Mechanisms of TiB2 and graphite nucleation during TiC–B4C high temperature interaction

Abstract

Reactive hot pressing of TiC-B4C precursors was undertaken at 1800 ℃ to produce TiB2 with carbon inclusions. Atomic mechanisms of titanium diboride nucleation, as well as spongelike carbon inclusions and submicron platelets of graphite precipitation has been investigated. Precursor grain size, green body composition and synthesis time were varied to analyse phases transformation. Boron from B4C grain sublimation is shown to result in carbon-based foam formation. Ab-initio calculations confirm that the boron atoms accumulation on (111) TiC plains leads to tensile stress. The developed stress cleaves TiC grains and enhances further reaction. Most of carbon expelled from TiC during its transformation into TiB2 forms graphite platelets.

Thermal conductivity and thermal shock resistance of TiB2-basedUHTCs enhanced by graphite platelets

“…6). Similar particles were also observed inside the graphite areas remaining after B 4 C decomposition during TiC-B 4 C interaction [41]. As is shown in [39], both silicon carbide and titanium diboride appear in TiC-B 4 C-Si powder mixture at temperatures below 1200°C.…”

“…Titanium impregnation creates some TiB 2 inside the foam [41]. As silicon melts, the interaction with carbon intensifies and the process of SiC formation approaches its conclusion.…”

Reactive sintering of TiB2-SiC-CNT ceramics

“…Chornobuk et al [18] created TiB2-SiC-C composites via hot pressing of a TiC-B4C-Si precursor powder mixture at 2150°C for 8 min. Recent investigations of the TiC-B4C high temperature interaction [19,20,21] however showed that the reaction can be finalized in 1-2 minutes at 1800°C.…”

Reactive hot pressing route for dense ZrB2-SiC and ZrB2-SiC-CNT ultra-high temperature ceramics

“…3b, 3c) that the amount of reaction product increases during the densification plateau. It was shown previously [32] that boron sublimates from boron carbide above 1400 °C and the sublimated boron interacts with ZrC crystals. Combined with the melting of the remaining silicon at 1414 °C, this allows for an efficient reaction continuation and second densification step.…”