纳米陶瓷涂层的性能及应用

纳米陶瓷涂层与微米级陶瓷涂层相比,晶粒更细化且分散均匀,晶界数量大幅度增加,其在硬度、韧性、耐磨性、结合强度、抗蚀性、致密度等方面有显著的提高,已在航空航天、船舶、化工等工业领域得到应用.本文针对纳米陶瓷涂层的性能及应用给予介绍.     

Fabrication of nano-structured HA/CNT coatings on Ti6Al4V by electrophoretic deposition for biomedical applications

In order to improve the bone bioactivity and osteointegration of metallic implants, hydroxyapatite (HA) is often coated on their surface so that a real bond with the surrounding bone tissue can be formed. In the present study, cathodic electrophoretic deposition (EPD) has been attempted for depositing nanostructured HA coatings on titanium alloy Ti6Al4V followed by sintering at 800 degrees C. Nano-sized HA powder was used in the EPD process to produce dense coatings. Moreover, multiwalled carbon nanotubes (CNTs) were also used to reinforce the HA coating for enhancing its mechanical strength. The surface morphology, compositions and microstructure of the monolithic coating of HA and nanocomposite coatings of HA with different CNT contents (4 to 25%) on Ti6Al4V were investigated by scanning-electron microscopy, energy-dispersive X-ray spectroscopy and Xray diffractometry, respectively. Electrochemical corrosion behavior of the various coatings in Hanks' solution at 37 degrees C was investigated by means of open-circuit potential measurement and cyclic potentiodynamic polarization tests. Surface hardness, adhesion strength and bone bioactivity of the coatings were also studied. The HA and HA/CNT coatings had a thickness of about 10 microm, with corrosion resistance higher than that of the substrate and adhesion strength higher than that of plasma sprayed HA coating. The properties of the composite coatings were optimized by varying the CNT contents. The enhanced properties could be attributed to the use of nano-sized HA particles and CNTs. Compared with the monolithic HA coating, the CNT-reinforced HA coating markedly increased the coating hardness without deteriorating the corrosion resistance or adhesion strength.     

The effect of impregnation with nanostructured boehmite on the structure and properties of plasma-sprayed ceramic coatings

It is shown that capillary phenomena can be used to nanostructure ceramic coatings via their impregnation with suspensions based on a nanostructured material. Boehmite with particle sizes of 30–50 nm was used as the nanostructured material. Two methods are suggested. When already-formed coatings are impregnated, the system of interconnected pores between particles is used, with the pores within the particles themselves being closed. If hydroxyapatite particles are impregnated before the spraying, boehmite is more uniformly and to a fuller extent distributed within the plasma-sprayed coating. In contrast to the first method, a coating is nanostructured in this case both within hydroxyapatite particles and on their surface. The adhesion increases from 8.4 to 17.1 MPa upon nanostructuring.     

Recent developments on WC-based bulk composites

In order to achieve improved properties and performance with WC-based cemented carbides, research efforts have been directed towards the development of nanostructured cemented carbides. With the recent development of ‘spray conversion process’ for synthesizing nanosized powders and the advent of spark plasma sintering technique, it has been possible to successfully develop bulk nanostructured cemented carbides, possessing improved hardness and wear resistance. On a different note, realisation of the fact that the presence of metallic binder phase is deleterious towards certain applications of WC-based cermets has led to a recent surge of interest towards the development of novel ‘binderless’ WC-based ceramics by replacing the metallic binder phase with ceramic sinter-additives. More recently, it has been possible to develop dense WC-based ceramic composites without considerable deterioration of fracture toughness in the absence of the metallic binder phase. In the above perspective, the present review focuses mainly on the recent research results concerned with the processing and characterisation of nanostructured WC-based cermets and binderless WC-based ceramic composites.     

Surface Modification of Press Dies Used in a Powder Metallurgical Production Process

Cold compaction in a press die and subsequent sintering of diamond particles, homogeneously distributed in a metallic powder as matrix, is one of the most economic ways for the production of diamond composites, used widely for cutting very hard materials like stone and glass. Owing to the very high hardness of diamonds, the wear of the press die is considerably high and because of a short life time, press tools must be substituted regularly. Recently, through plasma nitriding process and deposition of thin solid films, the wear resistance of the press dies has been significantly increased. This work aims at the investigation of the influence of roughness, friction coefficient, and hardness of the inner surface of various dies, which have been modified in different ways, on the physical properties of the compacted diamond segments. It was evidenced that improving the mechanical and tribological properties of the die surface leads to an increase of the hardness and density of the diamond composites produced.     

圆锥压头递增载荷对材料的划痕行为

用Rockwell C金刚石压头对16种材料(2种玻璃、2种聚合物、4种陶瓷、4种金属和4种金属玻璃)进行微米划痕测试。结果表明,这些材料都存在与弹性恢复相关的最大划痕保持率(残余深度与压入深度之比),可作为表观摩擦系数变化曲线的分段过渡点。划痕的表观摩擦系数由黏着摩擦系数和犁沟摩擦系数组成,使用三维力学接触模型可较为准确地表征除金属玻璃外的摩擦系数。材料的初始摩擦系数与泊松比有一定的关系。聚合物(PC和PMMA)因堆积和下沉效应出现独有的双划痕沟槽现象。16种材料的划痕硬度与压痕硬度的比值为0.33~2.5,划痕硬度与体积模量呈线性关系。使用线弹性断裂力学(LEFM)模型和微观能量尺寸效应(MESEL)模型计算了材料的断裂韧性。结果表明,LEFM模型、Akono's MESEL和Hubler's MESEL模型都能较为准确地表征断裂韧性较低材料(玻璃、陶瓷和高分子)的断裂韧性,而对断裂韧性较大的金属材料其表征结果偏差较大。用Liu's MESEL模型可表征断裂韧性较大材料(金属材料和部分金属玻璃)的断裂韧性。材料的断裂韧性,与泊松比呈分段线性相关。     

A comparative study of the mechanical strength of chemical vapor-deposited diamond and physical vapor-deposited hard coatings

Four mechanical parameters of physical vapor-deposited (PVD) hard coatings were obtained, which were the residual strain, Young's modulus, film toughness, and interface toughness, concerning titanium aluminum nitride (TiAlN) and titanium nitride (TiN) coatings deposited on WC-Co substrates. The results were quantitatively compared with the author's previous trials for the case of chemical vapor-deposited (CVD) diamond coatings. Due to the significant difference in the mechanical properties between PVD hard coatings and CVD diamond coatings, it was necessary to develop new experimental techniques, which could properly evaluate those parameters for the case of PVD hard coatings. As a conclusion, film toughness of PVD hard coatings was surprisingly brittle. It was an order of magnitude smaller than that of CVD diamond coatings. In contrast, no significant difference was found in interface toughness between these different kinds of coatings. Concerning the residual strain, TiN had far larger level than the other two. These differences in mechanical properties were further discussed in relation to the difference in their wear behavior.     

纳米结构陶瓷涂层的制备技术

与传统的微米级陶瓷涂层相比,纳米结构陶瓷涂层的结合强度、断裂韧性、耐磨性等会显著提高,目前已在军民领域开始应用。纳米陶瓷涂层的制备存在一定的特殊性和较大难度,并且制备工艺会对涂层的组织和性能产生直接影响。本文对纳米结构陶瓷涂层的制备技术进行了详细介绍。     

Relationships between the fretting wear behavior and mechanical properties of thin carbon films

Mechanical load can drastically affect the properties of orthopedic implant materials. Damage of these materials usually occurs in contact surfaces, caused by abrasion, adhesion, fretting, delamination, pitting and fatigue depending on friction, lubrication, contact area, surface finish and level of loads (stresses).Carbon-based films are biocompatible with good bearing capacity, wear resistance, corrosion resistance and have a low coefficient of friction. However, great intrinsic stress prevents their wider application, mainly as implant coatings. To reduce this undesirable effect special deposition procedures are under development and/or the films are doped with suitable elements. It must be emphasized that DLC is not a material but a group of materials with a variety of properties. The relationships between the fretting wear behavior and mechanical properties of films based on carbon deposited by DC using the pulsed arc discharge PVD nitrogen doped (a-C) and the filtered pulsed arc discharge deposition system (ta-C) were tested.The composition of carbon films (sp³, sp²) was determined by Raman spectroscopy. Mechanical properties of elastic modulus and hardness were determined by a NanoTest apparatus with diamond Berkovich tip using the Oliver-Pharr procedure and adhesion was measured by nanoscratch tests. Tribological behavior was analyzed by fretting tests with a corundum ball under dry sliding lubricated conditions.The good performance of the hard carbon coatings is often discussed. Results from this study of fretting and the associated lubrication (bovine serum) show that ta-C coatings, despite their high hardness, have very low friction coefficients and low volume losses.     

Mechanical properties of diamond thin films

Abstract

The mechanical properties of diamond films deposited via hot filament chemical vapour deposition have been determined using a range of techniques, and related to the composition and morphology of the diamond films as determined by laser Raman spectroscopy. As the quality of the film increases, its hardness (as determined by the volume law of mixtures hardness model) also increases until it is larger than values often reported for polycrystalline bulk material, a consequence of the very small grain size in the films. Coating adhesion, as determined from indentation adhesion tests, also appears to improve with coating quality. Variations in the behaviour of the friction coefficient between diamond films and diamond and steel counterfaces are less well defined, but it appears that the surface morphology of the film is important in dictating the behaviour rather than the quality of the diamond. These results are discussed in the context of the potential use of diamond coatings in tribological applications.

MST/1695     

Chemical vapour deposition of microdrill cutting edges for micro- and nanotechnology applications

Conventional cemented tungsten carbide-cobalt (WC-Co) microdrills generally have a low cutting efficiency and short lifetime mainly because they operate at very high cutting speeds. Since it is relatively expensive to make microtools it is highly desirable to improve their lifetime and in-service performance. Microtools used to make microelectronic and mechanical systems (M.E.M.S) devices with sharp cutting edges, such as milling or drilling tools need protective coating in order to extend life and improve performance. One method of achieving this objective is to use a suitable surface engineering technology to deposit a hard wear resistant coating, such as diamond. Diamond has excellent mechanical properties, such as ultra-high hardness and a low friction coefficient. One of the most promising surface treatment technologies for depositing diamond onto complex shaped components is chemical vapour deposition (CVD). However, CVD of diamond coatings onto the cemented WC-Co tool has proved to be problematic. Binder materials such as cobalt can suppress diamond nucleation resulting in poor adhesion between the coating and substrate. In this paper the effects of pre-treated substrate material on the coating structure are reported. The morphology and the crystallinity of the as-grown films was characterised by using scanning electron microscopy (SEM). Raman spectroscopy was used to assess the carbon-phase purity and give an indication of the stress levels in the as-grown polycrystalline diamond films. The diamond coated tools have potential applications in micro- and nanomachining of micro- and nano-sized components used in M.E.MS.     

Si、Ti、Mo添加剂对自蔓延防护涂层性能的影响

为了提升自蔓延涂层的各项性能,拓宽自蔓延涂层的应用领域,本文实验制备了两种自蔓延防护涂层,即Al和Fe₂O₃的自蔓延铝热涂层和含有Si、Ti、Mo添加剂的低温自蔓延铝热涂层,借助X射线衍射、扫描电子显微镜等技术对不同成分涂层的组织形貌和物相组成进行了对比分析。利用显微硬度计、万能实验机、多功能摩擦磨损试验机研究了两种涂层的力学性能和摩擦性能。研究表明,添加剂使得涂层的孔隙率降低了66.7%,结合强度提高32.3%,常温下显微硬度提高17.6%,断裂韧性提高了28%,耐磨性能提高约25%。两种涂层均呈现出以Al₂O₃相为主的陶瓷层、金属过渡层与基体的3层结构,Si、Ti、Mo添加剂使得涂层中出现了SiC、TiC、MoSi₂等硬质相,且反应更为充分,结合强度、硬度、断裂韧性、摩擦性能均得到提升。     

Effect of plasma CVD operating temperature on nanomechanical properties of TiC nanostructured coating investigated by atomic force microscopy

The structure, composition, and mechanical properties of nanostructured titanium carbide (TiC) coatings deposited on H₁₁ hot-working tool steel by pulsed-DC plasma assisted chemical vapor deposition at three different temperatures are investigated. Nanoindentation and nanoscratch tests are carried out by atomic force microscopy to determine the mechanical properties such as hardness, elastic modulus, surface roughness, and friction coefficient. The nanostructured TiC coatings prepared at 490 °C exhibit lower friction coefficient (0.23) than the ones deposited at 470 and 510 °C. Increasing the deposition temperature reduces the Young's modulus and hardness. The overall superior mechanical properties such as higher hardness and lower friction coefficient render the coatings deposited at 490 °C suitable for wear resistant applications.     

热喷涂纳米结构A1203／Ti02涂层及其应用

为进一步揭示热喷涂纳米结构A12O3／TiO2陶瓷涂层的强韧耐磨机制，通过对比力学性能试验，采用SEM，ESEM，TEM和XRD研究了这种新型纳米结构热喷涂涂层的组织特征，探讨了纳米稀土合金化对涂层微观组织和性能的作用．研究结果表明，这种新型纳米结构陶瓷涂层具有纳米和亚微米尺度三维网络状显微组织特征，呈现出高的韧性，耐磨性与涂层的韧性之间有密切的关系．     

An investigation into the mechanical and tribological properties of plasma electrolytic oxidation and hard-anodized coatings on 6082 aluminum alloy

A ceramic coating on AA6082 aluminum alloy prepared by plasma electrolytic oxidation (PEO) has been studied and compared against a sulphuric acid hard-anodized coating on the same alloy. Surface morphology and microstructures of the coatings have been examined by scanning electron microscopy. X-ray diffraction is used to determine the phase composition of the coatings. The adhesion strength of the coatings has been evaluated using a scratch test method. The coating's mechanical properties such elastic modulus and hardness data have been generated using a dynamic ultra-microhardness tester. Sliding wear tests with different loading rates are performed on the coatings in order to assess their wear resistance. Test results show that the PEO treated samples exhibit significantly better mechanical properties compared to hard anodized samples. The elastic modulus and hardness of the PEO coating are 2-3 times greater than of the hard anodized coating and subsequently, an improved wear resistance of the PEO coating has been achieved. The mechanical properties of the coatings and their relations to their tribological performance are discussed.     

Multilayer DLC coatings via alternating bias during magnetron sputtering

To combat the high residual stress problem in monolayer diamond-like carbon coatings, this paper fabricated multilayer diamond-like carbon coatings with alternate soft and hard layers via alternating bias during magnetron sputtering. The surface, cross sectional morphology, bonding structures and mechanical properties are investigated. The atomic force microscopy images indicate low bias results in rougher surface with large graphite clusters and voids suggesting low coating density. The multilayered coatings demonstrate relatively smooth surface stemming from higher bias. The cross sectional images from field emission scanning electron microscopy indicate coating thickness decreases as substrate bias increases and confirm that higher bias results in denser coating. Delamination is observed in monolayer coatings due to high residual stress. The trend of sp³/sp² fraction estimated by X-ray photoelectron spectroscopy is consistent with that of I_D/I_G ratios from Raman spectra, indicating the change of bonding structure with change of substrate bias. Hardness of multilayer diamond-like carbon coating is comparable to the coatings deposited at low constant bias but the adhesion strength and toughness are significantly improved. Alternately biased sputtering deposition provides an alternative when combination of hardness, toughness and adhesion strength is needed in an all diamond-like carbon coating.     

Improvement of structural and mechanical properties of alumina coatings by incorporation of TiO2 and α-Al2O3 nanoadditives

Abstract

Alumina coatings embedded with different nanoadditives were fabricated on aluminium alloy by microarc oxidation (MAO). Incorporation of nanograins into the prepared coatings was accomplished by dispersing nanoadditives into different electrolytes during the MAO process. Our results show that nanograins are successfully embedded in the ceramic coatings, and the embedded coatings are compact and have lower porosity. The mechanical properties of the nanograin embedded coatings such as hardness, adhesion and wear resistance are consequently improved, and the samples prepared in aluminate electrolyte with α-Al₂O₃ nanoadditive have better mechanical properties than those prepared in other electrolytes. Our results also show that the mechanical properties of MAO coatings are closely related to the surface structure. The introduction mechanism of nanograins into the ceramic coatings resulted from the reactions occurring in the microarc discharge channels such as diffusion and electrophoresis, which is believed to improve the structure of the prepared coatings.     

Adhesion of thermally sprayed hydroxyapatite–bond-coat systems measured by a novel peel test

Ti6Al4V foils, 100 m thick, were coated with thin (10–15 m) bond coats based on titania and zirconia, and subsequently coated with a thick (100–120 m) hydroxyapatite layer, using atmospheric plasma spraying. Peel adhesion tests of the coating systems performed on the foils showed that titania, and mixed titania/non-stabilized zirconia bond coats improved the adhesion of the ceramic layers to the metallic substrate in a statistically significant way, while a partially CaO-stabilized zirconia bond coat led to a decrease of the peel adhesion strength when compared to hydroxyapatite coatings without a bond coat.     

热喷涂生物陶瓷涂层的研究进展

采用热喷涂技术在金属(合金)基材表面制备的生物陶瓷涂层, 兼具金属材料较高力学强度和陶瓷材料优良生物学性能, 作为骨植入材料的研究和应用备受关注。本文介绍骨植入涂层材料的研究概况, 重点阐述热喷涂羟基磷灰石(HA)涂层的研究现状, 并概述新型生物活性硅酸钙陶瓷涂层的研究进展。     

Sputtered tungsten-based ternary and quaternary layers for nanocrystalline diamond deposition

Many of today's demanding applications require thin-film coatings with high hardness, toughness, and thermal stability. In many cases, coating thickness in the range 2-20 microm and low surface roughness are required. Diamond films meet many of the stated requirements, but their crystalline nature leads to a high surface roughness. Nanocrystalline diamond offers a smoother surface, but significant surface modification of the substrate is necessary for successful nanocrystalline diamond deposition and adhesion. A hybrid hard and tough material may be required for either the desired applications, or as a basis for nanocrystalline diamond film growth. One possibility is a composite system based on carbides or nitrides. Many binary carbides and nitrides offer one or more mentioned properties. By combining these binary compounds in a ternary or quaternary nanocrystalline system, we can tailor the material for a desired combination of properties. Here, we describe the results on the structural and mechanical properties of the coating systems composed of tungsten-chromium-carbide and/or nitride. These WC-Cr-(N) coatings are deposited using magnetron sputtering. The growth of adherent nanocrystalline diamond films by microwave plasma chemical vapor deposition has been demonstrated on these coatings. The WC-Cr-(N) and WC-Cr-(N)-NCD coatings are characterized with atomic force microscopy and SEM, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and nanoindentation.