Olivier Malek

Carbon nanofillers for machining insulating ceramics

The implementation of ceramics in emerging applications is principally limited by the final machining process necessary for producing microcomponents with complex geometries. The addition of carbon nanotubes greatly enhances the electrical properties of insulating ceramics allowing electrical discharge machining to be used to manufacture intricate parts. Meanwhile other properties of the ceramic may be either preserved or even improved. For the first time, a silicon nitride/carbon nanotubes microgear is electrically discharge machined with a remarkably high material removal rate, low surface roughness, and low tool wear. This offers unprecedented opportunities for the manufacture of complicated ceramic parts by adding carbon nanotubes for new engineering and biomedical applications.

Pulsed Electric Current Sintering of Electrical Discharge Machinable Ceramics

Pulsed electric current sintering allows densifying most ceramics at high heating and cooling rates within very short times at elevated temperature, allowing to minimise grain growth. In order to fully explore the PECS potential, it is beneficial to flow the current through the powder compact by either using conductive powder or a powder compact that becomes conductive during densification. Although in-situ Joule heating of the powder compact allows very fast heating rates, it does not necessarily result in a homogeneous temperature distribution. The influence of the current flow on densification and the impact of electrical conductivity on the temperature distribution during PECS are illustrated. The PECS technology at present is limited to the fabrication of simple geometrical shapes. Electrical Discharge Machining (EDM) on the contrary allows production of complex shapes, providing the ceramic has a minimum electrical conductivity. Although EDM has no mechanical impact, the thermal impact is high and the EDM parameters should be carefully selected in order to optimise surface quality and component strength. During wire-EDM, the fast and rough initial cut has to be followed by a sequence of lower energy finishing cuts to optimise the surface quality. The case studies presented are B4C-TiB2 ceramics and ZrO2-based composites with electrically conductive phase addition.

Electrical discharge machining of composites

Abstract: In this chapter the electrical discharge machining (EDM) of ceramic composites is discussed. First, an introduction to the machining methods and the ceramic materials used is given. Then a detailed study of the electrical discharge behavior of three ceramic systems is given: ZrO 2 , Si 3 N 4 and boride-based composites. It is shown that material properties such as secondary phase type, composition and grain size have a substantial influence on the material removal mechanisms, surface roughness, material removal rate and flexural strength. Finally, the application of EDM on high-end ceramics is demonstrated by two case studies, namely a Si 3 N 4 -TiN turbine impeller and a B 4 C spray nozzle.