A critical analysis of the parameters affecting the oxidation behavior of ultra-high-temperature diboride ceramics

In the last few decades, research on the processing and properties of ultra-high-temperature ceramics (UHTCs) has generated a substantial base of knowledge and left several unanswered questions. There is a large scatter in the literature data associated with the processing of UHTC borides prompting the non-reproducibility and non-uniformity in the microstructure and, thus, desired properties. Herein, the data on the oxidation behavior of UHTC borides ubiquitous in the entire literature are analyzed to understand the effect of composition, sintering parameters, densification, grain size, and oxidation conditions. A conjunction of graphical methods has been utilized to converge the scattered data and correlate the effect of variables and testing environment on the oxidation behavior. It was concluded that high densification (>95%), large grain size (∼8 μm), and 20–30 vol.% of Si-containing additives (SiC, Ta₅Si₃, and TaSi₂) could augment the oxidation resistance. The study elucidates that oxide scale thickness should be preferred over mass gain in future studies as a metric for measuring oxidation. The analysis presented here will allow the UHTC community to optimize diboride materials' design for hypersonic applications. The developed database on the oxidation performance of diborides will also transfer knowledge beyond the memory banks of the experts in the field. Furthermore, well-structured databases such as the one developed herein could be employed in data-driven approaches to optimize the design and manufacturing of ultra-high-temperature materials in an efficient scheme.