低烧损 复合粉末制备及涂层抗烧蚀性能研究

采用喷雾造粒-胶粘包覆的方法制备了一种低烧损核壳结构 ZrB2/SiC 复合粉末, 研究了胶粘包覆过程中不同清漆含量对粉末包覆效果的影响。 结果表明清漆含量不足时细粉包覆不完全, 细粉出现单独团聚的现象; 清漆含量过多时, 造成原始球形颗粒的粘连; 当清漆含量为 4.5% 时, 获得包覆效果良好的粉末, 外层包覆完整均 匀。 为了研究等离子喷涂过程中核壳结构粉末 SiC 发生分解烧损程度, 对比了分别采用核壳结构和均匀弥散结构ZrB2/SiC 复合粉末所制备涂层的微观形貌及涂层中元素分布。 结果表明核壳结构粉末喷涂涂层成分均匀性良好,高熔点 ZrB2 保护内层 SiC, 可有效减少 SiC 在等离子焰流中的烧损, 实现涂层和粉末成分的一致性。 对核壳结构复合粉末制备的涂层进行了 20s 的氧-乙炔火焰烧蚀试验, 涂层质量烧蚀率为 1.837×10-3g/s, 对涂层抗烧蚀机理进行了初步探讨。     

低烧损ZrB_2/SiC复合粉末制备及涂层抗烧蚀性能研究

采用喷雾造粒-胶粘包覆的方法制备了一种低烧损核壳结构ZrB_2/SiC复合粉末,研究了胶粘包覆过程中不同清漆含量对粉末包覆效果的影响。结果表明清漆含量不足时细粉包覆不完全,细粉出现单独团聚的现象;清漆含量过多时,造成原始球形颗粒的粘连;当清漆含量为4.5%时,获得包覆效果良好的粉末,外层包覆完整均匀。为了研究等离子喷涂过程中核壳结构粉末SiC发生分解烧损程度,对比了分别采用核壳结构和均匀弥散结构ZrB_2/SiC复合粉末所制备涂层的微观形貌及涂层中元素分布。结果表明核壳结构粉末喷涂涂层成分均匀性良好,高熔点ZrB_2保护内层SiC,可有效减少SiC在等离子焰流中的烧损,实现涂层和粉末成分的一致性。对核壳结构复合粉末制备的涂层进行了20s的氧-乙炔火焰烧蚀试验,涂层质量烧蚀率为1.837×10~(-3)g/s,对涂层抗烧蚀机理进行了初步探讨。     

超细25%NiCr-Cr_3C_2粉末制备及HVOF涂层性能研究

本文采用超细碳化铬粉末通过团聚烧结工艺制备球形25%NiCr-Cr3C2复合粉末,使用超音速火焰喷涂工艺制备耐高温磨损涂层,分析了超细25%NiCr-Cr3C2复合粉末的化学成分和表面形貌,通过涂层的结合强度和显微硬度与常规粉末的对比实验,研究超细Cr3C2颗粒对超音速火焰喷涂涂层的性能影响。     

球形复合氧化铬团聚粉末及等离子喷涂涂层性能研究

采用喷雾造粒 - 烧结的方法制备了一种球形复合氧化铬团聚粉末, 利用扫描电子显微镜 (SEM)、 霍尔流速 计和粉末颗粒强度仪对粉末性能进行了表征, 研究了团聚造粒过程中料浆不同粘结剂含量对粉末微观组织形貌的 影响以及烧结温度对粉末松装密度、 流动性及颗粒强度的影响。 采用大气等离子喷涂 (APS) 工艺制备了复合氧化 铬涂层, 并对涂层的微观组织、 显微硬度及涂层结合强度等力学性能进行研究。 研究结果表明： 适量的增加料浆 粘结剂含量, 粉末球形度变好, 粘结剂含量过高时, 粉末球形度变差, 当粘结剂含量为 8% 时粉末具有较好的球 形度; 随着烧结温度的升高粉末松装密度先降低后升高, 粉末流动时间先变长后变短, 粉末流动性先变差再变优, 当烧结温度达到 1300 ℃以上时, 粉末不具有流动性; 随着烧结温度的升高粉末颗粒强度逐渐升高; 该粉末经过 大气等离子喷涂沉积形成的复合氧化铬涂层孔隙率为 2.3%、 结合强度均值达到 39.74 MPa, 涂层平均显微硬度为 1197.6 HV0.3。     

热处理条件对WC-Co涂层性能的影响

采用喷雾转化法制备WC-Co复合粉末,再经超音速火焰(HVOF)喷涂制备WC-Co耐磨涂层,并分别在N₂和真空气氛中进行550、750、950℃热处理。研究了热处理条件对涂层物相、显微组织、硬度和耐磨性能的影响。结果表明:真空气氛热处理涂层较N₂气氛热处理涂层的脱碳程度更低,且孔隙率也更低;真空热处理工艺可显著提高涂层硬度,改善涂层耐磨性,750℃真空热处理涂层磨损率可降至喷涂态涂层的47%,HV_0.3硬度达到1 550。     

团聚钼粉和烧结钼粉等离子喷涂涂层的性能研究

本文通过喷雾干燥法制备了团聚钼粉,通过"喷雾干燥+烧结"的方法制备了烧结钼粉,然后对两种粉末进行了等离子喷涂实验,并对制备的涂层的形貌、粗糙度、硬度和孔隙率等进行了检测分析。结果表明,利用烧结钼粉制备的涂层的性能均优于团聚钼粉制备的涂层,其中烧结钼粉涂层的粗糙度为7μm,硬度为449.69HV和孔隙率为1.27%。     

致密化工艺对氧化钛粉末及等离子喷涂涂层性能影响研究

采用喷雾干燥法制备了一种球形氧化钛团聚粉末, 并通过高温烧结及感应等离子球化工艺对团聚粉末进行 致密化处理。 利用扫描电子显微镜 (SEM)、 霍尔流速计和粉末颗粒强度仪对粉末性能进行了表征, 研究了不同致 密化处理工艺对粉末颗粒强度、 松装密度及流动性的影响。 采用大气等离子喷涂 (APS) 工艺制备了氧化钛涂层, 并对涂层的微观组织进行研究。 研究结果表明, 高温烧结工艺及等离子球化工艺均可有效提升氧化钛团聚粉末 的致密度, 经过高温烧结工艺后氧化钛粉末内部的细小颗粒呈现烧结熔融的趋势, 而采用等离子球化处理后的 团聚粉末直接形成了致密球体结构。 相比于高温烧结工艺, 等离子球化工艺对氧化钛粉末的致密化效应更为明 显, 粉末的颗粒强度可达 187.86 MPa, 松装密度可由 0.79 g/cm3 提升至 1.69 g/cm3, 流动性由 163.22 s/50g 加快 至 100.27 s/50g。 该粉末经过大气等离子喷涂沉积形成的氧化钛涂层孔隙率为 2.8 %, 与未经致密化工艺处理的氧 化钛团聚粉末相比, 制备的涂层致密化水平有了较大程度的提升, 涂层的平均显微硬度值由 434.18 HV0.3 提升至 744.37 HV0.3, 涂层的结合强度均值由 11.07 MPa 提升至 29.93 MPa。     

低温超音速火焰喷涂纳米WC-10Co4Cr涂层的显微结构和性能

以纳米和微米WC-10Co4Cr粉末为热喷涂粉末,采用低温超音速火焰喷涂（LT-HVOF）和超音速火焰喷涂（HVOF）技术制备了WC-10Co4Cr涂层,采用SEM、XRD、和显微硬度仪等对LT-HVOF WC涂层显微结构和性能进行了表征.结果表明：n-WC涂层、lm-WC涂层的显微结构与普通超音速火焰喷涂WC涂层没有明显的区别,其主晶相为WC; m-WC涂层呈明显的层状结构,涂层中WC颗粒尖端发生了钝化和部分熔化,粒径变小,并形成了WC/的核壳结构;其主晶相为.n-WC涂层显微硬度较lm-WC涂层低,但其韧度高而使涂层的磨损失重最低;m-WC涂层的显微硬度和韧度最低,磨损失重最大.     

喷涂距离对超音速火焰喷涂WC10Co4Cr涂层沉积效率及耐磨粒磨损性能的影响

以-45~+15μm WC10Co4Cr团聚烧结球形喷涂粉末为原料,采用GTV超音速火焰喷涂(HVOF)系统K2喷枪,通过改变喷涂距离(300、340和380 mm)制备3种涂层,应用金相显微镜、X射线衍射仪、扫描电镜、显微硬度计等表征涂层结构和性能。结果表明:随喷涂距离减小,WC10Co4Cr涂层孔隙率降低、显微硬度增加、耐磨粒磨损性能增强,但粉末的沉积效率降低;喷涂距离为300~380 mm时,WC10Co4Cr涂层的物相组成均为WC、W2C及少量非晶相;喷涂距离为300~340 mm时,WC10Co4Cr涂层显微硬度和耐磨粒磨损性能变化较小;结合磨损区域中心位置的微观结构、涂层物理性能和表面粗糙度变化,探讨WC10Co4Cr涂层的磨粒磨损和喷涂距离的影响机制。     

高温耐磨损Cr3C2-25%NiCr涂层制备及其性能研究

采用超音速火焰喷涂球形烧结态Cr3C2-25%NiCr复合粉末制备高温耐磨损涂层,用扫描电子显微镜(SEM)分析粉末和涂层显微组织,用图像处理软件分析涂层孔隙率。通过结合强度、表面硬度和摩擦磨损等实验检测涂层机械性能。结果表明:粉末烧结状态、Cr3C2硬质相及粉末粒度因素影响涂层机械性能,KF-70涂层具有最高结合强度和表面硬度。     

新型 WC-MoCoB 金属陶瓷涂层制备及其性能研究

本文以碳化钨、碳化硼、钴和钼粉末为原料,按一定比例进行机械混合,采用团聚烧结工艺制备了WC-MoCoB复合金属陶瓷粉末,并利用扫描电子显微镜(SEM)、能谱分析(EDS)和X射线衍射分析(XRD)对其微观形貌、元素含量和相组成进行了表征;进而采用超音速火焰喷涂(HVOF)工艺制备了WC-MoCoB复合金属陶瓷涂层,并对涂层的微观组织、显微硬度、结合强度及抗腐蚀等性能进行研究。研究结果表明:该团聚烧结工艺制备的WC-MoCoB复合金属陶瓷粉末具有流动性好、松装密度较高的特点。该粉末经过超音速火焰喷涂加工形成的复合金属陶瓷涂层,结合强度高、孔隙率低,同时表现出优异的耐腐蚀性能。     

Evaluation of the in vitro direct and indirect genotoxic effects of cobalt compounds using the alkaline comet assay. Influence of interdonor and interexperimental variability

The mechanisms of cobalt-induced pulmonary interstitial fibrosis and cancer are incompletely understood. DNA damage, either induced by genotoxic (direct or via oxygen radicals) or co-genotoxic (e.g. inhibition of DNA repair) processes may play an important role in the initiation of cancer. The alkaline comet assay provides a sensitive tool to investigate these two processes. Cobalt metal, a mixture of cobalt with tungsten carbide and cobalt chloride, were compared for their DNA-damaging capacity. Concentrations from 0 to 6.0 microg Co-equivalent/ml were tested. All three compounds were able to induce DNA damage in isolated human lymphocytes from three donors, in a dose- and time-dependent way. A relatively large interexperimental and interdonor variability in response was observed. This was ascribed to technical parameters and unidentified individual factors. This confirms the importance of repeating experiments using the same and different donors. The DNA-damaging potential of the cobalt-tungsten carbide mixture was higher than that of cobalt metal and cobalt chloride, which had comparable responses. No significant increase of DNA migration was observed when the DNA of cells treated with cobalt metal, cobalt-tungsten carbide or tungsten carbide were incubated with the oxidative lesion-specific enzyme formamidopyrimidine DNA glycosylase. This suggests that during the short treatment period no substantial oxidative damage to DNA was produced. Cobalt metal was able to inhibit the repair of methylmethanesulphonate-induced DNA damage. This was concluded from simultaneous exposure to cobalt and methyl methanesulphonate, post-incubation and post-treatment with 1.2 microg/ml cobalt of methyl methanesulphonate-treated cells.     

活化烧结对金刚石增强型硬质合金复合齿性能的影响

在金刚石增强型硬质合金复合齿基体中球磨添加不同量红磷，比较相应的金刚石增强型硬质合金基体的性能，确定添加(质量分数)0．3％P的复合齿基体性能最好；同时采用化学镀Ni-P合金添加P结合球磨添加0．1％P的方式，其超硬复合齿基体力学性能及复合齿的磨耗比、抗冲击功远远优于单纯球磨添加0．3％P方式超硬复合齿的性能。说明为了实现金刚石增强型硬质合金复合齿的活化烧结方式，磷元素最优的添加方式是化学镀结合球磨的添加方式。     

Recycling of WC–Co from scrap materials

Abstract

WC-Co scrap generated by the cutting tool industries was electrochemically broken down to cobalt, which was deposited at the cathode and a mixture of tungsten oxide and tungstic acid was collected at the anode with an overall recovery efficiency of about 90%. The tungsten oxide/tungstic acid was reduced to produce nanostructural tungsten powders, which were subsequently carburised and chemically coated with cobalt to produce WC-Co powders. The powders synthesised were characterised for purity and size.The WC-Co powders, thus obtained were consolidated to near theoretical densities using a novel plasma pressure compaction (P²C) technique. The microhardness of the consolidated sample was measured to be 2200 HV, which is 20% higher than the reported literature values.     

DENSIFICATION PROCESSES IN THE TUNGSTEN CARBIDE-COBALT SYSTEM

Abstract

The tungsten carbide-cobalt system is one in which the carbide matrix phase is to some extent soluble in the cobalt binder and which readily sinters to give 100% density. The characteristics of this system have been examined by determination of densification curves and metallographic examination and compared with a previous investigation on the behaviour of the insoluble tungsten carbide-copper system.

It is found that the good densification characteristics of tungsten carbide-cobalt are due to the initial solution of the carbide by the cobalt. The cobalt diffuses in the solid state into interfaces between carbide particles and as the temperature increases dissolves carbide from the adjacent particle surfaces. Forces arising from minimization of surface energy then act to bring about close packing of the carbide. By this means 100% density is achieved with 8 wt.-%, or more, of cobalt. With between 5 and 8 wt.-% cobalt 100% density is obtained by initial solution followed by a few minutes further sintering during which a solution/reprecipitation mechanism is operative.

If sintering is prolonged, a rigid carbide network is formed and this then determines the contraction of the compact on cooling. Even when 100% density is attained at sintering temperature the cobalt contracts on solidification and cannot fill the intervening space between the carbide particles, so that shrinkage-pipe-porosity forms.

Porosity seals off from the surrounding atmosphere when ～90% density has been reached. If the gas entrapped is insoluble, then the pores shrink until the balance is attained between the surface energy and the excess pressure in the pores and this results in a porosity level of the order of 0·2%     

DENSIFICATION PROCESSES IN THE TUNGSTEN CARBIDE-COBALT SYSTEM

Abstract

Densification of the tungsten carbide-cobalt system has been investigated by determining the effect of the principal sintering variables-composition, temperature and time of sintering, particle size, ball-milling-and by studying the processes that occur. Considerable shrinkage takes place during heating, before the eutectic temperature is attained. A 9% cobalt alloy sintered entirely in the solid state to give comparable density and mechanical properties to those attained by liquid-phase sintering, but the sintering time was increased by a factor of 10. Densification proceeds from nuclei created by ball-milling, which packs the porous cobalt agglomerates with tungsten-carbide particles; if the cobalt particles are only mixed with the tungsten carbide, then on sintering they flow out into the matrix leaving behind voids that do not fill. Densification is characterizedby two features: first, tungsten-carbide particles cement together with cobalt between grains to form clusters and filaments; secondly, the clusters and filaments contract. The solubility of the tungsten carbide in the cobalt is important, since densification occurs far less rapidly when copper is used as the binder phase. Shrinkage can virtually cease before the compact is fully dense, either because voids form as a result of unsatisfactory mixing, or, with a small amount of cobalt, because the periphery of the compact sinters to full density before the interior, preventing further overall densification.     

WC/Co复合粉制备超细晶挤压圆棒工艺之研究

采用水溶液化学法制备的纳米复合粉作原料,研究制备超细晶挤压圆棒的生产工艺。含钴12%（质量分数）的WC/Co纳米复合粉中加入适量的复合抑制剂,经湿磨、挤压成型、加压烧结后检测其合金特性值,通过对比不同湿磨时间和烧结温度条件下的合金性能,研究复合粉生产挤压圆棒的工艺参数,研究结果表明：复合粉可应用挤压成型工艺生产出高性能的圆棒。钴12%合金圆棒的硬度可达92.8RA以上,抗弯强度达4 200MPa,碳化钨晶粒度小于0.4μm。     

Ceramic-Metal Composite Coating by Laser Cladding

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AN ELECTRON-MICROSCOPE AND X-RAY INVESTIGATION OF THE MILLING OF TUNGSTEN CARBIDE/COBALT MIXTURES

Abstract

It is well known that some interaction takes place between the two components when mixtures of cobalt and tungsten carbide are milled. To gain a further insight into this phenomenon, the milling process has been studied by means of the electron microscope and by the BET and X-ray methods.

During the milling of cobalt powder the number of stacking faults and the amount of the hexagonal phase both increase. On milling 80:20 tungsten carbide/cobalt mixtures increasing agglomeration of cobalt and fine tungsten carbide particles was found with rise in milling intensity. The larger tungsten carbide particles appeared to have a smooth surface. However, if the cobalt was dissolved in hydrochloric acid, the true surface of the tungsten carbide particles was revealed. This became rougher with increasing milling intensity. From this it can be concluded that, during milling, cobalt settles between the surface irregularities.

The variation in distribution of the cobalt that results from different milling conditions leads to a difference in sintering behaviour. A dilatometric study has been made of this aspect.

The original particle size of the cobalt used for hard-metal mixtures does not affect the properties of the sintered product, if the mixtures are milled very intensively.     

A STUDY OF THE FACTORS CONTROLLING GRAIN SIZE IN SINTERED HARD-METAL

Abstract

Previous experimental work concerning the grain growth observed during the sintering of tungsten carbide–cobalt alloys is reviewed. Particle-sizing methods suitable for the examination of hard-metal powders are described, and techniques for the evaluation of the carbide grain size in the sintered compacts are discussed.

By using a Model A Coulter Counter to examine the size distribution of the carbide grains (obtained from the milled hard-metal powders by dissolution of the cobalt with hydrochloric acid), and by counting techniques on electron photomicrographs of carbon replicas of the sintered compacts, it has been established that the increase in grain size during sintering is quantitatively related to the carbon content of the material after pre-heating. The results presented indicate that the cobalt content exerts little influence on the average grain size of the sintered structures A cobalt content >10% by weight is shown to exert a strong damping effect on the rate of comminution during milling.

The linear relationships between the specific surface area of the carbide grains in milled powders (obtained using a Perkin–Elmer Sorptometer) and the specific surface of the carbide phase in sintered compacts are given. The influence of sintering temperature and time on average grain size and contiguity in a commercial alloy is shown. Some preliminary work indicates that the morphologies of the initial carbide powders may be important factors with respect to the grain size of sintered hard-metal.