金刚石镀覆及热处理在金刚石工具中的应用

探究了金刚石镀覆工艺及镀覆金刚石热处理对提高金刚石在胎体中把持力的作用。结果表明:850°C真空镀铬的金刚石镀层中能检测到存在Cr_7C_3相,而化学镀铬的金刚石需经高温真空热处理后才能检测到Cr_7C_3,真空镀钛的金刚石热处理前后均没有检测到碳化物相。镀钛金刚石镀层改善了金刚石与金属胎体的浸润性,提高了金刚石的机械把持力,制备的组合绳锯切割寿命由3.44 m~2/m提高到了3.79 m~2/m。镀铬金刚石镀层改善浸润性提高机械包镶与Cr_7C_3相产生的化学结合力共同作用,提高了金刚石把持力;使用热处理真空镀铬金刚石的组合绳锯测试寿命提高到了3.95 m~2/m,而化学镀铬金刚石由于镀层过厚,在烧结中金刚石与镀层热膨胀差异导致结合层破裂,把持力减弱,组合绳锯寿命仅为3.50 m~2/m。     

镀膜金刚石与铜基结合剂间把持力提高方法探讨

在不改变成分的条件下,为了探讨将表面镀覆和表面刻蚀相结合来提高金刚石与金属结合剂把持力的方法和条件,将镀Ti、镀Cr和镀Ni金刚石在1050℃下保温1 h后,用真空热压烧结法制备未镀、高温处理前后镀覆金刚石的铜基结合剂样条。用扫描电子显微镜对金刚石镀层表面形貌进行观测,用金刚石高温热处理前后铜基结合剂样条的抗弯强度来评估金刚石与铜基结合剂的把持力,经1050℃高温处理1 h后,金刚石表面的镍镀层基本上保持完整,而钛镀层和铬镀层则出现脱落;镀覆金刚石的单颗粒抗压强度都下降;镀Ti和镀Cr金刚石铜基结合剂样条的抗弯强度下降,但镀Ni金刚石样条的抗弯强度却大幅度提高,达到833 MPa,增幅为12.1%。结果表明:只有高温处理后镀层保持完整而且镀层能使金刚石表面粗糙度提高的情况下,才能大幅度提高金刚石与金属结合剂之间的把持力。     

金刚石钎焊(上)

金刚石磨料主要靠机械夹持力把持在金属(烧结或电镀)胎体中。由于这一弱点,在切割过程中,金刚石不可避免地会从胎体中脱落或掉出。此外,金刚石突出高度较低,故金刚石工具的切割速度受到限制。而且,金属胎体和工作对象(被切割岩石)相互磨擦,将会导致金刚石和其它材料的热损伤,而且工作的功率消耗将增加。金刚石采用钎焊的办法牢固地把持在金属胎体中,可形成强力的化学结合,金刚石磨料的突出高度将成倍提高,而不会从胎体中脱落或碎裂。因此,金刚石工具的切割速度将会成倍提高。当钎焊料熔融时,碳化物形成物将向金刚石方向迁移而在界面上形成碳化物。这种反应可能过分而使金刚石质量明显下降。此时,可能需要对金刚石进行镀覆以便缓和与控制这种反应。当金刚石钎焊在基体的表面时,熔化趋向于将金刚石聚集在一起,可促使钎焊层局部加厚。这种金刚石晶粒的成簇聚集将降低金刚石工具的切割效率。一种金刚石矩阵有序排列设计(grid)是必要的,它可保持钎焊层具有均匀的厚度。因此钎焊合金可控熔融,可使每一粒金刚石晶体周围形成较缓的坡度。这种整体均匀焊层的支承可使金刚石工具高速有效切割,而功率消耗较低。     

金刚石钎焊(下)

金刚石磨料主要靠机械夹持力把持在金属(烧结或电镀)胎体中。由于这一弱点,在切割过程中,金刚石不可避免地会从胎体中脱落或掉出。此外,金刚石突出高度较低,故金刚石工具的切割速度受到限制。而且,金属胎体和工作对象(被切割岩石)相互磨擦,将会导致金刚石和其它材料的热损伤,而且工作的功率消耗将增加。金刚石采用钎焊的办法牢固地把持在金属胎体中,可形成强力的化学结合,金刚石磨料的突出高度将成倍提高,而不会从胎体中脱落或碎裂。因此,金刚石工具的切割速度将会成倍提高。当钎焊料熔融时,碳化物形成物将向金刚石方向迁移而在界面上形成碳化物。这种反应可能过分而使金刚石质量明显下降。此时,可能需要对金刚石进行镀覆以便缓和与控制这种反应。当金刚石钎焊在基体的表面时,熔化趋向于将金刚石聚集在一起,可促使钎焊层局部加厚。这种金刚石晶粒的成簇聚集将降低金刚石工具的切割效率。一种金刚石矩阵有序排列设计(grid)是必要的,它可保持钎焊层具有均匀的厚度。因此钎焊合金可控熔融,可使每一粒金刚石晶体周围形成较缓的坡度。这种整体均匀焊层的支承可使金刚石工具高速有效切割,而功率消耗较低。     

镀钛对金属结合剂金刚石节块把持力的影响

以铁基和铜基为结合剂,分别加入表面未修饰金刚石和真空蒸发镀钛金刚石,在不同的烧结温度下热压烧结得到铁基和铜基结合剂金刚石节块。用扫描电镜观测了节块的断面形貌,用三点弯曲法测试了节块的抗弯强度。结果表明:与表面未镀金刚石节块相比,表面镀钛金刚石的铁基和铜基结合剂节块的抗弯强度和把持力系数都有所提高。表面镀钛层能加强金刚石与金属基体间的结合,从而提高把持力。     

金刚石表面镀覆技术的发展及应用

介绍了金刚石的表面镀覆技术及其发展.由于表面镀覆层能提高金刚石颗粒的强度、抑制在高温条件下金刚石颗粒的石墨化与氧化腐蚀,从根本上实现金刚石磨粒与结合剂胎体的化学冶金结合,因此,增强了结合剂对磨粒的把持力,有效地防止金刚石脱落,提高了工具的使用寿命和加工效率.     

表面粗糙化金刚石在瓷砖切割片中的应用

胎体对金刚石把持力是影响金刚石圆锯片性能的一个重要因素,金刚石表面处理是提高这种把持力的一个有效方法。通过对一种表面粗糙化金刚石在瓷砖片中的应用试验,表明通过这种方法,可以有效提高胎体与金刚石的结合强度,从而提高产品的使用寿命。     

金刚石工具胎体材料机械性能的概述

金刚石具有高硬度、高强度、高耐磨性等一系列优异特性,被广泛地用来制备金刚石工具.金刚石工具工作寿命和性能的一个重要指标就是金刚石在金刚石工具中的把持强度,其在实际工作中的使用效果在很大程度上取决于胎体材料的性能.文章从固结温度、掺杂、金刚石表面涂层等几个方面对胎体材料机械性能的影响进行了概述,其中包括硬度,屈服强度,弯曲强度和冲击强度.最后指出了金刚石工具胎体材料性能研究存在的问题,并提出了解决对策,为胎体材料的设计提供了理论指导.     

提高金刚石把持力的三种方法

（1）提高机械把持力。这是由于金属粉末在烧结时产生收缩，形成压缩应力把持住金刚石。压缩应力的产生是由于金刚石与胎体金属热膨胀系数不同，由于烧结时或晶体形成与长大引起体积变化所致。由于胎体屈服强度有限，故产生的压缩应力与机械把持力有限。     

镀敷金刚石在金属结合剂中发挥作用的机理探讨(下)

文章分别对烧结后镀敷金刚石表面状态及元素分布、镀敷金刚石与胎体接壤部位的元素分布和显微硬度值进行了观察与检测,以及对试样的抗弯强度和实际工具的切割性能进行了测试。数据分析的结果表明,镀层中的Ti很容易扩散到金刚石周围约一个粒径范围内的胎体中,提高了该局部胎体区域的机械性能,达到了改善工具的实际切割性能的效果。     

Preparing SiC/diamond coatings via chemical vapor deposition of SiC on diamond-coated graphite and their frictional properties

SiC/diamond coatings with excellent frictional properties were successfully prepared using graphite as substrate. Diamond particles with size of 25–38 μm were firstly bonded on graphite substrate through PVA glue, followed by chemical vapor deposition (CVD) of SiC with varied MTS flow on the diamond-coated graphite substrate to enhance the adhesion of diamond particles. The influence of the MTS flow on the SiC coatings was investigated. The results showed that polycrystalline SiC coating with good crystallinity has been obtained. With MTS flow increasing, the SiC grains feature increased surface roughness and greater sizes of the SiC crystallite resulting from the co-deposition of SiC and carbon with increased carbon containing species. Reciprocating sliding wear tests were conducted to investigate the coefficient of friction. With increasing applied load, while the low-flow specimens showed a remarkable increase in the friction coefficient resulting from degradation of the SiC coatings, the high-flow specimens maintained a relatively low friction coefficient during wear tests indicating strong holding force to diamond particles of the SiC coatings. The reason for low friction coefficient of the high-flow specimens was that GCr15 steel ball was wearing by the SiC/diamond coatings with good affinity to the substrate resulting in a flat–flat contact on the contact area.     

金刚石表面金属化对电镀金刚石线锯性能及生产的影响

利用复合电镀法,分别选取未金属化和金属化的金刚石磨粒,以φ120μm的镀铜圆柱形琴钢丝为基体,氨基磺酸镍溶液为电镀溶液,通过落砂法制备了金刚石线锯。采用扫描电子显微镜观察线锯的表面形貌,并研究了金刚石磨粒金属化对线锯生产的各项参数的影响。结果表明,选用金属化的金刚石磨粒能够得到沉积速度快、密度高、均匀性好、把持力高、使用寿命长、切割效率以及生产效率高的高品质金刚石线锯。     

Tailoring structural,morphological and mechanical characteristics of mono-crystalline diamond-reinforced polyacrylonitrile based electrospun fibers

Composites of diamond-reinforced particles offer extraordinary thermal- and mechanical characteristics attributable to their manageable outer surface and huge available uppermost layer. Uniform distribution of diamond powder in polymeric matrix, and enhanced interactions between them are the two significant problems to attain robust polymer composites. In this work, the crystalline diamond particles as received and chemically modified ones were integrated in polyacrylonitrile (PAN) matrix uniformly by electrospinning method. This procedure avoided agglomeration of the reinforced diamonds through uniform distribution in the polymer matrix. The shapes of diamond-integrated PAN fibers were attuned by adapting diamond loading, polymer concentration, flow rate, and applied voltage to achieve beads free fibrous structures. PAN was chosen as a carrier polymeric-matrix to enhance the electrostatic forces between functionalized diamond-particles and PAN molecular chains. Tensile tests showed that the loading of 2 wt% modified diamond-particles improved Young’s modulus of fibers by 74.94% and tensile strength by 125%. Therefore, modification of the outer surface of the diamond particles improved the chemical interactions between the diamond surface and matrix, and stress was transferred to the diamond particles in composite fibers. Additionally, thermal stabilities of the diamond-based polymer composites were enhanced by the integration of diamond powder in composite fibers.

     

Fuzzy logic method to investigate grinding of alumina ceramic using minimum quantity lubrication

The use of nanofluid in lubrication during machining of advanced engineering ceramics has been found to be highly efficient and eco-friendly. This work involves experimental investigation of grinding Alumina (Al₂O₃) ceramic to determine the effect of the grinding variables. The grinding variables considered include depth of cut, feed rate, type of diamond wheel, and lubrication type. Moreover, the response parameters considered include grinding power, coefficient of friction, and surface quality. The responses obtained during the experiments were used to develop a fuzzy logic prediction model. The findings from this work can be concluded as follows: (a) The depth of cut and feed rate have direct proportional relationship with the grinding power and coefficient of friction. (b) The metallic bonded diamond wheel was found to have higher machining efficiency than the resinoid bonded one. (c) Higher number of diamond grits produces lower frictional coefficient. (d) The carbon nanotube based nanofluid when used in the minimum quantity lubrication (MQL) process proffers better lubrication capability than conventional flood cooling system. (e) The developed fuzzy logic models were found to have high prediction accuracies of 97.22%, 98.60%, and 96.8%, respectively, for grinding power, grinding force ratio, and surface roughness.     

金刚石增强Na2O-B2O3-Al2O3-SiO2系陶瓷基复合材料的界面研究

以Na₂O-B₂O₃-Al₂O₃-SiO₂系低温玻璃为基础结合剂烧制金刚石增强陶瓷基复合材料,利用扫描电子显微镜、X射线能谱、X射线光电子能谱、拉曼光谱及力学性能测试仪等对其界面结合强度、界面处元素分布及界面化学键进行了表征。结果表明,Na₂O-B₂O₃-Al₂O₃-SiO₂系陶瓷结合剂与金刚石颗粒界面结合强度高,790 ℃煅烧时试样抗折强度达到77.82 MPa。Si、B、Na、Zn各元素在界面位置发生扩散,而Al元素没有明显扩散,元素扩散提升了结合剂对金刚石的把持力。陶瓷结合剂与金刚石在界面处形成C-O、C=O和C-B键,化学成键进一步增进界面结合。另外,790 ℃煅烧的复合材料中金刚石颗粒保存完好,而850 ℃煅烧时金刚石出现石墨化迹象。     

Friction and wear at nanometer scale: a comparative study of hard carbon films

Tribological properties of nanostructured carbon (ns-C) and tetrahedral amorphous carbon (ta-C) thin films were investigated by friction force microscopy. It was found that the ns-C films have a smaller friction coefficient than ta-C films for relative humidity greater than 30%. In particular, at 40% of humidity, ns-C films have lower friction coefficient (0.11±0.02) than the ta-C films (0.13±0.02), which can be attributed to both the presence of closed graphite nanoparticles and the passivation of the dangling bonds at the ns-C surface. The friction coefficient did not vary as a function of the tip scanning velocity for both films. The nanoscale wear was studied in a very low force regime, in the range of nanonewton, using an atomic force microscope (AFM) with a Si₃N₄ tip and with forces in the range of micronewton with the AFM equipped with a stainless still cantilever and a diamond tip. The ns-C provides better wear resistance compared to ta-C films in the range of forces studied. The sp²-rich ta-C surface layer was easily scratched during the wear test in contrast to the ns-C films. The wear in ta-C in the low forces regime is attributed to the presence of this low density layer at the surface of the film due to subplantation of energetic ions during deposition while the better resistance to wear of ns-C films is attributed to its highly elastic nature.     

Friction force microscopy study of diamond films modified by a glow discharge treatment

A glow discharge treatment technique has been developed which enables control of the surface roughness and morphology of diamond films for applications in optical and electrical components. A conventional hot filament chemical vapour deposition (CVD) system was used to deposit the diamond films onto silicon substrates via a three-step sequential process: (i) deposition under normal conditions; (ii) exposure to either a pure hydrogen plasma or 3% methane in an excess of hydrogen using DC-bias; and (iii) diamond deposition for a further 2 h under standard conditions. The frictional characteristics and roughness of the film surfaces were investigated by atomic force microscopy (AFM) and the morphology and the growth rates determined from scanning electron microscope images. Lateral force microscopy (LFM) has revealed significant differences in frictional behaviour between the high quality diamond films and those modified by a glow discharge treatment. Friction forces on the diamond films were very low, with coefficients ∼0.01 against silicon nitride probe tips in air. However, friction forces and coefficients were significantly greater on the DC-biased films indicating the presence of a mechanically weaker material such as an amorphous carbon layer. A combination of growth rate and frictional data indicated that the exposure to the H₂ plasma etched the diamond surface whereas exposure to CH₄/H₂ plasma resulted in film growth. Re-Nucleation of diamond was possible (stage iii) after exposure to either plasma treatment. The resultant friction forces on these films were as low as on the standard diamond film.     

Growth of nanodiamond/carbon-nanotube composites with hot filament chemical vapor deposition

The growth of diamond/carbon-nanotube (CNT) composites by Hot Filament Assisted Chemical Vapor Deposition (HFCVD) was investigated. The growth was achieved by pre-dispersing commercially available multiwalled CNTs onto a Si(100) surface and subsequently growing diamond nanoparticles over this layer. The diamond/CNT composites were characterized with SEM, TEM, and Raman Spectroscopy. It was found that in a flow of 1% CH₄ in H₂ (a typical condition for microcrystalline diamond growth using HFCVD) most of the CNTs are destroyed by the harsh growth conditions. Reduction in the etching of the CNTs was achieved by reducing the H₂ partial pressure in the precursor flow. There exists an optimal between 2–5% of CH₄ in H₂ wherein the CNTs are not destroyed and the resulting diamond film retains a high percentage of its sp³ structure. The TEM analyses showed that nanometer sized diamond particles nucleate on the surface of the CNTs and grow radially outward. The retention of the CNT structure and the direct growth of the diamond on the CNTs, the two factors necessary for good load transfer between a matrix and reinforcement, suggest the possibility of using this material as a structural composite. Based on the characterization of the composite, a growth mechanism for diamond onto the CNTs was proposed.     

Fundamental research on machining performance of diamond wire sawing and diamond wire electrical discharge sawing quartz glass

In reciprocating diamond wire sawing of quartz glass, the reversing and acceleration and deceleration will cause the position change of diamond wire, resulting in the discontinuous wire sawing in the reversing stage, so as to leave residual material on the processing surface and form wire marks. Also, the cutting load will cause diamond wire deformation as bow shape, and affect the machining accuracy. In this paper, the evaluation of DWS machining performance of quartz glass focus on the sawing time, cutting force and vibration, wire tension, machining surface flatness and roughness, surface morphology and wire state. The theoretical analysis of wire mark was carried out, and the simplified wire bow model of quartz glass sawing was established. The existence of wire mark and wire bow were verified by detecting the 3D contour of the slice. In addition, a diamond wire electrical discharge sawing (DWEDS) was performed to find the differences to DWS in the above indicators. Experiments were presented in jet cooling and bath cooling conditions. It was found that the cutting force, vibration, and wire tension of DWEDS are more stable than that of DWS. The DWEDS has been proved helpful to improve machining performance of quartz glass from surface roughness, sawing time, processing state, and wire bow control as it reduces the macro cutting force acting on the diamond wire although the discharge effect is weak. The SEM of slice surface and diamond wire showed no significant difference between DWEDS and DWS. Also, the influence of feed speed and cooling methods on machining performance was investigated.