Structure and wear resistance of R6M5 steel based coatings

Features of the structure of R6M5 steel based coatings obtained by multiscan electron-beam fusion of a hardening composition in vacuum have been studied. It is established that the carbide subsystem of the hardened layer is characterized by a multimodal distribution of carbide particles with d ₁ = 3.8 μm, d ₂ = 0.65 μm, and d ₃ < 0.25 μm. The volume fraction of M₆C secondary carbide and retained matrix austenite can be controlled within broad limits by varying thermal parameters of the electron-beam fusion. An increase in the retained austenite fraction in the coating leads to improved wear resistance due to the γ → α′ marten-site transformation during friction and the presence of dispersed secondary carbides inside the matrix grains.     

Effect of WC Particle Size on the Abrasive Wear of Thermally Sprayed WC-Co Coatings

Four types of WC-Co powders with different WC particle sizes are sprayed to produce WC-Co coatings with a Jet-Kote gun using a gas mixture of C₂H₂-30% C₃H₆ and pure propylene as fuel gases. The carbide size in sprayed high velocity oxy-fuel (HVOF) WC-Co coatings is measured from the microstructure. The abrasive wear of the coatings is characterized using a Suga abrasive wear tester. The abrasive wear mechanism of thermally sprayed WC-Co is discussed. The relationship between the relative wear of WC-Co coatings and carbide sizes is established according to the strength theory on hard alloy. The correlation with experimental data proves that the relative abrasive wear of WC-Co coating is proportional to square root of relative carbide size.     

Influence of size and volume share of WC particles on the properties of sintered metal matrix composites

Steel matrix composites are being increasingly investigated because of their wear and corrosion properties, allowing their wide application in various industrial sectors. The interaction of tungsten carbide (WC) with the steel matrix, including an analysis of its volume share and particle size, is crucial in determining the resistance to wear and corrosion of the metal matrix composite (MMC). However, there is little information in the literature about sintered MMCs based on low-alloy steels. This paper presents the results of an analysis of the influence of the volume share of WC (5?vol.% and 20?vol.%) and carbide particle size (0.7?µm and 5.0?µm) on the resistance to abrasion of a friction pair: sintered composite and bearing steel, analysed using two rotational speeds (0.02?m/s and 0.2?m/s). Moreover, the resistance to corrosion in 3.5% NaCl solution is also characterized. It is shown that both the volume share and the size of the WC particles used as reinforcement of the steel matrix have a significant impact on the densification behaviour as well as the resistance to abrasive wear and corrosion of sintered MMCs based on low-alloy steel.     

Coarse WC Particles Ceramic-Metal Composite Coating by Laser Cladding

The coarse WC particles ceramic-metal com-posite coatings with WC density of 67 wt-% andthickness of 1.0-1.2 mm have been cladded on20Ni4Mo steel surface by a 2 kW CO_2 laser.Thesintered WC particles with the size of 600-1000 μmare chosen as the main strengthening phase,Ni-base self-flux alloy as the binder in the compo-site coatings.The microstructure andmicrohardness of both WC particles and binder areanalysed.The rigid ball indention with acousticemission technique is used to evaluate thebrittleness of the coating.Finally,the abrasive wearresistance of the coating is tested.Besides,thecoatings with the same ratio and size of WC parti-cles in low carbon steel tube rod were cladded on20Ni4Mo steel by atomic hydrogen welding tech-nique and analysed by the same way,their resultsare compared.     

Abrasive wear of Al‐SiC composites

The two‐ and three‐body abrasion of aluminium matrix composites, reinforced with silicon carbide particles, have been investigated. The metal matrix composites were fabricated by a powder metallurgy route involving a final hot extrusion step. Air atomised aluminium powder Al 1100 was used as matrix and α‐SiC_p as reinforcement with mean sizes of 10, 27 and 43 μm; in the proportions of 5, 10 and 20 vol.%. Using a pin‐on‐disc apparatus and a wet monolayer tester, two‐ and three‐body abrasion tests were carried out respectively against silicon carbide and alumina abrasives with four different grit sizes. The microstructural characterizations were performed using light microscopy. The dominant wear mechanisms were identified using scanning electron microscopy. The influence of type of the abrasive particles on wear resistance and dominating wear mechanisms was reported. Relationships between size and volume fraction of the SiC_p reinforcement and wear resistance were discussed. It was shown that SiC_p particles reinforcement increases the abrasion resistance against all the abrasives used. This increase was generally higher against alumina than against silicon carbide abrasives.     

Untersuchungen zur Beständigkeit thermisch gespritzter Schichten im Vergleich zu Hartchromschichten bei durch Abrasion dominierter tribologischer Beanspruchung

Investigations on thermal spray coatings resistance against abrasion dominated tribological load in comparison to hard chromium coatings HVOF iron and nickel based hard alloy as well as WC/Co(Cr) and Cr₃C₂/Ni20Cr coatings are compared to APS Al₂O₃/TiO₂ and Cr₂O₃, powder flame sprayed and fused composite coatings consisting of NiCrBSi and WC/Co and electrolytically deposited hard chromium coatings concerning their wear behavior for tribological load by lose abrasive particles (ASTM G65 and ASTM G75). Thereby the influence of newly developed HVOF torch combustion chambers with reduced critical diameter and divergent expansion nozzles that both permit increased combustion gas and therefore also particle velocities on microstructure and wear resistance of the produced coatings is studied. While there is no improvement of wear resistance for hard alloy coatings compared to mild steel substrates for the specific tribological boundary conditions of these tests, especially the carbide reinforced coatings permit improvement by more than one order of magnitude in ASTM G65 tests and even more than two orders of magnitude in ASTM G75 tests. Also, for both types of tribological load HVOF coatings with WC as reinforcing phase are clearly superior to electrolytically deposited hard chromium coatings. Both use of the combustion chamber with reduced critical diameter and the expansion nozzles with divergent contour result in improved wear resistance of the thereby produced coatings. The specific wear mechanisms are deduced based on SEM examination of worn specimen surfaces.     

Abrasive wear of plasma coatings with different structures on titanium alloys

We study the influence of plasma coatings having different structural and phase compositions on the serviceability of TS-5 titanium alloy under different kinds of abrasive wear. By means of X-ray phase analysis, we have detected significant changes in the composition of plasma coatings in comparison with the initial composition of the powders, interphase interaction between the components of these coatings, and the formation of complex coatings with nonidentified phases. We have corroborated that the intensity of abrasive wear under conditions of nonrigidly fastened abrasive particles is lower. The greatest changes in the test chart take place in the case of abrasive wear of the plasma coating POAN-30. The highest abrasive resistance is characteristic of a plasma coating with complex titanium and chromium carbide.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 4, pp. 63–69, July–August, 2004.     

NAK80模具钢表面2种激光器熔覆Ni基碳化钨合金层组织结构及耐磨性比较

为了研究激光器对Ni基碳化钨合金熔覆层组织结构和性能的影响,分别采用Nd:YAG与CO2激光熔覆技术在NAK80模具钢表面制备了Ni基碳化钨合金层,利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪、显微硬度计以及摩擦磨损试验机测试分析了2种熔覆层的组织结构、显微硬度及耐磨性能。结果表明:2种熔覆层与基体之间均呈现良好的化学冶金结合;熔覆层组织主要为粗大的未熔碳化钨颗粒和均匀分布的树枝晶,Nd:YAG激光熔覆层的组织比CO2激光熔覆层的细小;2种熔覆层相结构主要包括WC,W2C,Cr23C6,NiCr,CrB2以及γ-Ni等;2种激光器熔覆处理后,NAK80模具钢表面硬度和耐磨性都得到显著改善,CO2激光熔覆层的硬度和耐磨性高于Nd:YAG激光熔覆层,2种激光熔覆试样的磨损机制均为磨粒磨损。     

Grain size effect on wear resistance of WC-Co cemented carbides under different tribological conditions

The grain-size dependence of wear resistance of WC-Co cemented carbides(with mean WC grain sizes of 2.2 μm,1.6 μm,0.8 μm and 0.4 μm,respectively) was investigated under different tribological conditions.The results showed that the grain size had opposite effects on wear resistance of the cemented carbides in dry sliding wear and microabrasion tests.In the former condition,with decrease of WC grain size hence the increase of hardness,plastic deformation,fracture,fragmentation and oxidation were all mitigated,leading to a drastic decrease in the wear rate.In the latter condition,pull-out of WC grains after Co removal dominated the wear,so that the hardness of cemented carbide was not a core factor.As a result,the wear resistance of the cemented carbide generally showed a decreasing trend with decrease of the grain size,except for a slight increase in the ultrafine-grained cemented carbide.Single-pass scratching of the cemented carbides under various loads indicated the same failure mechanism as that in the sliding wear tests.Furthermore,the reasons for severe surface oxidation of the coarse-grained cemented carbides were disclosed.     

Complex carbide powders for plasma spraying

Various carbide-containing powders are used for plasma spraying. Most of these consist of tungsten carbide. Very frequently the tungsten carbide is mixed with cobalt to produce coatings similar to cemented carbides. The powders can be made by agglomeration of the carbides and the metal matrix powders or by coating the carbides with the matrix metal. As in cemented carbides, cobalt and nickel form the metal binder of the coatings. The coating metals can be increased to 20% of the total weight. Further metal matrix powders can be added also. The W₂C, WC, W₂C-WC eutectic phases and mixtures of them are used as tungsten carbide. The carbon content is very important and can be controlled better in coated particles than in an agglomerated powder. In the case of WCCo the carbon content has to correspond to MC to avoid the embrittling η phase and to achieve a strength of the coating comparable with that of cemented carbides. In addition to the composition, shape and grain size distribution of the powders, the spraying conditions are very important for the properties of the coating. Coated carbide powders are less sensitive to spraying conditions. When it is possible to control the carbon content in carbides better during spraying it will be feasible to use complex carbides also.Titanium carbide forms a solid solution with WC over a wide range of composition and forms mixed crystals with tantalum carbide and niobium carbide. These binary and ternary mixed carbide crystals, sometimes containing additional tungsten carbide, are used in cemented carbides to increase the wear resistance. By spraying these cobalt- or nickel-coated complex carbide powders similar properties of the coatings can be achieved. Spraying conditions and the shape, grain size and grain size distribution of the powders are important. Results will be given.     

Abrasive wear of epoxy composites filled by abrasive particles and reinforced by polyamide fibres

Abrasive wear caused by sandy soil of steel coated by epoxy resin was investigated. Experiments were carried out using an abrasive wear tester developed to simulate the wear of the tillage tools under controlled testing conditions. Epoxy coatings were filled by abrasive particles such as aluminium oxide, silicon carbide and silicon oxide of different particle size. Also, epoxy coatings were reinforced by polyamide fibres of different diameters. The test results showed that, relatively lower wear values were displayed by epoxy coatings filled by silicon oxide particles of 5 wt% content. The wear values performed by silicon oxide of (10–20) μm particle size were lower than that displayed by uncoated steel surface. Solid lubricant such as graphite and molybdenum disulphide as filling material caused significant increase in wear due to the weak adhesion between epoxy/solid lubricant layers. Wear of epoxy reinforced by polyamide fibres showed the minimum wear values. Orientation of fibres much affected wear. Parallel fibres represented higher wear than perpendicular ones. The minimum wear was observed for cross plied coatings where shorter wear tracks and higher tensile strength in both perpendicular and parallel directions were existed. The minimum wear values which were lower than that displayed by uncoated steel test specimens were displayed by 0.1 and 0.3 mm polyamide fibre diameters. This observation confirmed the application of the polyamide fibres as reinforcement in epoxy coatings.     

Microstructure and mechanical characteristics of iron-based coating prepared by plasma transferred arc cladding process

This paper investigated the effect of electromagnetic stirring (EMS) on the microstructure and abrasive wear behavior of iron-based coatings. A series of coatings were prepared by using plasma transferred arc cladding (PTAC) process. The phase and structure of the coatings were characterized by means of SEM, EDXA and X-ray diffraction. The microstructure of the coatings was mainly γ-Fe matrix and (Cr, Fe)₇C₃ carbide reinforced phases. Without EMS, the average size of (Cr, Fe)₇C₃ carbide was about 73 μm, while that of the carbide reached a minimum value of about 20 μm with stirring current of 3 A. The mechanical properties, especially wear resistance, were analyzed in detail. The results showed that the microstructure of the coating plays an important role on abrasive mechanism and the main mechanism is micro-cutting. When the stirring current is 3 A, the coating exhibits excellent wear resistance, which contributes to the good microstructures that hexagonal (Cr, Fe)₇C₃ carbide with the highest volume fraction are uniformly distributed in the matrix. The microhardness of the coatings increase at first, and then decrease as a function of stirring current. The maximum microhardness value of the coating is about 1050 HV.     

Laser surface alloying of case hardening steel with tungsten carbide and carbon

Abstract

The laser surface alloying process was used to introduce two different alloying materials, tungsten carbide (WC/Co) and carbon, into the molten surface of a case hardening steel (16MnCrS5), to improve its hardness and wear resistance. The chemical composition and the resulting microstructure in the alloyed layers were of particular interest in this investigation, because the strengthening mechanism was strongly dependent upon the type and amount of the alloy material. For laser alloying with carbon the increase in hardness and wear resistance was based on the martensitic transformation in the composition range concerned. For alloying with tungsten carbide it was necessary to consider two different strengthening mechanisms, namely, martensitic transformation and precipitation of carbides. In both cases the grain refinement in the laser affected zone had an additional effect. Resistance to dry abrasive sliding wear was measured using a conventional pin-on-disc wear testing machine. For both alloy materials the wear rate was substantially lower than that of a substrate that had been laser remelted without alloying additions.

MST/1556     

The structure and properties of a hard alloy coating deposited by high-velocity pulsed plasma jet onto a copper substrate

Using a plasmatron operating in specially calculated regimes, tungsten carbide (WC) based coatings were deposited onto a copper crystallizer plate. It was found that a local hardness of the WC-Co coating may reach up to 1.3×10₄ N/mm² and the coating adhesion to substrate may be as high as 270 MPa. The elemental and phase compositions of coatings were studied by Rutherford backscattering spectroscopy, X-ray diffraction, and transmission electron microscopy with electron diffraction. The surface morphology and depth-composition profiles of the coatings were studied by optical and scanning electron microscopy. The coating is composed of WC crystal grains with hexagonal close packed (hcp) lattice, α-and β-Co grains, and cubic WC grains. The average size of the hcp WC grains is 0.15 μm and that of the cobalt particles is about 25 nm. In addition, the grain boundaries contain W₃Co₃C particles with an average size of 15 nm.     

Verschleiß von TaC- und TiC-Laserdispersionsschichten durch weiche und harte Abrasivstoffe

Wear of TaC and TiC steel composite hardfacings by soft and hard abrasives TiC and TaC steel composite layers were produced on a die steel 90MnCrV8 (0.9% C) by using a CO₂-laser. The hard particles of it median size of 3 μm and 30 μm, respectively, and a volume fraction of about 50% were homogeneously distributed in the steel matrix. Hardness of the martensitie matrix was variied by heat treatments. Wear resistance of the hardfacings against flint and SiC with varying mesh sizes were measured using an abrasive wear tester at laboratory atmosphere. Abrasive wear resistance was increased by more than one magnitude of order by embedding the hard phases in the steel surface. The results showed the effects of type and size of the hard phase, hardness of the steel matrix and also of the type and mesh size of abrasive grits on wear resistance. Experimental results arc discussed as a function of those parameters and theoretical models arc developed.     

放电等离子烧结WC/Fe复合材料摩擦磨损性能

采用放电等离子烧结技术制备了WC质量分数为40%的WC/Fe复合材料,研究了不同烧结温度条件下WC/Fe复合材料的致密度、组织、硬度及干摩擦磨损性能。利用SEM和XRD分析了不同烧结温度条件下存在的物相;采用销-盘摩擦磨损试验机(盘试样选用~80μm的Al2O3砂纸,滑动距离约为950m)测量了马氏体耐磨钢和WC/Fe复合材料在不同载荷下相对磨损率;用SEM观察磨损形貌,确定WC/Fe复合材料的磨损机制。结果表明:烧结温度为1080℃时,WC/Fe复合材料实现完全致密,WC陶瓷颗粒均匀分布在基体中并与基体界面结合良好;随着WC/Fe复合材料完全致密化,其硬度及耐磨性能逐渐提高;WC/Fe复合材料的耐磨性能远优于马氏体耐磨钢。WC/Fe复合材料磨损机制主要为氧化磨损和磨粒磨损。在低载荷条件下,颗粒脱离基体造成氧化膜破裂,促使材料表面受损;较高载荷条件下,WC陶瓷颗粒破碎加速氧化膜破裂,加快了材料的磨损。     

粗晶TM52钢结硬质合金的冲击磨料磨损性能研究

系统对比研究了粗晶粒TM52钢结硬质合金与分别采用真空烧结和低压烧结制备的细晶粒TM52钢结硬质合金在不同冲击功工况下的抗磨料磨损性能与行为,并在对磨损面形貌进行电镜观察分析的基础上探讨了粗晶粒TM52钢结硬质合金的磨损机理。研究发现,粗晶TM52合金的抗磨料磨损性能随着冲击功的逐步提高呈现先下降后增强的变化规律,这与其高锰钢基体在高冲击功条件下的高硬化速率及硬化效果更快、更充分有关。相对于细晶粒钢结硬质合金,粗晶粒TM52钢结硬质合金在抗冲击磨料磨损方面具有明显的性能优势,尤其在高冲击功(3~4J/cm~2)条件下,耐磨性能可提高40%~80%。在此工况下磨损机制主要为碾碎性磨料磨损、擦伤式磨料磨损和疲劳磨损,凿削式磨料磨损不明显。     

Effects of high temperature treatment on microstructure and mechanical properties of laser-clad NiCrBSi/WC coatings on titanium alloy substrate

Laser-clad composite coatings on the Ti6Al4V substrate were heat-treated at 700, 800, and 900 °C for 1 h. The effects of post-heat treatment on the microstructure, microhardness, and fracture toughness of the coatings were investigated by scanning electron microscopy, X-ray diffractometry, energy dispersive spectroscopy, and optical microscopy. The wear resistance of the coatings was evaluated under dry reciprocating sliding friction at room temperature. The coatings mainly comprised some coarse gray blocky (W,Ti)C particles accompanied by the fine white WC particles, a large number of black TiC cellular/dendrites, and the matrix composed of NiTi and Ni₃Ti; some unknown rich Ni- and Ti-rich particles with sizes ranging from 10 nm to 50 nm were precipitated and uniformly distributed in the Ni₃Ti phase to form a thin granular layer after heat treatment at 700 °C. The granular layer spread from the edge toward the center of the Ni₃Ti phase with increasing temperature. A large number of fine equiaxed Cr₂₃C₆ particles with 0.2–0.5 μm sizes were observed around the edges of the NiTi supersaturated solid solution when the temperature was further increased to 900 °C. The microhardness and fracture toughness of the coatings were improved with increased temperature due to the dispersion-strengthening effect of the precipitates. Dominant wear mechanisms for all the coatings included abrasive and delamination wear. The post-heat treatment not only reduced wear volume and friction coefficient, but also decreased cracking susceptibility during sliding friction. Comparatively speaking, the heat-treated coating at 900 °C presented the most excellent wear resistance.     

Ni基WC合金3D激光熔覆工艺研究

以正交实验规则设计3D激光熔覆试验来研究不同工艺参数对熔覆指标的影响,实验表明,WC添加量对熔覆层硬度、抗磨性影响最大,激光功率影响稍次之,激光扫描速度影响次之,送粉速度影响最小。对熔覆层组织分析表明,随WC添加量增多,更易生成CrB、W2B等硬质相,未分解的WC颗粒也越多,粘结相Ni枝晶越细小。激光熔覆Ni基WC合金涂层表面摩擦磨损特性表现为以磨粒磨损为主,塑性变形、粘着磨损和磨粒磨损相结合。     

A study on the abrasive and erosive wear behavior of arc-deposited Cr-N-O coatings on tool steel

In this study, the cathodic arc evaporation technique, by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases, was utilized to deposit three different Cr-N-O coatings (CrN, CrN/Cr(N,O), CrN/Cr₂O₃) on AISI M2 tool steel. Two types of wear tests were applied to evaluate the abrasive and erosive wear behavior of the coated and uncoated specimens. One was the ball-on-disk abrasion test to measure the friction coefficient of these specimens. The other was the erosion test using Al₂O₃ particles (~ 177 µm in size and Mohr 7 scale) of about 5 g, and then the surface morphologies of the eroded specimens were observed. To further understand the coating effects on the two wear behaviors of M2 steel, coating structure, morphology, and adhesion were analyzed using XRD, SEM, and TEM, respectively. The results showed that surface roughness and adhesion of the double-layered coatings (CrN/Cr(N,O) and CrN/Cr₂O₃) were inferior to those of monolithic CrN, but their hardness and elastic modulus were superior to those of CrN. In the abrasive behavior, Cr-N-O coatings reduced the friction coefficient of M2 substrate. In particular, the CrN/Cr₂O₃ has the highest hardness/elastic (H/E) modulus ration, therefore the lowest friction coefficient, among all the coated-specimens tested. In the erosive behavior, the coated specimens exhibited better erosion resistance as compared to the uncoated ones, at the impingement angles of either 30^o or 90^o. Moreover, the erosion resistance of CrN/Cr(N,O) coatings was superior to that of CrN/Cr₂O₃ coatings due to its better adhesion.