RESEARCH ON ELECTROPHORETIC DEPOSITION IN HINDSIGHT AND FORESIGHT

Since the 1990’s my research group has published widely in the field of electrophoretic deposition with focus on the modeling of the process for coatings as well as for freestanding objects. The highlights of this research will be reviewed and the lessons learned, in particular with respect to operative mechanisms during EPD. In passing, some of the practical realizations will be illustrated such as ceramic laminates, which show (pseudo-)ductile behavior, functionally graded cutting tools, bioceramic implants with tailored nanostructure as well as functional ceramics with enhanced properties. Recent literature will be summarized as well, in order to formulate a vision for further research in the field

Manufacturing Ti-6Al-4V components by shaped metal deposition : microstructure and mechanical properties

The urge in aeronautics to reduce cost and time to flight of components without compromising safety and performance stimulates the investigation of novel manufacturing routes. Shaped Metal Deposition (SMD) is an innovative time-compression technology, which creates near-net shaped components layer by layer by weld deposition. Especially for Ti alloys, which are difficult to shape by traditional methods such as forging, machining and casting and for which the loss of material during the shaping process is also very expensive, SMD promises great advantages. Applying preliminary SMD parameter, four different tubular components with a square cross section and wall thicknesses of about 9 mm were built. The microstructure of the Ti-6Al-4V components consists of large prior β grains, elongated along the temperature gradient during welding, which transform into a lamellar α/β substructure at room temperature. The ultimate tensile strength was between 880 and 1054 MPa. The strain at failure was between 3.0 and 11.3 % for tensile testing parallel to the deposition plane and between 9.1 and 16.4 % perpendicular to the deposition plane. The micro-hardness (3.1 - 3.4 GPa), the Young's modulus (117 - 121 GPa) and the oxygen and nitrogen content are comparable to cast Ti-6Al-4V material

Ceramics in energy supply, transformation, transport, storage and usage

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Chemical reactivity of nickel and nickel-based alloys with a SiAlON ceramic

At the high cutting speeds typical for machining with ceramics and the concomitant high temperatures generated at the cutting edge and the rake face of the tool, chemical interaction between tool and workpiece material becomes the predominant mode of tool wear, To obtain more information concerning this chemical interaction mechanism, the chemical interaction of a beta'-O' SiAlON ceramic with pure nickel, Inconel 600, and Nimonic 105 is studied. The chemical reactivity was assessed by studying ceramic-alloy interaction couples after exposure at elevated temperatures (1100-1200 degrees C) for times long enough to be able to characterize the interaction layer. At 1200 degrees C, the beta'-O' SiAlON ceramic dissociates in contact with pure nickel, Silicon from the dissociation of the ceramic dissolves and diffuses into the nickel, whereas Al and O form Al2O3 particles. At the interface, a nitrogen pressure is built up, Inconel 600 is very reactive with the SiAlON ceramic, with the formation of molten silicides at 1200 degrees C, Cr3Ni2Si, Al2O3, and Ni31Si12 are the major reaction products, The reactivity of Nimonic 105 is less than that of pure nickel because of the formation of a continuous protective TiN layer at the ceramic-metal interface.status: publishe

Recent advances in the use of the impulse excitation technique for the characterisation of stiffness and damping of ceramics, ceramic coatings and ceramic laminates at elevated temperature

In this paper, recent advances in the impulse excitation technique (IET) are presented. IET is based on the frequency analysis of the resonant vibration of a gently struck test sample. IET has become a widely accepted standard method for the determination of accurate stiffness and damping values for monolithic materials. The non-destructive, non-contacting character of the technique has made it possible to implement IET in high temperature furnaces. Results are shown from tests on SiC samples up to 1450 degreesC. In addition, two new developments are reported. First, the measurement of the stiffness of small disk-shaped samples is discussed. A solution for the suspension of small disk samples in furnaces will be demonstrated. Further, the use of the technique for the investigation of layered materials will be discussed. The elastic properties of a symmetrically applied coating (coating/substrate/coating) can be deduced from the flexure resonance frequency of the composite body, given the properties of the substrate. Similar analytic solutions exist for multilayer systems composed of two materials, involving the flexure as well as the longitudinal resonance frequencies. An example will be shown of a Al2O3-Y-TZP/Y-TZP laminate consisting of 9 layers.status: publishe

A model for the transverse strain response of unidirectional ceramic matrix composites during tensile testing

A comprehensive micromechanical model relating the longitudinal stress and transverse strain of unidirectional fibre toughened ceramic matrix composites (CMCs) is presented. The model uses different cylindrical unit-cells to describe the composite throughout a tensile test and considers all relevant damage mechanisms. The proposed model takes into account the Poisson contraction of fibre and matrix, the relief of thermal residual stresses upon damage development, and the build-up of compressive radial stresses at the interface due to mismatch between fibre and matrix after debonding and sliding. Thus the modelled transverse strain response depends on a wide range of microstructural and micromechanical parameters. The approach is checked by comparing the experimentally observed and simulated response of a unidirectional SIC/CAS composite of which all constituent properties were determined experimentally. The agreement between experiment and theory is excellent. (C) 1998 Elsevier Science S.A. All rights reserved.status: publishe

Chemical wear mechanisms of innovative ceramic cutting tools in the machining of steel

It is commonly known that commercially available uncoated hardmetals, cermets and Si3N4-based inserts are not suitable for high speed and dry machining of steel because of the chemical incompatibility of the above mentioned materials at elevated temperatures. Based on thermodynamic equilibrium solubility calculations, a number of potentially suitable ZrO2- and sialon-based ceramic composites with 30 vol.% of TiB2, TiC0.5N0.5 or TiN were selected and manufactured by means of uniaxial hot pressing. The calculated chemical stability was verified by means of static steel-ceramic interaction couple experiments at elevated temperatures. Actual turning tests were performed and the: predictive capabilities of the chemical stability calculations and interaction couple results were evaluated. In this paper, thermodynamic stability calculations, abrasive wear susceptibility estimates and interaction couple experiments are used in order to elucidate the chemical compatibility of novel ceramic composites and steel and to predict the actual relative wear behaviour under those conditions in which chemical wear is the predominant mode of tool wear. (C) 1999 Elsevier Science S.A. All rights reserved.status: publishe