基于表面超声波无损评价激光熔覆层厚度的实验研究

针对目前激光熔覆层厚度无损评价的重要性,本工作结合表面超声波在介质中的传播特性对其进行测量,并在互相关函数基础上对熔覆层厚度进行了表征和评价。结果表明:随着激光熔覆层厚度的增加,表面超声波在其中的传播速率逐渐变小,在互相关函数计算微小时间差的基础上,建立了可用于评价激光熔覆层厚度的厚度-时间差关系曲线,并采用三次多项式对其进行拟合,进而得到可用于评价激光熔覆层厚度的拟合公式。最后采用不同厚度的激光熔覆层试样对拟合结果进行了验证,并同时对影响计算结果的因素进行了分析。结果表明:采用该方法对激光熔覆层厚度进行评价是可行的。     

A Remote,Non-destructive Laser Ultrasonic Material Evaluation System with Simplified Optical Fibre Interferometer Detection

An optical non-contact ultrasonic testing system is presented. It uses broadband surface acoustic wave impulses generated with a cylindrical lens focused laser line source. The detection of the ultrasound is achieved by a simple and yet effective design of optical fibre interferometer which provides good sensitivity and manoeuvrability. The effectiveness of the fibre interferometer is demonstrated by accurately measuring the broadband surface waves on various common metal structures. The measurement system’s ability for surface material evaluation is also demonstrated from fitting experimental surface wave dispersion curves with theoretical simulations. This measurement system can test small localised areas and miniature samples that were previously difficult to examine.     

Effect of Laser Shock Peening on the Microstructures and Properties of Oxide‐Dispersion‐Strengthened Austenitic Steels

Oxide‐dispersion‐strengthened (ODS) austenitic steels are promising materials for next‐generation fossil and nuclear energy systems. In this study, laser shock peening (LSP) has been applied to ODS 304 austenitic steels, during which a high density of dislocations, stacking faults, and deformation twins are generated in the near surface of the material due to the interaction of laser‐driven shock waves and the austenitic steel matrix. The dispersion particles impede the propagation of dislocations. The compressive residual stress generated by LSP increases with successive LSP scans and decreases along the depth, with a maximum value of ?369 MPa. The hardness on the surface can be improved by 12% using LSP. In situ transmission electron microscopy (TEM) irradiation studies reveal that dislocations and incoherent twin boundaries induced by LSP serve as effective sinks to annihilate irradiation defects. These findings suggest that LSP can improve the mechanical properties and irradiation resistance of ODS austenitic steels in nuclear reactor environments.

     

Plasmaunterstützte DLC‐Beschichtung von Kunststoffen

Plasmaenhanced deposition of DLC on polymers The formation of diamond‐like carbon (DLC) coatings on polyethylene (PE) is accompanied with the formation of an interlayer. Therefore the original surface structure of the plastic material is reorganized and gradually changes into the disordered structure of the DLC layer. Before DLC can be deposited in a hydrocarbon plasma with the PECVD method, all substrates are cleaned using an oxygen plasma. This first step is extremely important for the growth of the DLC layer since the sample's surface is already ablated and partly flattened. Plastic materials can be successfully improved in stability and provided with extra properties and new functionalities due to the deposition of DLC. First microscopic explanations for the macroscopic phenomena and application‐relevant questions have been identified. In spite of this limits of production are also addressed. Methods shown here will now be adapted for other materials and coatings.     

Writing,Self‐Healing,and Self‐Erasing on Conductive Pressure‐Sensitive Adhesives

A simple strategy for enabling conductive pressure sensitive adhesives (PSAs) to work as light‐responsive materials is reported. Direct laser‐writing of PSA substrates was achieved by means of a continuous‐wave He‐Ne laser focused through the objectives of an optical microscope. This approach takes advantage of cooperative interplay between viscoelastic properties of PSAs and enhanced thermal conductivity provided by an extra overlayer of gold. In particular, the thickness of the gold layer is a crucial parameter for tuning the substrate responsiveness. Self‐healing and self‐degradation processes can be exploited for controlling the lifetime of the written information, whereas additional protective coatings can be introduced to achieve permanent storage.     

Dispersion error reduction for acoustic problems using the edge‐based smoothed finite element method (ES‐FEM)

The paper reports a detailed analysis on the numerical dispersion error in solving 2D acoustic problems governed by the Helmholtz equation using the edge‐based smoothed finite element method (ES‐FEM), in comparison with the standard FEM. It is found that the dispersion error of the standard FEM for solving acoustic problems is essentially caused by the ‘overly stiff’ feature of the discrete model. In such an ‘overly stiff’ FEM model, the wave propagates with an artificially higher ‘numerical’ speed, and hence the numerical wave‐number becomes significantly smaller than the actual exact one. Owing to the proper softening effects provided naturally by the edge‐based gradient smoothing operations, the ES‐FEM model, however, behaves much softer than the standard FEM model, leading to the so‐called very ‘close‐to‐exact’ stiffness. Therefore the ES‐FEM can naturally and effectively reduce the dispersion error in the numerical solution in solving acoustic problems. Results of both theoretical and numerical studies will support these important findings. It is shown clearly that the ES‐FEM suits ideally well for solving acoustic problems governed by the Helmholtz equations, because of the crucial effectiveness in reducing the dispersion error in the discrete numerical model. Copyright © 2010 John Wiley & Sons, Ltd.     

薄膜和镀层力学性能的物理方法测试

讨论了薄膜和镀层力学性能的测试方法，包括布里渊散射、表面声波、声显微术及微压入方法。前三种方法是非接触法，最后一种是接触法。声学方法可测量弹性系数的各个分量，在薄膜和镀层情况下这些系数是和大块试样不同的，在弹性各向异性情况下可测出对应某个特定方向的弹性系数。微压入法只能测量各向同性的薄膜和镀层，但它还能测量若干塑性以至断裂的行为。最后，根据弹塑性理论进行的计算机数字模拟可以给出各种应力应变状态下的力学性能。     

Laser heat treatment of titanium GRADE 1 with iron‐nickel powder

Titanium alloys thanks to their low density and high mechanical properties are a group of materials that are being used willingly nowadays. A promising method of titanium heat treatment is laser alloying. Process parameters like laser beam power, its traverse speed, amount of alloying elements and shield gas, have influence on the resulting material. Different chemical composition and morphology can be achieved resulting in a change of properties on the surface of the material. The paper presents the investigation of titanium GRADE 1 processed with iron‐nickel powder using laser alloying. The treatment was performed using a high power diode laser. Different laser beam power values were used. Treatment resulted in obtaining good‐adhere, porous‐free, uniform composite material with no cracks. Formation of new phases and solid solution was the reason why it was possible to achieve an increase in microhardness on the surface. Light microscopy, scanning electron microscopy with energy dispersive X‐ray spectroscopy examination, microhardness results and X‐ray diffraction are presented within the paper.     

A discontinuous Galerkin method with plane waves for sound‐absorbing materials

Poro‐elastic materials are commonly used for passive control of noise and vibration and are key to reducing noise emissions in many engineering applications, including the aerospace, automotive and energy industries. More efficient computational models are required to further optimise the use of such materials. In this paper, we present a discontinuous Galerkin method (DGM) with plane waves for poro‐elastic materials using the Biot theory solved in the frequency domain. This approach offers significant gains in computational efficiency and is simple to implement (costly numerical quadratures of highly oscillatory integrals are not needed). It is shown that the Biot equations can be easily cast as a set of conservation equations suitable for the formulation of the wave‐based DGM. A key contribution is a general formulation of boundary conditions as well as coupling conditions between different propagation media. This is particularly important when modelling porous materials as they are generally coupled with other media, such as the surround fluid or an elastic structure. The validation of the method is described first for a simple wave propagating through a porous material, and then for the scattering of an acoustic wave by a porous cylinder. The accuracy, conditioning and computational cost of the method are assessed, and comparison with the standard finite element method is included. It is found that the benefits of the wave‐based DGM are fully realised for the Biot equations and that the numerical model is able to accurately capture both the oscillations and the rapid attenuation of the waves in the porous material. Copyright © 2015 John Wiley & Sons, Ltd.     

Laplace‐domain,high‐order homogenization for transient dynamic response of viscoelastic composites

This paper presents a high‐order homogenization model for wave propagation in viscoelastic composite structures. Asymptotic expansions with multiple spatial scales are employed to formulate the homogenization model. The proposed multiscale model operates in the Laplace domain allowing the representation of linear viscoelastic constitutive relationship using a proportionality law. The high‐order terms in the asymptotic expansion of response fields are included to reproduce micro‐heterogeneity‐induced wave dispersion and formation of bandgaps. The first and second‐order influence functions and the macroscopic deformation are evaluated using the finite element method with complex coefficients in the Laplace domain. The performance of the proposed model is assessed by investigating wave propagation characteristics in layered and particulate composites and verified against direct numerical simulations and analytical solutions. The analysis of dissipated energy revealed that material dispersion may contribute significantly to wave attenuation in dissipative composite materials. The wave dispersion characteristics are shown to be sensitive to microstructure morphology. Copyright © 2015 John Wiley & Sons, Ltd.     

一种基于数据间相关性的激光喷丸声学监测技术

激光喷丸作为一种新兴的金属材料表面强化技术,与普通喷丸相比,具有更显著的改性作用,使其在航空等领域有着重要的应用价值。随着该技术的工业化程度不断加深,需要加强对其工作状态的监测诊断,保证其良好的运行状况。由于声学信号不仅携带有丰富的工作特征信息,而且获取成本较低,并能够实现无损检测,所以将声学信号应用于激光喷丸的状态监测。通过分析由等离子体冲击波衰减所产生的声波信号,提取信号特征,进行过程监测。针对于冲击信号的非线性特征,从信号内相邻数据间相关性的角度,提出了一种新的冲击声信号特征挖掘方法。一方面对于模拟冲击信号进行了分析,另一方面,对于激光喷丸实际声信号进行了处理,表明该方法能够识别冲击信号的特征变化,可以用于监测激光喷丸的工作过程,操作简单且速度较快,具有较好的应用前景。     

Easy‐to‐clean Schichten – spezielle Anwendungen

Easy to clean surfaces – special applications Easy to clean surfaces can be made by wet‐chemical coating with subsequent heat‐treatment. Organically modified metal oxide films form the base reinforced by nano composite structures. The hydro‐ and oleophobic effect is obtained by perfluorinated organic molecule chains in the nano composite sol‐gel coatings. Application specific materials can be synthesized by the proper choice of suitable starting compounds and process parameters. The resulting coatings consist of a three‐dimensional cross‐linked inorganic part (such as a silica network) combined with an organic part. The organic material acts either as a surface modifier (example: alkyl, phenyl) or as crosslinker (example: acrylic, epoxy). The properties of such coating systems can be adjusted to obtain a wide range of glass‐ceramic or polymer‐like properties. The incorporation of nanoparticles into these materials significantly enhances the abrasion and the scratch resistance. Such coatings mainly on metal parts are used in diagnostics, analytical chemistry and medical technology.     

Einfluss der Mikrostruktur auf das Verschleiß‐ verhalten der hartanodisierten Aluminium‐legierungen EN AW‐6082 und EN AW‐7075

Microstructural effect on the wear behaviour of the hard‐anodised aluminium alloys EN AW‐6082 and EN AW‐7075 The suitability of hard‐anodising of high‐strength Al alloys (EN AW‐7075‐T651) for the fabrication of protective coatings which are also applicable on screws was investigated. A medium‐strength AlSi1MgMn alloy (AA60682‐T6), generally rated as applicable for anodising, was used as reference material. After possible setting phenomena of a screw joint, the load‐bearing surface of the screw can be subjected to an oscillating relative movement. The damaging tribological load was simulated in an oscillation wear test. The resulting wear appearances have revealed that the untreated oxide coatings on the EN AW‐6082 substrate are not capable of providing protection against tribological load. Since hot‐water sealing increases the hardness of the coating but also contains the technology‐induced risk of softening the substrate material, other tribological protection methods have been looked for. The analysis of the tribological tests (characterisation of the structure and the resulting properties of the material, measurement of the wear amount and analysis of the wear appearance) have shown that the films sealed with wax emulsion on both substrate materials are the most promising candidates for the application of devices under oscillation wear. The obtained roughness, friction coefficients and hardness values confirm the positive behaviour of the anodically oxidised EN AW‐7075‐T651 alloy under the chosen tribological load.     

Electrochemical performance and microstructural evolution of laser deposited Al‐Sn coating in acidic environment

Outstanding performance of materials is one of the requirements of modifying the existing materials in order to meet a global demand necessary in technology innovation. Direct laser metal deposition technique due to excellent properties has replaced conventional techniques in modifying the surface of materials. The interplay between melting, fusion and optimised laser parameters are very important factors to be considered when using laser metal deposition technique. ASTM A29 steel property was enhanced through this technique by Al‐Sn reinforcements. A 3‐kW continuous wave ytterbium laser system was employed by this process. This research investigated the microstructure and corrosion properties of fabricated laser metal deposited ASTM A29 steel. The resulting microstructure and content of the inconsequential elements in the coatings fabricated were studied to obtain the results achieved. Observation of the microstructure showed typical phase of acicular α′‐martensite attributed to rapid cooling of the molten pool. The electrochemical behaviour was investigated in 1 M HCl solution at 27 °C via potentiodynamic polarization technique. The fabricated coatings had corrosion rate of 0.03435 mm/yr, current density of 3.95 ? 10^?6 A/cm², and polarization resistance of 7093.4 Ω ? cm². While the control had corrosion rate of 16.308 mm/yr and polarization resistance of 8.0631 Ω ? cm².     

Entwicklung von Diffusionsschichten auf Nickelbasiswerkstoffen für den Einsatz in chlorhaltigen Hochtemperaturprozessen

Development of diffusion coatings on nickel base alloys for the use in chlorine‐containing high temperature processes To open up the possibility of using sewage sludge ashes as fertilizers the removal of their heavy metal contents is obligatory. A process newly developed at the BAM Berlin executes this separation in highly chlorine‐containing atmospheres at temperatures of up to 1000 °C [1]. Unfortunately there are no materials available which can withstand such conditions over longer periods of time. This project deals with the development of materials that allow the operation in highly corrosive environments. The corrosion resistance of nickel base alloys against chlorine‐induced high‐temperature corrosion will be optimized by application of aluminum‐ and/or silicon‐containing diffusion coatings. As coating method the pack cementation process was selected. In this process, the metal to be coated is embedded in a powder, consisting of the coating metal, a halogen‐distributor (e.g. ammonium chloride) and aluminum oxide as filler material. During an annealing process of several hours at temperatures of 800 to 1000 °C, gaseous metal halides form. They diffuse through the powder pack and decompose at the substrate surface, thereby depositing the coating metal. Subsequent solid phase diffusion results in the formation of a protective diffusion layer. From the thermodynamic point of view, materials with a high content of aluminum and silicon show best prerequisites to build up slow‐growing, stable oxide layers with a high potential to protect the material against corrosive attacks. The actual performance of the materials will be examined in long‐time tests under simulated field conditions (high temperatures and chlorine‐containing atmospheres).     

水声吸声高分子材料的发展及应用

综述了水声吸声材料的发展、应用状况及吸声机理的研究进展。     

Mikrostrukturieren von thermisch gespritzten Mo‐Schichten für Anwendungen im Bereich hoher Reib‐ und Verschleißbeanspruchungen

The properties of thermally sprayed coatings are dependent on many parameters such as the spraying material, substrate properties, and the injection parameters. In this study, the influence of two variable spray parameters (spraying distance and current) were investigated on molybdenum‐containing thermal spray coatings. Particularly, materials and surface characterizing properties were analyzed, and the dependence on each other was examined. The important surface parameters studied in this case are the porosity and the pore depth of the coatings. Following the correlation between spray parameters and coating properties, the influence of surface properties on the tribological behavior will be discussed, in comparison to an uncoated steel surface.     

Template‐Assisted Electroforming of Fully Semi‐Hard‐Magnetic Helical Microactuators

The authors report on the fabrication of semi‐hard‐magnetic microhelices using template‐assisted electroforming. The method consists of electrodepositing a material on a sacrificial mandrel on which a pattern has been previously written. To electroform the helical microswimmers, a helical template on a polymer‐coated metallic mandrel is created using a laser, which precisely ablates the polymer coating and exposes the mandrel surface. Subsequently, the semi‐hard‐magnetic material is electrodeposited in the trenches produced by the laser. In this investigation, the helical structures are obtained from an electrolyte, which enables the production of hard‐magnetic CoPt alloys. The authors also show that electroformed semi‐hard‐magnetic helical microswimmers can propel in viscous environments such as silicon oil in three dimensions and against gravity. Their manufacturing approach can be used for the fabrication of more complex architectures for a wide range of applications and can be potentially extended to any electroplatable material.

     

Testing of Thermal Barrier Coatings by Laser Excitation

Thermal barrier coatings (TBCs) are used to increase the operating temperature of land‐, sea‐, or air‐based turbines. As failure of the coating may result in serious damage of the turbine, reliable estimation of the lifetime is essential. Most experiments to assess the lifetime or to determine parameters for simulations of the behavior of TBCs are done by burner‐rig‐tests, where the operating conditions are simulated by cyclic heating of the surface and cooling of the backside of a coated sample. In this work a possibility is presented to do comparable experiments by heating the surface with laser irradiation instead of a burner. For this purpose a Nd:YAG‐laser with a maximum output power of 1 kW and a wavelength of 1064 nm is used. The laser spot can be moved by integrated optics across the sample surface to achieve homogeneous heating of the coating. Cooling of the backside is done by air. The temperature of the sample surface is determined by an infrared‐camera which also enables the possibility to detect failures in the coating via thermography. Additionally, acoustic sensors attached to the sample holder are used to detect failures in the sample. The investigated ceramic material (yttria stabilized zirconia) has a very low absorption coefficient at the used laser wavelength. Therefore, a pre‐treatment of the samples was needed to increase the absorption coefficient to be able to heat up the samples. In this paper, the experimental setup and first experimental results are presented.     

爆炸物检测SAW传感器膜材料研究进展

爆炸物检测SAW传感器的膜材料是国外目前研究的热点之一,综述了近几年这方面的研究状况.依据膜材料在检测中的作用,从3个方面进行了系统的阐述,包括膜材料的选择、制膜方法以及膜的表征;列举了大量国内外有关的最新工艺和研究进展,简要地分析了今后爆炸物检测SAW传感器膜材料的发展趋势和前景.