电火花表面强化过程中的"阳极粘连"现象

通过对TC1合金表面强化WC—Co过程中的“阳极粘连”现象研究,揭示出电极旋转式电火花表面强化过程的实质是一种混合冶金过程。由于存在“阳极粘连”现象,电火花强化过程中两极间的放电过程具有不规律交变放电的特征。上述结论为解释TC1合金表面WC—Co电火花强化层中存在TiC等新相提供了理论依据。     

40Cr钢表面电火花沉积WC的界面行为

以WC合金作为电极,氩气为保护气体,采用电火花沉积技术在40Cr钢表面沉积WC合金层,通过显微硬度计、扫描电镜(SEM)及能谱分析(EDS),X射线衍射等测量方法,研究了40Cr钢表面电火花沉积WC层的显微硬度、表面状态、界面行为及相结构组成.结果表明,WC合金电火花沉积层存在微裂纹及气孔,主要由W、Fe6W6C、Fe3C和Cr23C6等相组成;沉积层显微硬度达820 HV,为基体的4.5倍;沉积层断面连续、致密,厚度为30 μm;沉积层与基体之间发生了元素的相互扩散与合金化过程,呈冶金结合,无明显界面.     

35CrMo钢表面电火花沉积WC合金涂层的界面行为

以WC合金为电极,采用电火花沉积技术在35CrMo钢表面沉积WC合金强化涂层,考察了涂层的断面显微硬度,并通过金相显微镜、扫描电镜(SEM)、能谱(EDX)、X-射线衍射(XRD)等表征了强化涂层的微观结构.结果表明:涂层的表面显微硬度约为基体的2.5倍.涂层的耐磨性显著提高;涂层与基体的主要元素发生了相互扩散,所获涂层是由基体与WC合金电极发生反应的冶金结合层,涂层的主要成分是Fe7C3、Fe3W3C、Fe7C3、Fe7W6、Fe3W3C和Fe7W6.     

钛合金表面电火花沉积WC涂层的研究

以WC为电极,采用不同的电火花强化工艺,在钛合金表面制备了强化涂层。为了比较不同工艺条件下获得涂层的组织结构,确定最佳的电火花沉积工艺,通过金相、SEM、EDS等试验方法对涂层的微观组织结构进行了研究。结果表明,仅改变电火花沉积参数对获得性能优良的沉积涂层效果不明显,当复合超声加工,并且达到一定频率范围时,可以明显改善涂层质量。所获涂层是由基体中Ti元素与WC电极发生反应生成的反应涂层,涂层的主要成分是TiC、W和W2C。     

BT20钛合金表面电火花沉积WC涂层微观组织研究

以WC为电极,氩气为保护气,采用电火花沉积方法在BT20钛合金基体上制备了强化沉积层。利用SEM、EDS和XRD分析了沉积层的微观结构和物相,利用显微硬度计测试了沉积层截面的显微硬度。结果表明,沉积层主要由TiC、WC、W和W2C相组成,TiC是电极材料与基体材料反应形成新相,是沉积层的主要组成相;沉积层与基体结合致密,形成良好的冶金结合。沉积层表面呈"泼溅状"形貌,截面组织形貌中观察到纳米级微晶堆垛结构和少量的树枝晶,反映了电火花沉积过程的快速加热和冷凝机制。沉积层显微硬度呈梯度变化,涂层最大硬度是基体的3倍。     

点焊电极表面电火花振动熔敷TiC工艺参数优化

为了改善镀锌钢板点焊电极的寿命,选用铬锆铜球型电极,以TiC作熔敷材料,对点焊电极表面进行了电火花振动熔敷功能强化层工艺试验.通过正交试验考察了沉积工艺参数(电容、基体转速、振动频率、沉积时间)对沉积层硬度和厚度的影响.结果表明,电容是影响电火花沉积层硬度和厚度的主要因素;振动频率对沉积层性能有一定的影响;基体转速、沉积时间对沉积层性能影响较小.试验条件下最优工艺参数为电容量30000 μF,基体转速1320 r/min,振动频率50 Hz,沉积时间120 S.     

H13钢表面电火花沉积WC涂层

利用DZ-4000(Ⅲ)型电火花沉积/堆焊机,以WC为电极材料,采用氩气为保护气对H13钢基体进行了电火花表面强化.利用扫描电镜、能谱分析仪、X射线衍射仪和显微硬度计等对沉积层的成分、组织、硬度和表面粗糙度进行了研究.结果表明,利用电火花沉积工艺可获得组织均匀、致密,且与基体呈冶金结合的沉积层,沉积层平均厚度约60μm.沉积层主要由Fe3W3C、(CrFe)7C3和W2C等相组成.沉积层的平均显微硬度为1321.4 HV0.05,约为基体硬度的3倍.     

TA2表面电火花沉积Zr/WC复合涂层特性及界面行为研究

目的通过在TA2表面进行电火花沉积改变其表面性能。方法采用电火花沉积技术,在基体TA2表面制备Zr/WC复合涂层,然后分别用扫描电镜(SEM)、能谱分析仪(EDX)、X射线应力分析仪、显微硬度计和摩擦磨损试验机分析涂层的微观组织、化学成分分布、残余应力、显微硬度分布以及涂层的耐磨性。结果复合涂层连续、均匀,厚度约为50~80μm;涂层表面不平整,存在很多小坑和粘连,涂层内部有少量气孔和裂纹;复合涂层与基体的主要元素Ti、Zr、W之间发生相互扩散,并发生冶金反应;经过电火花沉积后TA2表面存在较大的残余应力,通过改变工艺参数可有效控制残余应力;复合涂层表面显微硬度值最高能达到960.5HV200g,约为基体的4倍;经过电火花沉积Zr/WC复合涂层的试样磨损量远远小于TA2试样,ε_w=4.1,沉积层的耐磨性比基体材料提高了3.1倍,经电火花沉积制备复合涂层后表面的耐磨性显著提高。结论在TA2表面电火花沉积Zr/WC复合涂层可以改善其表面性能。     

不锈钢1Cr18NigTi电火花沉积层的组织和成分

以YG8合金为电极，1Cr18Ni9Ti不锈钢为基体，研究了电火花沉积工艺对沉积层组织结构及沉积层性能的影响。研究结果表明，电火花沉积功率和沉积时间对电火花沉积层的厚度和硬度有一定的影响；沉积工艺影响沉积层内合金元素的分布，导致沉积层内的碳化物有明显的差异。当小功率短时间沉积时，白亮层的物相主要为Cr0．19Fe0．07Ni0．01、WC（1-x）、CoCx和少量的Ni-Cr-Fe；使用大功率长时间沉积时，白亮层的物相主要为（CrFe），C3、CrC、Co3W3C和Ni-Cr-Fe。     

电火花沉积修复铝合金组织与可降解性能

目的 采用电火花沉积技术修复铝合金铸造缺陷。方法 采用两种电极（ER5356电极和自制电极）,在优化电火花沉积工艺条件下,修复铝合金表面气孔,系统研究电火花沉积工艺、电极材料、沉积气氛对修复层的影响。采用扫描电子显微镜（SEM）结合能谱仪（EDS）对修复层界面组织和成分进行表征;用显微硬度计测试修复层的硬度;用电化学工作站测试修复层的Tafel曲线,在水浴中测试修复层的降解速率,从热力学与动力学两方面对修复层的降解性能进行全面评价。结果 在氩气气氛中的最佳修复工艺参数为：频率5000 Hz,电容150 μF,沉积角度45°,此时的热输入为0.480 J。在氩气气氛中的修复层组织致密,且元素均匀分布,减小了成分偏析。由于消除了枝晶,修复层的硬度相对于基体的硬度略有提高。自制电极修复层的自腐蚀电位（–1.493 V）低于基体的自腐蚀电位（–1.421 V）,ER5356电极修复层不溶于水,自制电极修复层降解速率稍快于基体。结论 使用电火花沉积技术,可对3.5英寸压裂球表面缺陷进行修复,经测试,硬度和降解性能达到工程指标。     

3Cr13厨刀碟片激光同轴送粉熔覆层的显微硬度与组织

针对家用3Cr13不锈钢厨刀硬度低、耐磨性差、使用寿命短等问题，采用激光熔覆技术对其进行处理，改善厨刀的性能.研究了激光熔覆层的显微硬度及显微组织.结果表明，采用经优化的激光熔覆处理工艺，可以获得无气孔、裂纹和夹杂等缺陷的熔覆层，熔覆层与基体结合良好；熔覆层的显微硬度在7~12 GPa之间波动，平均显微硬度约为9 GPa，是基体的2.3倍，大大提高了刀刃的硬度；熔覆层中含有大量未熔的硬质颗粒WC，并镶嵌到相对较软的304L基体中，这种结构对WC颗粒起到韧化缓冲作用，保证刀具使用过程中WC颗粒不易脱落，从而可提高刀具的使用性能.     

Microstructure and properties of CVD coated on gradient cemented carbide with different WC grain size

In this paper, cemented carbides with gradient surface enriched in Co phase and depleted of cubic phases were prepared by one-step vacuum sintering. The gradient cemented carbides of different WC grain size were used as the substrates of CVD coatings. The effects of WC particle size on the formation of gradient layer, microstructure and properties of the gradient cemented carbides were investigated. Besides, the influence of WC grain size and gradient layer on microstructure, growth and adhesion strength of the coatings were studied. The results showed that the thickness of surface gradient layer decreased with increasing WC particle size, which was attributed to the decreased diffusion paths and the increased diffusion distance. The interface between the surface gradient layer and the bulk was disordered due to abnormal grain growth of WC in ultrafine cemented carbide. The microhardness across the direction of the fcc-free (Face Center Cubic Free) surface layer to the bulk were similar in the three gradient cemented carbides, and could be expressed as: from the surface to the inner, the microhardness decreased firstly, then increased sharply around the interface, and subsequently dropped to the bulk level. The coating on the fcc-free surface layer was thicker than that on bulk, and the coating on the substrate with fine-sized WC grains is the thickest. The increase of the WC grain size in the substrate could improve the bonding strength of the coating. Furthermore, the presence of Co-rich layer could improve the bonding strength. However, bonding strength was poor for the grain size of ultrafine.     

WC/钢复合材料渗硼中WC颗粒对硼化物生长的影响

采用粉末渗硼法,对三种WC含量不同的WC/钢复合材料进行渗硼处理.利用SEM、XRD及自制的黑白图片伪彩色处理仪等方法对渗硼层的组织结构、硬度分布、渗硼层厚度及渗硼层内裂纹萌生进行研究,重点分析了WC含量及分布状况对硼化物生长的影响.结果表明：进行渗硼后,材料表面可获得高硬度FeB＋Fe2B的渗硼层,且随WC含量的增加,Fe2B含量相对增加.在渗硼过程中,WC颗粒对硼化物的生长起阻碍作用,而且含量愈多,阻碍作用愈大,渗硼层愈浅.当WC颗粒的分布方向与渗硼方向平行时,对硼化物生长的阻碍作用最小,渗硼层厚且致密,且在冷却时不易产生裂纹;当WC颗粒的分布方向与渗硼方向垂直时,对硼化物的生长阻碍作用最大,获得的渗硼层较浅,并且在渗层中出现明显的疏松区;当WC粒子呈无序分布,对硼化物的生长阻碍作用介于上面两者之间.硼化物生长时,遇到大颗粒WC其尖端变钝并停止生长;遇到小颗粒WC可以＂吞食＂.     

采用WC过渡层增加金刚石薄膜附着力的研究

在微波等离子体化学气相沉积装置中，以WC-8％Co为基体，采用氢等离子体脱碳、磁控溅射镀W、碳化等方法，制备了微晶WC过渡层。研究了金刚石薄膜与基体的附着力。结果表明，表面脱碳后再镀W膜，W填充了氢等离子体脱碳时刀具表面因钴蒸发而留下的空洞，形成过渡层，在随后的碳化中和基体WC连接较为紧密，能增加金刚石薄膜与基体附着力，克服单纯的氢等离子体脱碳还原法降低刀具基体硬度、不能完全消除钴的有害影响的缺点。     

Ni+WC基粉末激光熔覆对柱塞组织和硬度的影响

采用Ni+WC基粉末激光熔覆对严重磨损的高压水除鳞机用柱塞表面进行修复,利用光学显微分析和扫描电子显微分析方法,对熔敷层、结合层和基体进行显微组织观察及能谱分析,并测定了不同区域的显微硬度.结果表明:国外试样的基体是铁素体和奥氏体组成的双相钢,过渡层为Ni25、熔覆层为Ni60+WC的试样,熔覆层的组织分布均匀,熔覆层有大量的WC质点分布,显微硬度值较高,峰值硬度为1000 HV.     

钛过渡层与硬质合金基体表面结合状况对金刚石薄膜附着力的影响

以WC-6％Co为基体,采用磁控溅射法,在原始试样、酸腐蚀试样以及酸蚀后进行氢等离子体脱碳处理的试样上制备Ti过渡层,然后碳化过渡层为TiC。在热丝化学气相沉积装置中,制备金刚石薄膜。研究三种不同试样上的金刚石薄膜与基体的附着力。结果表明,在原始试样上的金刚石薄膜在冷却过程中自动脱落;在经等离子体处理后的试样上,金刚石薄膜与基体间附着力高于在经酸蚀处理的试样上的金刚石薄膜与基体附着力。造成这种现象的主要原因可能是等离子体脱碳还原处理降低WC晶粒表面能,增强Ti与WC间的结合强度,导致TiC过渡层与WC基体结合强度增加,从而增加金刚石薄膜附着力。     

Mechanical and tribological evaluation of PVD WC/C coatings

Five different WC/C coatings deposited by physical vapour deposition (PVD) on high speed-steel (HSS) have been evaluated with respect to their mechanical and tribological properties. For all coatings a chromium layer was deposited first to enhance coating adhesion. The carbide phase (WC) and the carbon (C) phase were deposited simultaneously by direct-current magnetron sputtering of a WC target and plasma-assisted chemical vapour deposition using hydrocarbon gas, respectively. The influence of the chromium interface layer thickness, the amount of WC phase and the flow of hydrocarbon gas on the mechanical and tribological properties of the coatings have been investigated. The coatings have been characterised with respect to their chemical composition (glow discharge optical emission spectroscopy), hardness (Vickers microhardness), morphology (scanning electron microscopy, SEM), roughness (profilometry), residual stress (beam bending), critical load (scratch testing) and abrasive wear resistance (the “dimple grinder test”). Furthermore, a ball-on-plate test was employed to obtain information about the frictional properties and sliding wear resistance of the coatings. The wear mechanisms and wear debris were analysed by SEM, Auger electron spectroscopy and electron spectroscopy for chemical analysis. All WC/C coatings displayed a thickness between 2 and 4 μm and a surface roughness in the range of 10 to 70 nm. The hardness varied between 1500 and 1800 HV. The coating residual stress was found to range from −2.5 to −0.5 GPa. The scratch test revealed a relatively high critical normal load, i.e., a relatively good adhesion of the WC/C coatings to the HSS. The abrasive wear resistance was found to be very high, in fact equally as high as that of PVD TiN. In the sliding wear test it could be seen that the coating containing the lowest amount of carbide phase (WC), i.e., the highest amount of carbon phase (C), and which had the highest compressive residual stress yielded the lowest friction and wear rate against steel. In addition, this coating was also found to yield the lowest wear rate of the counter material. In summary, a WC/C coating with overall good mechanical and tribological properties was obtained provided a relatively thin chromium layer was deposited first and if a relatively high acetylene gas flow was utilised during deposition of the WC/C layer.     

A novel technique for production of nano-crystalline mono tungsten carbide single phase via mechanical alloying

Due to simultaneous synthesis of WC and W₂C phases in most of the synthesis processes and lower mechanical properties of W₂C than WC, in this work the possibility of production of nano-crystalline WC single phase as a useful refractory ceramic by means of mechanical alloying has been investigated. The raw materials containing W and C with WC were milled in a planetary ball mill. The sampling has been done in different times. As it was expected, XRD studies showed that after 75 h of milling the WC with W₂C were produced. By adding WC to the raw materials in the beginning of the process it led to the fact that after 50 h of milling WC was synthesized only without any other phases which remained stable at the higher times while milling. During broadening of XRD peaks, the size of synthesized crystalline WC was estimated in the order of nano-meter. Crystalline size and mean strain of synthesized WC in the system without additive were higher and lower than the system containing WC, respectively.     

Chemical mechanism of chemical mechanical polishing of tungsten cobalt cemented carbide inserts

To explore the chemical mechanism of tungsten‑cobalt cemented carbide inserts in H₂O₂-based polishing fluid. Before and after the YG8 cemented carbide inserts were corroded, surface phase, element and structure were characterized by XRD and SEM/EDS. The chemical mechanism of tungsten‑cobalt carbide inserts during chemical mechanical polishing (CMP) was analyzed. XPS was utilized to analyze the corrosion products formed on the surface of YG8 cemented carbide inserts during chemical reaction to determine the chemical reaction equation. In the H₂O₂ environment, the electrode potential of the Co layer at the boundary between the binder phase with larger crystal domains and the hard phase is greater than the electrode potential of the intermediate layer γ(Co-W-C solid solution) phase and WC, which creates a potential difference between the three, and occurs galvanic corrosion. The hard phase WC is protected as the cathode of the entire battery and has a tendency to stabilize. The Co layer at the phase boundary is the most anode feature to be corroded and dissolved first. The γ phase of the intermediate layer serves as the secondary anode feature and serves also as the cathode of the Co layer. When the Co layer at the phase boundary is corroded to a certain extent, a galvanic couple is formed between the γ phase and the testing phase WC to cause corrosion. In addition, the binder phase with smaller crystal domains directly forms galvanic corrosion with WC. The chemical products created on the surface of the blades are Co₃O₄ and WO₃. However, Co₃O₄ and WO₃ oxide films are small in size and have little effect on material removal during polishing. When the binder phase corrosion on the blades surface reaches a critical point, the stress exerted by the polishing abrasive is basically concentrated on the WC particle surface. The strength of the WC particles that have lost the supporting effect of the binder phase becomes low and the structure becomes brittle. Under the mechanical scratching and compressive stress of the abrasive particles of the polishing solution, the smaller WC particles are directly pulled out. The surface layer of the larger WC particles is broken into WC grains, and then the surface layer is mechanically removed.