Oxidation of Ceramic Materials Based on HfB2-SiC under the Influence of Supersonic CO2 Jets and Additional Laser Heating

Abstract

The features of oxidation of ultra-high-temperature ceramic material HfB2-30 vol.%SiC modified with 1 vol.% graphene as a result of supersonic flow of dissociated CO2 (generated with the use of high-frequency induction plasmatron), as well as under the influence of combined heating by high-speed CO2 jets and ytterbium laser radiation, were studied for the first time. It was found that the addition of laser radiation leads to local heating of the central region from ~1750 to ~2000–2200 °C; the observed temperature difference between the central region and the periphery of ~300–550 °C did not lead to cracking and destruction of the sample. Oxidized surfaces and cross sections of HfB2-SiC-CG ceramics with and without laser heating were investigated using X-ray phase analysis, Raman spectroscopy and scanning electron microscopy with local elemental analysis. During oxidation by supersonic flow of dissociated CO2, a multilayer near-surface region similar to that formed under the influence of high-speed dissociated air flows was formed. An increase in surface temperature with the addition of laser heating from 1750–1790 to 2000–2200 °C (short term, within 2 min) led to a two to threefold increase in the thickness of the degraded near-surface area of ceramics from 165 to 380 microns. The experimental results indicate promising applications of ceramic materials based on HfB2-SiC as part of high-speed flying vehicles in planetary atmospheres predominantly composed of CO2 (e.g., Venus and Mars).

Short-Term Oxidation of HfB2-SiC Based UHTC in Supersonic Flow of Carbon Dioxide Plasma

“…Analysis of the microstructure of the bubbles preserved on the oxidized surface of the ceramic material has shown (Figure 8e,f) that there are 40-80 nm pores between the flat aggregates of the HfO 2 particles, probably bound from the inside by silicate melt. In general, the microstructure of the oxidized surface is close to that previously observed in our studies of the interaction of HfB 2 -SiC-based materials with supersonic flows of dissociated CO 2 [29] and air [31,32,60,61]. However, in the present experiment, a greater number of preserved bubbles and their remnants are present on the surface where silicate glass is preserved, whereas in previous work, due to higher thermal stress and longer exposure times, only craters were recorded at their rupture sites.…”

“…Only a slight increase in defect/porosity can be observed at the interface between the unoxidized material and the HfO 2 -SiO 2 layer (Figure 9c,d) with a thickness of less than 1 µm. This structure of the oxidized region is probably due to the fact that the exposure to a high-enthalpy CO 2 flow was stopped at the initial stage of oxidation of the HfB 2 -30vol.%SiC ceramics, since for a similar material composition in a previous experiment, characterized by a higher heat flux and exposure duration, the formation of a conventional multilayer structure was observed [29], including a depleted SiC layer.…”

“…The pressure in the test chamber was monitored by a pressure transducer Elemer AIR-20/M2-DA (NPP "Elemer", Moscow, Russia). The geometry of the holder in which the sample was fixed is described in detail in [29,39]. The sample was installed on the friction in the socket of the water-cooled calorimeter; the gap was filled with a flexible thermal insulation based on SiC and carbon fibre in order to minimize heat loss into the water-cooled holder.…”

“…Studies of UHTC's behavior in high-enthalpy carbon dioxide jets may be of interest for modeling the effects of Venus's atmosphere, which presents more demanding entry conditions than on Earth [26][27][28]. Previously, our team studied the behavior of HfB 2 -SiC material doped with 1 vol.% graphene under the influence of a supersonic CO 2 plasma jet, including additional laser heating [29]. It was found that in this case a traditional multilayer oxidized near-surface region was formed: the upper oxide layer HfO 2 -SiO 2 , and below the porous SiC-depleted layer, passing into the unoxidized volume of the ceramics.…”