Titanium diboride thin films produced by dc-magnetron sputtering: Structural and mechanical properties

The use of titanium diboride films as protective coatings was proposed for several applications because of its mechanical and tribological properties, as well as chemical and thermal stabilities. The aim of this work is to evaluate the effects of the deposition parameters on the microstructure and mechanical properties of titanium diboride films. All films were deposited on silicon substrates by dc-magnetron sputtering from a stoichiometric TiB2 target in argon atmospheres. The chemical composition was determined by Rutherford backscattering spectroscopy (RBS), while structural information was obtained by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The intrinsic stress of the films was determined by measuring the change of the substrate curvature due to film deposition. Surface roughness was studied by Atomic Force Microscopy (AFM). The film hardness and elastic modulus were determined by nanoindentation measurements. The correlation between the mechanical properties with the film density is presented. The internal stress reduction occurs with substantial reduction of the film hardness, and it occurs for films with low mass density.     

Substrate effect on mechanical characterizations of aluminum-doped zinc oxide transparent conducting films

The measurements of thin-film mechanical properties are generally influenced by the elastic and plastic responses of substrates and consequently may be inaccurate. Thus in this study, the effects of three different substrates, including sapphire, glass and polyimide, on the mechanical characterizations of aluminum-doped zinc oxide transparent conducting films are evaluated. From nanoindentation tests, it was found that a high film/substrate hardness ratio contributed an early-initiated substrate effect. For a hard film/soft substrate system (zinc oxide on polyimide), the measured hardness and elastic modulus markedly dropped at very small indentation depths due to the insufficient strength of the soft substrate to sustain the applied stress. A modification of the Bhattacharya model and the calibration of the King model were also made in this study; some important factors were established. Moreover, the interface adhesion energy between the film and soft substrate, measured by nanoscratch, was high because the compliant deformation of the soft substrate released accumulated stresses and then retarded interface delamination.     

附加几何形貌特征对Steel/CFRP无铆连接接头性能的影响

基于无铆连接技术,提出对钢板和碳纤维预浸料进行热冲压局部成形的Steel/CFRP连接工艺,设计了平板型及具有矩形凹槽、弧形凹槽、分布式圆柱形凹坑、分布式球形凹坑等几种不同附加几何形貌特征的Steel/CFRP连接接头。采用Hashin损伤准则及内聚力模型,通过系列有限元仿真实验,研究了有效粘结长度、不同附加几何形貌特征、尺寸及分布对接头性能的影响。仿真与拉伸剪切实验结果对比分析发现:仿真建模时所采用的理想结合界面假设,以及对胶黏剂性能、局部成形界面内应力重新分布的忽略,是造成仿真结果与实验结果出现较大出入的主要原因,可以通过对附加几何形貌特征参数和连接工艺条件优选,促使接头处形成理想的结合界面和机械镶嵌作用,以提高Steel/CFRP接头性能。     

磨削对氧化膜去除质量影响的稳定性与敏感性

目的研究磨削参数对电化学加工氧化膜去除质量的影响规律,以及各参数对氧化膜去除质量影响的稳定性和敏感性。方法在试件表面形成均匀一致,无缺陷电化学加工氧化膜的前提下,借助自主搭建的机械磨削实验平台,分别研究磨粒尺寸、工件速度、磨削压强和加工时间对氧化膜去除质量的影响,使用精密电子天平和扫描电子显微镜对实验前后的试件进行测量,结合稳定性与敏感性分析理论对实验结果进行分析。结果不同的加工参数对氧化膜去除程度的影响不尽相同,氧化膜既存在不完全去除的现象,也存在完全去除的现象。扫描电子显微镜结果也显示,不同尺寸的磨粒对氧化膜的破坏程度不同,其表面氧化膜的沟槽深浅不同。结论受氧化膜硬度低、容易去除和基体金属硬度高、不容易去除的影响,氧化膜去除质量随着工件速度和加工时间的增加呈现三次曲线的规律增加,随磨削压强和磨粒尺寸的增大呈线性增加趋势。磨削参数对氧化膜去除质量影响的稳定性与敏感性不同,而且在电化学机械加工生产应用中不改变磨削工具,所以在磨削参数相对值较低的区间,其对去除质量影响的稳定性由大到小(敏感性由小到大)为:磨粒尺寸、加工时间、磨削压强、工件速度。在磨削参数相对值较高的区间,稳定性由大到小(敏感性由小到大)为:磨粒尺寸、磨削压强、工件速度、加工时间。加工中优先选择稳定性高(敏感性低)的参数作为调整电化学机械加工效果的主要因素,可在提升经济性的同时,提高加工精度。     

Substrate-affected contact deformation and hardness of an elastoplastic film coated on purely elastic substrates

The elastoplastic contact deformation of coating/substrate bilayer composites is examined through finite element analyses. The author focuses on the plastic flow within an elastoplastic film that is enhanced by the geometrical constraint of elastic substrate. To gain a deep physical insight into the effect of the substrate on the plastic flow of film, a specific elastoplastic film is supposed to be coated on purely elastic substrates, ranging from very compliant to very stiff. The elastic mismatch of coating/substrate plays an essential role in controlling the elastoplastic deformation and flow of the film. The film significantly changes its characteristic elastic/plastic and contact behaviors, depending on the substrate compliance; a stiffer substrate enhances the plastic flow within the coated film, while a more compliant substrate, in contrast, depresses the plastic flow. In other words, at a given depth of penetration, the film accommodates the penetration in a more elastic manner, when the substrate is compliant, whereas the film becomes more plastic and ductile, when the substrate is stiff. Accordingly, the concept of “substrate-independent-film-only properties” has none of engineering significances from a practical point of view, if the information on the mechanical characteristics of the substrate is limited.     

Microscopic properties of passive films on Ti and Zr from optical,electrochemical and SXM-measurements

A combined application of several microtechniques is presented and discussed with the Ti/TiO₂ and Zr/ZrO₂-systems as an example. All measurements were carried out on single grains of technical materials in order to detect and quantify the effect of substrate microstructure on the properties of anodic passive films formed potentiodynamically in 0.5 M H₂SO₄ (dU/dt = 20 mVs⁻¹). Anisotropy-Micro-Ellipsometry (AME) was employed to determine the crystallographic orientation of the substrate grains along with passive film thickness and crystallinity in dependence on the anodization potential. Both the isotropic (amorphous) TiO₂- and the anisotropic (crystalline) ZrO₂-films exhibit a systematic dependence of film thickness on the grain orientation. Local LASER-scanning photocurrent measurements (λ=257 nm) on the same grains likewise show a heterogeneity of the photoelectrochemical reactivity in all cases. This is quantitatively explained by the results from local electro-chemical measurements on single grains using photoresist-microelectrodes. From oxide formation charges and Mott-Schottky evaluation of capacitance data, differences in reactivity due to different donor densities are found from grain to grain and are a strong function of the substrate packing density. Additional information on corresponding topographical and mechanical properties of different grains is obtained from Scanning Probe Microscopy (SXM) techniques, i.e. AFM-measurements. The grain topography is dominated by the material loss during electropolishing, which decreases with increasing packing density. The mechanical properties (stiffness) of the passive film as obtained from AFM-Force modulation techniques are correspondingly related to the substrate texture. In all cases investigated here, a systematic correlation of optical, structural, electronic and mechanical properties of the passive oxides on the substrate grain orientation is found, thus proving a strong texture-dependence of anodic film growth.     

Stress Study on CrN Thin Films with Different Thicknesses on Stainless Steel

The reliability of a substrate curvature-based stress measurement method for CrN thin films on substrate with fluctuant surface was discussed. The stress error led by the ignorance of substrate thermal deformation was studied. Results showed that this error could be as large as several hundred MPa under general deposition conditions. Stress in the CrN thin films with different thicknesses ranging from 110 to 330 nm on stainless steel was studied by this method, in comparison with conventional results on silicon wafer. The thin films' morphology and structure were investigated and related to the film stress. A significant result of the comparison is that stress evolution in the thin films on steel obviously differs from that on silicon wafer, not only because the two substrates have different coefficients of thermal expansion, which provokes thermal stress, but also the considerable discrepancy in the thin films' grain coarsening rate and structure that induce different intrinsic stresses.     

Finite element and dimensional analysis algorithm for the prediction of mechanical properties of bulk materials and thin films

In this work, the applicability of a new algorithm for the estimation of mechanical properties from instrumented indentation data was studied for thin films. The applicability was analyzed with the aid of both three-dimensional finite element simulations and experimental indentation tests. The numerical approach allowed studying the effect of the substrate on the estimation of mechanical properties of the film, which was conducted based on the ratio h_max/l between maximum indentation depth and film thickness. For the experimental analysis, indentation tests were conducted on AISI H13 tool steel specimens, plasma nitrated and coated with TiN thin films. Results have indicated that, for the conditions analyzed in this work, the elastic deformation of the substrate limited the extraction of mechanical properties of the film/substrate system. This limitation occurred even at low h_max/l ratios and especially for the estimation of the values of yield strength and strain hardening exponent. At indentation depths lower than 4% of the film thickness, the proposed algorithm estimated the mechanical properties of the film with accuracy. Particularly for hardness, precise values were estimated at h_max/l lower than 0.1, i.e. 10% of film thickness.     

Adhesion of Sputtered Nickel Films on Polycarbonate Substrates

Nickel films were deposited by radio frequency magnetron sputtering on top of polycarbonate substrates. Surface energy of the substrate was measured by means of the contact angle technique. Effects of sputtering parameters on the critical load between the film and the substrate were determined by the universal mechanical testing system. Optimized fabrication parameters and their influence on the critical load between sputtered nickel films and polymer substrate were studied by means of the orthogonal experimental design. Increasing radio frequency power and time improved film critical load. The radio frequency power had a more pronounced effect on critical load than the sputter power. The plasma pretreatment with Ar gas modified the surface, leading to an increased surface energy, improving the chemical bonds between nickel and carbon atoms, and thereby enhanced the critical load. The adhesion mechanism is also discussed in this paper.     

Electrochemical synthesis of polypyrrole macro-tubes on aluminum substrate

A novel structure of conductive polymer films was synthesized by electropolymerization on aluminum substrate under potentiostatic condition at a relatively high applied potential. A thick film of polypyrrole was electrodeposited onto aluminum substrate from an aqueous electrolyte solution of NaNO₃ with pH 12 by applying a constant potential of 2.0 V versus SCE. This polypyrrole film has a good stability with strong adhesion to the substrate surface. However, the morphological structure of the film is different from those previously observed for conductive polymers. Large tubes (ca. 100–200 μm in diameter) are formed, which are spiraled around the cylindrical substrate electrode. Although, the internal channels of these polypyrrole macro-tubes are very wide, the polypyrrole synthesized is sufficiently dense, guaranteeing excellent mechanical stability for this novel morphological structure. On the other hand, such large walls of the macro-tubes have nano-structures.     

高熵薄膜和成分梯度材料

针对高熵合金薄膜的研究现状,围绕成分设计、制备工艺、相结构、力学性能、高温性能、耐蚀性能等方面进行了讨论。分析了合金薄膜相结构受氮气流率、基底偏压、基底温度等工作参数影响的规律。其力学性能随着C、B、N等小半径非金属原子含量的增加而强化,文中从固溶强化理论角度进行了分析和解释。同时高熵合金薄膜展现出了优异的高温和耐蚀性能,在高温、强酸等极端条件下具有良好的稳定性。此外,高熵材料成分复杂且体系多样化,可通过高通量制备实现多组分材料的平行制备,为高通量筛选提供一个高效平台。针对未来可用于高熵合金高通量制备的几种技术进行了讨论。     

低频机械谱术测量薄膜切变模量及微量油膜探测

描述了工作在共振和次共振模式下的低频机械波谱仪的基本原理．主要介绍了研究金属衬底上薄膜的物理性质的两种方法：第一种方法，用于测量沉积在钼丝上的TiN／Ti(C，N)多层膜的切变模量和内耗；第二种方法，用于探测钢片表面微量油膜的存在．尽管这两种技术有着各自不同的应用目的及对象，但它们均源自能够导致机械能损耗的表面效应。     

Characterization of magnetron sputtered rhodium films for reflective coatings

Preparation and detailed characterization of metallic rhodium films prepared by magnetron sputtering on silicon substrates have been carried out. Different deposition conditions such as gas pressure, deposition rate and substrate temperature were investigated. The films were characterized by XPS, SEM, XRD, AFM and reflectivity measurements. No impurities were detected on the surface after deposition. The films have a low roughness and their structure exhibit nanometric crystallites with a dense columnar structure. Amongst all investigated parameters, only the gas pressure during deposition was observed to have an influence on the optical properties of the film. Otherwise, the measured reflectivity is close to the reflectivity calculated from optical constants of pure rhodium films.     

类金刚石薄膜的摩擦性能及其应用

首先从成键结构的角度分析了DLC薄膜摩擦性能的由来,然后分别从DLC薄膜的沉积工艺(包括制备方法、气源种类和掺杂元素)、摩擦环境条件和基底材料选择等三方面入手,讨论了影响DLC薄膜摩擦性能的主要因素及其影响规律。经过总结发现,通过调节DLC薄膜的沉积工艺可以改变DLC薄膜中sp~2杂化碳的含量以及氢的含量,进而影响DLC薄膜的摩擦性能;真空、惰性气体和低湿环境有利于获得更好的摩擦效果;过渡层和偏压有利于提高DLC薄膜与基底之间的附着力,其摩擦性能也会得到提升。最后对DLC薄膜在机械加工及耐磨器件、光学和电子保护以及生物医学领域的应用进行了综述,并对应用过程中存在的两大问题——DLC薄膜的内应力和热稳定性进行了分析,归纳了一些具体的解决方案,并对DLC薄膜的发展趋势进行了展望。     

Highly enhanced mechanical stability of indium tin oxide film with a thin Al buffer layer deposited on plastic substrate

We here report that the mechanical stability of indium tin oxide (ITO) film deposited on the plastic substrate can be highly enhanced by a thin metal buffer layer with a minimized loss of transparency. Neither cracks nor fragmentation was observed for a 75 nm-thick ITO film with a 5 nm-Al layer even after severe bending to a radius of curvature of 1.25 mm, while a 160 nm-ITO film of similar surface resistance was cracked at 9 mm. The improved crack resistance is accounted for by the fact that the effective elastic mismatch between the film and the substrate can be alleviated with a ductile buffer layer, thus the crack propagation is suppressed.     

Effects of phosphorus on the stability of the passive state of Fe and Fe-Ni base glasses

The effects of substituting P for B in Fe base and Fe-Ni base glasses have been investigated. The electrochemical measurements have shown that a substitution of B by P increases the ability of the alloys to passivate and stability of their passive state. Surface analysis with AES revealed that for Fe-Ni base glasses the main constituents of the passive film were: iron oxides, phosphorus-oxygen species (mostly phosphates) and boron oxide whereas Ni oxides were depleted. There was a certain similarity between the Auger spectra for phosphorus in the passive film on the glassy substrate and for segregated, and subsequently oxidized, phosphorus on a (100) oriented Fe single crystal. The results suggest, moreover, in agreement with the previous findings for crystalline Fe that the electrolyte components are incorporated into the passivating film on glassy substrates.     

316L不锈钢表面Ni-Ti合金薄膜的力学特性研究

目的提高316L不锈钢表面的硬度及耐磨性能。方法采用磁控溅射法在316L不锈钢表面制备Ni-Ti合金薄膜,并通过纳米压入法对316L不锈钢表面、Ni-Ti合金薄膜和Ni-Ti合金材料的力学性能进行测试,分析不锈钢基Ni-Ti薄膜的耐磨性能。应用有限元反演分析方法求解基体和薄膜的弹塑性幂本构关系。结果316L不锈钢与Ni-Ti合金抵抗载荷的能力较弱,但316L不锈钢表面Ni-Ti薄膜抵抗外加载荷的能力较强,且抵抗塑性变形的能力得到强化。Ni-Ti薄膜、316L不锈钢基体和Ni-Ti合金的硬度分别为8.2795、5.2405、2.9498 GPa,薄膜的硬度明显大于基体和Ni-Ti合金,说明Ni-Ti薄膜使得316L不锈钢的耐磨性显著提高。薄膜的弹性性能较基体与Ni-Ti合金有明显优势。为研究薄膜的弹塑性性能,建立ABAQUS二维有限元模型,考虑Berkovich压头和试样之间摩擦系数为0.16,通过纳米压入实验和有限元分析的对比,反演分析分别计算得到基体和薄膜的特征应力、特征应变、应变强化因子,继而确定初始屈服应力,得到Ni-Ti合金薄膜和316L不锈钢基体的弹塑性幂本构关系。结论 Ni-Ti薄膜具有良好的力学特性,使316L不锈钢表面的硬度显著提高,因此有效提高了不锈钢的耐磨性能。     

Electrochemical synthesis of novel conductive polymer and corrosion protection properties on aluminium

Abstract

In this study, the new original copolymer film of pyrrole and 2-amino-4-methyl-pyridine has been electrochemically synthesised on 7075 aluminium alloy. The synthesis was achieved in aqueous oxalic acid containing 1∶1 monomer feed ratio. The characteristics of copolymer film were compared with polypyrrole film on Al under the same conditions. The characterisation of synthesised polymers was realised with the help of scanning electron microscopy. Fourier transform infrared spectroscopy and gel permeation chromatography techniques. The conductivity values of films were measured with four-probe technique. The stability of copolymer film as a coating material has also been investigated in 3·5% NaCl solution. The quantum theoretical calculations have been employed, and some parameters (dipole moment, energy of the highest occupied molecular orbital and lowest unoccupied molecular orbital) were determined. The calculated quantum parameters revealed correlation with experimental data. Under such severe conditions, the copolymer film exhibits protective coating behaviour on Al. This original, highly stable and conductive copolymer film can find wide application area for various purposes (anticorrosive, electrocatalytic, etc.).     

冷轧AGC静-动压轴承油膜厚度的分析与补偿

论述了冷轧AGC过程中动-静压轴承油膜厚度变化对带钢厚度精度的影响，对静-动压轴承油膜的形成机理进行了分析，并推导出适合现场应用的数学模型，在此基础上设计了现场空压靠测试实验，在空压靠条件下，针对不同轧机转速对压下缸位移进行测量，并根据误差溯源理论剔除了测量结果中轧辊偏心引起的干扰量。然后由现场数据对公式中的关键系数进行回归分析，得出适合现场应用的数学模型，并应用到AGC模型中，对油膜厚度变化对带钢厚度的影响进行补偿。     

Atmospheric Plasma-Sprayed Hydroxyapatite Coatings with (002) Texture

Hydroxyapatite (HA) coatings are being widely used in biomedical applications owing to their excellent biocompatibility and osteoconductivity. Recent studies have demonstrated that the crystallographic texture plays an important role in improving the chemical stability and mechanical properties of HA coatings. In this study, optimized APS parameter was selected to deposit HA coatings with strong (002) crystallographic texture, high phase purity and enhanced melting state. Cross-sectional SEM images show uniformly distributed columnar grains perpendicular to the coating surface. To study the formation conditions of columnar grains, coatings with distinct microstructure were deposited with different spray parameters. Moreover, HA coatings were deposited on substrates with varying temperatures such as 25, 300 and 600 °C at a long stand-off distance to evaluate the role of the substrate temperature in the formation of columnar grains. The results indicate that completely molten in-flight particles and slow cooling rate are necessary conditions to form a strong crystallographic texture. The present study suggests that the crystalline structure of HA coatings deposited and formed by APS could be well controlled by modifying spray parameters and substrate temperature.