗热震性能.     

超音速火焰喷涂(HVAF) WC-Co合金涂层微观组织与耐磨性分析

采用超音速火焰喷涂(HVAF)工艺在Q235基体上制备了WC-Co涂层,并研究了涂层的显微组织和磨损性能。结果表明:WC-Co涂层与基体结合良好,涂层致密,孔隙率较低,微观形貌呈层状结构。EDS能谱表明涂层发生了较低氧化。涂层的显微硬度高达1244HV0.1。涂层开始时失重磨损率较高,而且随着法向载荷的增大而增加,随着时间增加磨损率不断降低,体现了WC-Co涂层优异的耐磨性能。     

NiCoCrAlYTa/WC-Co复合涂层的制备及摩擦学性能研究

目的 为了改善MCrAlY涂层的耐磨损性能,通过在NiCoCrAlYTa粉末中添加不同比例的硬质相WC-Co粉末（质量分数为25%、50%、75%）,将2种粉末充分地机械混合、振荡均匀后,采用超音速火焰喷涂（HVOF）技术,制备不同配比的NiCoCrAlYTa/WC-Co复合涂层。方法 利用SEM、XRD、EDS等分析了复合涂层的微观形貌、物相组成和元素分布规律等;研究该复合涂层的力学性能、摩擦学性能以及摩擦磨损机理等。结果 采用HVOF技术制备的Ni CoCrAlYTa/WC-Co复合涂层结构致密,各元素及物相分布均匀;硬质相WC-Co的添加提高了涂层的显微硬度,同时也可显著改善复合涂层的耐磨损性能;复合涂层的摩擦因数随着WC-Co含量的增加逐渐增大,而磨损率逐渐减小。当WC-Co的添加量为75%时,复合涂层的摩擦因数最大,约为0.84;磨损率最小,约为9.28×10^-6 mm³/（N·m）。结论 在金属基涂层中引入硬质相WC-Co可有效提高涂层的硬度,并且提升该涂层的耐磨损性能,为金属基涂层发挥优异的摩擦学性能提供理论基础。     

超音速火焰喷涂铁基非晶涂层的微观组织及性能

为增强海洋工程装备中关键部件的耐磨与抗腐蚀性能,采用超音速火焰喷涂(HVOF)技术在不锈钢基体表面喷涂Fe基非晶涂层。利用SEM、XRD和DSC等,对该涂层的微观组织、相结构及性能进行了分析。研究了喷涂中煤油流量、氧气流量、喷距对非晶涂层微观组织和性能的影响。结果表明,超音速火焰喷涂制备的铁基非晶涂层组织结构均匀致密,呈完全非晶态结构。喷涂工艺参数对涂层的显微硬度具有重要影响,在优化工艺参数下获得的显微硬度为912.1 HV0.3。不锈钢喷涂非晶涂层后耐磨性提高。     

HVOF技术制备的WC涂层的耐磨性

采用超音速火焰喷涂技术在45钢基体上制备WC-Co涂层,利用扫描电镜、X射线衍射仪、显微硬度计等设备对所获涂层的组织结构与性能进行分析.并通过磨粒磨损试验研究了WC涂层的耐磨性能.试验结果表明:所获WC-Co涂层与基体金属结合良好,界面处未发现污染.涂层较为致密,其显微硬度在HV1000以上;WC-Co涂层的耐磨性非常优异,经20 min磨损后,其磨损量仅为0.1 g左右;WC-Co涂层的磨损率一直呈下降趋势,与之相对比,电镀硬铬层的磨损率却呈先下降后上升的趋势,所获WC-Co涂层显示了更加稳定的耐磨性.     

Design of a separation device used in detonation gun spraying system and its effects on the performance of WC-Co coatings

During the detonation gun (D-gun) spraying process, the detonation products showed an undesirable dispersion when they were spurted out from the nozzle of the barrel at high velocity and pressure. To resolve this problem, a separation device was designed and constructed in the detonation gun spraying system. The WC-Co coatings were synthesized by the D-gun spraying system with and without using a separation device, respectively. The results showed that the use of the separation device resulted in better properties of the D-gun sprayed WC-Co coatings, e.g., lower the surface roughness, lower the porosity, higher the microhardness, higher the elastic modulus, and higher the interfacial adhesive strength. Also, the tribological performance of the WC-Co coatings was improved. The relationship of surface roughness, microhardness, elastic modulus, adhesive strength, and wear resistance of the WC-Co coatings with porosity was discussed. At the same time, there is an inevitable disadvantage for using the separation device, i.e., the relatively lower effective utility rate of the feedstock powder. Therefore, the separation device is suitable to be applied in occasions of high-performance requirements where increased costs are acceptable.     

The Influence of Spraying Angle on Properties of HVOF Sprayed Hardmetal Coatings

The spraying angle is one of the deposition parameters that influence the quality of thermally sprayed coatings. In theory, decreasing the spraying angle results in lower process deposition efficiency, whereas the porosity of coatings increases, becoming a cause of poorer microstructure and mechanical properties. In this study, the dependence of microstructure together with the basic mechanical properties and wear of WC-Co and Cr₃C₂-NiCr high-velocity oxyfuel (HVOF) sprayed coatings on the spraying angle was investigated. For each coating, the maximum spraying angle was determined that can be used without significantly decreasing coating quality. Based on the changes in properties of coatings and requirements for the process deposition efficiency, a maximum 30° diversion from the normal spray direction is recommended for WC-Co and 15° diversion for Cr₃C₂-NiCr coatings.     

A comparative study of tribological behavior of plasma and D-gun sprayed coatings under different wear modes

In recent years, thermal sprayed protective coatings have gained widespread acceptance for a variety of industrial applications. A vast majority of these applications involve the use of thermal sprayed coatings to combat wear. While plasma spraying is the most versatile variant of all the thermal spray processes, the detonation gun (D-gun) coatings have been a novelty until recently because of their proprietary nature. The present study is aimed at comparing the tribological behavior of coatings deposited using the two above techniques by focusing on some popular coating materials that are widely adopted for wear resistant applications, namely, WC-12% Co, A1₂O₃, and Cr₃C₂-MCr. To enable a comprehensive comparison of the above indicated thermal spray techniques as well as coating materials, the deposited coatings were extensively characterized employing microstructural evaluation, microhardness measurements, and XRD analysis for phase constitution. The behavior of these coatings under different wear modes was also evaluated by determining their tribological performance when subjected to solid particle erosion tests, rubber wheel sand abrasion tests, and pin-on-disk sliding wear tests. The results from the above tests are discussed here. It is evident that the D-gun sprayed coatings consistently exhibit denser microstructures and higher hardness values than their plasma sprayed counterparts. The D-gun coatings are also found to unfailingly exhibit superior tribological performance superior to the corresponding plasma sprayed coatings in all wear tests. Among all the coating materials studied, D-gun sprayed WC-12%Co, in general, yields the best performance under different modes of wear, whereas plasma sprayed Al₂O₃ shows least wear resistance to every wear mode.     

超音速等离子喷涂WC-17Co涂层的工艺及性能分析

以低成本压缩空气和丙烷作为工作气体,采用超音速等离子喷涂制备了WC-17Co涂层,研究了喷涂功率对涂层组织、孔隙率和相组成的影响,测试了涂层的抗压性和耐磨性.结果表明,喷涂功率显著影响粉末的熔化和脱碳程度,功率过小时,WC颗粒熔化程度低;功率过大时,WC严重脱碳生成W₂C甚至W相.喷涂功率为65 kW制备的涂层孔隙率最低（0.87%）,未出现严重脱碳产物钨,涂层具有很强的抗压入变形能力,由于高硬度WC颗粒的存在,涂层的耐磨性显著提高,其磨损量仅为基体的15%,磨损形式由基体的严重磨粒磨损+粘着磨损变为涂层的轻微磨粒磨损.     

Influence of Detonation Gun Spraying Conditions on the Quality of Fe-Al Intermetallic Protective Coatings in the Presence of NiAl and NiCr Interlayers

The paper presents results of detailed research of the application of detonation gun (D-gun) spraying process for deposition of Fe-Al intermetallic coatings in the presence of NiAl and NiCr interlayers. A number of D-gun experiments have been carried out with significant changes in spraying parameters which define the process energy levels (changes in volumes of the working and fuel gases, and the distance and frequency of spraying). These changes directly influenced the quality of the coatings. The initial results underlay the choice of the process parameters with the view to obtain the most advantageous of geometric and physical-mechanical properties of the coating material, interlayer and substrate. The metallurgical quality of the coatings was considered by taking into account grain morphology, the inhomogeneity of chemical content and phase structure, the cohesive porosity in the coating volume, and adhesive porosity in the substrate/interlayer/coating boundaries. The surface roughness level was also considered. It was found that the D-gun sprayed coatings are in all cases built with flat lamellar splats. The splats develop from powder particles which are D-gun transformed in their plasticity and geometry. A significant result of the optimization of D-gun spraying parameters is the lack of signs of melting of the material (even in microareas) while the geometry of the subsequently deposited grains is considerably changed and the adhesivity and cohesion of the layers proves to be high. This is considered as an undeniable proof of high plasticity of the D-gun formed Fe-Al intermetallic coating.     

Powder/processing/structure relationships in WC-Co thermal spray coatings: A review of the published literature

Thermally sprayed coatings based on tungsten carbide are widely used but not yet fully understood, particularly with regard to the chemical, microstructural, and phase changes that occur during spraying and their influence on properties such as wear resistance. The available literature on thermally sprayed WC-Co coatings is considerable, but it is generally difficult to synthesize all of the findings to obtain a comprehensive understanding of the subject. This is due to the many different starting powders, spray system types, spray parameters, and other variables that influence the coating structures and cause difficulties when comparing results from different workers. The purpose of this review is to identify broad trends in the powder/processing/structure relationships of WC-Co coatings, classified according to powder type and spray method. Detailed comparisons of coating microstructures, powder phase compositions and coating phase compositions as reported by different researchers are given in tabular form and discussed. The emphasis is on the phase changes that occur during spraying. This review concerns only WC-12% Co and WC-17% Co coatings, and contrasts the coatings obtained from the cast and crushed, sintered and crushed, and agglomerated and densified powder types. Properties such as hardness, wear, or corrosion resistance are not reviewed here.     

Selection criteria for wear resistant powder coatings under extreme erosive wear conditions

Wear-resistant thermal spray coatings for sliding wear are hard but brittle (such as carbide and oxide based coatings), which makes them useless under impact loading conditions and sensitive to fatigue. Under extreme conditions of erosive wear (impact loading, high hardness of abrasives, and high velocity of abradant particles), composite coatings ensure optimal properties of hardness and toughness. The article describes tungsten carbide-cobalt (WC-Co) systems and self-fluxing alloys, containing tungsten carbide based hardmetal particles [NiCrSiB-(WC-Co)] deposited by the detonation gun, continuous detonation spraying, and spray fusion processes. Different powder compositions and processes were studied, and the effect of the coating structure and wear parameters on the wear resistance of coatings are evaluated. The dependence of the wear resistance of sprayed and fused coatings on their hardness is discussed, and hardness criteria for coating selection are proposed. The so-called “double cemented” structure of WC-Co based hardmetal or metal matrix composite coatings, as compared with a simple cobalt matrix containing particles of WC, was found optimal. Structural criteria for coating selection are provided. To assist the end user in selecting an optimal deposition method and materials, coating selection diagrams of wear resistance versus hardness are given. This paper also discusses the cost-effectiveness of coatings in the application areas that are more sensitive to cost, and composite coatings based on recycled materials are offered.     

Tribological properties of plasma sprayed zircon-alumina powder mixture with and without laser re-melting

ABSTRACT

This investigation focusses on the wear mechanism of as-sprayed and laser treated mullite based coatings, produced by plasma spraying, under sliding wear condition. First, an alumina powder and zircon sand mixture was plasma sprayed to produce a mullite coating. Selected as-sprayed coatings were subsequently laser treated. The tribological performances of both as-sprayed and laser re-melted coatings were assessed using a pin-on-disc wear apparatus. Hardened steel and WC-Co balls served as rubbing counterparts. A plasma sprayed alumina coating was used for bench marking purposes. Plastic deformation was the dominant wear mechanism under low load-low speed condition for both as-sprayed and laser treated coatings. However, at higher loads and speeds the coatings were found to undergo micro-fracture followed by pulverisation. Wear resistance of the coatings improved following laser treatment.     

Study of the influence of microstructural properties on the sliding-wear behavior of HVOF and HVAF sprayed WC-cermet coatings

The microstructural properties of WC-Co-Cr and WC-Co coatings deposited by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) processes were investigated. The tribological behavior of the coatings was studied by means of pin-on-disk tests. Microcracking of the HVOF sprayed WC-Co coatings did not allow preparation of suitable disks for wear tests. The wear rates of the remaining coatings were determined, and wear tracks on the coatings and counterbodies were investigated by SEM. The HVAF sprayed coatings showed greater sliding-wear resistance compared to the HVOF coatings. The prime wear mechanism in the WC-Co HVAF coatings was adhesive wear. The cobalt matrix is lubricious, resulting in very low wear rates and low debris generation. The main wear mechanisms in the WC-Co-Cr coatings were adhesive and abrasive wear. Adhesive wear results in coating material dislodgments (i.e., “pullouts”) that become trapped in the contact zone and act as a third-body abrasive. Particle pullout from the coating significantly increases the wear rate of the coated specimen. The HVAF/WC-Co-Cr coatings exhibited better resistance to particle pullout, resulting in a considerably lower wear rate than the HVOF/WC-Co-Cr coatings.