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。     

MA-SPS法制备WC颗粒增强钢基复合材料的耐磨性研究

采用机械合金化和放电等离子体法(MA-SPS)制备了WC颗粒增强钢基复合材料,对复合材料的组织形貌、耐磨性及耐磨机理进行研究.结果表明:该方法改善了复合材料的组织形貌,晶粒比较细小且均匀;同时显著提高了材料的硬度和耐磨性,随WC含量的增加,复合材料的致密度、硬度和耐磨性增加,最高硬度达70 HRC,相比基体材料的耐磨性提高了8倍;该材料的主要磨损机制为粘着磨损和磨粒磨损.     

WC颗粒增强Cr系白口铸铁复合材料的三体磨损性能的研究

系统研究了在三体磨损条件下,WC颗粒增强Cr系白口铸铁表层复合材料的抗磨损性能,并与相应的Cr系白口铸铁的抗磨损性能进行了比较.结果表明,铸态去应力处理时,Cr系白口铸铁随着金属Cr含量的增加,其耐磨性有所增强;Cr含量从2%增加到26%,相对耐磨性从1增加到1.39,而复合材料相对于基体材料的耐磨性提高到了6以上.硬化态去应力处理时,Cr系白口铸铁随着金属Cr含量的增加,其耐磨性略有增强;Cr含量从2%增加到26%,相对耐磨性从1增加到1.29,而复合材料相对于基体材料的耐磨性提高到5以上.可见,为了提高Cr系白口铸铁材料表层的耐磨性能,采用制备WC颗粒增强Cr系抗磨白口铸铁表层复合材料的途径十分有效.     

WC颗粒增强Cr系抗磨白口铸铁表层复合材料的抗磨损性能研究

通过销盘磨损试验,研究了在两体磨损条件下,WC颗粒增强抗磨白口铸铁表层复合材料的抗磨损性能;并与相应的抗磨白口铸铁的抗磨损性能进行了比较.结果表明,铸态去应力处理时,抗磨白口铸铁随着金属Cr含量的增加,其耐磨性有所增强.Cr含量从2%增加到26%,相对耐磨性从1增加到1.48,而复合材料的相对耐磨性提高10倍以上;硬化态去应力处理时,抗磨白口铸铁随着金属Cr含量的增加,其耐磨性略有增强.Cr含量从2%增加到26%,相对耐磨性从1增加到1.32,而复合材料的相对耐磨性高达30左右.可见,为了提高材料表层的耐磨性能,采用制备WC颗粒增强Cr系抗磨白口铸铁表层复合材料的途径十分有效.     

WC颗粒增强Cr系抗磨白口铸铁表层复合材料抗磨损性能的研究

本文研究了在三体磨损条件下,WC颗粒增强Cr系白口铸铁表层复合材料的三体磨损性能;并与相应的Cr系白口铸铁的三体磨损性能进行了比较.结果表明,铸态去应力处理时,Cr系白口铸铁随着金属Cr含量的增加,其耐磨性有所增强.Cr含量从2%增加到26%,相对耐磨性从1增加到1.39,而复合材料相对于基体材料的耐磨性提高到了6以上;硬化态去应力处理时,Cr系白口铸铁随着金属Cr含量的增加,其耐磨性略有增强.Cr含量从2%增加到26%,相对耐磨性从1增加到1.29,而复合材料相对于基体材料的耐磨性提高到5以上.可见,为了提高Cr系白口铸铁材料表层的耐磨性能,采用WC颗粒增强Cr系抗磨白口铸铁表层复合材料的途径十分有效.     

SiC_p对铝基复合材料组织和磨损性能的影响

通过粉末冶金制备了不同SiCp含量的SiCp增强铝基复合材料,研究了不同含量的SiCp对铝基复合材料工艺及组织性能的影响。结果表明,在压制成型时增加SiCp含量对模具有磨损;但在烧结时却能促进致密化。SiCp增强铝基复合材料的硬度开始是随SiCp含量增加而增加,在SiCp达到一定程度后反而呈下降趋势。SiCp含量在15%~30%时,复合材料具有较好的耐磨性。磨损机制是磨粒磨损和剥离磨损。     

微晶和纳晶Co–Ni–Fe合金摩擦磨损特性的比较

用脉冲电沉积技术制备了表面平整光亮的纳晶Co–Ni–Fe合金镀层。将纳晶镀层退火获得微晶Co–Ni–Fe合金镀层。采用XRD、TEM、EDS等方法研究了微晶和纳晶镀层的微观组织结构和合金成分。在干滑动条件下测定了微晶和纳晶镀层的摩擦磨损性能,并研究了磨痕的组织结构和硬度变化。结果表明:微晶和纳晶镀层均为单相面心立方结构。微晶和纳晶镀层磨损过程的塑性变形机制存在明显差异。摩擦磨损使纳晶发生晶粒长大,而对其硬度影响不大;摩擦磨损使微晶镀层表面发生纳米化,且存在明显的加工硬化现象。纳晶镀层的耐磨性能优于微晶镀层,但两者的主要磨损机制均为粘着磨损。     

Co含量对MOFs衍生的片状Co/C复合材料吸波性能的影响

金属有机骨架(MOFs)衍生的磁性金属/碳复合材料在轻质吸波材料领域展现出巨大的潜力。以二维片状结构Co/Zn双金属MOFs为前驱体通过高温热解合成片状Co/C复合材料,系统研究了前驱体中Co/Zn摩尔比对复合材料形貌结构、石墨化程度、磁性能和吸波性能的影响。结果表明：金属Co纳米微粒在碳骨架中均匀分布,随着Co含量的减少,复合材料中碳组分的石墨化程度逐渐降低,铁磁特性逐渐减弱;片状Co/C复合材料的吸波性能随着Co含量的降低先增强后减弱,填充比例为30 wt%、Co/Zn摩尔比为4:1时片状Co/C复合材料具有最佳吸波性能,厚度为2.11 mm时在10.8 GHz处最小反射率为-23.09 dB,最大有效带宽(反射率小于-10 dB)在厚度为1.62 mm时达到4.96 GHz。复合材料良好的吸波性能是由于均匀分布的磁性Co纳米粒子和碳骨架的协同作用,在增强电磁波导电损耗和界面极化损耗的同时,改善了阻抗匹配性能。     

金刚石–SiC/Al复合材料的构型设计与导热性能

以SiC和镀钨金刚石增强体为原料制备预制体,通过气压浸渗技术在800 ℃,5 MPa条件下制备金刚石–SiC/Al复合材料。利用扫描电镜、红外热成像仪、激光导热仪等对复合材料性能进行分析,研究SiC和金刚石的含量与粒径比对复合材料构型的影响,从而优化复合材料导热性能。结果表明:在相同的SiC粒径下,金刚石体积分数的增加将使复合材料的导热性能明显提升。当金刚石体积分数为30%时,含F100 SiC的复合材料导热性能最佳,其热导率为344 W/(m?K)。当金刚石体积分数相同,粒径比从0.07增大到0.65时,复合材料导热性能依次提升;且在金刚石体积分数为15%时,复合材料的热导率增幅最大,从174 W/(m?K)增大到274 W/(m?K),增长了57%。通过改善金刚石–SiC/Al复合材料中增强体的含量和粒径比可以调控复合材料构型,充分发挥复合材料的导热潜力。      

纳米稀土改性热喷涂WC/12Co涂层的摩擦磨损性能研究

利用超音速火焰喷涂技术在45#钢表面制备了不同稀土含量的WC/12Co涂层.在HV-5型小负荷维氏硬度计上测定了涂层的显微硬度,在WTM-2E微型摩擦磨损试验仪上测定了涂层的摩擦磨损性能.结果表明:适量稀土的加入使WC/12Co涂层的显微硬度提高,耐磨性增强.当稀土含量在1.5%时,涂层的硬度提高42%,磨损体积最小.     

Influence of B4C coating on graphitization for diamond/WC-Fe-Ni composite

Diamond/WC-Fe-Ni composite is a potential composition for impregnated diamond drill bits. It is necessary to avoid the graphitization of the diamond from Fe and Ni under the powder metallurgy process. Boron carbide (B₄C) was coated on diamond, and diamond/WC-Fe-Ni composites were consolidated by hot pressing at different temperatures. The influences of sintering temperature and interfacial structure on bending strength and wear behavior were investigated. The bending strength for diamond/WC-Fe-Ni composite was dependent on matrix densification and interfacial graphitization. Un-coated diamond was eroded by Fe-Ni matrix and partially converted to graphite during the sintering process at all sintering temperatures. In opposite, B₄C coating was beneficial to matrix densification at a lower sintering temperature, and delayed the appearance of graphitization to around 1300 °C. Therefore, the diamond/WC-Fe-Ni composites with B₄C coating exhibited larger bending strength and better wear behavior at a relative low sintering temperature.     

CVD金刚石薄膜涂层整体式刀具的制备与应用

化学气相沉积(chemical vapor deposition,CVD)金刚石薄膜具有硬度高、摩擦系数低、耐磨性强以及表面化学性能稳定等优异的机械及摩擦学性能,这使其在硬质合金工模具领域具有广阔的应用前景.本文采用热丝化学气相沉积法(hot filament chemical vapor deposition,HFC...     

Comparative investigation of smooth polycrystalline diamond films on dental burs by chemical vapor deposition

Depositions of hot filament chemical vapor-deposited diamond on cobalt-cemented tungsten carbide (WC-Co) rotary cutting dental burs are presented. Conventional dental tools made of sintered polycrystalline diamond have a number of problems associated with the heterogeneity of the crystallite, decreased cutting efficiency, and short life. A preferential (111) faceted diamond was obtained after 15 h of deposition at a growth rate of 1.1 μm/h. Diamond-coated WC-Co dental burs and conventional sintered burs are mainly used in turning, milling, and drilling operations for machining metal ceramic hard alloys such as CoCr, composite teeth, and aluminum alloy in the dental laboratory. The influence of structure, the mechanical characteristics of both diamond grains and hard alloys on the wear behavior, as well as the regimen of grinding on diamond wear are considered. Erosion wear properties are also investigated under air-sand erosion testing. After machining with excessive cutting performance, calculations can be made on flank and crater wear areas. Diamond-coated WC-Co dental burs offered significantly better erosion and wear resistance compared with uncoated WC-Co tools and sintered burs. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

金刚石增强稀土纳米硬质合金复合齿研究

以液相复合—连续还原碳化方法制备的纳米复合WC-Co粉末、共沉淀法制备的Ni-Ce粉末和真空蒸镀W膜金刚石为原料,采用热压活化烧结,在1050℃的烧结温度、70MPa烧结压力、保温(3～5)min烧结条件下,制取了具有良好抗冲击性能和耐磨性的金刚石增强稀土纳米硬质合金复合齿。复合齿基体的维氏硬度HV1≥1800,抗弯强度TRS≥2800MPa,合金晶粒度在(200～400)nm之间,复合齿超硬部分的磨耗比≥80。结果表明共沉淀法制备的Ni-Ce粉末显著降低了合金中微孔和杂质等组织缺陷,大大提高了金刚石增强纳米硬质合金复合齿的整体性能。     

Wear characteristics of Fe-based diamond composites with cerium oxide (CeO2) reinforcements

To obtain better wear resistance for the metal bond diamond grinding tools, cerium oxide (CeO₂) with different contents were introduced into Fe-based diamond composites. A pin-on-disc wear test was performed to assess the wear properties of the fabricated specimens, and the morphological properties of the worn surface and corresponding wear debris were evaluated to examine the wear mechanism. Results show that the Fe-based diamond composites with CeO₂ addition exhibited an improvement in the densification, mechanical properties and wear resistance. The original long rod-shaped CeO₂ particles converted into the spherical particles <1 μm, dispersing in the Sn phase. The cerium oxide acted as a sintering aid, promoting the diffusion of Fe in the Sn phase during the sintering process. The dominant wear mechanism of the specimen with CeO₂ addition was the adhesive wear, compared with the abrasive wear in the specimen without CeO₂. With the increase in CeO₂ addition amount, the wear rate decreased. But an excessive amount of CeO₂ was detrimental to mechanical and wear performances. The optimal amount of cerium oxide to achieve the best wear resistance was investigated to be 0.8 wt%.     

Diamond-coated cutting tools for biomedical applications

Diamond coatings are attractive for cutting processes due to their high-hardness, low-friction coefficient; excellent wear resistance, and chemical inertness. The application of diamond coatings on cemented, tungsten carbide (WC-Co) burs has been the subject of much attention in recent years as a method to improve cutting performance and tool life. WC-Co burs containing 6% Co and 94% WC substrate, with an average grain size of 1–3 μm, were used in this study. To improve the adhesion between diamond and WC substrates, it is necessary to etch away the surface Co and prepare the surface for subsequent diamond growth. Hot filament chemical vapor deposition (HFCVD), with a modified vertical filament arrangement, has been used for the deposition of diamond films. Diamond film quality and purity has been characterized using scanning electron microscopy (SEM) and micro-Raman spectroscopy. The performance of diamond-coated WC-Co burs, uncoated WC-Co burs, and diamond-embedded (sintered) burs have been compared by drilling a series of holes into various materials such as human teeth, borosilicate glass, and acrylic teeth. Flank wear has been used to assess the wear rates of the burs when machining biomedical materials such as those just described. This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September 15–17, 2003, in Indianapolis, Indiana, and appears on pp. 273–82 of the Proceedings.     

Examination of the wear properties of HVOF sprayed nanostructured and conventional WC-Co cermets with different binder phase contents

There has been an increase in interest of late regarding the properties of thermally sprayed WC-Co cermets with nanograin carbide particles. These powders have shown interesting properties in sintered components, giving high values of hardness (2200–2300 VHN) and improved wear properties. The method used for the processing for these materials—solution formation, spray drying and chemical conversion, rather than introduction of WC as solid particles to a molten binder—allows the formation of sub-100 nm WC particles as a hard second phase. The work presented here examined the effect of composition on the microstructure and wear properties of some nanostructured WC-Co materials. WC-Co cermets with 8, 10, 12, and 15% Co binder phase were deposited using a Sulzer Metco hybrid DJ HVOF thermal spray system. Optimization of deposition conditions was necessary because of the unique morphology of the powders (thick-shelled hollow spheres) to produce dense consolidated deposits. There is a higher degree of decarburization of the WC phase in the nanostructured materials compared with the conventional WC-Co. This dissolution of the hard phase is also noted to increase on decreasing binder phase content. The nanostructured WC-Co coatings have a lower wear resistance compared with the conventional WC-Co for abrasive wear and small particle erosion. The abrasive wear resistance of these nanostructured materials was found to increase on decreasing cobalt binder content. This trend in abrasive wear resistance is consistent with studies on conventional sized cermets and is believed to be more dependent upon proportion of binder phase content than degree of decarburization for the materials studied. The small particle erosion resistance of the nanostructured coatings was found to increase on increasing cobalt content.     

Improving oxidation resistance of diamond by adding silicon into diamond-borosilicate glass composites

Diamond-borosilicate glass composites have been used for vitrified diamond tools. The major challenge in the development of these composites is to avoid oxidation of diamond during sintering. In this study, silicon powder was added into the diamond-borosilicate glass composites to enhance oxidation resistance of diamond. The results showed that silicon powder was oxidized prior to diamond and its oxide products could enter into the glass network. Consequently, the oxidation resistance of the diamonds was improved, and the bending strength and volume expansion ratio of the composites with silicon additive were evidently changed compared to that of composites without silicon powder. A maximum bending strength of 60.94 MPa, and a minimum volume expansion ratio of − 11.3% were obtained in the composite containing 8 wt.% silicon powder.     

Wear resistance and thermal stability enhancement of PDC sintered with Ti-coated diamond and cBN

Ti-coated diamond with different particle sizes and proper amounts of cubic boron nitride (cBN) was used to fabricate polycrystalline diamond composite (PDC) with improved wear resistance and thermal stability under high temperature and high pressure (5.5–6.5GPa, 1500–1650 °C). The ratio of Ti-coated diamond powder, cBN powder and normal diamond powder was W_30–50: W_4–8: W_0–1 = 70: 15: 15. Cobalt (Co) was used as a binder, and cemented tungsten carbide was used as a substrate to sinter a new high-performance PDC. Ti and TiC on the surface of Ti-coated diamond reacted with cBN under high temperature and high pressure to generate new ceramic phases such as TiB₂, TiN and TiN_0.3, which have high hardness and good wear resistance. Compared with the conventional PDC, the impact toughness and wear resistance of PDC with Ti-coated diamond and cBN addition were enhanced by 19% and 28%, respectively. The ceramic phase acts as a protective barrier, which enhances the initial graphitization and oxidizing temperature to 942–950 °C, which were 162–170 °C higher than the conventional PDC. The new ceramic barrier wrapped around the surface of the diamond and Co after the formation of the D-D (diamond-diamond) bonding will give priority to the oxidation reaction of Co and diamond with oxygen, which prohibits cobalt-catalytic graphitization of diamond, meeting the needs of PDC thermal stability and wear resistance in the field of drilling.     

Fracture toughness of cemented carbides obtained by electrical resistance sintering

The unique combination of hardness, toughness and wear resistance exhibited by WC-Co cemented carbides (hardmetals) has made them a preeminent material choice for extremely demanding applications, such as metal cutting/forming tools or mining bits, in which improved and consistent performance together with high reliability are required. The high fracture toughness values exhibited by hardmetals are mainly due to ductile ligament bridging and crack deflection (intrinsic to carbides). In this work two WC-Co grades obtained by using the electric resistance sintering technique are studied. The relationships between the process parameters (cobalt volume fraction, sintering current and time, die materials, etc.), the microstructural characteristics (porosity, cobalt volume fraction, carbide grain size, binder thickness and carbide contiguity) and mechanical properties (Vickers hardness and fracture toughness) are established and discussed. Also the presence of microstructural anisotropy and residual stresses is studied. The sintering process at 7 kA, 600 ms and 100 MPa, in an alumina die, followed by a treatment of residual stress relief (800 °C, 2 h in high vacuum), allows to obtain WC-Co pellets with the best balance between an homogeneous microstructure and mechanical behaviour.