Critical parameters in hot filament chemical vapor deposition of diamond films on tool steel substrates with CrN interlayers

The accomplishment of adherent and continuous diamond coatings on tool steel substrates with CrN interlayers is determined by many key parameters such as appropriate surface finish, interlayer thickness, substrate temperature and system pressure. A detailed study is carried out to probe the effect of these parameters on diamond nucleation and growth. Substrates with different surface finishes are prepared by electrical discharge machining (EDM) and CrN interlayers of various thicknesses are deposited onto these substrates by arc plating. Samples with a CrN interlayer of 2.5 μm are found to provide a continuous diamond film at a low pressure value of about 5 mbar. Nonetheless, the process window for obtaining such diamond layers is small, which results in limited reproducibility.     

不同沉积功率对CVD金刚石涂层性能的影响

利用热丝化学气相沉积法(HFCVD),固定其他工艺参数,通过改变沉积功率在YG6硬质合金上制备金刚石涂层,并利用扫描电镜(SEM)、洛氏硬度计和Raman光谱对涂层进行性能测试。结果表明:两步法处理硬质合金基体,可以有效去除表层的Co,同时增大表面粗糙度,提高金刚石形核率,提高涂层附着力;涂层表面形貌观察可知,沉积功率4kW时,晶形完整,晶粒大小非常均匀致密,晶面主要呈现金刚石典型的(111)面生长;压痕测试表明,当功率为4kW时,涂层的结合力最好,表面均匀、平整;结合Raman光谱分析,功率4kW时,涂层质量很好。     

YBCO Films Grown on Sapphire with YSZ Buffer Layer

ＹＢＣＯＦｉｌｍｓＧｒｏｗｎｏｎＳａｐｐｈｉｒｅｗｉｔｈＹＳＺＢｕｆｆｅｒＬａｙｅｒＳｈｉＤｏｎｇｑｉ，ＹａｎｇＢｉｎｇｃｈｕａｎ，ＷａｎｇＸｉａｏｐｉｎｇ，ＰｅｎｇＺｈｅｎｇｓｈｕｎａｎｄＣｈａｎｇＳｈｉａｎ（石东奇）（杨秉川）（王小平）（彭正顺）...     

Nanocrystalline diamond coating tools for machining high-strength Al alloys

Diamond coating tools have been increasingly used for machining advanced materials. Recently, a microwave plasma-assisted chemical vapor deposition (CVD) technology was developed to produce diamond coatings which consist of nano-diamond crystals embedded into a hard amorphous diamond-like carbon matrix. In this study, the nanocrystalline diamond (NCD) coating tools were evaluated in machining high-strength aluminum (Al) alloy. The conventional CVD microcrystalline diamond coating (MCD) tools and PCD tools were also tested for performance comparisons. In addition, stress distributions in diamond coating tools, after deposition and during machining, were analyzed using a 2D finite element (FE) thermomechanical model.

The results show that catastrophic failures, reached in all except one machining conditions, limit the NCD tool life, which is primarily affected by the cutting speed. In addition, coating delamination in the worn NCD tools is clearly evident from scanning electron microscopy (SEM) and force monitoring in machining can capture the delamination incident. At a high feed, coating delamination may extend to the rake face. Furthermore, SEM observations of coating failure boundaries show intimate coating-substrate contact. Though the NCD tools are inferior to the PCD tools, they substantially outperform the MCD tools, which failed by premature delamination. The diamond coating tools can have high residual stresses from the deposition and stresses at the cutting edge are highly augmented. Further machining loading causes the stress reversal pattern which seems to correlate with the tool wear severity.     

直流辉光氧等离子体刻蚀金刚石膜的研究

在直流辉光放电等离子体装置上，利用不同直流功充和工作气压下产生的氧等离子体对CVD金刚石厚膜的表面进行了刻蚀。利用扫描电子显微镜、Raman光谱和电子微量分析天平，分别对刻蚀前后金刚石膜表面的形貌、结构和刻蚀速率进行了观测。结果发现：在工作气压一定时，刻蚀速率随着直流功率的增加而增大，并且刻蚀由各向同性转变为各向异性。但过高的直流功率会导致金刚石膜表面沉积出无定形碳。基于实验研究结果和相关基本理论建立了刻蚀模型，并根据模型得到了影响刻蚀的主要原因在于等离子体中的电子温度和金刚石膜的悬浮鞘电位。     

Effects of Cu and Cu/Ti interlayer on adhesion of diamond film

Diamond film were deposited on the cemented WC + 6% Co substrates by a microwave plasma chemical vapor deposition (CVD) system. The effects of Cu and Cu/Ti as interlayer on adhesion of diamond film were investigated. The surface morphology and composition of the film and microstructure of film/substrate interface were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA) and Raman spectrometer, respectively. The adhesion of diamond film was evaluated by indentation adhesion testing. The results show that Cu/Ti would be a suitable interlayer system to improve film adhesion. It was considered that Cu atoms replaced most voids left by leached Co, recovered the surface strength and toughness, and inhibited the diffusion of Co to the substrate surface. Ti atoms act as promoter for diamond nucleation, and the formation of TiC enhanced the adhesion of diamond film. Furthermore, Cu/Ti interlayer system restrained the growth of diamond grain and promoted the formation of nano-crystalline, which increased the contact area of the film/substrate interface.     

Structure and characteristics of Si-coated diamond grits

IntroductionThe properties of diamond tools are determined bythe quality of diamond abrasive and the adhesion betweenthe diamond grits and the bond[1-3].However,duringsintering process,metal bond containing graphitizing ele-ments seriously erodes diamond grits,which reduces thestrength of the diamond grits.Furthermore,diamondstend to be oxidated when the temperature reaches as highas 700℃.Therefore,sintering process of diamond toolsleads the diamond grits to oxidization,significantly de-creas…     

Thermal stresses in diamond coatings and their influence on coating wear and failure

Thermal stresses in diamond coatings deposited onto cemented carbide substrates are calculated using the finite element method. The thermo-elastic stress fields for some coating-substrate geometries are presented. The results are compared with experimental data on the tribological behaviour of diamond coatings. Residual stresses can explain many of the observed patterns of coating wear and failure. A model for the abrasive wear of brittle coatings under large compressive biaxial stresses is described. These stresses prevent cracks initiated at the surface to propagate towards the interface and may promote crack paths parallel to the interface, thus causing the formation of a smooth coating surface. Once the smooth appearance is reached it will become extremely hard to initiate and propagate cracks into the coating and consequently the wear rate becomes very low. Thus, large compressive residual stresses increase the already high wear resistance of diamond coatings. When diamond coatings are deposited onto substrate edges, intense concentrations of normal and shear stresses may lead to coating failure by interfacial spalling. These stresses are lowered by increasing the ratio r/h, where r is the edge radius and h is the coating thickness.     

Direct manufacturing of diamond composite coatings onto silicon wafers and heat transfer performance

This paper reveals new insights on how to achieve direct deposition of functional materials onto silicon wafers for cooling purposes. Manufacturing heat spreaders directly onto a microprocessor will negate the need for Thermal Interface Materials (TIMs) which often account for the highest resistances in a typical CPU thermal circuit. In this work we demonstrate that Cold Spray can be tailored to directly print onto a silicon wafer with a layered structure of aluminum, copper and diamond. The thermal performance of the copper/diamond coating was also separately measured using an in-house testing apparatus showing heat-transfer enhancements in agreement with theoretical predictions.     

Interface of YBa_2Cu_3O_7 Thin Films Grownon Sapphire with Epitaxial Yttria－stabilized Zirconia Buff

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大孔径内孔表面金刚石薄膜涂层的制备

应用热丝化学气相沉积（HFCVD）工艺,并采用合适的衬底预处理方法和优化的工艺参数,在大孔径硬质合金内孔表面沉积了金刚石薄膜。分别采用SEM、EDS和喇曼光谱依次对衬底预处理前后内孔表面及沉积的金刚石薄膜进行了表征,并通过压痕实验评估了薄膜的附着强度。该压痕实验结果与薄膜的SEM及喇曼光谱表征的结果具有一致性。结果表明：采用合适的衬底预处理方法和优化的HFCVD工艺,可以在大孔径硬质合金内孔表面沉积高质量的金刚石薄膜。     

Preparation,characterization and electrochemical properties of boron-doped diamond films on Nb substrates

A series of boron-doped polycrystalline diamond films were prepared by hot filament (HF) chemical vapor deposition on Nb substrates. The effects of B/C ratio of reaction gas on film morphology, growth rate, chemical bonding states, phase composition and electrochemical properties of each deposited sample were studied by scanning electron microscopy, Raman spectra, X-ray diffraction, microhardness indentation, and electrochemical analysis. Results show that the average grain size of diamond and the growth rate decrease with increasing the B/C ratio. The diamond films exhibit excellent adhesion under Vickers microhardness testing (9.8 N load). The sample with 2% B/C ratio has a wider potential window and a lower background current as well as a faster redox reaction rate in H₂SO₄solution and KFe(CN)₆ redox system compared with other doping level electrodes.     

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.     

WC–Co substrate surface pretreatments with aluminum compounds prior to polycrystalline CVD diamond deposition

Without pretreatment, the adherence of polycrystalline chemical vapour deposition (CVD) diamond films on WC–Co substrates is rather poor due to Co presence in the binder phase. Therefore several attempts to immobilize the Co on the substrate surface have already been investigated. However, results are not fully satisfying. In this paper, solutions or suspensions of various Al compounds have been applied to the WC–Co surface to form stable Co/Al compounds before diamond deposition. By means of SIMS depth profile analysis it is shown that surface pretreatment with Al(OC₂H₅)₃/conc. CH₃COOH or Al(NO₃)₃ leads to the formation of Co/Al compounds which suppress the Co mobility resulting in improved adherence of the diamond layer. Evidence for Co/Al compounds has also been found after pretreatment with Al(OH)₂–OOCCH₃ in neutral solution, although the quality of the diamond crystals was changed to ballas. The use of Al(OH)₂–OOCCH₃ in a basic as well as an acid medium produced no Co/Al reaction.     

Experimental and gas phase modeling of nanocrystalline diamond films grown on titanium alloys for biomedical applications

For biomedical applications, it is highly desirable to be able to deposit smooth adherent diamond films on various complex-shaped substrates using the hot filament chemical vapor deposition technique (HFCVD). The properties of these films are affected profoundly by process parameters such as filament temperature, gas composition, and pressure. In this study, we present an insight into the gas phase chemistry involved in HFCVD of smooth nanocrystalline diamond films using Ar/CH₄/H₂ precursor mixtures. Experimental results on the growth, surface morphology, and crystalline structure are also presented. It is evident that the addition of a noble gas such as argon has a considerable effect on the gas surface chemistry. Notably at high concentrations of inert gas dilution (>90 vol.% argon) there are significant changes in diamond crystallinity ranging from polycrystalline through microcrystalline, and at argon concentrations >98 vol.%, nanocrystalline facets are observed. Modeling of the gas phase chemistry showed that the relative concentrations of CH₃ and C₂H alter significantly in this region, and these in turn influence surface morphology and crystallinity of the deposited films.     

非金刚石相碳成分对金刚石薄膜晶形的影响

应用Raman光谱和SEM方法研究了在用热丝CVD方法生长金刚石薄膜中,生长膜中非金刚石相碳成分对金刚石晶粒晶形的影响。还讨论了生长条件如碳源浓度、衬底温度等对生长膜中非金刚石相碳成分的影响     

铁触媒表面的氧化铁包覆层对金刚石成核的影响

为了研究氧化后的触媒对金刚石成核的影响，将α-Fe粉在400℃的空气氛中分别处理1，1．6，2．4和4小时，制备了不同包覆厚度的氧化铁包覆铁粉。采用氧化铁包覆的铁触媒粉末和石墨体系进行了金刚石合成研究。研究发现在5．7GPa和1600℃的条件下，铁触媒表面的氧化铁包覆层与石墨碳发生了氧化还原反应生成Fe3O4和FeO，同时包覆层内部的铁熔融渗出，并与石墨碳源接触促使了金刚石的成核生长。与纯铁触媒相比，氧化铁包覆层对金刚石成核具有明显的抑制作用，而且随着包覆层厚度的增加，抑制作用越明显。文中还借助穆斯堡尔谱、X-ray衍射和扫描电镜测试手段对上述实验机理进行了深入的探讨。     

提高CVD金刚石涂层刀具附着力的应用研究

介绍了影响CVD金刚石涂层刀具附着力的因素,并重点对提高其附着力的工艺措施进行了较深入的研究,对解决刀具基体与金刚石薄膜之间的附着力过小问题有一定的指导意义.     

Tribological behaviour and internal stress of diamond coating deposited with a stationary d.c. plasma jet

A diamond coating was produced by a stationary d.c. plasma jet in a confined circular area. Using scanning electron microscopy, optical microscopy, laser profilometry and Raman spectroscopy, it was found that the diamond coated area is inhomogeneous with respect to morphology, purity, thickness, and internal stress. Surrounding the diamond coated central area, an amorphous carbon rich area was identified. The morphologically distinct regions were evaluated separately in a fretting wear test against a corundum counterbody. The frictional behaviour was observed to be dependent on the morphology and structure of the coating and the diamond crystal size and orientation in the diamond coated area. No evidence of any fretting wear damage was found in the diamond coated area, whereas a lot of fretting induced scratches were observed in the amorphous carbon rich area. The presence of wear debris was clearly observed in the fretting contacts both inside and outside the diamond coated area.