高温高压下金刚石/碳化硅体系烧结反应机理研究

本文研究了微米级金刚石与硅粉在高温(800~1 200℃)高压(5.1 GPa)下的反应机理。通过对金刚石与硅粉反应过程的研究,发现微米级金刚石与硅粉在硅熔点以下发生了反应;并指出高温高压下微米金刚石与硅粉的反应分为两个阶段:硅未熔化前的金刚石与硅的反应,硅熔化后的金刚石与硅、石墨与硅的反应。最后提出了一种新的合成金刚石/碳化硅复合材料的工艺,即采用高压熔渗法合成金刚石/碳化硅复合材料时,在温度略高于硅熔点之后保温一段时间,再升温到合成材料的设定温度,可以合成出结构更加均匀的、高质量的金刚石/碳化硅复合材料。     

Fracture resistant super hard materials and hardmetals composite with functionally designed microstructure

Polycrystalline diamond and other hard materials are widely used in earth boring, mining, and construction tool applications. Chipping and fracture resistance is often improved by various means at the expense of hardness and wear resistance. This trade-off between wear resistance and chipping resistance hinders the development of hard and super hard materials for many industrial applications. A new approach, characterized as “hard materials composites with functionally designed microstructure” including polycrystalline diamond and cemented tungsten carbide, is discussed. The functionally designed microstructure offers enhanced chipping resistance and toughness without significantly sacrificing wear resistance.     

SiC基底HFCVD金刚石薄膜摩擦磨损性能

利用热丝化学气相沉积技术在碳化硅基底上制备微米金刚石薄膜、纳米金刚石薄膜和金刚石–石墨复合薄膜,采用扫描电子显微镜、原子力显微镜和拉曼光谱仪对不同金刚石薄膜的表面形貌和微观结构进行表征,通过摩擦磨损实验测试金刚石薄膜的摩擦系数并计算其磨损率,对比研究不同种类金刚石薄膜的摩擦磨损性能。结果表明：金刚石–石墨复合薄膜具有较好的摩擦磨损性能,薄膜表面粗糙度为53.8 nm,摩擦系数为0.040,和纳米金刚石薄膜(0.037)相当;金刚石–石墨复合薄膜的磨损率最低,为2.07×10^-7 mm³·N^-1·m^-1。在相同实验条件下,同碳化硅基底的磨损率(9.89×10^-5 mm³·N^-1·m^-1)和摩擦系数(0.580)相比,所有金刚石薄膜的磨损率和摩擦系数均有明显提升,说明在SiC基体表面沉积金刚石薄膜能够显著提高碳化硅材料在摩擦学领域的使役性能。     

A study of grinding silicon nitride and cemented carbide materials with diamond grinding wheels

This paper presents selected results of the grinding of silicon nitride and cemented carbide materials with diamond grinding wheels, which will in later research be extended to the grinding of ceramic-cemented carbide compound drill tools. In these fundamental experiments four different types of diamond grinding wheels were used in face grinding processes. The diamond grinding wheels vary by the grain size, the grain concentration and the bonding material. The relevant influencing variables such as the cutting and feed speed and the coolant supply method were varied to investigate the effect on grinding of the two different workpiece materials, the brittle silicon nitride workpiece material and the ductile cemented carbide workpiece material. Some factors, which have significant effects, like the radial wear of the grinding wheel, the components of the grinding forces, the normal and the tangential grinding force, and the surface quality of the ground workpieces are discussed in detail.     

Polishing of polycrystalline diamond by the technique of dynamic friction, part 3: Mechanism exploration through debris analysis

This paper investigates the mechanisms of material removal in dynamic friction polishing of polycrystalline diamond composites through the analysis of polishing-produced debris. The specimens used were PCD compacts composed of diamond and silicon carbide. In order to uncover the debris’ structure, high-resolution transmission electron microscopy (HRTEM), electron diffraction and electron energy loss spectroscopy (EELS) were used. Additionally, the density and the sp² to sp³ ratio in the hybridized carbon materials of the debris were estimated from the EELS spectra. It was found that the debris were mainly of amorphous structure and consisted of different forms of carbon, silicon oxide/carbide, iron oxides, etc. The results show that during polishing, the diamond has transformed to non-diamond carbon, and silicon carbide to amorphous silicon carbide/oxide.     

Drilling of graphite/bismaleimide composite material

Drilling study of graphite/bismaleimide composite material was conducted by using different cutter materials (high-speed steel, carbide, and polycrystalline diamond) and drill geometries. It was found that polycrystalline diamond tools outperformed all other tools in terms of minimal surface damage, delamination, and fiber pullout. The drilling forces exerted in machining graphite/bismaleimide were recorded by using a dynamometer, and the morphology of drilled surfaces was evaluated with surface profilometry and optical and scanning electron microscopy. The drilling characteristics were evaluated in terms of cutting forces, tool wear, and surface morphology.     

ZL101/SiCp复合材料制备及其缺陷分析

对于高增强体含量的复合材料,其材料的致密性显得尤为重要,本文采用冷等静压结合热等静压的方式制备SiCp/Al复合材料克服了这个困难,实现净成形,具有工艺简单等优点,使用180#α-SiC颗粒作为增强体,体积分数为20%,同时采用ZL101铝粉作为基体,其中采用冷等静压方法能制备出冷坯料材料的理论密度可达75%,后续采用热等静压制备出的碳化硅颗粒增强铝基复合材料具有致密性良好,颗粒分布均匀,无明显的聚集现象。同时结合SEM和EDS对界面的分析表明碳化硅颗粒增强铝基复合材料产生的缺陷主要是增强体碳化硅颗粒和铝基体结合的界面处有细小的气孔存在,使材料的有效承载面积减小,最终导致材料破断。初步分析了复合材料微缺陷产生的机理。界面处反应生成的界面相对于复合材料的影响。     

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.     

The application of polycrystalline diamond (PCD) tool materials when drilling and reaming aluminium based alloys including MMC

Following a review of metal matrix composite (MMC) materials and production methods, the paper outlines the development and application of PCD cutting tools. Experimental data are presented for the drilling and single blade reaming of aluminium-silicon alloys containing 7% and 13% silicon and aluminium 2618 MMC alloy reinforced with 15 vol% silicon carbide (SiC) particulate. Though initially aimed only at aerospace and defence products, MMCs have progressively moved into higher volume applications and are currently under evaluation for volume automotive components. Compared with standard hypoeutectic and hypereutectic cast aluminium-silicon alloys, tool wear when machining MMC is shown to be up to seven times more severe. Tools used for drilling include HSS-M2, diamond plated HSS, WC, TiN coated WC and PCD. Other than when using PCD drills, tool life was extremely short due to the abrasive nature of the (SiC) reinforcement. Similarly, results from PCD reaming tests confirmed that diamond tooling provides the only realistic tooling option.     

A Comparative Evaluation of the Wear Resistance of Various Tool Materials in Friction Stir Welding of Metal Matrix Composites

Friction stir welding (FSW) is the preferred joining method for metal-matrix composites (MMCs). As a solid-state process, it precludes formation of the intermetallic precipitates responsible for degradation of mechanical properties in fusion welds of MMCs. The major barrier to FSW of MMCs is the rapid and severe wear of the welding pin tool, a consequence of prolonged contact between the tool and the harder reinforcements which give the material its enhanced strength. This study evaluates the effectiveness of harder tool materials to combat wear in the FSW of MMCs. The tool materials considered are O1 steel, cemented carbide (WC-Co) of the micrograin and submicrograin varieties, and WC-Co coated with diamond. The challenges which accompany the application of harder tool materials and diamond coatings in FSW are also discussed. This study represents the first use of diamond-coated tools in FSW and the first comparative evaluation of tool materials for this application.     

Mechanical,physical properties and tribological behaviour of silicon carbide composites with addition of carbon nanotubes

Four types of silicon carbide/carbon nanotubes composites were prepared with the main aim to develop ceramics with enhanced electrical conductivity. The SiC/CNT composites were prepared by in-situ growth of CNT on the SiC powder grains. Three types of SiC/CNT composites, where the precursor SiC/CNT powder mixture was prepared by Catalytic Chemical Vapour Deposition (CCVD) method and different amounts of Fe catalytic nanoparticles (2.5, 5, 10 wt% Fe), were designed. In addition, one reference material containing 2.5 wt% Fe catalytic nanoparticles but without CCVD application, i.e. without CNT, was prepared in order to correctly assess the role of CNT. The experimental materials were compacted by hot pressing (1850 °C/Ar/60 min/40 MPa). Mechanical properties such as hardness and elastic modulus of experimental materials were determined. Electrical conductivity as a function of CNT content was measured. The effect of the CNT addition on tribological properties (coefficient of friction, wear) of SiC/CNT composites was also observed.Hardness of the reference sample was relatively high (HV1 = 24 GPa) and it decreased down to HV1 = 17–19.8 GPa with presence of CNT. Similarly, the fracture toughness decreased with presence of CNT from 4.99 MPa.m^1/2 for the reference sample down to 3.4–4 MPa.m^1/2 for the SiC/CNT composites. Nanoindentation showed that hardness H_IT of reference sample without CNT was around 26 GPa and with increasing amounts of CNT it decreased down to 21 GPa. The composites had similar modulus of elasticity (E_IT = 337–348 GPa), while for the reference sample it was E_IT = 434 GPa. Electrical conductivity increased with amount of CNT (1.76 S/m for the reference sample, 484.3 S/m for the composite with 2.5 wt% Fe, and up to 2873.6 S/m for the composite with 10 wt% Fe). Specific wear rate increased with presence of CNT from 7.7 × 10⁻⁷ mm³/Nm for the reference sample to 2.4–2.9 × 10⁻⁶ mm³/Nm for the composites. Complex wear behavior common for all types of experimental materials was observed: mainly abrasion, mechanical wear (micro-fractures) and tribochemical reactions with created SiO₂ layer. In the reference sample the dominant wear mechanism was abrasion, in SiC/CNT composites formation of transferred films in wear tracks consisting of oxides and carbon phases formed by crushing the CNT were observed.     

SiC contents and pin temperature effect on tribological properties of Al25Zn/SiC composites

In this investigations, an effect of silicon carbide addition on dry sliding wear behavior of Al25Zn/SiC composites was studied at different temperature, load and sliding speed for a sliding distance of 1400 m using a pin on disc tribometer with EN24 shaft steel disc as per Taguchi L₁₆ orthogonal array. Under equal test situation, highest wear resistance, hardness, tensile strength and lowest coefficient of friction were observed for the composite with 15 wt% of SiC. The pin temperature is identified as the most influencing factor for the wear and friction characteristics of the composites. Regression model and Artificial Neural network model developed were found capable of predicting wear behavior of the composite. The mechanism of wear observed is adhesion, abrasion and delamination.     

碳化硅颗粒增强铝基复合材料的界面特征及力学性能

研究了氧化态和原始态碳化硅颗粒增强铝基复合材料的界面结构及其对复合材料弯曲强度的影啊。结果发现．氧化处理后碳化硅与基体铝界面上有一ＳｉＯ２非晶层，该非晶层内由于铝的扩散作用而形成铝的浓度梯度。原始态碳化硅与铝的界面上则无此非晶层．由于此非晶层的作用．导致界面结合强度的提高从而增加了复合材料的弯曲强度。     

Tool wear control in diamond turning of high-strength mold materials by means of tool swinging

A tool-swinging method was proposed to reduce tool wear in diamond turning of high-strength mold materials. A round-nosed diamond tool was swung by rotating the B-axis rotary table of the machine, the center of which was aligned with the tool center. The tool-decentering error was detected and compensated for by an on-machine measurement system. The effects of tool-swinging direction, swinging speed, lubricant type, and tool rake angle were investigated. The tool wear was greatly reduced compared to the conventional method. A surface finish of 4 nm Ra was obtained on reaction-bonded silicon carbide by generating continuous chips.     

Investigation on the constitution and mechanical characteristic of composite containing silicon-carbide produced by electroless co-deposition

The constitution and mechanical characteristics of the composites containing silicon carbide and Ni-P alloy matrix produced by electroless co-deposition were investigated in this article. The experimental results indicate that SiC particles with high hardness obviously strengthen the Ni-P alloy matrix, leading to an increase in both the hardness and surface roughness of the composites in comparison with pure Ni-P alloy. The hardness of the composites reaches the maximum value when heat treated at 673 K for 1 h. During the friction and wear process, the wear resistance of SiC composites is higher than that of Ni-P alloy and hard chromium plating, although the friction coefficient of the composite is comparatively high, which is attributed to the worn-resistant hard phase.     

Three-body abrasive wear behaviour of particulate-filled glass–vinyl ester composites

The incorporation of silicon carbide (SiC) and graphite fillers on three-body abrasive wear behaviour of glass–vinyl ester (G–V) composites has been investigated. Dry sand/rubber wheel abrasion tests (RWAT) were carried out at 200 rpm test speed. The tests were carried out at 22 and 32 N loads by varying the abrading distance from 270 to 1080 m in steps of 270 m. The worn surfaces were examined using scanning electron microscopy (SEM). The wear volume and specific wear rate of G–V composite reduces significantly on the addition of SiC filler. Graphite filler, however, performed poorly resulting deterioration in wear performance of SiC-filled G–V composite. The SEM studies indicate the reasons for failure of composites and influencing parameters.     

Processing iron-aluminide composites containing carbides or borides

Iron-aluminide composites containing 30–90 vol. % carbides or borides can be processed to near full density (greater than 97% theoretical density). This wide range of ceramic contents enables the tailoring of the composite properties to a variety of applications requiring a combination of the corrosion and oxidation resistance of iron aluminides and the hardness and wear resistance of the ceramic phases. The composites are processed by conventional liquid-phase sintering of mixed powders as well as pressureless melt infiltration. Typical mechanical properties such as hardness, flexure strength, and fracture toughness were evaluated for composites containing different volume fractions of carbide or boride particulates. Furthermore, evaluations of the wear resistance, oxidation resistance, aqueous corrosion resistance, and thermal expansion of the iron-aluminide composites suggest many potential applications for these new materials.     

钎焊金刚石磨粒钻钻削C/SiC陶瓷基复合材料孔时切屑对钻削过程的影响

钎焊金刚石磨粒钻适合钻削碳纤维增强碳化硅陶瓷基复合材料孔,但大量切屑会对孔的钻削过程产生不利影响。为此,针对切屑排出过程,分析切屑形貌,研究钻削时切屑对轴向钻削力、孔加工质量、钻头磨损的影响。结果表明：切屑对轴向钻削力有影响,尤其钻削深孔时影响显著。切屑对孔进口的加工质量几乎没有影响,只表现为孔进口处的轻微崩边;切屑对孔出口的加工质量影响显著,可引起严重的纤维断裂、撕裂缺陷以及基体的大区域脱落。同时,切屑加剧钻头磨损,使钻头不仅出现崩刃、微裂纹等轻微磨损,而且还产生基体剥落、金刚石剥落等严重磨损行为。     

A brief review of brazing diamond in cutting tools

Diamond has high hardness and good wear resistance. It is widely used in cutting tools and workpieces. Brazing is an effective method to realize high quality cemented carbide joints in various materials connection technologies. This paper analyzes the research status of diamond brazing in detail. The materials used as brazing filler in diamond brazing are reviewed. Copper base filler and nickel base filler are the most commonly used brazing filler in diamond brazing. The advantages and disadvantages of diamond grinding tools under different production methods are analyzed. In addition, a series of new brazing alloys such as amorphous Ni based brazing filler metals are analyzed. Finally, the development trend of diamond brazing is pointed out.     

摩擦速度对原位自生钢基复合材料Fe(Ti,W,Cr,V,Nb)Cp磨损性能的影响

用铸造的方法制备了原位自生复合碳化物(Ti,W,Cr,V,Nb)Cp增强钢基复合材料(In-situMMCs),并对该复合材料的高速磨损性能及磨损机理进行了研究。结果表明,原位自生复合材料中自生碳化物颗粒细小、圆整、分布均匀,自生碳化物体积分数达到42.8%;在低速150N载荷下,自生复合材料的耐磨性能随着自生碳化物体积分数的增加而提高;摩擦系数随摩擦速度的增大先减少后增大,自生碳化物体积分数大的自生复合材料的摩擦系数先快速减小后慢速增大,磨损率先减小后迅速增加。