碳化钨颗粒尺寸对超音速火焰喷涂WC-Co涂层形成的影响

通过探讨WC颗粒对扁平粒子厚度及喷涂后WC颗粒尺寸变化的影响，研究了超音速火焰喷涂过程中WC－Co深层的沉积过程。使用具有不同WC尺寸的四种WC-Co粉末，采用JET－KOTE喷枪系统喷制了WC－Co涂层。结果发现涂层中WC颗粒的大小主要取决于原始粉末中WC的尺寸．在粉末穿越火焰的过程中，大多数WC处于固态；WC-Co涂层的沉积涉及固液两相离子的扁平化，而不是象在优化条件下金属或陶瓷材料喷涂过程中仅存在单一液相的情况。很明显WC-Co粉末中的WC的大小对涂层的形成影响很大、在超音速火焰喷涂条件下当液固粒子碰撞到已形成的涂层表面上时，其中的大颗粒WC粒子容易被反弹脱落。基于实验结果，提出了计算由液相聚积固相形成的波固两相颗粒碰撞到表面时形成扁平粒子的厚度的模型。     

镍基合金电子束熔覆表面改性及高温耐磨性研究

利用电子束在Inconel 617高温合金表面熔覆WC-CoCr复合涂层,设计正交试验分析了工艺参数对熔覆层的影响,研究了优化后涂层的组织与性能.结果表明,电子束扫描束流对熔覆质量特性影响最为显著,优化工艺下获得的熔覆层与基体合金相互扩散并形成良好的冶金结合,熔覆层内出现了WC、CoCr、(Fe,Ni)C6、Fe3W3...     

电火花沉积工艺及沉积层性能的研究

为了研究电火花沉积工艺对沉积层组织结构及沉积层性能的影响,改善电火花沉积层的表面质量.采用新型电火花沉积设备,以YG8电极材料,H13(4Cr5MoSiV)钢为基体材料进行了沉积实验.通过工艺实验,研究了沉积时间、沉积功率、沉积电压、沉积频率和沉积气氛对沉积层的影响规律,用X射线衍射仪分析了沉积层的组织结构,通过硬度实验和抗磨损实验测定了沉积层的纤维硬度和抗磨损性能.试验表明,电火花沉积工艺对沉积层的组织结构和沉积层性能有影响,沉积层内的白亮层含有大量复杂化合物,具有高的纤维硬度和高的耐磨性.     

粉末预置法电火花沉积WC-8Co涂层分析

针对传统电火花沉积技术存在电极制备工艺复杂、涂层存在较多裂纹及孔洞的不足,把WC-8Co粉末置于电极与基体之间的脉冲放电通道内,利用电火花沉积工艺制备了WC-8Co涂层.对比分析了新工艺与传统工艺制备的涂层表面形貌、显微组织及摩擦磨损性能.结果表明,用新工艺制备的涂层表面平整、粗糙度低、组织致密,与基体呈冶金结合.与传统工艺相比,新工艺制备的涂层有良好的耐磨粒磨损性能.用粉末预置法制备涂层能提高电火花沉积效率,适于制备大面积的涂层.     

纳米结构WC/12Co涂层精密磨削的磨削力研究

本文对金刚石砂轮平面磨削纳米结构WC／12Co涂层材料时得到的磨削力进行了试验研究，研究了涂层材料的磨削力与磨削工艺参数以及砂轮特性之间的关系。通过各项试验研究得出，用金刚石砂轮磨削纳米结构WC／12Co涂层时，磨削力与当量磨削厚度基本成一元线性关系，它随磨削深度、工件速度的增加而增加：当磨粒尺寸减小时。总磨削力增加，但单颗磨粒磨削力减小。材料以非弹性变形的材料去除方式为主。通过试验采集的数据，使用当量磨削厚度作为磨削基本参数建立了法向磨削力理论模型。     

Accelerated electrospark deposition and the wear behavior of coatings

Electrospark deposition (ESD) is a coating process that is featured by low heat input to the substrate. Low coating efficiency and other limitations influence its wider application. The present paper introduces newly designed ESD equipment, by which a higher coating rate can be reached. The relationship among coating thickness, surface roughness, and process parameters such as pulse energy, pulse frequency, and deposition time are presented. Electrospark deposition coating by the new equipment on AISI 1045 steel (with WC-8% Co as electrode) increases the wear resistance by 5 to 8 times. The micromechanism is investigated by scanning electron microscopy observation.     

粘结相Co的切变机制及微观结构的研究

本文以工业纯钻粉、钴基合金、硬质合金作为研究对象,分别运用X射线衍射、金相、扫面电镜能谱、EBSD等分析技术,并结合晶体学的相关知识研究了钴的基本特性、微观结构及其切变机制。通过研磨工业纯钴粉,比较分析研磨前后X射线衍射分析结果,定性描述了钻粉的α-Co向ε-Co的转变过程;实验制备了不同固溶W含量的Co基合金,并对合金金相组织及相结构进行了分析;对淬火后的WC-10％Co硬质合金,研究了在不同回火温度、时间工艺参数条件下合金粘结相Co的微观组织结构变化规律及其主要影响因素;通过离子束抛光制样,运用背散射电子衍射（EBSD）技术研究了WC-20％Co硬质合金中的α-Co与ε-Co形貌特征及其分布状态。实验结果表明：α-Co结构的稳定性较差,α-Co向ε-Co的转变的相变驱动力仅几J/mol;固溶W含量对钴基合金中晶粒的孪晶组织有重要的影响,Co基合金中固溶的W含量越多其孪晶组织越少,且α-Co含量越多;硬质合金淬火后回火实验说明硬质合金粘结相Co的8马氏体相变过程既可在较高温度、短时间内形成变温马氏体ε-Co,也可在较低温度、长时间下形成恒温马氏体ε-Co,合金内部组织内应力的释放会引起α-Co向ε-Co的转变;EBSD分析发现硬质合金中粘结相大部分是以α-Co结构存在,ε-Co呈条带状,厚度在2μm以下,长度在6μm左右,主要分布在粘结相与WC相的界面处或较厚钴层的中间部位。文中重点论述了硬质合金ε-Co马氏体的基本特征及其切变机制。     

Disperse-strengthening by nanoparticles advanced tribological coatings and electrode materials for their deposition

Two types of electrode materials were developed using self-propagating high-temperature synthesis (SHS) and powder metallurgy: 1- composite with nanosized additives; 2- nanostructured cemented carbide WC-Co. Electrospark deposition (ESD) was applied to produce tribological coatings which were disperse-strengthened by incorporation of nanosized particles. Nanostructured electrodes of cemented carbides WC-8% Co provide increasing density, thickness, hardness, Young's modulus, and wear resistance of ESD-coatings. Positive effects of nanostructural state of the electrodes on the deposition process and structure/properties of the coatings are discussed. In that case the tungsten carbide phase becomes predominant in the coatings. A mechanism of the dissolution reaction of WC in Ni at the contact surface of the electrode was proposed. It was shown that formation of the coating structure is initiated on the electrode and accomplished on the substrate.     

Improvement of the wear resistance of Ti-based coating sliding against copper alloy

The multilayer coating, Ti10%-C:H/TiC/TiCN/TiN, was deposited on cemented tungsten carbide (WC-Co) substrate by an unbalanced magnetron sputtering system. Tribological characteristics of this coating were compared with the coatings of TiN, TiCN, and TiC/TiCN/TiN deposited on WC-Co substrates and the WC -Co substrate itself. The coating displayed excellent tribological properties, i.e., both low value and smooth curve of friction coefficient, and also, compared with the other tested materials, yielded the lowest wear depth when sliding against bronze under dry conditions. The coating thus protects against the high wear experienced when Ti-based coatings rub against copper alloy.     

电火花沉积技术研究现状与展望

电火花沉积技术被广泛地应用于零部件表面涂层的制备与损伤的修复.简要介绍了电火花沉积技术的原理,概括了其进行表面强化与修复的优点.系统地讨论了电火花沉积技术主要工艺参数(电压、电容、比沉积时间和氩气流量)对涂层的沉积效率、形貌、缺陷、组织结构和性能的影响规律,其中热量的输入与释放速率是工艺参数对涂层制备产生影响的关键因素...     

Ti合金表面WC92-Co8电火花强化层形成规律

电火花强化技术可在Ti合金表面制造0．05mm以上的硬质合金强化层，彻底改变Ti合金表面性能。通过微分电火花强化过程，研究了单脉冲、多脉冲放电时强化点的形成规律；不连续、连续强化点的形成及最终形成一定厚度强化层的规律性。认为Ti合金表面的WC92-Co8强化层是通过无数次合金化过程实现的；基体的单脉冲强化点具有明显的“坑涌”现象。旋转的电极对熔池有搅动作用。     

粉末致密度对碳化钨涂层结构特征的影响

利用超音速火焰喷涂技术将4种不同致密度WC10Co4Cr粉末制备成涂层。采用扫描电镜、X射线衍射仪、显微硬度计、表面粗糙度仪等设备对涂层的微观组织、结构特征进行分析。结果表明,随着致密度的降低,团聚烧结型粉末与基体撞击后更容易铺展,碳化钨微粒分布变得更均匀,形成的涂层具有更低的孔隙率和表面粗糙度;但是随着致密度的降低,碳化钨分解率升高,形成更多的脆硬相,最终使得涂层断裂韧性下降。由此可知,致密程度影响粉末颗粒在热喷涂过程中加热、加速和铺展状态,从而影响涂层的结构特征。     

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。     

Phase transformation of NiCrBSi–WC and NiBSi–WC arc sprayed coatings

The coating microstructures of electric arc sprayed NiCrBSi–WC and NiBSi–WC coatings were investigated. It was found that, for NiCrBSi–WC coating, the resulting microstructure consists of NiCr, NiCrW solid solutions and WC/W₂C as major phases. For NiBSi–WC coating, the major phases are Ni, NiW solid solution and WC/W₂C. Some B is present within the coatings as inclusions. The amount of WC/W₂C was reduced in both coatings due to the formation of the NiCrW and NiW solid solutions containing a large amount of W. Precipitation of W-rich phase from NiCrW and NiW solutions was also observed but the transformation is restricted by the fast cooling rate characteristic of the spraying process. There is more dissolution of WC/W₂C into the matrix in NiBSi–WC coating resulting in a greater reduction in the microhardness of this coating. Wear test results, however, show that even though the NiBSi–WC coating possesses lower microhardness, it is more effective against dry sliding wear than the NiCrBSi–WC coating, owing to better metallurgical bonding between the matrix and the carbide as a result of WC/W₂C dissolution.     

超音速火焰喷涂低碳WC/12Co涂层的组织及性能研究

采用离心雾化干燥法制得团聚颗粒,经连续高温烧结成两种不同松装密度的热喷涂粉末。采用以C3H8/O2为燃料的超音速火焰喷涂（HVOF）工艺制备了WC/12Co涂层。对粉末及涂层做了显微组织观察和XRD分析,测定了涂层的厚度、显微硬度和粉末沉积效率。结果表明,在1120℃、1180℃烧结的粉末中主要有WC和W6Co6C,但无Co相;涂层有脱碳,有Co6W6C相,但未出现单质Co。涂层组织均匀致密,沉积效率可达65%。     

WC对激光熔覆层组织及耐磨耐冲击性的影响

激光熔覆Ni基合金涂层具有良好的综合性能,但耐磨与耐冲击性能仍有待提高。分别采用含微米与纳米WC颗粒的Ni基粉末激光熔覆制备WC/Ni涂层,研究两种WC颗粒对Ni基涂层组织及耐磨耐冲击性的影响。利用SEM与XRD对涂层进行微观组织分析,利用高速摄像机分析熔覆过程中的熔池形态。采用磨损试验机、夏比冲击试验机对涂层进行耐磨性与耐冲击性测试。纳米WC对熔池流动的促进作用强于微米WC,并使涂层组织得到更显著的细化。由于微米WC与Ni45涂层结合紧密,磨损试验中能有效抵抗配磨件微凸体的切削,最终显著增强涂层耐磨性,磨损率较Ni45涂层降低88.38%。但微米WC的高脆性不利于涂层耐冲击性的提高,冲击韧性仅为Ni45涂层的91.28%。由于纳米WC在细化晶粒的同时会弥散分布于晶界与共晶区,在磨损过程中阻碍位错运动,抑制晶粒塑性变形,进而减弱配磨件对涂层的切削,提高涂层耐磨性,磨损率较Ni45涂层降低53.43%。由于在晶界与共晶区的纳米WC会阻碍裂纹扩展并改变扩展方向,进而提高形成贯穿裂纹的能量,增加涂层断裂所需的冲击功,使涂层耐冲击性得到显著提高,冲击韧性较Ni45涂层提高13.37%。通过有限元分析可知,在冲击过程中涂层中的高脆性微米WC会形成高应力集中,证明其对涂层耐冲击性具有不利影响。而纳米WC能降低位错的不均匀滑移,缓解位错堆积,进而有效分散涂层在冲击过程中形成的应力集中,证明其能显著提高复合涂层的耐冲击性能。研究证明,纳米WC能实现涂层耐磨性与耐冲击性的同步提升。     

Electrospark coatings deposited onto an Armco iron substrate with nano- and microstructured WC-Co electrodes: Deposition process, structure, and properties

Nano- and microstructured electrodes WC-8%Co were used for electrospark deposition (ESD) of coatings onto an Armco iron upon variation in the energy P of single discharge pulses between 0.01 and 1.2 J. Considered are the physical and chemical processes taking place at the surface of electrodes: in the coating formed on a substrate (cathode), and in the secondary structure of electrode (anode). The resultant coating was found to contain largely an amorphous phase and tungsten semicarbide W₂C. In case of nanostructured electrodes, an increase in P above some threshold value gives rise to an increasing content of crystalline phases and formation of a structure comprising of sub-micron W₂C/WC grains surrounded by an amorphous binder. In case of microstructured electrodes, the amount of the amorphous phase is predominant for any P. The use of nanostructured electrodes in ESD onto an Armco iron substrates seems expedient only for P < 0.23 J.     

热处理对超细晶WC-15Co-0.2VC-0.4Cr_3C_2组织和性能的影响

分析了淬火和回火对WC-15Co-0.2VC-0.4Cr3C2超细晶硬质合金力学性能、微观组织及相结构的影响。研究发现,1 050℃淬火后横向断裂强度(TRS)由烧结态的4 020 MPa提高到4 590 MPa。TEM观察发现WC晶变得圆整,XRD分析显示高温淬火后的试样中塑性粘接相α-Co的含量明显高于烧结态,这使得合金的横向断裂强度显著提高。淬火后低温回火时消除淬火残余应力,TRS进一步提高,但回火温度高于300℃后TRS值下降,原因是高温回火时塑性粘结相α-Co转变成为ε-Co。     

淬火处理对硬质合金性能的影响

硬质合金往往不能同时兼备高的硬度和高的韧性,而淬火处理可以在不降低硬度的同时提高硬质合金的韧性。通过X射线分析研究了淬火处理以后C0相的变化规律及合金表层应力的变化情况。采用电解脱溶的方法分析了淬火处理以后Co相中α-Co的含量,通过TEM分析,观察了WC棱角的情况和Co相的微观结构,分析发现,经淬火后,WC棱角普遍变为圆滑状,Co相层错密度减小,从而,有效的抑制了α-Co向ε-Co的转变,提高了硬质合金的强度和韧性。     

Influence of SiC + WC addition to Cr(VI) bath on corrosion behaviour of coatings in sulphate solution

Abstract

Cr–WC–SiC coatings were deposited from Cr(VI) baths containing a mixture of both WC and SiC particles in the ratio of 1 : 1. X-ray photoelectron spectroscopy data indicated relatively low percentages of both WC (about 2˙68–2˙85 at.-% of W4f) and SiC (0˙16–0˙45 at.-% of Si2p) particles in the top layers of the Cr–WC–SiC coatings. However, these particles have some effect on the morphology and corrosion properties of the Cr coating. Protective properties of the coatings obtained were studied at different exposure times of samples in sulphate solution (pH=2˙8), using the electrochemical impedance spectroscopy method (EIS). Equivalent circuits, based on the electrophysical model describing the electrochemical corrosion at the coated surface, were proposed. The simulation of EIS data with the proposed equivalent circuit models made it possible to reveal the details of the corrosion processes occurring at coated systems (steel/Cr–WC–SiC coatings) immersed in the sulphate solution. Based on EIS data, diffusion in the coating was found to be a significantly controlling factor in the corrosion process for the system under investigation. The electrochemical impedance spectroscopy tests indicated a better corrosion resistance of Cr–WC–SiC coating than that of Cr. Analysis of the EIS data suggests that the enhanced corrosion resistance of Cr–WC–SiC coating was due to the microstructural features of these coatings, presumably containing smaller pores than Cr coating.