Machinability of ultrafine-grained copper using tungsten carbide and polycrystalline diamond tools

Equal channel angular extrusion (ECAE) is an effective process to produce bulk ultrafine-grained (UFG) materials from regular coarse-grained materials. Such ECAE-processed materials typically excel in strength, wear resistance, ductility, and high strain-rate superplasticity, with promising applications in lightweight transportation and medical industries. Precision machining work is generally indispensable for further applications after bulk materials are produced by ECAE. To effectively and efficiently machine such ECAE-processed materials for further broad applications, machining issues such as machinability and tool material selection should be considered. This study was undertaken to investigate the machinability of ECAE-processed pure copper using both tungsten carbide (WC) and polycrystalline diamond (PCD) cutting tools in order to facilitate broad applications of ECAE-processed UFG coppers. It is found that despite its higher cost, PCD is favored to machine UFG copper based on this study since it has better wear resistance, gives lower cutting forces, yields a better workpiece surface finish, and results in no smearing on the workpiece. In machining UFG copper, depth of cut notching was observed as the wear pattern and abrasion as the wear mechanism for the WC tool, while flank wear was observed as the wear pattern and diffusion as the wear mechanism for the PCD tool.     

Material transfer during machining of aluminum alloys with polycrystalline diamond cutting tools

An analysis of a polycrystalline diamond (PCD)-tipped tool after drilling 40,000 holes in aluminum (Al) 319 alloy under fully lubricated conditions is reported. It is found that aluminum adheres to the PCD tip surface during the machining process under lubricated condition. The aluminum transferring leads to poor surface finishing. Surface morphology analysis and element mapping suggests that the cobalt (Co) binder in the PCD tips is responsible for the adhesion of aluminum to the PCD surface, due to the chemical affinity between aluminum and cobalt. Approaches to prevent the adhesion of aluminum to the tool are discussed.     

Research on polycrystalline diamond compact (PDC) with low residual stress prepared using nickel-based additive

Polycrystalline diamond compact (PDC) with low residual stress was synthesized using nickel-based additive (Ni₇₀Mn₂₅Co₅) as sintering solvent at high temperature/pressure (HTHP). A systematic study of the residual stress in a polycrystalline diamond (PCD) layer was performed using micro-Raman spectroscopy. The stress was measured by determining the Raman shift and was approximated as being biaxial to calculate the magnitudes of stress. Sintering process parameters such as temperature, the diamond size and content of binder additive were all found to affect residual stress levels. The sample with low stress measured on the surface of PCD is compressive and has an average value of 0.10 GPa. Scanning electron microscopy (SEM) analysis of morphology shows that the dense microstructure with diamond-diamond (D-D) direct bonding has formed in the PCD layer. X-ray diffraction (XRD) performed in the cross-section of PCD confirmed the presence of diamond, nickel-based alloy, WC and Co_xW_xC.     

聚晶金刚石的应用现状和发展趋势

详细介绍了聚晶金刚石的性能特点,聚晶金刚石在汽车、航空航天、木材加工、电子行业、石油地质钻探、线材模具、玻璃切割和宝石加工行业的应用现状,并对其发展趋势进行了展望。     

Characterization of N-doped polycrystalline diamond films deposited on microgrinding tools

Chemical vapor deposited diamond films have many industrial applications but are assuming increasing importance in the area of microengineering, most notably in the development of diamond coated microgrinding tools. For these applications the control of structure and morphology is of critical importance. The crystallite size, orientation, surface roughness, and the degree of sp ³ character have a profound effect on the tribological properties of the films deposited. In this article, we present experimental results on the effects of nitrogen doping on the surface morphology, crystallite size, and wear of microgrinding tools. The sp ³ character optimizes at 200 ppm nitrogen, and above this value the surface becomes much smoother and crystal sizes decrease considerably. Fracture-induced wear of the diamond grain is the most important mechanism of material removal from a microgrinding tool during the grinding process. Fracture occurs as a consequence of tensile stresses induced into diamond grains by grinding forces to which they are subjected. The relationship between the wear of diamond coated grinding tools, component grinding forces, and induced stresses in the model diamond grains is described in detail. A significant correlation was found between the maximum value of tensile stress induced in the diamond grain and the appropriate wheel-wear parameter (grinding ratio). It was concluded that the magnitude of tensile stresses induced in the diamond grain by grinding forces at the rake face is the best indicator of tool wear during the grinding process.     

Micromilling characteristics and electrochemically assisted reconditioning of polycrystalline diamond tool surfaces for ultra-precision machining of high-purity SiC

The production of extremely thick silicon carbide (SiC) has recently become possible with the advent of a specific chemical vapor deposition process. Ultra-precision machining of high-purity SiC has been performed by using a polycrystalline diamond (PCD) micromilling tool to investigate the machining characteristics. Results indicate that a high-quality surface (R_a = 1.7 nm) can be obtained when the removed chips are thin enough to achieve ductile mode machining. Micron-sized wells and groove structures with nanometer-scale surface roughness were successfully machined by using the PCD tool. In addition, a new electrochemically assisted surface reconditioning process has been proposed to remove the contaminant material adhered onto the PCD tool surfaces after prolonged machining.     

Polishing of polycrystalline diamond by the technique of dynamic friction. Part 2: Material removal mechanism

This paper investigates the material removal mechanisms of PCD using the dynamic friction polishing technique. Scanning electron microscopy, energy dispersive X-ray, X-ray diffraction and Raman spectroscopy were used to identify the mechanisms by analyzing the specimen surfaces and debris produced by polishing. It was found that the material removal occurred in a rather complex way, which can be a chemo-mechanical process, diffusion, oxidization and evaporation, or their combinations.     

Nanosized polycrystalline diamond cladding for surface protection of zirconium nuclear fuel tubes

A 300 nm thick polycrystalline diamond layer has been used for protection of zirconium alloy nuclear fuel cladding against undesirable oxidation with no loss of chemical stability and preservation of its functionality. Deposition of polycrystalline diamond layer was carried out using microwave plasma enhanced chemical vapor deposition apparatus with linear antenna delivery (which enables deposition of PCD layers over large areas). Polycrystalline diamond coated zirconium alloy fuel tubes were subjected to corrosion tests to replicate nuclear reactor conditions, namely irradiation and hot steam oxidation. Stable radiation tolerance of the polycrystalline diamond layer and its protective capabilities against hot steam oxidation of the zirconium alloy were confirmed. Finally, the use of polycrystalline diamond layers as a sensor of specific conditions (temperature/pressure dependent phase transition) in nuclear reactors is suggested.     

oSa安全性要求以及对我国金刚石工具业的影响

欧洲磨切工具安全组织oSa有45个成员,生产世界70%的手持磨切工具.oSa以维护消费者利益为宗旨,要求oSa成员为市场提供安全产品.oSa认证针对体系,认证对象是组织而不仅是产品.oSa概念不但依据EN13236标准认证产品,而且强调生产设备、安全测试、质量管理体系的自我监控,提高企业交付安全产品的综合能力.oSa产品具有可追溯性,成为安全象征.DSA和MPA认证已经落后于磨切工具安全性发展的国际趋势.oSa概念发展迅速,一旦oSa伴随EN13236上升为欧洲新的强制性安全措施,将对我国出口企业产生重大影响.因此,遵守oSa规则,加入oSa组织,提升产品的安全性信誉,是我国金刚石工具进入国际主流市场的必要条件.     

金刚石复合片微观组织结构的研究

采用SEM、EDX和XRD分析手段对一种高温高压合成的金刚石复合片(PDC)进行抛光面和纵切断口的显微形貌、元素能谱成分及物相组成分析研究.结果表明:①在抛光面上:金刚石颗粒连接紧密,黏结剂Co分布均匀呈断续的“网格”结构,其质量分数稍低于纵切断口面.②在纵切断口面上:结合界面处结合紧密,实质是Dia - Co - W...     

Polishing of polycrystalline diamond by the technique of dynamic friction, part 1: Prediction of the interface temperature rise

This paper investigates the interface temperature rise in polishing a polycrystalline diamond (PCD) surface. First, the Greenwood–Williamson's statistical asperity model is applied to characterise the surface roughness of a PCD specimen. The result is then used to estimate the contact area and total number of contact asperities under an applied polishing load. The heat generated is taken as the product of the friction force and the relative sliding velocity between the PCD asperities and the metal disk surface. The Jaeger's moving heat source analysis is then applied to determine the fractions of heat flux flowing into the PCD asperities and their counterpart in contact sliding and to give rise to the average temperature rise. A comparison with the observations made in the authors' experiments and those reported in the literature showed that the model predicts very well the temperature rise at the polishing interface.     

砂轮修整工具用金刚石的性能研究

对用作修整工具的金刚石而言,天然大单晶价格高昂,修整接触面不稳定,使用过程中需要翻修。近年来,修整工具的制造商们在不断开发它们的替代产品。本文对S i-Ti-B系粘结相,WC-Co粘结相聚晶金刚石,及CVD金刚石对其微观结构进行SEM分析;并分别对样品加热500℃、800℃,测其磨耗比,进行耐磨性和耐热性分析;并制作成修整工具修整P400×50×100WA46NV535M/s砂轮,做使用性能对比实验。研究结果表明:(1)CVD金刚石的耐磨性能和耐热性最好;(2)中等粒度PCD的耐磨性、耐热性和抗冲击性等综合性能更好,更适合制作砂轮修整工具;(3)可选用不同截面尺寸和数量的条状金刚石,来增加修整工具的适应性。     

Effect of various parameters on the surface roughness of an aluminium alloy burnished with a spherical surfaced polycrystalline diamond tool

The effect of various parameters on the surface roughness of an aluminium alloy burnished with a spherical surfaced polycrystalline diamond tool are studied experimentally with a theoretical analysis. Problems in selecting the optimum burnishing parameters and some burnishing mechanisms are discussed. With suitable parameters employed, the new no-chip finishing process developed can eliminate or reduce the cutting marks left on the workpiece surface by diamond cutting tools, with its surface roughness reduced to Ra=0.026 μm from the original 0.5 μm.     

多孔含硼金刚石多晶体的制备与结构研究

本文介绍了一种多孔含硼金刚石多晶体的制备方法.以含硼金刚石微粉为原料,Co合金为粘结剂,高温高压烧结制备D-D键合的金刚石多晶烧结体.烧结体经强酸处理,蚀出残余的金属,得到多孔含硼金刚石多晶体.实验结果表明:温度在金刚石-钴共熔温度以上,压力在6.0GPa左右,粒度在W20～W28之间,金属含量在14～16vol%范周内,易于获得D-D键合的多孔金刚石烧结体.保温较短时,金刚石烧结不充分,晶粒结合松散,得到的多孔材料孔径较大,但烧结体强度很低.延长保温时间,烧结充分,致密性增加,但孔径减小.     

金刚石制品的金属胎体的研究现状

对金刚石制品的金属胎体的研究归纳为金刚石与金属胎体的结合机理、金属胎体体系、金属胎体材料制备方法以及金属胎体的性能表征及评价体系四方面的研究。对各方面的研究现状进行了较详细的分析,指出了存在的问题。提出了解决这些问题的对策,尤其提出了独特的且有效的金属胎体性能表征方式和评价体系,可为金属胎体的深入研究的提供有力的参考。     

钎焊单层金刚石磨具的研究进展

钎焊单层金刚石磨具的研究和应用在国内外越来越受重视,与电镀单层金刚石磨具相比,钎焊单层金刚石磨具具有金刚石出刃高、容屑空间大、金刚石与基体之间的结合强度高等无可比拟的优点。从钎焊机理、钎料选择和钎焊工艺流程三方面介绍国内外钎焊单层金刚石磨具的研究现状,并分析大批量制造单层金刚石磨具存在的问题,指出下一步的研究有四项关键技术值得关注:钎料厚度的实用化控制、优质钎料的开发、钢基体受热变形、金刚石磨粒有序排布技术,为钎焊单层金刚石磨具的产业化提供借鉴。     

金刚石复合片的微观分析研究

本文对一种金刚石复合片抛光面和横断面的组织形貌、微区成分、相组成进行了分析研究.结果表明:抛光面金刚石生长连接明显,其钴含量低于横断面中含量,黏结相断续分布,有被腐蚀的孔穴,物相由金刚石相(fcc)、Co4C相(fee)、α-Ti相(hop)、β-Ti相(bec)组成;横断面上,在0.5 mm厚金刚石层内,钴、钨质量分...     

Thermal residual stress of polycrystalline diamond compacts

Thermal residual stresses in polycrystalline diamond compact(PDC)cutter arising from the difference in thermal expansion between the polycrystalline diamond(PCD)and the supporting tungsten carbide substrate after sintering at high pressure and high temperature were investigated using finite element simulation,laboratory tests and theoretical analysis.The obtained results show that although compressive residual stresses exist both in the interface of PCD table and in the most region of PCD table surface, the...     

金刚石工具预合金代钴粉末的研究及应用

近年,国内外开展了金刚石工具代钻粉末的研究。本文采用水雾化法开发了三种预合余代钻粉末：对粉末的基本属性、形貌,粉末的相组成,粉末的差热性进行了分析研究;测定了它们的烧结密度、硬度、抗弯强度、弹性模量随热压烧结温度变化的规律;采用作者自行建立的磨料磨损试验方法,测定了它们的质最磨损阿分率（即耐磨性）;测定了它们的冷压生坯密度、模拟生坯强度以及高频钎焊的结合力矩;观察了热压烧结SEM腐蚀组织和SEM断口形貌。结果表明：三种预合金粉末有着优良的低温烧结性能和耐磨性,表现出接近于超细钴和相当于国外代钴粉末的优良的物理、机械性能,对金刚石把持力高;具有高的高频钎焊结合力矩;粉末成本较低,用粉量可降低。实际切割花岗石、混凝土,切割锋利,使用寿命长。     

聚晶金刚石刀具研磨质量及去除机理研究

针对聚晶金刚石（PCD）刀具的研磨质量问题,选择刃口钝圆半径、刃口缺陷度、后刀面粗糙度作为评价指标进行工艺参数的优化试验,并分析PCD的研磨去除机理。结果表明:工作台调定压力对刃口钝圆半径影响最显著;金刚石砂轮对刃口缺陷度影响最显著;砂轮转速对后刀面粗糙度影响最显著。选择4/5陶瓷基金刚石砂轮、1 000 r/min砂轮转速、170 N工作台调定压力可以获得研磨质量较高的PCD刀具。试验条件下,PCD的主要去除方式为划擦作用与微细破碎。1 000 r/min砂轮转速、170 N工作台调定压力下的微细破碎在保证较小刃口钝圆半径与刃口缺陷度的同时,可以获得相对平整的PCD表面。