Self passivating behavior of multilayer SiC under simulated atmospheric re-entry conditions

In view of possible application of multilayer SiC as oxidation resistant and self-passivating component of re-usable thermal protection systems for space re-entry vehicles, this material was tested in a re-entry simulation chamber. A multilayer SiC laminate was processed by tape casting and pressure less sintering. Both the as-processed multilayer SiC and a similar passivated material, with a surface silica layer obtained by high temperature oxidation, were investigated. The microstructure and the mechanical features of these two materials were compared before and after the re-entry test. Microstructure was investigated by XRD, SEM-EDS, XPS and density measurements. Flexural strength, Young modulus and hardness were measured as well. Oxidation, occurring during re-entry test or resulting from the pre-test oxidation treatment, only affected the external part of the multilayer, while the material core was practically unchanged after oxidation. Every kind of specimen retained almost completely the original mechanical features after 100 re-entry simulations.