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Material models are the basis of most numerical simulations in mechanical engineering. In the field of elastic deformation, the material models are quite simple but plasticity and material destruction are very difficult to calculate. For developing and testing material models, an easily and quickly accomplishable test is necessary to verify the results. The scratch test is a good choice for the modeling of surfaces. For that test, a diamond tip (indenter) moves onto the material with either constant or progressive normal force. First, the material will be deformed elastically; with increasing force, plastic deformation occurs, leading to crack and chip formation, depending on the ductility of the material. The result can be directly compared to the simulation of this test.

Due to their outstanding specific mechanical and high-temperature properties, titanium aluminides exhibit a high potential for lightweight components exposed to high temperatures. However, their application is limited through their low wear resistance and the increasing high-temperature oxidation starting from about 750 °C. By the use of oxide ceramic coatings, these constraints can be set aside and the possible applications of titanium aluminides can be extended. The plasma electrolytic oxidation (PEO) represents a process for the generation of oxide ceramic conversion coatings with high thickness. The current work aims at the clarification of different electrolyte components' influences on the oxide layer evolution on alloy TNM-B1 (Ti43.5Al4Nb1Mo0.1B) and the creation of compact and wear resistant coatings. Model experiments were applied using a ramp-wise increase of the anodic potential in order to show the influence of electrolyte components on the discharge initiation and the early stage of the oxide layer growth. The production of PEO layers with technically relevant thicknesses close to 100 μm was conducted in alkaline electrolytes with varying amounts of Na2SiO35H2O and K4P2O7 under symmetrically pulsed current conditions. Coating properties were evaluated with regard to morphology, chemical composition, hardness and wear resistance. The addition of phosphates and silicates leads to an increasing substrate passivation and the growth of compact oxide layers with higher thicknesses. Optimal electrolyte compositions for maximum coating hardness and thickness were identified by statistical analysis. Under these conditions, a homogeneous inner layer with low porosity can be achieved. The frictional wear behavior of the compact coating layer is superior to a hard anodized layer on aluminum.

The potential of lightweight construction with composite materials is frequently not fully tapped. The reason is that the complex anisotropic properties are not fully reflected in the design. Instead, to be on the safe side, more or thicker material has been used. The numerical structural optimization is a way to calculate the optimal load-dependent material distribution or fibre orientation in complex fibre-reinforced components. This method was used to design the chassis of the ultra-lightweight, extremely energy-saving vehicle “Sax 3” of the student project “fortis saxonia” for the Shell Eco-marathon. Thus it has become possible to keep the weight of the chassis under 10 kg. This shows the high potential of the implementation of this optimization approach for fibre-reinforced composites.

This paper deals with the production of aluminium matrix composites through high-energy milling, hot isostatic pressing and extrusion. Spherical powder of the aluminium alloy AA2017 (grain fraction > 100 μm) was used as matrix material. SiC and Al2O3 powders of submicron and micron grain size (< 2 μm) where chosen as reinforcement particles with contents between 5 and 15 vol.% respectively. The high-energy milling process was realised in a Simoloyer mill (Zoz). The milling time was about 4 hours. Hot isostatic pressing (HIP) was used to convert the compound powder into compact material. The extrusion process realises semi-finished products with different geometrical shapes.

Fibre-reinforced ceramics have a higher fracture toughness compared to monolithic ceramics. Therefore, they are an attractive material for lightweight structural components in high-temperature applications. The liquid-silicon infiltration (LSI) process is a cost-efficient manufacturing route for fibre-reinforced ceramics consisting of three processing steps. A carbon-fibre-reinforced plastic (CFRP) composite is fabricated, which is converted in a porous C/C composite by pyrolysis. Liquid silicon is infiltrated to form a dense C/C-SiC composite. The performance of the composites strongly depends on the raw materials. The matrix chemistry in particular plays a key role in developing composites with tailored functional properties. The aim of this work is to investigate the mechanical properties and the failure behaviour of CFRP, C/C and C/C-SiC composites in dependence on the matrix chemistry. The composites are fabricated by the liquid-silicon infiltration process. Different phenolic resins as matrix polymers are used. The mechanical properties are characterized by bending tests and the failure behaviour is observed in-situ. Additionally, microstructural and fractrographic analyses are done. It can be shown that the formation of the microstructure and therefore the mechanical properties and the failure behaviour are strongly influenced by the matrix chemistry over all processing steps.

To produce silver-based contact materials such as silver/tin oxide different ways are possible. All usual technologies have their typical advantages and disadvantages. Expensive techniques are characterised by a very fine reinforcement distribution. Techniques with a high output quantity display a very limited particle distribution within the matrix material.

A comparative evaluation has been carried out on the microstructure of aluminum based SiC and Al2O3 particle reinforced composites produced by semi-solid direct squeeze forming of composite powder at temperatures of 635–645 °C. The study is focused on the distribution of the reinforcement and the intermetallic phases, the porosity content, the microstructure of the matrix phase, the interfacial state and mechanical properties. The particle size of the reinforcements, the time of the high-energy ball milling procedure for the fabrication of composite powder and the semi-solid forming temperature had a strong influence on the quality of sample in terms of distribution of reinforcement and interfacial interaction. Ball milling improves the interface formation between reinforcement and matrix and influences the remelting behaviour. Increasing ball milling time and decreasing semi-solid forming temperature with isothermal holding time resulted in relatively homogenous microstructures and in a reduced amount of interaction between SiC and metal matrix. Best results were obtained for 5 vol.% SiCp composites after 3 h ball milling, semi-solid formed at 635 °C and held for 10 min.

The use of embedded sensors and actuators for condition assessment of machines and structures is on rising demand [1]. The load monitoring of parts made of composite materials, known as structural health monitoring, is of growing interest. Certainly, composite parts with high demands on safety and a long economic life-time, e. g. parts in airplanes and blades of wind turbines, will be equipped with strain- and impact-sensitive sensors in future. The monitoring will lead to a better understanding and a safer application of composite materials. Different types of sensors based on different physical effects are available.

Metal and ceramic materials were sprayed on polished steel and iron substrates using atmospheric arc (nickel, molybdenum) and plasma (Al 2 O 3 , ZrO 2 -7Y 2 O 3 ) spraying. The bonding quality at the substrate-coating interface depends on the size and depth of the contact zones. The chemical-metallurgical interactions (diffusion, reactions) between the sprayed particles and the metal substrate as a function of the properties of the sprayed materials, contact temperature and solidification time were analysed. Higher contact temperature and longer interaction time for spraying of metals result in better bonding. Moreover, oxidation of the metal substrate to a limited degree by spraying of oxides allows one to improve the bonding quality. It is possible to correlate the results of microscopical investigations of the interface phenomena with the results of quantitative measurement of the bonding tensile strength.

Electroplated composites with incorporated nanoparticles become a key material in the fabrication of microsystem devices. A good survey of composites with nickel matrix is given in [1]. Electrodeposition of alumina particles (13 nm diameter, content around 1 Wt %) in nickel from an acidic electrolyte has been investigated using a nickel sulfamate bath with a particle loading of 10 g/l. Direct current (DC) deposition was compared to pulse-reverse plating (PRP) which can facilitate higher amounts. Details are given in [2]. Materials properties depend on the particle distribution, their bonding to the matrix and their influence on the microstructure of the matrix which has been characterized by TEM, STEM, SEM and EBSD.

Composites based on the nanocrystalline aluminum alloy EN AW-2017 (3.9Cu, 0.6Mn, 0.7Mg, bal. Al, wt.%) and reinforced with 5 and 15 vol% SiC and Al2O3 particulates were successfully produced by high-energy ball milling process (HEM). The cellular structure of the CuAl2 intermetallic phase initially present in the matrix and forming a net at the grain boundaries is fully destroyed and distributed along the deformation axis after 2 h milling. It was found that reinforcing matrix alloy with fine Al2O3 particles (-22 + S mu m) slightly accelerates the milling process in contrast to using coarse SiCp (-55 + 25 mu m). The results indicate that the particle size of the SiCP, Al2O3p and CuAl2 was refined greatly after high-energy ball milling. However, it is clear that the reinforcing particle size distribution for both type of reinforcing particulates showed also a broad range of particle size even after the longest period of milling. Based on the X-ray line broadening analysis, namely the Williamson-Hall method, the crystallite size of the both type of composites was reduced to below 45 nm. (c) 2007 Elsevier B.V. All rights reserved.

This paper reports on the use of Auger electron spectroscopy (AES)/ depth profile analysis for the investigation of plasma-sprayed coatings. Prior to spraying the St 37 substrates are heated to 300 °C or 500 °C for ceramic or metallic layers, respectively. Studies of the starting materials and of the interfaces are important if the adhesion mechanism is to be understood. Therefore the initial components—the unheated and heated substrates and the powder particles NiCrAl, Al2O3 and ZrO2-7.25Y2O3—are analyzed. Depth profiles obtained from two coatings St 37/NiCrAl and St 37/Al2O3 show the influence of plasmaspraying on substrate surfaces and sprayed particles. Plasma-spraying mainly causes a decrease of superficial carbon contamination for both coating layers. In the case of St 37/NiCrAl incorporation of carbon in the sprayed layer is observed. The whole layer is almost completely oxidized except for some areas where substrate and particle material are present. It is assumed that these areas are identical with so-called adherence zones.

Composites are materials with an increasing importance for the industry. A newly developed method for fabrication of fibre-reinforced metal matrix composites permits the production of composites with metal or ceramic fibres by thermal spraying. An improvement of coatings properties and the removal of flaws by post treatment is possible. This paper presents the thermal treatment by laser beam, electron beam and hot isostatic pressing (HIP) process and the mechanical treatment by shot peening.

Co–doped ZnO nanoparticles were synthesised by combustion method using polyvinyl alcohol and zinc nitrate. Both X–ray diffraction (XRD) and selected area electron diffraction (SAED) analyses showed the single phase of hexagonal structure (PDF2 card: 01–070–8072) in all the samples. Transmission electron microscopy (TEM) and HRTEM images show that most of the particles have spherical shape and their grain size is ranging from 10 nm to 60 nm in diameter, which depended on both the Co ratio and the annealing temperatures. Energy–dispersive X–ray (EDX) spectrum analysis showed the proportion of elements in the nanoparticles in accordance with the original composition. The photocatalytic activity of samples was studied by measuring the decomposition of methylene blue in aqueous solution using UV–VIS spectroscopy. The results showed that the photocatalytic ability to decompose methylene blue reached 70% with ZnO and 98% with Zn0.97Co0.03O samples after 150 min of irradiation.

Thermal sprayed coatings are used in various applications often dedicated to corrosion and wear protection.Poresand other coating imperfections reduce corrosion and wear resistance and/or necessitate higher coating thicknesses. To improve the quality of thermal sprayed coatings, various post-treatment processes can be used. Characterisation of the efficiency of sealing was studied by metallographic examination andcomparative investigation of the corrosion and wear behaviour of the thermal sprayed coatings used with and without sealing and also by measuring the insulation resistance of the coating system. The results differ among the sealants. It is possible to remove the sealants from the coatings by mechanical treatment. Corrosion tests of the sealants demonstrate their efficiency in closing the interconnected pores and, consequently, preventing corrosion.

Two Focused Ion Beam based transmission electron microscopy (TEM) thin film preparation techniques are introduced. One is dedicated to the preparation of single fibres, the other to fibre/matrix interfaces of fibre reinforced composites. Due to their thin film quality, reliability and predictable processing times both techniques are suited for routine applications in material science like TEM studies of fibre microtextures and fibre/matrix interfaces. Exemplarily they are applied to Carbon Fibres and Carbon Fibre reinforced Carbon Matrix Composites (C/C). The achieved preparation standard in both cases is substantiated by TEM investigations.

The preparation of thermally sprayed, dense, Si3N4-based coatings can be accomplished using composite spray powders with Si3N4 embedded in a complex oxide binder matrix. Powders with excellent processability were developed and produced by agglomeration (spray drying) and sintering. Optimization of the heat transfer into the powder particles was found to be the most decisive factor necessary for the production of dense and well-adhering coatings. In the present work, different thermal spray processes such as detonation gun spraying (DGS), atmospheric plasma spraying (APS) with axial powder injection, and high-velocity oxyfuel spraying (HVOF) were used. The coatings were characterized using optical and scanning electron microscopy (SEM), x-ray diffraction (XRD), and microhardness testing. The wear resistance was tested using a rubber wheel abrasion wear test (ASTM G65). In addition, thermoshock and corrosion resistances were determined. The microstructure and the performance of the best coatings were found to be sufficient, suggesting the technical applicability of this new type of coating.

Molybdenum silicides have the potential as protective coatings for high-temperature applications because of their high melting point and their high-temperature oxidation resistance. Reinforcing MoSi2 with SiC shows an improvement of its low toughness at room temperature and low creep resistance at temperatures above the brittle-ductile transition temperature of approximately 700-1000 °C. A new kind of powder processing was used to produce MoSi2 and MoSi2-SiC as a feedstock for thermal spraying. Mixtures of the elemental powders, molybdenum and silicon, were prepared by milling and subsequent heat treatment to get highly dispersed, pre-reacted powders. As high-energy milling equipment, a planetary ball mill was used to prepare the powders. In the case of reinforcement, SiC was mixed to the pre-reacted MoSi2 at the end of the milling process, that means before heat treatment. On these as-milled powders, X-ray diffraction characterization (XRD), scanning electron microscopy (SEM), electron probe micro analysis (EPMA) and determination of the oxygen level were carried out. Vacuum plasma spraying has been used to deposit the powders onto a carbon steel substrate. Evaluated coating characteristics were the microstructure (SEM), phases (XRD), EPMA, oxygen content, microhardness and surface roughness. Tests at high temperatures will be considered in future work.

High Velocity Oxygen Fuel (HVOF) spraying established itself as an effective method in addition to the conventional thermal spray processes within a very short period. Self fluxing nickel alloys, cermets (e.g. WC-Co / Cr3C2-NiCr) as well as oxide ceramic coatings have proved themselves suitable for wear protection applications. Weight reduction, the care of resources and the increase of efficiency for structural components leads to the substitution of customary hard particles. Titanium carbide (TiC) characterizes itself on account of the material features such as the high hardness, the high melting point, the high strength and the low density for the substitution of conventional carbides. The Self Propagating High Temperature Synthesis (SHS) is a suitable process for the production of composite powders. The powders produced by SHS show a high carbide content, which is finely distributed with an almost stoichiometric composition of the TiC inside the powder particles. The carbides are protected against dissociation and oxidation during the thermal spray process by a complete velum of matrix alloy. The current investigations deal with the wear resistance of TiC-composite coatings produced by HVOF compared to conventional wear resistant coatings. The investigations contain the analysis of the microstructure by optical and scanning electron microscope (SEM) and the measurement of the microhardness of the deposited coatings. Special attention is drawn to the interface between the hard particles and the matrix alloy. The optimized coatings are tested with different wear tests, such as Taber-Abraser test, sliding and oscillating wear test and are compared with common wear resistant coatings in order to underline the high potential for different wear applications. Moreover an additional corrosion test (salt fog test) is carried out with regard to the corrosion resistance of the different matrix alloys.

Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

This work evaluates the potential of using new competitive powders of Fe/TiC system for plasma spraying of wear resistant coatings. To improve coating properties, Cr and Ni were added to the iron matrix. The results of complex investigations of plasma coatings from such materials are presented.

Thermal spraying of silicon nitride has been considered impossible because the high temperatures involved lead inevitably to decomposition/oxidation of the material. To address these issues, improved silicon nitride-based powders were developed, two of which have been tested as reported in this paper. The powders were applied using low pressure plasma spraying (LPPS) and the resulting coatings characterized based on microhardness, adhesion, and cohesion strength. Phase transformations of the powders during spraying were also investigated and preliminary optimization strategies by statistical variation of plasma spray parameters were tested.

For reasons of the decrease in weight in the industry light cage design materials like aluminum alloys are frequently used. Because the wear resistance of aluminum alloys and/or aluminum generally is not sufficient, an increased wear resistance can be reached by means of particle reinforced aluminum coatings. The installation of ceramic reinforcing components (for example oxide particles) in the ductile metal matrix brings an essential improvement of the wear resistance particularly with regard to abrasion and short time fatigue wear. The results presented in the paper refer to research works concerning thermally sprayed Al - coatings with Al2O3- and SiC - particles as reinforcement components by vacuum plasma spraying.

T HERE was a mistake in Fig. 8 of the original article. The thermogravimetric analysis of the uncoated fibres was assigned to the wrong time scale and this gave rise to incorrect assignments of oxidation temperatures. The correct diagram is shown below. Taking the corrected diagram into account, the following passages in the text need to be replaced. In the abstract, the last two sentences need to be replaced by: The oxidation onset temperature was 630°C for both uncoated fibers and fibers coated with a 30-nm-thick layer of alumina. The oxidation onset temperature increased gradually with increasing coating thickness up to 660°C at a thickness of 120 nm.

Metallic and ceramic materials were sprayed using atmospheric arc (Ni and Mo on mild steel and Fe) and plasma (Al2O3 on NiCr20 substrate) spraying techniques. The aim of the investigations was to analyse the interfacial phenomena and particle microstructure and morphology. The phase composition of sprayed particles and substrates in the interface area was investigated by optical and electron microscopical (SEM, TEM) methods. The bond quality was also determined by bond strength measurements. It is possible to correlate the results of microscopical investigations of interface phenomena with results of quantitatively measured bond strength of plasma sprayed Ni coatings.

With the aim of simulating the thermo-elastic behaviour of a slide bearing with a sleeve made of woven fabric ceramic composite material, a new approach is used to determine the material properties of the composite. Therefore a small cutout of the fabric pattern was discretised with the Finite-Element Method (FEM). The properties of the woven roving part of the model come from the well-known methods for computing unidirectional composites. The model also allows for describing porosity and determining materials behaviour more accurately than other approaches. The calculated properties have been applied to another FEM model to simulate the thermo-elastic behaviour of the bearing, combining a steel bearing box and a Ceramic Matrix Composite (CMC) bearing sleeve. The main problem arises from the different thermal expansion coefficients of both materials. In the heating stage, the bearing surface changes its shape. Without constructive changes resulting from the simulation, the dissipation loss rises and leads to galling of the bearing. The article shows that the deformation can be predicted by means of the developed model.

Investigations of residual stresses have been carried out on unidirectionally carbon fibre reinforced aluminium using X-ray diffraction. It was found that the carbon exists in compression parallel to the fibre axis and in tension perpendicular to the fibre axis after the fabrication of the MMCs by a liquid infiltration process. Furthermore, it was observed that the intermetallic phase Al3Ni was in tension (+ 100 MPa) parallel to the fibre axis and in considerable residual compression (– 400 MPa) perpendicular to the fibre axis.

Oxide-bonded silicon nitride (OBSN) powders have been developed to address thermal spray problems associated with high temperatures. This paper examines how such powders perform when applied via detonation gun (DGS) and atmospheric plasma spraying (APS) with axial powder injection. All coatings were characterized using optical microscopy and X-ray diffraction with additional tests being performed on DGS coatings. For the first time, relatively dense Si3N4-rich coatings with an oxide binder phase were produced, and some of the DGS coatings were found to be sufficiently wear resistance for industrial use.

The thermal behaviour of variably separated flax and hemp fibres was characterised by means of thermogravimetric and differential scanning calorimetric analyses. Reference measurements of cellulose served to describe the degradation behaviour. Furthermore, thermoanalytic investigations on polypropylene were carried out to evaluate the thermal stability and the respective activation energy of the materials. The results prove the thermal stability necessary for the consolidation process of composite materials.