Ceramic multilayer based on ZrB2/SiC system for aerospace applications.

The work of this PhD thesis is focused on the processing and characterisation of ZrB2/SiC based multilayer materials, produced by tape casting and sintered without pressure assistance for aerospace applications. The multilayer components were processed in order to be used as external part of a thermal protection system; because of they directly face the atmosphere, in order to withstand high temperature, high heat fluxes and oxidizing environment, they have to show good oxidation and thermal shock resistance, high emissivity, thermal management capability, suitable strength, stiffness and hardness. The development of materials was directed along three main concepts: SiC based multilayer system was developed for the back shield part of the re-entry vehicle which was moderately loaded; ZrB2/SiC composite multilayers showing different ZrB2:SiC ratio were mainly designed for the front shield where the operating condition should be more severe (that means both higher temperature and thermal loads respect to those expected for the back shield). Moreover, in the context of development of reusable TPS to be used for consecutive missions, hybrid multilayer with ZrB2/SiC composite layers in between SiC ones have been prepared: the aim was provide for the degradation of SiC/SiO2 external part inserting an underlying material showing good mechanical and thermal properties at the higher temperature (over 1700°C). These three kinds of ceramic multilayer were processed and characterized from mechanical point of view; short and long term oxidation resistance have been detailed investigated. Tests under re-entry conditions have been performed.