薄膜结合强度的刮剥式测量方法

本文介绍了一种薄膜结合强度的新型测量方法～刮剥法的测量原理、特点以及应用范围。所谓薄膜结合强度的刮剥式测量方法（简称刮剥法），实际上是一个使用特制刮剥刀具、以类似于薄层金属刮削方式工作，并以从基底上剥离薄膜所需能量作为其结合强度量度的测量方法。刮剥法与现广泛使用的划痕式结合力测量法的区别主要表现为：（１）该法是一个能量测量方法，即以薄膜的剥离能量作为薄膜与基体的结合强度的描述；（２）测量时采用的是对膜／基界面的切向加载方式；（３）测量结果是对膜／基结合强度的直接描述，并对基底表面状态、材质等不敏感；（４）可以对其它方法无法进行测量的超硬材料薄膜，如金刚石和立方氮化硼等，进行结合强度测量。本文通过对刮剥过程中刮剥刀刃附近区域的受力分析，得出了成功实现沿界面剥离薄膜的必要条件以及刮剥法测试对试样的要求和应用范围。     

CVD nanocrystalline diamond coatings on Ti alloy: A synchrotron-assisted interfacial investigation

Diamond coating on Ti-6Al-4V alloy was carried out using microwave plasma enhanced CVD with a super high CH₄ concentration, and at a moderate deposition temperature close to 500 °C. The nucleation, growth, adhesion behaviors of the diamond coating and the interfacial structures were investigated using Raman, XRD, SEM/TEM, synchrotron radiation and indentation test. Nanocrystalline diamond coatings have been produced and the nucleation density, nucleation rate and adhesion strength of diamond coatings on Ti alloy substrate are significantly enhanced. An intermediate layer of TiC is formed between the diamond coating and the alloy substrate, while diamond coating debonding occurs both at the diamond-TiC interface and TiC-substrate interface. The simultaneous hydrogenation and carburization also cause complex micro-structural and microhardness changes on the alloy substrates. The low deposition temperature and extremely high methane concentration demonstrate beneficial to enhance coating adhesion strength and reduce substrate damage.     

Interfacial structure, residual stress and adhesion of diamond coatings deposited on titanium

The interfacial structures of diamond coatings deposited on pure titanium substrate were analyzed using scanning electron microscopy and grazing incidence X-ray diffraction. Results showed that beneath the diamond coating, there was one titanium carbide and hydride interlayer, followed by a heat-affected and carbon/hydrogen diffused Ti layer. Residual stress in the diamond coating and TiC interlayer under different process parameters were measured using Raman and X-ray diffraction (XRD) methods. Diamond coatings showed large compressive stress on the order of a few giga Pascal. XRD analysis also showed the presence of compressive stress in the TiC interlayer and tensile stress in the Ti substrate. With increasing deposition duration, or decreasing plasma power and concentration of CH₄ in gas mixture, the compressive residual stress in the diamond coating decreased. The large residual stress in the diamond coating resulted in poor adhesion of the coatings to substrate, but adhesion was also related to other factors, such as the thickness and nature of the TiC interlayer, etc. A graded interlayer design was proposed to lower the thermal stress, modify the interfacial structure and improve the adhesion strength.     

Study of the delamination of diamond coatings under thermal stress

The influence of the thickness of CVD diamond coatings on the adhesion to a substrate, after cooling down from deposition temperature to room temperature, has been studied experimentally and theoretically. Diamond layers have been deposited at 850°C on W substrates by microwave plasma enhanced CVD. Cooling down of the substrate-diamond coating system to room temperature induces thermal stresses, due to different thermal expansion coefficients of coating and substrate. For thick diamond coatings a total and sudden delamination could be observed as a consequence of these stresses. On the contrary thin coatings, produced under identical circumstances, adhered well. These phenomena have been modelled and explained by the use of an energetic criterion for the delamination of a two-layer system under thermal stress. From the model a critical thickness of the coating can be calculated. Above this critical thickness, delamination will suddenly occur. The calculations also predict that for intermediate coating thicknesses delamination can easily be induced by external causes.     

Adhesion and hardness of ion-plated TiC and TiN coatings

The microhardness and adhesion of TiC coatings on steel and cemented carbide are studied. A comparison with TiN coatings is also made. It is found that the minimum coating thickness in which a reliable microhardness measurement can be made is described satisfactorily by existing standards; departures can be expected if the coating is strongly textured. The critical load for the removal of the coating by the scratch test depends on both the coating and the substrate and is thought to reflect their mechanical properties. It appears that marked variations in the strength and nature of adhesion on cemented carbides can occur.     

低磁不锈钢表面处理工艺及防护涂层体系设计研究

研究了不同表面处理工艺对低磁不锈钢基材自身耐蚀性能及涂层附着性能的影响,通过电化学阻抗及耐阴极剥离性测试确定了适用于低磁不锈钢表面的防护涂层体系。研究结果表明,以棕刚玉为喷砂磨料对基材进行喷砂处理,不仅可以提高基材表面粗糙度,满足涂层高附着需求,同时可降低基材表面残留粒料对基材引起的电化学腐蚀。以环氧锌黄为底层的防护涂层体系,可在不锈钢表面形成一层致密氧化膜,极大限度的阻止膜下扩蚀,使涂层的耐腐蚀性数倍增加。     

Influence of ion implantation and overlay coatings on various physico-mechanical and wear properties of stainless steel,titanium and aluminium

This work represents the data on the wear behaviour of 304 stainless steel, commercial grade titanium and commercial grade aluminium without and with different surface treatments, namely ion implantation of boron and nitrogen and overlay coatings of titanium carbide and nitride.The surface treatments were characterized by phase identification, hardness, bend strength, as well as adhesion of overlay coatings. Wear properties were evaluated in adhesive, erosive and abrasive modes of wear.The experimental results showed that surface treatments produced measurable changes in hardness and strength. The results of adhesive wear tests indicated that the wear resistance of all the substrate materials can be considerably improved by overlay coating with superhard materials in dry as well as lubricated test conditions. Ion implantation resulted in improvement of wear properties for only a limited regime of adhesive wear under lubricated conditions and for the abrasive mode of wear. Overlay coatings produced a marked improvement in abrasive wear tests under lubricated conditions on all substrate materials.     

磁控溅射工艺参数对Cu,Al薄膜与Gd基底附着性的影响

为了探讨Gd表面溅射保护膜的附着性能,利用直流磁控溅射技术在Gd基体上分别镀Cu和Al膜.用扫描电镜(SEM)和能谱仪对薄膜进行表征,用引拉法测定了薄膜的附着强度.结果表明:A1膜表面质量好,Al/Gd界面结合好,附着强度高,在优化工艺参数条件下薄膜附着强度可达到27.60 MPa;Cu膜表面质量较差,Cu/Gd界面结合差,附着强度低,在优化工艺参数条件下薄膜附着强度最高仅为3.02 MPa.     

Diamond deposition onto WC-6%Co cutting tool material: coating structure and interfacial bond strength

Diamond coatings were grown on WC-6%Co cutting tool material. Measurements were carried out to investigate the effects of diamond seeding of the substrate before deposition, removal of cobalt from the substrate before deposition, and boron incorporation into the coating during growth on the growth rate, morphology and structure of the coating, and coating-substrate edhesion. Diamond seeding of the substrate resulted in a higher growth rate and diamond fraction of the coating relative to a polished and unseeded surface. Etching of cobalt from the substrate resulted in a higher growth rate, diamond fraction and adhesion strength relative to the unetched surface. Introduction of methanol into the gas phase led to a lower growth rate, diamond fraction and adhesion strength relative to the case when no methanol was injected. Introduction of boron oxide (B₂O₃) along with methanol into the gas phase did not affect the growth rate but increased both the diamond fraction and adhesion strength relative to the case when only methanol was added. It is believed that adhesion failure occurs at the diamond-substrate interface, possibly within a soft nanocrystalline graphite transition layer.     

Development of diamond coated tool and its performance in machining Al-11% Si alloy

An attempt has been made to deposit CVD diamond coating on conventional carbide tool using hot filament CVD process. ISO grade K10 turning inserts with SPGN 120308 geometry were used to deposit diamond coating. This diamond coating well covering the rake surface, cutting edges and flank surfaces could be successfully deposited. The coatings were characterized by SEM, XRD and Raman spectroscopy for coating quality, morphology etc. Performance of diamond coated tool relative to that of uncoated carbide tool was evaluated in turning Al-11% Si alloy under dry environment. The diamond coated tool outperformed the uncoated carbide tool which severely suffered from sizeable built-up edge formation leading not only to escalation of cutting forces but also poorer surface finish. In contrast, the diamond coated tool, owing to chemical inertness of diamond coating towards the work material, did not show any trace of edge built-up even in dry environment and could maintain low level of cutting forces and remarkably improved surface finish. It has been further revealed that success of the diamond coated tool depends primarily on adhesion of the diamond coating with the carbide substrate and this is strongly influenced by the pre-treatment of the carbide substrate surface before coating.     

Synthesis and characterization of functionally graded nickel‐nickel coated ZrO2 composite coating

Electroless‐nickel plated ZrO₂ (NCZ) particles have been used to produce a functionally graded nickel‐electroless‐nickel plated ZrO₂ composite coating. So, electroless‐nickel plated ZrO₂ particles concentration was continuously increased from 0 to an optimum value in the electroplating bath (Watt's bath). The substrate was ST37 steel and the thickness of the coating was approximately 50 μm. Also a uniformly distributed nickel‐electroless‐nickel plated ZrO₂ composite coating has been manufactured as comparison. The composite coatings were characterized by scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Structure and phase composition were identified by X‐ray diffraction analysis. Microhardness of the coatings was evaluated by employing a Vickers instrument. Three‐point bend test was carried out to compare the adhesion strength of the coatings. Dry sliding wear tests were performed using a pin‐on‐disk wear apparatus. The electrochemical behavior of the coatings was studied by electrochemical impedance spectroscopy. The microhardness measurements showed that, with increasing the co‐electrodeposited electroless‐nickel plated ZrO₂ particle content in the nickel matrix, the microhardness increases from interface towards the surface of the functionally graded composite coating. Bend, wear and electrochemical test results confirmed that the functionally graded composite coating has higher adhesion, wear resistance and corrosion resistance as compared with the uniformly distributed coating. This has been attributed to lower mechanical mismatch between coating and substrate in functionally graded composite coating with respect to the uniformly distributed one.     

Mechanical properties and adhesion strength of TiN and Al coatings on HSS, steel, aluminium and copper characterized by four testing Methods

TiN and Al coatings on substrates of high-speed steel, steel, aluminium and copper have been used to study mechanical properties of coating systems, especially the adhesion of the coating. The quantities measured are internal stress of the coating, determined by X-ray diffraction, the critical load of the scratch test, the microhardness obtained by the indenter technique, and the interface fracture energy, determined by a three-point bend test developed recently by the authors. The fracture energy, G_c, is a measure for the adhesion strength of a coating system. The effect of bias voltage, sputter cleaning and contamination of the substrates on the adhesion strength and other mechanical properties are investigated with the four methods mentioned. Each of the testing methods reveal only specific aspects of the behaviour of the coating systems. The data obtained depend on bulk properties of the film and the substrate material and on properties of the interface. Variation of the bias voltage can change them in quite different ways. In addition, the inter-relations between the adhesion strength of the coating and the failure behaviour of the three-point bend test samples are discussed.     

Residual stress, Young''s modulus and fracture stress of hot flame deposited diamond

Chemical vapour deposition (CVD) diamond coatings deposited on various substrates usually contain residual stresses. Since the residual stress affects the adhesion of the coating to the substrate, as well as the performance of the coating/substrate composite in many technical applications it is of importance to study the magnitude of these stresses.

In the present study the hot flame method was used to deposit diamond coatings on cemented carbide inserts by scanning the surface with a nine flame nozzle. By varying the oxygen to acetylene flow ratio and the deposition time coatings of different qualities and thicknesses were obtained. The residual strain/stress of the coatings was measured by three different methods: X-ray diffraction using the sin² (Ψ) method, Raman spectroscopy and disc deflection measurements. To extract the residual stress from the strain data the Young's modulus was obtained from bending tests of diamond cantilever beams manufactured from free standing diamond films. The latter technique was also used to determine the fracture stress of the diamond films.

All deposited coatings displayed a residual compressive strain/stress state. The residual strain in the diamond coatings did not vary with coating thickness (1.5 μm to 20 μm) but was found to increase from −1.8 × 10⁻³ to −2.2 × 10⁻³ with decreasing diamond quality. The compressive residual stress was found to decrease from −2 GPa to −1.3 GPa with decreasing diamond quality. This is mainly due to a decrease in Young's modulus (from 1.1 TPa to 0.6 TPa) with decreasing diamond quality. Also the fracture stress was found to decrease (from 1.8 GPa to 0.8 GPa) with decreasing diamond quality. The three methods used for measuring the stress state in the coatings, X-ray diffraction, Raman spectroscopy and deflection measurement, all give the same result. The deflection technique has the advantage that no information about the elastic properties of the coating is needed, whereas Raman spectroscopy has the best lateral resolution (≈5 μm) and is the fastest method (≈5 min).     

Scratch adhesion testing of hard coatings

The scratch test for adhesion is reviewed as the only method currently available for testing thin, hard and well-adhering coatings such as TiC on steel or cemented carbide substrates. The critical load, mode of coating removal and acoustic signals are discussed. It is found that the combination of acoustic signal with microscopic observations can indicate whether failure occurs following a cohesive or an adhesive mode. The critical loads increase with increasing coating thickness in a manner which is a characteristic of the coating-substrate combination being studied. Critical loads are higher for harder tougher substrate materials; they also appear to depend on the elastic modulus and the coefficient of friction of the coating itself.     

Diamond deposition on Mo with thermal stress buffer layer coated mild steel substrate by combustion flame CVD

In order to develop wear resistance diamond/molybdenum (Mo) hybrid coating process can be conducted in open air. Diamond deposition on the molybdenum with thermal stress buffer layer coated mild steel substrate by the combustion flame chemical vapor deposition (CFCVD) was carried out. As the thermal stress buffer layer, atmospheric plasma sprayed Mo/Fe mixture coating was deposited between Mo top coat and mild steel substrate. Consequently, crack generation and peeling off of the coating occurred due to thermal influences on the condition of Mo coated mild steel substrate in our previous study, diamond particles could be created on the Mo coating without fracture and peeling off. Besides, an additional Mo coating after diamond deposition increases the adhesion force between the diamond coating and the initial Mo coating. This encapsulation of the diamond particles between two Mo layers dramatically improves the resistance of the global coating making it strong enough to resist to the wearing test. These results demonstrate the high potential of thermal sprayed coating for the wear resistance improvement.     

DEPOSITION OF DIAMOND FOR CUTTING TOOL APPLICATIONS

The poor adhesion of diamond film to substrates is one of the major problems for practical use in a cutting tool (1-4). in this study, sintered tungsten carbide (WC) body without Co metal, not cemented carbide, was used as the substrate (5), and the effects of surface decarburization of the substrate for improvement in the adhesion of diamond films were investigated. The surface decarburization and diamond coating were carried out in a microwave plasma CVD system. From the results of several adhesion tests, including the cutting tests, it is concluded that the good adhesion is obtained by surface decarburization of the substrate before diamond coating. The reasons for improvement in adhesion are considered by observing the interface structure between the film and the substrate. The damage mechanism of diamond coating on cutting an AI-18%Si alloy with increasing cutting speed is also discussed.     

加工7075航空铝合金用金刚石涂层刀具的制备及其切削性能

采用热丝化学气相沉积(HFCVD)技术在WC-Co8%硬质合金刀具表面制备金刚石涂层,调节甲烷浓度等沉积工艺制备了单层金刚石涂层刀具和微米金刚石涂层(1.2 μm)、纳米金刚石涂层(200 nm)交替多层金刚石涂层刀具。以7075航空铝合金作为切削工件,在无润滑干切条件下测试了单层金刚石涂层刀具和多层金刚石涂层刀具的切削性能。实验结果表明,切削2 h后单层金刚石涂层刀具涂层脱落宽度达到35 μm,刀刃钝化;有多层金刚石涂层刀具的刃型保持完整,涂层无脱落。对单层金刚石涂层和多层金刚石涂层平面样品进行了洛氏压痕实验。结果表明,多层金刚石涂层的脱落面积约为单层金刚石涂层脱落面积的1/5到1/10,进一步说明多层金刚石涂层有更强的抵抗裂纹产生的能力。这些结果表明,金刚石多层结构能提高涂层与基体的界面结合力,延长金刚石涂层刀具的使用寿命。     

Combinatorial approach to the edge delamination test for thin film reliability—adaptability and variability

We have demonstrated the adaptability and variability of a newly developed combinatorial edge delamination test. This was accomplished through studying the effect of substrate surface energy on the adhesion of thin films. In this combinatorial approach, a library (a single specimen) was fabricated with a polymethyl methacrylate (PMMA) film on a silicon substrate. The film has thickness gradient in one direction and the substrate has an orthogonal surface energy gradient. The thickness gradient was produced with a flow coating technique, and the surface energy gradient was controlled by partial oxidation of an alkylsilane layer on a silicon wafer. Applying a constant temperature to the specimen, interfacial debonding events were observed and a distribution of failure was constructed. Our results demonstrate the proposed combinatorial methodology for rapidly and efficiently evaluating the adhesion of general film/substrate systems as a function of many controllable parameters. In addition, this methodology can be used to predict the reliability distributions of the adhesion for practical parameters.     

Interfacial study of magnesium-containing fluoridated hydroxyapatite coatings

Magnesium-containing fluoridated hydroxyapatite (Mg_xFHA) coatings have been developed to improve the biological performances of fluoridated hydroxyapatite (FHA) coatings. The coatings are deposited on Ti6Al4V substrates via a sol-gel process. The interface between the coating and substrate is characterized by scanning electron microscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy for coating thickness, elemental distribution and chemical states. Pull-off test is used to evaluate the adhesion strength. The results show that the interdiffusion of elements happens at the coating/substrate interface. The incorporation of Mg ions into FHA coatings enhances the pull-off adhesion strength between the coating and the substrate, but no significant difference is observed with different Mg concentrations.