Papers by Author: Cengiz Kaya

Abstract: Recent developments in the processing, understanding and mechanical/thermomechanical properties of oxide fibre reinforced oxide ceramic matrix composites for high temperature applications are reported. Two dimensional composite plates and uni-directional tubular composite (so called mini-composite) specimens are successfully manufactured and their microstructure, matrix/ fiber interface as well as mechanical properties are examined. It is shown that the microstructural variations, such as porosity size and interface between fibre and matrix determine the fracture behaviour and high temperature performance of the composites. The optimised components produced are considered to be suitable for gas turbine applications.

Abstract: Electrophoretic deposition (EPD) has been demonstrated to be a convenient processing technique to fabricate composite ceramic coatings containing ordered arrays of carbon nanotubes. In this investigation, EPD was used to coat Ti6Al4V medical implants with hydroxyapatite (HA) layers reinforced with surface functionalized multi-walled carbon nanotubes (MWCNTs). The functionalization of MWCNTs by treating them with an acid mixture was successfully achieved in order to create functional groups on the MWCNT surfaces enabling them to be homogeneously dispersed in water. The surface treatment was also used to induce the adsorption of HA nanoparticles on MWCNT surfaces. Some critical issues, such as microcracking and peeling of HA layers after EPD, were effectively solved by the use of MWCNTs.

Abstract: A combined technique comprising electrophoretic deposition (EPD) and low-pressure infiltration was used for the fabrication of multi-layer woven mullite ceramic fabric reinforced alumina ceramic matrix composites (CMCs) for high temperature applications. Two different interface materials, NdPO4 and ZrO2 were synthesised and used for coating the woven ceramic fibres by EPD. The manufactured CMC components with suitable interface material are targeted for use at 1300-1400 oC in an oxidising atmosphere and have shown very good mechanical properties in multi-layer plate forms. Damage mechanisms, such as debonding, fibre fracture, delamination and matrix cracking within the composite plates subjected to flexural loading are analysed. It is shown that the composites with NdPO4 interface and 40 vol.% fibre loading have better mechanical properties in terms of strength and damage-tolerant behaviour. The final components produced are considered to be suitable for use as shroud seals and insulating layers for combustor chambers in aircraft engines.