Influence of carbon content on the fabrication of ZrB₂-SiC-YSi₂ ultra-high temperature ceramics via reactive melt infiltration

To address the requirements for reusable thermal protection materials, ZrB₂-SiC-YSi₂ ceramics were developed for the first time using the reactive melt infiltration (RMI) technique. This study systematically examines the influence of carbon content on the densification and microstructural of ZrB₂-SiC-YSi₂ ceramics. The results demonstrate that with increasing carbon content, the bulk density initially increases and then decreases, while the open porosity decreases initially before rising. The maximum density of the ceramics is 3.80 g/cm³ and the open porosity is as low as 0.17 % when the graphite carbon content is 20 wt%. Further analysis of densification behavior and phase morphology showed that the residual Si ratio of ZSY-2 specimen decreased from 10 % to about 4.2 %, while the SiC ratio increased from 24.6 % to 29.8 %. The primary phases present in the ZrB₂-SiC-YSi₂ ceramics synthesized via the RMI process include ZrB₂, YSi₂, and SiC, with minor phases of Y₅Si₃C and free Si detected. Finally, the oxidation behavior of ZrB₂-SiC-YSi₂ ceramics at an oxidation temperature of 1550 °C was verified. Its main oxidation products are ZrO₂, Y₂O₃, SiO₂, ZrSiO₄, Y₂Si₂O₇, and yttrium silicate phase with excellent oxidation resistance is determined to be generated. These advantages demonstrate the significant potential of the RMI process in advancing the fabrication of ultra-high-temperature ceramics.