S. Biamino (Sp), L. Camedda, M. Pavese, P. Fino, C. Badini, Politecnico di Torino (Italy)
Silicon carbide is a promising material for high temperature application because of its excellent mechanical
properties and resistance to high temperature corrosion.
The aim of this work consists in the processing of multilayer ceramics for application as thermal and oxidation
barriers requested to operate at very high temperature (up to 1900 °C) which are proposed as an economically
attracting alternative to the more recently developed TPSs based on CMCs and consisting of a CVD surface
coating of SiC and an internal panel made of 2D SiC/SiCf or SiC/Cf composite (fibres allows better thermal
conductivity along their direction and poor thermal conductivity thorough the panel thickness, due to the porosity
of the composite matrix).
A behaviour similar to that displayed by CMCs-based system can be achieved by using multilayer ceramics.
Specimens of multilayer SiC have been processed by slurry tape casting, stacking layers, de-binding and final
sintering treatment performed at a temperature in the range 2100-2250 °C.
Assuming that the thermal conductivity through the multilayer can be decreased by stacking some layers
exhibiting a certain amount of residual porosity thus preferentially driving the heat flux along the plane of each
single dense layer than along the thickness of the sample, we tested different ways of introducing porous layers.
Particularly three methods have been investigated: placing PVA at interfaces between SiC layers (by wetting SiC
tape surfaces with a solution containing PVA before stacking the layers); integrating in the multilayer ceramics
SiC layers with reduced content of sintering aids; integrating in the multilayer ceramics SiC layers containing
voids left by the burning-out of starch.
These samples were characterized in terms of microstructure and main mechanical properties. The passivating
behaviour of multilayer SiC, caused by the formation of a silica layer on the material surface, has been confirmed
by XRD and SEM-EDS characterization.