Microstructure and Sliding Wear Resistance of Laser Cladded WC/Ni Composite Coatings with Different Contents of WC Particle

The aim of this article was to address the effect of WC content on the microstructure, microhardness, and sliding wear resistance of laser cladded WC/Ni composite coatings. The content of WC particle in the feed powder varied in the range of 0-80 wt.%. Experimental results showed that the laser cladded coatings exhibited homogeneous microstructure without pores or cracks. By comparing with the 45# steel substrate, the microhardness of WC/Ni composite coatings was relatively high. The microhardness of coating increased with increasing the content of WC particles. The wear resistance of WC/Ni composite coatings was strongly dependent on the content of WC particle and their microstructure. When the WC content was lower than 40 wt.% in the feed powder, the wear rate of the coatings decreased with increasing WC content. The two-body abrasive wear was identified as the main wear mechanisms. For the coatings with WC content higher than 40 wt.% in the feed powder, their wear rate increased with increasing WC content. The three-body abrasive wear and fatigue wear were the main failures. The coating with 40 wt.% WC in the feed powder exhibited the best wear resistance.     

Microstructure and Wear Behavior of Conventional and Nanostructured Plasma-Sprayed WC-Co Coatings

WC-12%Co coatings were deposited by atmospheric plasma spraying using conventional and nanostructured powders and two secondary plasmogenous gases (He and H₂). Coating microstructure and phase composition were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray diffraction techniques (XRD) techniques. This study examined wear and friction properties of the coatings under dry friction conditions. SEM was used to analyze abraded surface microstructure. Coating microhardness and fracture toughness were also determined. All coatings displayed strong decarburization as a result of WC decomposition, which gave rise to the formation of secondary phases (W₂C and W). A very fine undissolved WC crystalline dispersion coexisted with these new phases. TEM observation confirmed that the matrix was predominantly amorphous and filled with block-type, frequently dislocated crystallites. Wear was observed to follow a three-body abrasive mechanism, since debris between the ball and the coating surface was detected. The main wear mechanism was based on subsurface cracking, owing to the arising debris. WC grain decomposition and dissolution were concluded to be critical factors in wear resistance. The level of decomposition and dissolution could be modified by changing the plasmogenous gas or feed powder grain size. The influence of the plasmogenous gas on wear resistance was greater than the influence of feedstock particle size.     

Abrasive wear behaviour of laser clad and flame sprayed-melted NiCrBSi coatings

In this work, the influence of the processing conditions on the microstructure and abrasive wear behaviour of a NiCrBSi hardfacing alloy is analysed. The hardfacing alloy was applied in the form of coatings onto a mild steel substrate (Fe–0.15%C) by different techniques: laser cladding (LC) and flame spraying (FS) combined with surface flame melting (SFM). In both cases, the appropriate selection of the process parameters enabled high-quality, defect-free NiCrBSi coatings to be obtained. The microstructure of the coatings was analysed by scanning electron microscopy (SEM), with attached energy dispersive spectroscopy (EDS) microprobe, and by X-ray diffraction (XRD). Their tribological properties were evaluated by micro-scale ball cratering abrasive wear tests using different abrasives: diamond, SiC and WC. Microstructural characterisation showed that both coatings exhibit similar phases in their microstructure, but the phases present differ in morphology, size distribution and relative proportions from one coating to another. Wear tests showed that in three-body abrasive conditions, despite these microstructural differences, the wear behaviour is comparable for both coatings. Conversely, in two-body wear conditions with diamond particles as the abrasive, it was observed that the specific wear rate of the material is sensitive to microstructural changes. This fact is particularly apparent in LC coatings, in which the zones of the layers with higher proportions of very small hard particles present a lower wear resistance. These results indicate that it is important to have good microstructural control of this material, in order to obtain coatings with an optimized and homogeneous tribological behaviour.     

Performance of Flame Sprayed Ni-WC Coating under Abrasive Wear Conditions

This paper describes the influence of a post spray heat treatment on the microstructure, microhardness and abrasive wear behavior of the flame sprayed Ni-WC (EWAC 1002 ET) coating deposited on the mild steel. Coatings were deposited by using an oxy-acetylene flame spraying torch (Superjet Eutalloy L & T, India). The wear behavior of the coating was evaluated using a pin on disc wear system against SiC abrasive medium of 120 and 600 grades at 5, 10, 15, and 20 N normal load. Results revealed that the influence of normal load on wear is governed by the microstructure, hardness and abrasive grit size. The heat treatment increased average microhardness of the coating. However, it was found that the hardness does not correctly indicate the abrasive wear resistance of Ni-WC coating in an as sprayed and heat treated condition. The heat treatment of the coating improved its abrasive wear resistance against fine abrasive medium while the wear resistance against coarse abrasive was found to be a function of a normal load. At low-normal load (5 and 10 N) the heat treated coating showed lower-wear rate than as spayed coating while at high-normal loads (15 and 20 N) heat treated coating was subjected to higher-wear rate than as sprayed coating. In general, an increase in normal load increased the wear rate. The scanning electron microscopy study indicated that the wear largely takes place by groove formation and scoring of eutectic matrix and the fragmentation of the carbide particles.     

等离子熔覆添加和内生联合WC颗粒增强铁基涂层的组织和性能

采用等离子熔覆技术,以铸造碳化钨、钨铁粉、镍包石墨和铁基合金粉为原材料,在Q235钢基体上制备了外加和内生联合WC颗粒增强铁基复合涂层,通过扫描电镜和能谱分析、X射线衍射、硬度测试和磨料磨损试验对其微观组织、物相组成、硬度和耐磨性能进行了表征。结果表明,在优化的工艺参数下,可以获得与基体冶金结合良好的涂层,硬质相除外加的WC颗粒,还有内生的WC、W₂C、W₃C、Fe₃W₃C和Fe₂W₂C等;随着混合粉末中除外加WC之外的W含量增加,熔池中合金液密度增大,可以减弱外加WC颗粒下沉;当W含量达到15%时,外加WC颗粒均匀分布在涂层中,没有团聚现象发生,且在外加WC颗粒周围有细小的原位WC颗粒生成,涂层的显微硬度和耐磨损性能显著提高,涂层的平均硬度约为1300 HV0.2,耐磨性为Q235钢基体的10倍。     

不同尺度碳化物粉末冷喷沉积WC-17%Co涂层的组织及性能

采用团聚烧结和机械混合工艺制备的4种纳米与微米碳化物比例的WC-17%Co粉末,运用冷喷涂进行涂层定点沉积试验,通过扫描电镜和X-射线衍射分别分析了涂层的组织结构和相结构,并测定了涂层的显微硬度和磨粒磨损失重量.结果表明,4种碳化物尺度粉末沉积涂层具有致密的组织结构,喷涂态涂层保持与原始粉末相同的相结构,涂层显微硬度随碳化物尺度在12 897～15 925 MPa范围变化,粉末中纳米碳化物与微米碳化物颗粒重量比为50∶50时,沉积涂层具有较好的磨粒磨损性能.涂层磨损表面分析表明,涂层的磨损行为表现为涂层的磨粒磨损失重量在2.67～5.53 mg范围变化.     

Erosive Wear Study of Rare Earth-Modified HVOF-Sprayed Coatings Using Design of Experiment

In the present study, the effect of CeO₂ addition in 1006 powder coatings on microstructure, microhardness, and high-temperature erosion resistance were studied. The CeO₂ addition refines microstructure, forms new phases, and increases microhardness of HVOF-sprayed coatings. The erosive wear behavior of coatings were investigated by Response Surface Methodology (RSM). To investigate and develop an erosive wear model of unmodified 1006 (without CeO₂) and modified 1006 (CeO₂ addition) coatings’ four factors: velocity, impact angle, temperature, and feed rate, each factor at three levels were used. ANOVA was carried out to determine the significant factors and interactions. Thus, an erosive wear model was developed in terms of main factors and their significant interactions. A comparison of modeled and experimental results showed 4-7% error. The modified 1006 coating showed high erosive wear resistance as compared with unmodified 1006 coating. This is due to increase in hardness and refined microstructure of the modified 1006 coating.     

铁基含TiC陶瓷粉电弧喷涂粉芯丝材的研究

采用电弧喷涂含TiC陶瓷粉末的粉芯丝材，在低碳钢基体上制备了铁基复合涂层。用MLS-225型湿砂橡胶轮磨损试验机测试了涂层的抗磨粒磨损性能。利用光学显微镜、SEM、XRD分析技术对涂层的显微组织结构、磨损表面和相组成进了研究。结果表明：采用电弧喷涂工艺可制备含TiC陶瓷硬质相的复合涂层，在铁基体上弥散分布着一定量的TiC硬质颗粒，使整个涂层得到强化，涂层显微硬度平均值约为1137HV0.1，涂层的抗磨粒磨损性能较好，相对Q235钢提高T6倍。涂层磨损机制主要为犁沟切削和脆性断裂。     

不同参数下超音速火焰喷涂Cr_3C_2-NiCr涂层磨粒磨损性能

通过超音速火焰(HVOF)技术,采用不同的工艺参数在低碳钢表面喷涂Cr_3C_2-NiCr涂层;对所得涂层进行磨粒磨损实验.同时考察低碳钢磨损性能,比较喷涂层之间的磨损性能及其与基体的磨损性能.采用光学金相显微镜观察涂层断面的形貌,通过显微硬度计测试涂层的显微硬度.结果表明.Cr_3C_2-NiCr涂层磨损质量损失与磨程基本呈线性关系;涂层的磨损性能高于低碳钢;不同参数制备的涂层,其磨粒磨损性能也不一样,其中燃气流量为38 L/min时的涂层磨损性能较好,该条件下涂层的断面显微组织呈现层状结构,其显微硬度也较高.     

爆炸喷涂WC-12%Co涂层的滑动磨损性能

采用爆炸喷涂技术制备纳米和普通WC-12%Co涂层,用往复试验机对涂层的干滑动磨损性能进行了研究,分析了涂层磨损前后的形貌、结构及成分变化.结果表明:相同的喷涂条件下,WC-12%Co纳米涂层比普通涂层结构均匀、致密,但碳化物分解严重.尽管纳米涂层与普通涂层具有相近的硬度,但普通涂层的耐磨性优于纳米涂层,尤其是在重载条件下.普通涂层的磨损机制为微切削;纳米涂层在轻载(10 N)下,以塑性变形为主要磨损机制,随载荷增加至30 N,纳米WC粒子不能起到阻抗陶瓷球对磨副的磨削作用,而是随粘结相一起被去除,同时由于纳米涂层脱碳导致的层间结合薄弱,在滑动磨损中易发生成片剥落,耐磨性大幅下降.     

HVOF-Deposited WCCoCr as Replacement for Hard Cr in Landing Gear Actuators

WCCoCr coatings deposited by HVOF can replace hard Cr on landing gear components. Powders with two different WC particle sizes (micro and nano-) and geometries have been employed to study the effects on the coating’s properties. Moreover, coatings produced employing two sets of parameters resulting in high and low flame temperatures have been evaluated. Minor differences in microstructure and morphology were observed for the two powders employing the same spraying parameters, but the nano-sized powder exhibited a higher spraying efficiency. However, more significant microstructural changes result when the low- and high-energy spray parameters are used. Moreover, results of various tests which include adhesion, wear, salt fog corrosion resistance, liquid immersion, and axial fatigue strength, indicate that the coatings produced with high-energy flame are similar in behavior. On the other hand, the nanostructured low-energy flame coating exhibited a significantly lower salt fog corrosion resistance.     

激光熔覆Ni基微-纳米WC金属陶瓷涂层组织及干滑动磨损性能

在45钢表面进行添加微一纳米WC颗粒的镍基自熔粉末激光熔覆处理.得到不同Ni基WC合金涂层.对熔覆层进行显微组织观察、硬度测定以及室温千摩擦磨损试验.结果表明,纳米品WC的加入能改善涂层的耐磨性能,在本试验条件下,当添加的纳米级WC和微米级WC各为15%时.涂层耐磨性能最佳;但纯纳米晶WC增强涂层耐磨性不佳,其主要磨损破坏方式随涂层中WC晶粒尺寸变化而有所变化.     

Influence of Plasma Intensity on Wear and Erosion Resistance of Conventional and Nanometric WC-Co Coatings Deposited by APS

The effects of plasma intensity and powder particle size on wear and erosion resistance have been evaluated for WC-12 wt.%Co coatings deposited by Air Plasma Spraying. Coatings were deposited from micrometric and nanostructured powders. SEM and XRD characterization showed the presence of WC, W₂C, W, and an amorphous Co-rich matrix. The performance of the different coatings was compared in sliding wear tests (ball-on-disk), under dry friction conditions. Wear debris and tracks were analyzed by SEM. The debris generated during the test was found to have a great influence on the sliding properties. Wear follows a “three-body abrasive mechanism” and is dominated by coating spallation because of sub-surface cracking. In order to evaluate erosion behavior, solid particle erosion tests were conducted. Eroded coatings were analyzed by SEM, and erosion mainly occurs by a “cracking and chipping mechanism.” The study shows that wear and erosion behavior is strongly affected by plasma arc intensity.     

纳米WC增强Ni基合金喷熔层组织结构与抗磨粒磨损特性

目的研究纳米WC对Ni基合金喷熔层抗磨粒磨损性能的影响。方法采用扫描电镜、X射线衍射分析了氧乙炔火焰喷熔Ni基合金层和两种不同结构WC增强Ni基合金喷熔层的微观组织和相结构,并通过磨粒磨损试验平台对三种涂层进行磨损性能测试。结果纳米WC粉末的加入,能有效提高喷熔层的宏观硬度。通过组织分析得出纳米WC增强Ni基喷熔层中除含有γ-(Ni,Cr)固溶体、Cr的碳化物、硼化物以及微米级WC颗粒之外,还含有一定量的纳米WC团聚体和少量高硬度的W_2C相。磨粒磨损实验结果显示,纳米WC增强Ni基喷熔层的磨损失重分别为Ni60和NiWC35涂层失重的56%和73%。对比磨损后涂层的表面微观形貌可知,纳米WC颗粒在涂层中能有效降低磨粒压入喷熔层的深度,从而控制磨粒对喷熔层的犁削量。结论纳米WC增强Ni基合金喷熔层中含有的γ-(Cr,Ni)固溶体、Cr_(23)C_6、Cr_7C_3、Cr_3Ni_2及未熔化的WC颗粒和WC脱碳形成的W_2C等硬质相,使镍基自熔合金涂层的硬度有较大提高,同时也大大提高了涂层的抗磨粒磨损性能。     

Microstructure and Wear Performance of Arc Sprayed Fe-FeB-WC Coatings

Two Fe-FeB-WC coatings were deposited on the Q235 steel substrate by arc spraying. The microstructure and the abrasive wear performance of the coatings were characterized by x-ray diffraction (XRD) and scanning electron microscope (SEM). The wear mechanisms of the coatings were examined. It was found that Fe-Cr alloy and Fe₂B are present in the coating as the main phases. The results showed that adding hard particle powders could obviously increase the hardness and wear resistance of the coatings. The average microhardness of the coatings was about 870 to 920 HV_0.1. The coatings exhibited excellent abrasive wear resistance, being 3.3 to 4.8 times higher than that of arc sprayed 3Cr13 coating.     

Propylene flow,microstructure and performance of WC–12Co coatings using a gas-fuel HVOF spray process

Five WC–12Co coatings were deposited by a high velocity oxy-fuel (HVOF) system using constant oxygen flow and varying propylene flow. The phase composition, microstructure, as well as abrasive and sliding wear performance of the as-sprayed coatings were investigated. The degree of tungsten carbide (WC) decarburization in the as-sprayed coatings increases while the coating porosity decreases with the increase of the propylene flow. The coating hardness, fracture toughness, resistance to abrasive and sliding wear increases with the increase of the propylene flow, reaches maximum and then decreases. At the low flow of the propylene, relatively loose coating microstructure is formed, which leads to fracturing and pulling off the WC particles during abrasive and sliding wear process. Herewith, at the high flow of the propylene, the high degree of the WC decarburization and high brittleness of the coating leads to micro-cutting during abrasive wear as well as to cracking and delamination of the coating in the sliding wear process.     

粉末原料粒径对WC-17Co涂层性能的影响

本文利用超音速火焰喷涂技术喷涂四种不同粒径的WC-17Co粉末,评价粉末粒径对涂层机械性能和抗磨粒磨损性能的影响。结果表明,粉末的粒径越小,在超音速焰流作用下获得的速度和温度越高,形成的涂层越致密,颗粒间的粘接强度越高,同时涂层的显微硬度也越高。WC-17Co粉末的粒径越小,获得涂层的孔隙直径越小,颗粒间的粘接缺陷越少,因此涂层的抗磨粒磨损性能越好。但是当WC-17Co粉末的粒径过于微小时,涂层的断裂韧性将受到影响。在本文研究的四种粒径分布的WC-17Co粉末中,中间粒径且分布范围集中的粉末制得的涂层兼具良好的机械性能和抗磨粒磨损性能。     

高速火焰与等离子喷涂WC／Co涂层的性能比较

分析比较了超音速喷涂与等离子体喷涂的ＷＣ／Ｃｏ涂层的形貌,显微组织结构,孔隙率,硬度及其耐磨性,结果表明超音速火焰喷涂的ＷＣ／Ｃｏ涂层具有与粉末相近的相结构,也说ＷＣ颗粒在超音速火焰喷涂过程中,只有极少部分被分解和氧化,同时涂层具有很高的致密度,硬度和良好的耐磨性,涂层与基体的结合情况也得到很大的改善。     

La_2O_3稀土对激光熔覆WC/Ni基复合涂层性能改善的研究

向WC陶瓷镍基合金粉末中添加不同质量分数的La2O3粉末制成混合粉末,采用大功率半导体激光器通过同轴送粉方式,在A3钢基材上制备熔覆层。利用SEM、EDAX、XRD分析研究了不同稀土加入量对熔覆层显微组织和相结构的影响,用显微硬度计、滑动摩擦磨损试验机分别测试了复合涂层的硬度、耐磨性。结果表明:由于稀土的加入,复合涂层的晶粒进一步细化,组织趋向均匀,硬度和耐磨性得到了提高,最终得出涂层粉末的最佳配比为(质量分数)59%Ni60,40%WC,1.0%La2O3。     

高频微振对激光熔覆镍基WC增强涂层的影响

目的改善传统激光熔覆工艺制备的涂层组织粗大,物相分布不均匀,易出现气孔裂纹等缺陷。方法采用松香酒精溶液作为粘接剂,将涂层材料(镍包碳化钨粉末)预置于Q235钢基体表面,选用最优激光参数(功率P=1600 W、光斑直径d=5 mm、扫描速度ν=4 mm/s),并在高频微振辅助工艺下进行熔覆试验,最终制备出镍基碳化钨增强涂层。分别使用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、显微硬度仪及万能摩擦磨损试验机(UMT)对涂层的显微组织、元素成分及物相、显微硬度和耐磨性能进行测量分析。结果在高频微振产生的激振力作用下,涂层组织由粗大的树枝晶向等轴晶及细小枝晶转变,物相成分主要为γ-Ni(Fe)、Ni3Fe、WC、M(23)C6型化合物等,深色硬质相分布均匀,气孔裂纹等缺陷基本消失,涂层磨损机制主要为轻微磨粒磨损。与无高频微振辅助的涂层相比,显微硬度提高了17%,摩擦系数减小了29%,耐磨性提高了49%。结论利用高频微振辅助激光熔覆工艺,可使制备出的涂层质量显著改善,微观组织更加致密,成分分布更加均匀,细晶强化和弥散强化效果增强,硬度、耐磨性等力学性能得到明显提升。