Effect of TM-Si2 on the Oxidation behavior of ZrB2-composites

Zirconium diboride (ZrB2) is one of the most investigated compounds in the ultra-high temperature ceramics (UHTCs) class of materials, thanks to its unique combination of chemical and structural properties and its potential employ in aerospace industry. One of the drawbacks of borides is their critical oxidation resistance that induces the formation of a porous ZrO2 scale and a borate-glass which tends to vaporize above 1000°C. Silicon carbide (SiC) is the secondary phase generally added to boride matrices up to 30 vol%, due to its ability to form a more stable borosilicate glass on the surface upon exposure to oxidizing environments. Other strategies to improve the oxidation performance of ZrB2 foresee the addition of dopants capable of modifying the glass properties or even those of the solid oxide formed. In the present study, several transition metal disilicides, TM-Si2, were added to a ZrB2 matrix in order to investigate their effect on the oxidation performances of this boride. The additives object of this study include TaSi2, WSi2 and MoSi2. This study presents the microstructure evolution of a series of ZrB2 composites, from the as-sintered state and upon oxidation in the 1500 - 1800°C temperature range, and correlates it to the basic phenomena occurring at the various temperatures. Transmission electron microscopy enabled to disclose microstructural features never observed before.