WC含量对铁基涂层非晶形成能力及其性能影响

采用电弧喷涂技术喷涂不同WC含量的Fe基粉芯丝材,在Q235低碳钢基体上制备5种不同非晶含量的Fe基合金涂层.利用光学显微镜、透射电子显微镜、扫描电子显微镜和X射线衍射仪对涂层的显徼组织结构、磨损表面及其相组成进行分析,用MLS-225型湿砂橡胶轮磨损试验机评价铁基复合涂层的磨粒磨损性能.结果表明,制备的几种涂层中均含有非晶相,当粉芯中WC质量分数在30%以内时,随着WC含量的增加,涂层中的非晶含量增加,相应涂层的硬度增加,耐磨性保持稳定;涂层的磨损机制主要为硬质相的脆性剥离和轻微的塑性切削,在磨粒磨损情况下硬度较低的金属基体先磨损,硬度高的Fe2B硬质相起到了阻止石英砂磨损的作用,从而降低了涂层的磨损.     

WC晶体结构特征对HVOF喷涂纳米结构WC-CoCr涂层组织及性能的影响

为提高纳米结构WC-CoCr涂层的综合力学性能,采用超音速火焰喷涂（HVOF）工艺制备纳米结构和超细结构WC-CoCr涂层。探讨了不同晶体特征的WC粉末对颗粒飞行和沉积变形过程的脱碳行为、涂层微观组织及力学性能的影响。结果表明：含有高密度位错的超细WC粉末在喷涂过程中发生了严重的氧化脱碳,形成了大量的W₂C相,涂层孔隙率较大,断裂韧性显著降低。而含有显著孪晶的纳米WC颗粒具有抑制WC脱碳和增强涂层断裂韧性的作用,纳米结构涂层呈现低脱碳率、高致密性、高硬度和高断裂韧性的优良综合性能。     

超音速等离子喷涂WC-17Co纳米涂层的性能研究

采用超音速等离子喷涂在0Cr13Ni5Mo不锈钢表面制备了纳米和微米WC-Co涂层,并对比了两种涂层的孔隙率、结合强度、硬度和耐磨性。结果表明,纳米涂层的致密性和结合强度均高于微米涂层,其孔隙率仅为0.56%,结合强度大于69.2 MPa;纳米涂层和微米涂层的硬度是基体的3.9和3.8倍,硬度值从涂层的表面到底部逐渐增加;基体磨损为磨粒磨损 粘着磨损 层状剥落,两种涂层磨损均为磨粒磨损。纳米涂层的孔隙率低、硬度高、表面抗压性强使其表现出更优的耐磨性。     

纳米稀土对热喷涂WC-12Co涂层的改性作用

利用超音速火焰喷涂技术在45钢基体上制备了不同纳米稀土含量的WC-12Co涂层。通过物相分析并测定材料的显微硬度、结合强度、磨损性能,研究纳米稀土对WC-12Co涂层的改性作用。结果表明:适量纳米稀土的加入使WC-12Co涂层的显微硬度和结合强度显著提高,并且纳米稀土的加入有效地抑制了WC颗粒的脱碳,使组织细化。当纳米稀土含量在1.5wt%时,涂层的耐磨性最好。     

氧燃比对爆炸喷涂WC-17Co涂层组织和性能的影响

选用WC-17Co喷涂粉末,采用爆炸喷涂工艺,通过改变乙炔和氧气流量等喷涂参数在316L钢基体上制备了4种WC/Co涂层.采用X衍射仪、扫描电镜对对涂层的相结构和微观组织进行了研究;采用灰度法测试了涂层的气孔率;采用拉伸法测试了涂层的结合强度;采用小负荷维氏硬度计测试了开裂韧性;最后采用湿砂橡胶轮磨粒磨损试验机对各涂层磨粒磨损行为进行了研究.结果显示:随着氧燃比的增加,涂层中的WC分解程度增加,涂层的硬度增加,韧性、气孔率和抗磨粒磨损性能都是先增加后降低.氧燃比为1.5时,涂层具有最优的综合力学性能.     

粉末粒度对WC-Co涂层结构和性能的影响

采用低功率内送粉等离子喷涂设备,选择两种粒度不同的WC-Co粉末,在不同功率下,在不锈钢基体上制备WC-Co涂层。利用XRD、SEM等分析手段对原始粉末和涂层的显微结构和物相组成进行观察和分析,利用显微硬度仪测量涂层显微硬度。结果表明:与细粉相比,粗粉喷涂涂层的组织致密、均匀,孔隙率小。粗粉喷涂涂层显微硬度可达1500 HV以上,涂层主晶相是WC,也存在少量W2C相,随着等离子能量增加,W2C增多;细粉喷涂涂层,WC发生大量的脱碳分解,涂层主晶相是W2C,显微硬度低。因此粗粉在适当功率下更适合低能等离子喷涂。     

亚微米WC添加对超音速火焰喷涂WC-Co涂层磨损性能影响

采用超音速火焰喷涂方法(HVOF)在304不锈钢基体表面制备WC和WC-12Co的复合涂层WC-Co,研究亚微米WC的添加对涂层相组成、显微硬度、耐磨性能和表面形貌的影响。利用X射线衍射、压痕法、往复式摩擦磨损实验和扫描电子显微镜(SEM)分别对涂层的相组成、显微硬度、磨损性能和表面形貌进行分析测试,并分析涂层的磨损过程和机制。结果表明,添加质量分数5%的亚微米WC颗粒显著提高了涂层的显微硬度(16.3%);增强了涂层的耐磨性,磨损率从6.09×10-7 mm3/Nm减小到5.15×10-7 mm3/Nm(减小13.8%);亚微米WC颗粒喷涂后在涂层中保持了WC相,并主要存在于WC-Co扁平粒子界面和孔隙。基于涂层中扁平粒子的结合特性与磨损失效特征,建立强化模型,分析亚微米WC颗粒对涂层扁平粒子界面的强化机制。     

CeO2对等离子喷涂Ti-Al/WC金属陶瓷复合涂层组织和摩擦学性能的影响

通过等离子喷涂方法在45钢基体上制备添加不同含量稀土氧化物CeO_2的Ti-Al/WC金属陶瓷复合涂层,利用扫描电镜和能谱仪等检测设备探究CeO_2对涂层组织及摩擦学性能的影响。结果表明:CeO_2细化了等离子喷涂涂层的层片状结构,改善了其结合性;添加不同含量CeO_2的涂层耐磨性均高于未添加涂层,其中2%的添加量,涂层表现出更加优良的性能; CeO_2的加入改变了涂层的磨损机理,由黏着磨损为主过渡为磨粒磨损为主,提高了涂层强度,减轻了磨损程度。     

亚微米WC添加对超音速火焰喷涂WC–Co涂层磨损性能影响

采用湿法球磨将亚微米WC（~300 nm）和WC–12Co粉末混合均匀并使亚微米WC均匀粘附于WC–12Co粉末的表面,采用超音速火焰喷涂方法（HVOF）在304不锈钢基体表面制备WC和WC–12Co的WC–Co复合涂层,研究亚微米WC的添加对涂层相组成、显微硬度、耐磨性能和表面形貌的影响。利用X射线衍射分析涂层相组成,压痕法测试涂层的显微硬度,通过往复式摩擦磨损实验测试磨损性能,扫描电子显微镜（SEM）对涂层磨损表面和断面进行微观形貌观察,并分析涂层的磨损过程和机制。结果表明,添加质量分数5%的亚微米WC颗粒显著提高了涂层的显微硬度（16.3%）;增强了涂层的耐磨性,磨损率从6.09×10-7 mm3/Nm减小到5.15×10-7 mm3/Nm（减小13.8%）;亚微米WC颗粒喷涂后在涂层中保持了WC相,并主要存在于WC–Co扁平粒子界面和孔隙。基于涂层中扁平粒子的结合特性与磨损失效特征,建立强化模型,分析亚微米WC颗粒对涂层扁平粒子界面的强化机制。     

微米WC增强Ni60合金高频感应熔覆涂层耐磨性能

采用高频感应熔覆方法在Q235低碳钢基体上制备了不同含量的微米WC增强Ni60A合金复合涂层.用MLS-225型湿砂橡胶轮磨粒磨损试验机评价了涂层的耐磨性能,利用SEM,XRD观察并分析了涂层的显微组织和磨损表面形貌.结果表明,在相同试验条件下,涂层的硬度和耐磨性随WC含量的增加而提高,当WC含量少于30%时,WC分布不均匀,主要集中于涂层的中部,涂层中Cr7C3相以粗大的六方状和长条状存在,不利于涂层耐磨性的提高;当WC含量达到50%时,Ni基合金中加入WC的含量达到了合适比例,耐磨性最佳,相对耐磨性为Ni60A涂层的6.5倍;当WC含量达到60%时,涂层的硬度最高,但出现了较多的孔洞,大量未熔的WC颗粒在磨粒的反复作用下剥落形成了大的剥落坑,导致耐磨性下降.涂层与基体实现了冶金结合,涂层的磨损机制主要为轻微的塑性切削和硬质相的脆性剥落.     

Effect of flame conditions on abrasive wear performance of HVOF sprayed nanostructured WC-12Co coatings

Nanostructured WC-12Co coatings were deposited by high velocity oxy-fuel (HVOF) spraying with an agglomerated powder. The effect of flame conditions on the microstructure of the nanostructured coatings was investigated. The wear properties of the coatings were characterized using a dry rubber-wheel wear test. The results show that the nanostructured WC-Co coatings consist of WC, W2C, W and an amorphous binder phase. The microstructure of the coating is significantly influenced by the ratio of oxygen flow to fuel flow. Under the lower ratio of oxygen/fuel flow, the nanostructured coating presents a relative dense microstructure and severe decarburization of WC phase occurs during spraying. With increasing ratio of oxygen/fuel flow, the bonding of WC particles in the coating becomes loose resulting from the original structure of feedstock and the decarburization of WC becomes less owing to limited heating to the powder. Both the decarburization of WC particles in spraying and the bonding among WC particles in the coatings affect the wear performance. The examination of the worn surfaces of the nanostructured coatings reveals that the dominant wear mechanisms would be spalling from the interface of WCCo splats when spray particles undergo a limited melting. While the melting state of the spray particles is improved,the dominant wear mechanisms become the plastic deformation and plowing of the matrix and spalling of WC particles from the matrix.     

Plasma spraying of Wc-Co part II: Experimental study of particle deposition and coating microstructure

WC-Co base wear-resistant coatings deposited by plasma spraying are widely used to enhance component longevity in a variety of wear environments. During spraying of WC-Co, ideally only the cobalt phase should melt and act as a binder for the WC particles. Although it is undesirable to fully melt WC because it can cause decarburization, complete melting of the cobalt phase and its satisfactory flattening on impacting the substrate is necessary to minimize porosity and achieve good substrate/coating adhesion. In this article, the influence of the primary plasma spray variables on the melting characteristics of WC-Co powders is investigated with respect to the microstructure of these coatings. This experimental work complements an analytical study on plasma spraying of WC-Co, and thus, observations are presented to support the predictions of the modeling effort.     

Effect of adding WC powder to the feedstock of WC-Co-Cr based HVOF coating and its impact on erosion and abrasion resistance

HVOF grade powders are now commercially available and being used in large scale for different components prone to abrasion/erosion. The literature on HVOF coatings based on WC-Co powder shows that there is a huge difference in hardness between the pure WC powder and WC-Co based HVOF coatings. The objective of this study was to improve the hardness of WC based HVOF coatings by adding pure WC powder to the commercially available powder. The hardness data shows that 20% addition of WC powder will improve the hardness of HVOF coating from 1106 to 1395 Hv_0.3. Hardness increase is due to the embedding of tungsten carbide hard metal matrix. This HVOF coated sample was tested for dry sand abrasion and slurry erosion as per ASTM standards. These tests show that abrasion and erosion resistance of HVOF coated samples goes down with the addition of tungsten carbide powder even though coating hardness has gone up. To understand the negative trend, porosity and SEM studies were carried out. SEM studies show that the porosity of the HVOF coating is higher than the conventional HVOF coating. With increase in WC content (30%), the porosity of the HVOF coating increased up to 10%. The higher porosity is believed to be the reason for poor abrasion and slurry erosion resistance.     

超音速等离子喷涂制备金属陶瓷涂层的抗冲蚀性能

通过高效能超音速等离子喷涂(SAPS)制备WC-Co及WC-Ni Cr金属陶瓷涂层,对比研究了2种涂层的抗冲蚀性能及在热腐蚀条件下的结构和性能演变。结果表明:2种涂层在喷涂过程中均会发生一定程度的脱碳,表现为W_2C相的形成;同时在WC-Co涂层中有少量的Co_3W_3C和Co_6W_6C相生成,且该涂层在热腐蚀后表层的WC相出现了分解与氧化,形成了W_3C、W_6C_(2.54)等脱碳相与CoWO_4、WO_3等氧化物相。在普通冲蚀条件下,WC-Co涂层的抗冲蚀性能更为优异,但热腐蚀会极大降低WC-Co涂层的抗冲蚀性能;与之相反,WC-NiCr涂层中的NiCr相在热腐蚀环境下生成的Cr_2O_3可以有效阻挡涂层内部与外部之间的物质扩散,从而降低了热腐蚀对涂层结构的破坏,在热腐蚀条件下表现出了优良的抗冲蚀性能。     

电弧电压对低能等离子喷涂WC-Co涂层组织及性能的影响

使用烧结破碎的WC-12%Co粉末,采用轴向送粉等离子喷涂系统制备WC-Co涂层。保持电弧电流不变,增加工作气体中的氢气含量来提高电弧电压,以研究电弧电压对于涂层微观结构的影响。使用X射线衍射仪(XRD)分析WC-Co涂层的脱碳相变,使用扫描电子显微镜(SEM)观察粉末的熔化程度、扁平化状态和涂层的微观结构,使用MH-6维氏硬度计和MM200磨损试验机分别测量了涂层的显微硬度和耐磨性。结果表明,提高电弧电压有利于粉末的熔化。根据熔化程度的不同,粉末会呈现四种典型的扁平化状态。提高电弧电压促使碳化钨脱碳生成的W_2C和Co_3W_9C_4,涂层中硬质相体积增加,钴基体积减小。适当提高电弧电压有利于增加涂层的硬度和耐磨性,但过高的电弧电压会恶化涂层质量,反而降低涂层的硬度和耐磨性。     

Multimodal coatings: A new concept in thermal spraying

Recently, considerable emphasis has been placed on HVOF thermal spraying of nanostructured WC/Co with the intention of achieving high hardness combined with excellent wear resistance. However, depositing dense coatings and simultaneously preventing decarburization has remained a challenge. We have approached the problem by developing a novel feedstock material that consists of a mixture of coarse and fine particles of WC/Co. Particles of different sizes have a different response in the combustion flame. The resultant coating is dense and has no decarburized phases. The abrasion wear resistance is at least 50% better than that of a pure coarse-grained WC/Co coating.     

HVOF喷涂纳米结构WC-12Co涂层的组织结构分析

纳米结构WC-12Co涂层的研究目前已受到了广泛重视,对其组织结构及影响因素的研究有利于提高涂层性能.采用HVOF工艺制备了纳米结构、多峰结构及普通微米结构3种WC-12Co金属陶瓷复合涂层,并采用SEM、XRD等对粉末及涂层的显微形貌、组织结构进行了分析;探讨了粉末在喷涂过程中的氧化脱碳机理,并指出了与之相关的影响因素.结果表明:纳米结构WC-12Co涂层结构致密,孔隙率低,与基体结合状态良好;纳米粉末在喷涂过程中比微米粉末氧化失碳严重,并发生了不同的纳米晶粒的长大;纳米粉末在喷涂过程中的氧化脱碳程度不仅与喷涂工艺有关,还在很大程度上取决于粉末本身的结构特性.     

Influence of feedstock powder characteristics and spray processes on microstructure and properties of WC-(W,Cr)2C-Ni hardmetal coatings

The composition WC-(W,Cr)₂C-Ni (commercial designations WC-‘CrC’-Ni, WC-Cr₃C₂-Ni and WC-NiCr) is unique among the WC-based materials used for the preparation of thermally sprayed hardmetal coatings. These coatings show a significantly higher oxidation resistance and high-temperature sliding wear resistance than WC-Co and WC-CoCr coatings do. Unlike WC-Co and Cr₃C₂-NiCr, WC-(W,Cr)₂C-Ni is not a simple binary hard phase-binder metal composite as it is composed of two hard phases: WC and (W,Cr)₂C. Surprisingly this composition has been poorly investigated in the past.In this paper coating microstructures and properties obtained from five commercial feedstock powders of different origins using two different liquid-fuelled high velocity oxy-fuel (HVOF) systems (K2 and JP-5000) were investigated. Additional experiments were performed with one powder using atmospheric and vacuum plasma spraying (APS and VPS, respectively). The microstructures and phase compositions of the powders and the coatings were studied. Focus was on the appearance, composition and distribution of the (W,Cr)₂C phase which might form or might change its Cr/W ratio during the spray process. The composition of the (W,Cr)₂C phase was estimated from the lattice parameters. Hardness HV0.3 was measured for all coatings. The density, Young's modulus and abrasion wear resistance of HVOF-sprayed coatings were studied.