Abrasive wear behaviour of powder flame sprayed coatings on steel substrates

The main purpose of thermal spraying method is to produce wear resistant surfaces. Easy applicability, very low possibility of metallurgical changes and low distortion of coated parts due to low heat transfer to the substrate and salvation of worn parts are some of the practical advantages of this process. In this study, abrasive wear behaviour of powder flame sprayed coatings on steel substrates has been investigated. Coating was carried out onto both hot and cold substrates by using four types of powders. Prior to the wear tests, the coated specimens were machined on a lathe and surface roughness and hardness measurements were carried out on the machined surfaces. Heating the substrates prior to the coating led to the decrease in the hardness of the coating layers. Abrasive wear resistance of flame sprayed coatings was seen to be dependent on the chemical composition and characteristics of coating materials and coating condition.     

Effect of Substrate Type on Deposition Behavior and Wear Performance of Ni-Coated Graphite/Al Composite Coatings Deposited by Cold Spraying

This work focused on the deposition characteristics and wear behavior of Ni-coated graphite mixed with40 vol.% Al(Ni-Gr/Al) composite coatings sprayed on an Al alloy and a steel substrate by cold spraying(CS). The morphology of the ?attened Ni-Gr particles was examined by single-impact tests. Crosssectional microstructure and wear performance of the Ni-Gr/Al composite coatings were studied. Results showed that a larger number of Ni-Gr particles were ?nally bonded with the steel substrate, whereas many craters existed on the Al alloy substrate after the single-impact tests. The coating on the steel substrate had a high thickness, high graphite content and low coe?cient of friction(COF) compared to those on the Al alloy substrate. In addition, the CS coatings presented a homogeneous distribution and uniform morphology of graphite, and a comparative COF to that of conventional thermal sprayed coatings. It was shown that CS could avoid the decomposition and transformation of graphite phase.     

Development of wear resistant composite surface on mild steel by laser surface alloying with silicon and reactive melting

The present study concerns laser surface alloying with silicon of mild steel substrate using a high-power continuous wave CO₂ laser with an objective to improve wear resistance. The effect of surface remelting using nitrogen as shrouding environment (with and without graphite coating) on microhardness and wear resistance has also been evaluated. Laser surface alloying leads to formation of a defect free microstructure consisting of iron silicides in laser surface alloyed mild steel with silicon and a combination of silicides and nitrides when remelted in nitrogen. Carbon deposition prior to remelting leads to presence of a few martensite in the microstructure. A significant improvement in microhardness is achieved by laser surface alloying and remelting to a maximum of 800 VHN when silicon alloyed surface is melted using nitrogen shroud with carbon coating. A detailed wear study (against diamond) showed that a significant improvement in wear resistance is obtained with a maximum improvement when remelted in nitrogen atmosphere followed by carbon coating.     

Ni60喷焊层与ZG06Cr13Ni5Mo抗气蚀性能的研究

采用火焰喷焊法在低碳钢试样表面制备了Ni 60喷焊层,与水力机械材料ZG06Cr13Ni5Mo的抗气蚀性能进行对比.借助光学显微镜、X射线衍射仪、显微硬度计、磁致伸缩气蚀仪等设备对涂层的组织、结构和性能进行了研究,利用扫描电镜对气蚀形貌进行了观察.结果表明:Ni 60喷焊层组织较细,显微硬度远高于ZG06Cr13Ni5Mo;其抗气蚀性能和ZG06Cr13Ni5Mo相比有所提高.     

热丝CVD法制备金刚石涂层刀具的研究现状

金刚石涂层刀具具有优异的硬度、耐磨性及导热性,在军事、航空航天等高精尖应用领域加工石墨、高硅铝合金、碳纤维增强塑料等难切削材料时无可替代,但目前金刚石涂层刀具存在两个问题:一是涂层与刀具间膜基结合力较差,导致涂层在使用中过早脱落;二是涂层表面粗糙度较大,难以保证被加工面的平整度与尺寸精度。本文从增强涂层结合力与降低涂层粗糙度两方面,将近年来科研人员对HFCVD法制备金刚石涂层的研究成果加以综述,并分析了各种因素对金刚石涂层刀具性能的影响。     

Mechanical properties of thermally sprayed Fe based coatings

Abstract

An additional coating against wear or corrosion on component parts is required for many applications. These coatings protect the substrate material against external influences, thus increasing the economic lifetime of the component. Coating processes such as build-up welding and thermal spraying are well established and commonly used. The thermal spray process, in particular, permits deposition of metals, ceramics, or cermets materials to produce near net shape coatings on complex surface geometries. However, commonly used coating materials suffer from high raw material costs, thus decreasing the cost effectiveness of the coating process. Fe based materials are low priced and possess noteworthy mechanical properties; they thus provide the possibility of substituting the expensive Ni and Co based materials commonly used for thermal spray processes. In this work, 2 mm thick high velocity oxyfuel sprayed Fe based coatings in the as sprayed and thermally sprayed and hot isostatic pressed condition were investigated with respect to their mechanical and wear properties. Additionally, the fracture surface was investigated by scanning electron microscopy to characterise the fracture behaviour. It could be demonstrated that the substrate and the heat treatment have the greatest impact on the shear strength of thermally sprayed cold work tool steel. It is shown that the substrate materials as well as the heat treatment are promoting diffusion processes across the interface between the coating and the substrate. Hence, a material integrated bond is formed. The microstructures of the thermally sprayed coatings become more important regarding the mechanisms of failure of the four point bending tests. The material strength is influenced by quenching and tempering and the specimen deflection is influenced by diffusion reactions induced by hot isostatic pressing treatment. The thermally sprayed coatings in the as sprayed condition feature the highest wear resistance due to their hardness.     

化学镀镍对碳纤维增强聚酰亚胺表面WC/Co涂层抗热震性能的影响

在航空发动机涡轮叶片用碳纤维增强聚酰亚胺(C/PMR15)复合材料表面喷涂WC/Co涂层可以提高其抗氧化耐冲刷性能,采用整体热震法能够评定涂层与基体的结合力.研究了在C/PMR15基体上化学镀镍作为粘结底层对WC/Co喷涂层抗热震性能的影响,并与喷涂PMR15粉末作为过渡层的方法进行了比较.结果表明,在PMR15过渡层上不能得到完整的后续涂层,在化学镀镍粘结底层上可得到连续致密的镍基合金层和WC/Co涂层,镀镍层大幅度提高了基体抗氧化能力,缓和了WC/Co涂层和基体界面位置的热应力,涂层抗热震性提高.     

Effects of surface alloying on microstructure and wear behavior of ductile iron

In this research, the effect of austenitic stainless steel cladding on improving the wear behavior of ductile iron was studied. Samples made of ductile iron were coated with steel electrodes (E309L) by manual shielded metal arc welding. The effect of coated layer thickness on microstructure, hardness, and wear resistance of the surface were investigated. Wear resistance of the samples was measured using the pin-on-plate technique. Optical microscopy and scanning electron microscopy were used to investigate microstructure and wear mechanisms. The phases in the interface of both the coating and the substrate were studied by X-ray diffraction. The results showed that a film of white chromium-enriched iron formed at the interface between the substrate and coating which contained iron–chromium complex carbides. It was, therefore, concluded that enhanced properties would be obtained if the coating thickness and the carbides deposited on the surface were reduced. In samples with a thin coating, surface hardness rose to above 1150 HV (five times higher than that of the substrate) and wear resistance increased significantly.     

Effect of Mo on the VC–VB particles reinforced Fe-based composite coatings

VC–VB particles reinforced Fe-based composite coatings with different molybdenum contents were in-situ fabricated by laser cladding. The microstructure and properties of the coatings were systematically investigated by means of micro hardness tester, XRD, SEM, EDS, ring-block wear testing machine and box-type resistance furnace. The results showed that both hardness and wear resistance of the coatings were greatly improved. When the content of Mo exceeds 3%, anti-oxidation of the coating decreased. Through analysing of the oxidation kinetics curves at different temperatures of the samples, it can be found that the coating with 2.5% Mo has the preferable oxidation resistance at 600°C, and its antioxidant property is five times of the coating without Mo, two times of the substrate.     

Chemically vapour deposited diamond coatings on cemented tungsten carbides: Substrate pretreatments, adhesion and cutting performance

Chemical vapour deposition (CVD) of diamond films onto Co-cemented tungsten carbide (WC-Co) tools and wear parts presents several problems due to interfacial graphitization induced by the binder phase and thermal expansion mismatch of diamond and WC-Co. Methods used to improve diamond film adhesion include substrate-modification processes that create a three-dimensional compositionally graded interface. This paper reviews substrate pretreatments and adhesion issues of chemically vapour deposited diamond films on WC-Co. The combined effect of pretreatments and substrate microstructure on the adhesive toughness and wear rate of CVD diamond in dry machining of highly abrasive materials was analyzed. The role of diamond film surface morphology on chip evacuation in dry milling of ceramics was also investigated by comparing feed forces of coated and uncoated mills. The overall tribological performance of diamond coated mills depended on coating microstructure and smoothness. The use of smother films did allow to reduce cutting forces by facilitating chip evacuation.     

Effects of friction stir processing on wear properties of WC–12%Co sprayed on 52100 steel

A WC–12%Co coating was thermally sprayed on a 52100 steel substrate and subsequently friction stir processing (FSP) was performed on this layer. The wear resistance and hardness was compared before and after FSP. Optical and SEM revealed that FSP intermixes the sprayed layer with the substrate, reduces porosity, and enhances both hardness and wear performances. 3D profilometry mapping was conducted to evaluate the wear track depth and its morphology. Refined grain structures and a martensitic structure with retained austenite are promoted by the FSP treatment. This leads to formation of new intermetallic and carbides which were detected by X-ray diffraction, thus accounting for the increased hardness and improved wear resistance.     

Keramik-Polymer Kombinationsschichten

Ceramic Polymer Composite Coatings The tribological properties of ceramic-polymer composite coatings which consist of thermal sprayed oxide ceramics coated with polymer lacquers for numerous industrial applications are discussed in this paper. The surface of these coatings match the requirements of high wear resistance and low coefficient of friction which is desired for many industrial applications. For experimental evaluation, samples were fabricated by coating aluminum substrates with titanium dioxide by means of atmospheric plasma spraying (APS). This oxide ceramic surface was successively coated by means of air spraying with a polymer lacquer containing molybdenum disulphide (MoS₂) and polytetrafluor ethylene (PTFE) as solid lubricants. The tribological properties (coefficient of friction and wear) of this combination layer were determined using a tribometer under oscillating sliding movement.     

Construction and characterization of a sputter deposition system for coating granular materials

In many modern ceramic or metal matrix composites the interface between the matrix and the reinforcements (particles or fibres) plays an important role. Either no or only weak mechanical bonding is observed or severe reactions between the matrix and the filler during the manufacturing process take place. A method to promote adhesion or to avoid severe reactions is to use coated reinforcements. A uniform film can act as an adhesion promoter, a compliant layer, a reaction inhibitor or a promoter of thermal transport across the interface.The aim of this work was to construct a particle coating system based on magnetron sputter deposition which allows to keep the particles or the granular material in motion during the deposition process to guarantee a homogenous coating on every single particle. As particles to be coated diamond granulates and carbon fibres were investigated. For transparent diamond particles the uniformity of a metallic coating could be evaluated by transmission optical methods and was found to be quite high. Carbon fibres, on the other hand, could only partially be coated due to agglomeration and shadowing effects. The system presented here can be considered as suitable for coating spherical or close to spherical granular matter.     

Preparation and Microstructure of a Si-Mo Fused Slurry Coating on Carbon/Carbon Composites for Oxidation Protection

A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure St slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation resistance and the thermal shock resistance of the Si-Mo fused sluury coating were quite excellent at 1730℃     

激光熔覆镍基合金层的组织与高温耐磨性能

为了改善304不锈钢工件的高温耐磨性能,利用CO2激光器在其表面熔覆了Ni基高温合金层。研究了熔覆层的物相组成、显微组织、成分分布,测试了其显微硬度、高温耐磨性能等,并与基材进行了对比。结果表明:Ni基合金熔覆层的组织从熔池底部到表层为胞状晶—柱状枝晶—树枝晶;熔覆层的主要组成相是Ni3Cr2,NbC,Mo2C与Cr23C6;Ni基合金粉末中添加难熔元素Cr,Mo,Nb等对熔覆层的组织起到了固溶强化、硬质相强化和弥散强化作用;熔覆层的平均显微硬度达到了405 HV,高温耐磨性能是基体的2倍多。     

超音速火焰喷涂Cr3C2-NiCr涂层腐蚀冲蚀磨损特性

在腐蚀冲蚀磨损试验机上,用5%H2SO4和质量分数15%棕刚玉组成的腐蚀-冲蚀磨损介质,对不同燃气流量下HVOF喷涂Cr3C2-25%NiCr涂层腐蚀冲蚀磨损性能进行了试验研究,测定了涂层单位面积失重量随腐蚀冲蚀磨损时间和冲蚀角度的变化,用扫描电镜观察了涂层断面组织形貌,分析了涂层腐蚀冲蚀磨损机制.研究表明,涂层的腐蚀...     

Wear of metal/PTFE coatings in rolling line contact

The paper presents results of an investigation to assess the performance of aluminium bronze coatings and molybdenum coatings both filled with PTFE and deposited on steel substrate in rolling line contact. The experimental results show that both types of coating studied have an outstanding wear and surface fatigue resistance. Under pure rolling conditions, the aluminium bronze coating was found to be more wear resistance than molybdenum coating. However, after 1.2 × 10⁶ load cycles under the normal load of 36 N and 98 N, both coatings did not suffer any serious surface damage. Optical and scanning electron microscopy studies indicated that surface asperity peaks present in the coating supported the load. PTFE initially present in the coating was mainly lost due to a mild adhesive wear resulting in transfer film formation on the steel couter-surface. This, in turn, provided efective solid lubrication for the contact zone.     

电磁轨道失效与表面喷涂Mo技术研究

为提高电磁轨道材料性能,采用等离子喷涂技术在45CrNiMoVA钢表面制备了Mo涂层,观察了涂层显微形貌,测试了显微硬度和载流摩擦磨损性能,并与基体进行了比较。结果表明:Mo涂层显微硬度平均值为482.3HV1 N,比基体45CrNiMoVA钢硬度提高1倍。涂层与基体结合强度为41.5 MPa,结合方式为机械结合;同等载流摩擦磨损试验条件下,与基体45CrNiMoVA钢相比,Mo涂层磨合时间较短,摩擦系数更小(0.6),耐电弧烧蚀能力强,磨损量小;涂层磨损机理为断续式黏着磨损。     

铝合金内表面电爆炸喷涂不同比例钼-高碳钢的性能对比研究

为了提高铝合金工件内表面的耐磨损能力,采用电爆炸喷涂技术在LY12基体上进行了制备钼和80号高碳钢复合涂层的实验研究.通过钼/高碳钢交替喷涂制备了钼和高碳钢的喷涂次数比分别为1:1和1:2的复合涂层,并对涂层进行了检测.结果表明,电爆炸喷涂的复合涂层形成了良好的冶金结合,涂层具有硬度高、抗磨损、粗糙度小、结合强度好的优点,层数比为1:2时涂层的性能更加优越.     

Bilayer systems of tantalum or zirconium nitrides and molybdenum for optimized diamond deposition

Thermo chemical computing validates the stability of different nitrides against Co, Mo, and methane up to 1150 K, showing the highest chemical stability against carburization for ZrN and TaN under static conditions.Single zirconium and tantalum nitrides layers have been sputtered onto WC-Co substrates as diffusion barriers and buffer layers under specific reactive sputtering conditions. To improve the nuclei density of diamond during CVD processing, a thin Mo extra layer has been added (< 500 nm). In this study, two bilayer systems have been tested: TaN-Mo and ZrN-Mo. Nano crystalline diamond has been grown under negative biased substrates.After diamond deposition, a massive carburization of molybdenum and tantalum nitride is observable whereas zirconium nitride is not. Nevertheless, a small amount of cobalt has migrated through the ZrN layer. The better efficiency of the ZrN layer to prevent diffusion of the Co element, leads to expect an increased adhesion of diamond on ZrN-Mo bilayer coating. A TEM study is done to improve understanding of phenomena occurring at the interfaces during process.