ceramics

T. Hanemann (a), (b) and J. Aroni (a)

(a) Forschungszentrum Karlsruhe, Institut f. Materialforschung III, D-76021 Karlsruhe, Germany
(b) Albert-Ludwigs-Universität Freiburg, Institut f. Mikrosystemtechnik (IMTEK), D-79110 Freiburg, Germany

Abstract

With respect to feedstock development for different ceramic injection molding techniques the influence of various process parameters during feedstock development was investigated systematically. First the dispersant concentration at the fillers surface was changed in a wide range. The impact on the particle size distribution was measured. Second the size and the geometry of the used stirrers for compounding in an unsaturated polyester resin as polymer matrix were varied. The resulting composite flow properties at a fixed solid load and different temperatures were determined experimentally using a cone and plate rheometer. Increasing dispersant amounts at the alumina surface lead to a change of the particle size distribution and to a significant composite viscosity drop. The use of different stirrers affects directly the composite viscosity as well as the flow behaviour to a certain extent.

K. Liu, J. Peirs, E. Ferraris, B. Lauwers, D. Reynaerts
Afd. PMA, Department of Mechanical Engineering, Katholieke Universiteit Leuven, Leuven, BE-3001, Belgium

Abstract

The Electrical Discharge Machining (EDM) behaviour and machining properties of advanced engineering Si3N4-based ceramic composites Si3N4-TiN are investigated and discussed in this paper. Two types of EDM machining configurations, micro-EDM milling and die-sinking EDM, are employed in the investigation. Relaxation type of pulse is used, and the performances of EDM process in the form of material removal rate, tool wear and surface quality are studied. These tests result in a performance comparison and a discussion on the ceramic composites material removal mechanism. The feature of material removal mechanism is characterised as chemical decomposition of Si3N4 and TiN at elevated temperature rather than melting/evaporation. The generation of nitrogen gas bubbles leads to a porous and foamy top surface structure. Due to the ideal mechanical and physical property of Si3N4-TiN ceramic composites, an application example - a turbine impeller -
as a crucial component in a micro power generation system is manufactured with obtained knowledge in both
machining configurations.

J.P. Gittings (1), C.R.Bowen (1), I.G.Turner (1), A.C.E.Dent, F.R.Baxter (1), (2) and J.B. Chaudhuri (2)

(1) Department of Mechanical Engineering, University of Bath,BATH, BA2 7AY.
(2) Department of Chemical Engineering, University of Bath,BATH, BA2 7AY.

Abstract

This paper studies the ac conductivity and permittivity of hydroxyapatite based ceramics (HA) at temperatures from room temperature to 1000ºC. HA ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of surface adsorbed water on conductivity and permittivity. Surface bound water was thought to contribute to conductivity for both dense and porous materials at temperature below 200ºC. At temperatures below 700ºC the permittivity and ac conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000ºC), bulk ionic conduction was dominant and activation energies are in the range of ~2eV, indicating that hydroxyl ions are responsible for conductivity.

V. Piotter, K. Plewa, J. Prokop, A. Ruh, H.-J. Ritzhaupt-Kleissl, J. Hausselt
Forschungszentrum Karlsruhe, Institute for Materials Research III P.O. Box 3640, 76021 Karlsruhe, Germany

Abstract

Although microsystems technologies products have been steadily launched worldwide markets the development and improvement of manufacturing processes suitable for medium or large-scale production is still one of the most important prerequisites.
A well-known technology to meet such demands is micro injection moulding which has already reached an industrial viable status for polymeric materials. Nevertheless, there is still a lack of methods for the processing of materials with a wider range of properties.
A promising option to close this gap, development of the so-called MicroPIM process to facilitate the fabrication of metal and ceramic micro components was started.
Presently, the smallest dimensions achievable are 25-50μm of part thickness or minimum structural details of less than 5μm. Theoretical densities of up to 99% were achieved depending on the particular powder applied. As further improvement, the technology to produce rotational-symmetric parts by making use of a special head spindle system has been developed.
To enlarge the application possibilities of MicroPIM further, micro two-component injection moulding enables, for example, the fabrication of micro components consisting of two ceramic or metal materials with different physical properties and, not less important, significantly minimises assembly expenditure.

Per Johander (a) , Urban Harrysson (b) , Ulrike Kaufmann (c), H.-J. Ritzhaupt-Kleissl (c)

a IVF Industrial development and production, Argongatan 30, 431 53 Mölndal, Sweden
b Fcubic Argongatan 30, 431 53 Mölndal, Sweden
c Forschungszentrum Karlsruhe, Institute for Materials Research III

Abstract

Layered manufacturing has mainly been used for prototype manufacturing in product development. Direct manufacturing of small components is very favourable due to the scaling effect. The number of components that could be manufactured in one batch grows by the square if the size of the parts is reduced to half. The ceramic material used is yttrium-stabilised zirconium. The structural information is printed by ink jet in powder layers of only 80 μm thickness. The actual part creation is done in a subsequent heat treatment process where a development process takes place. This is an advantage as the machine speed could be increased considerably compared to other layer manufacturing principles. The parts manufactured are impregnated with epoxy and the material properties are comparable or better than injection molded parts. The other option is sintering of the parts to full density. The sintering process has been studied and the shrinkage and material properties evaluated. A cost analysis has been performed comparing direct manufacturing of small batches of components to plastic mouldinginjection.