Materials Science Forum Vols. 825-826

Abstract: Due to an increasing use of composite materials in various applications and related open questions concerning structural health monitoring and damage detection, the realisation of function integrating lightweight structures with sensory properties is subject of numerous research activities. Main objective is the transfer of already in laboratory and prototype scale established methods for the integration of sensory elements on serial applications. Here, combining the previously separated processing steps sensor manufacturing, component manufacturing and sensor integration can help to make a significant step forwards. Therefore, as part of the activities in the Collaborative Research Centre/Transregio (CRC/TR) 39, a highly productive spray coat method based on the long fibre injection (LFI) process is developed, which allows the process-integrated manufacturing and embedding of novel piezoelectric sensor modules into fibre-reinforced polyurethane composite structures.Based on studies on the technological implementation of the newly developed process, theoretical and experimental studies for contacting and polarisation of the novel sensor elements are presented. In addition, the characterisation of the adhesion properties of thermoplastic films on the used fibre-reinforced polyurethane composites is part of the presented research to evaluate the possibility of integrating thermoplastic-compatible piezo modules for actuator applications.

Abstract: For the continuous and non-destructive structural health monitoring (SHM) of fiber reinforced plastics (FRP), a one-step integration of one-or two-dimensional strain sensors based on piezo-resistive carbon filament yarns (CFY) into textile reinforced structures of subsequent FRP components has been realized during textile-technological manufacturing processes. The two-dimensional alignment of the sensor layouts is realized by a special process-integrated warp yarn path manipulation (WPM). With suchlike manufactured semi-finished reinforcement structures, a functional model of a small wind turbine blade in glass-fiber thermoset composite design has been build up. Using the CFYs’ piezo-resistive effect, mechanical strains can be measured and visualized due to a correlative change of the carbon filaments resistance. Performing quasi-static load tests on the blade and additional test specimens, comprehensible results of the electro-mechanical behavior and spatially resolving capacity of different sensor integration lengths have been achieved. The performed tests demonstrate, that global and even local mechanical stresses within complex FRP components can be measured spatially resolved using the approach of textile technologically integrated textile sensors.

Abstract: In recent years fibre-reinforced polymers (FRPs) gained importance in a wider field of application due to such favourable properties as low mass and tailorable mechanical strength. However, water penetrating into the lightweight material can lead to a loss of shear strength and finally to a collapse of the whole mechanical structure. Consequently, the integration of humidity sensors into compound materials is able to promote the reliability via online condition monitoring. An innovative concept is the use of ceramics-polymer-composites, which are well suited for the integration into lightweight structures during inline production. Composite and polyimide based humidity sensors have been manufactured by flexographic printing and spin-coating processes. A 5-fold increase in sensor’s capacity related to a humidity change from 10 to 80 % r.h. manifests the outstanding sensitivity of manufactured composite sensors. In addition, FRP-integrated polyimide sensors showed a significant response to water penetration, whereby the capability of condition monitoring could be confirmed.

Abstract: Structural health monitoring is an important research topic in the field of fiber reinforced plastics (FRP). An effective way to detect defects or overloads in these FRP has still not been found. One way to monitor the actual state of FRP components is via integrated sensors. Integrating current standard sensors negatively affects the flux of force. Therefore investigations about integration methods of sensors in FRP components have been made. The integration of an optical fiber sensor into FRP profiles via a pultrusion process was investigated. It could be shown that the pultrusion process is suitable method for the integration of fiber optic sensors for strain measurements. Another investigated sensor principle was the integration of piezoelectric polyvinylidene fluoride (PVDF) fibers via a vacuum assisted process. The PVDF fibers were integrated into 3-point bending specimen and the piezoelectric effect was tested with and without polarization. The investigation showed that it is possible to measure the piezoelectric effect of PVDF fibers integrated into a 3-point bending test specimen. It could also be shown that carbon fibers can be used as textile electrodes for the measurement of the generated charge on the PVDF surface.

Abstract: In this contribution the authors will present a short summit of the state of the art in the field of nanostructured coatings and will then emphasise on the most recent developments concerning the possible changes in the coating architecture of CVD AlTiN, which can be achieved by changing some of the process parameters

Abstract: Diamond deposition on carbon substrates is difficult, because atomic hydrogen needed for the diamond growth, attacks the graphitic and amorphous carbon of the substrate. To reduce the etching effect, the duration till diamond layer formation should be short.By controlling the diamond deposition conditions, boron addition and seeding with diamond prior to the deposition, the formation of diamond coatings is possible.Diamond coated carbon substrates are of high interest for electrochemical applications because they show electrical conductivity and are chemically inert in a wide range. Boron doped diamond shows high overvoltage for hydrogen and oxygen and allows electrochemical reactions in water without decomposing it. Diamond was deposited on glassy carbon and electro-graphite.

Abstract: Cadmium coatings are used in aerospace and offshore industries for parts in corrosive environments. Since cadmium is a highly toxic heavy metal, it is subject to strong restrictions. Alternatives include Al-based alloys. The present work describes preliminary results for Cd substitution by using Al-Mn with 25 at.-% Mn deposited on 42CrMo4 steel by atmospheric plasma spraying (APS). The prepared alloy powder for the APS process was characterized by laser granulometry, SEM/EDX, and STA. A fraction with particle sizes ranging from 20 µm to 45 µm was used for the thermal spraying process. The APS coating and an Al reference sample were characterized by image analysis, Vickers hardness, and Standard Salt Spray (SSP) testing. The Al-Mn coating exhibits a significantly higher hardness in comparison to pure Al. In both cases, red iron corrosion did not appear during SSP testing. The Al coating was partially covered by a thick oxide film, whereas Al-Mn showed only moderate oxidation but lower adhesion to the substrate

Abstract: Service and downtimes of waste incineration plants generate high expenses for their operators. State of the art is to protect high corrosion exposed components by cladding them with a nickel based alloy. The welded overlay is 2-3 mm thick and very expensive. It needs to be repaired at each service interval. An alternative coating consists of a thermal sprayed multilayer of a nickel based bondcoat and a ceramic topcoat. Thickness and costs of this multilayer are assumed to be in the range of about 10% of the currently used coating. A solvothermal treatment chemically densifies the coating. This leads to a significantly lower porosity whilst improving cohesion and hardness properties. This innovative process leads to a self-healing layer caused by the high temperature waste gas exposition as the driving force.

Abstract: In this work, the oxidation behavior of Ti₂AlN coating deposited on nickel super alloy IN718 was investigated. The coating was obtained by DC-magnetron sputtering at 540°C and subsequent vacuum annealing at 800°C for 1h. The coating morphology as well as the chemical composition were analyzed using SEM, EDS and XRD, respectively. The XRD results revealed that the coating mainly composed of Ti₂AlN MAX phase. Cycling oxidation was performed at 700 °C and 800 °C in air. The XRD and SEM results proved the interaction between substrate and coating and the formation of the quaternary Ti₃NiAl₂N phase during oxidation at the interface. Due to the Ni diffusion towards the surface, the Ti₃NiAl₂N phase grew continuously and the Ti₂AlN phase decomposed gradually resulting in a coating failure. The results indicate that the oxidation behavior of the coating is essentially controlled by the interdiffusion of Ni from substrate into the coating.

Abstract: Aluminium matrix composites (AMCs) consisting of high-strength, age-hardenable aluminium alloys and homogeneously dispersed hard particles open up new possibilities in designing light-weight material based security related structures. The susceptibility of the matrix alloy to selective corrosion can be reduced significantly by anodic oxidation. A powder-metallurgical processed alloy AlCu4MgMn with hard particles and a commercial wrought alloy for reference were used for the investigations.In order to control the microstructure of anodic aluminium oxide (AAO) formed on AMCs, it is necessary to understand the formation mechanism and the influencing parameters. Therefore in a first run, the anodizing behaviour of matrix alloy was separated from the behaviour of hard particles. The AAO coatings show small growth rates on the matrix and the reference alloy accompanied by a complex pore structure which differs from the ordered vertical pore structure on pure aluminium. Depending on the type and the size as well as the anodizing parameters, the particles are either incorporated into the AAO coating unchanged or partly resp. completely oxidized. The AAO microstructure changes significantly in dependence of the anodizing parameters. It is shown that a technically relevant coating thickness can be achieved on AMCs by choosing appropriate process parameters.