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-C_G 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).

Keywords: SiC; UHTC; borides; induction HF-plasmatron; laser heating; oxidation; supersonic carbon dioxide jet.

Figure 1

Variation of the average surface temperatures of samples 1 (green) and 2 (pink) from IR pyrometer data (a) (inset shows the appearance of the samples in a water-cooled model under CO₂ plasma), as well as the temperature distribution (in °C) on the surface of these samples at specific moments of the test (b).

Figure 2

Appearance of samples in water-cooled copper model after cooling (a) and surface X-ray images before (green) and after thermochemical treatment (b): sample 1 (purple) and sample 2 in the central (red) and peripheral (orange) regions.

Figure 3

Raman spectra of the starting material, HfB₂-SiC-C_G (black), and the oxidized surface of samples 1 and 2 in the central and peripheral regions (points 1 and 2, respectively, marked in Figure 2a).

Figure 4

Microstructure of the oxidized surface of sample 1 in the central region according to SEM data: SE2 detector (a–c) in the medium atomic number contrast mode—ESB detector (d).

Figure 5

Microstructure of the oxidized surface at the edge of sample 1 from SEM data: SE2 detector (a–c) in mean atomic number contrast mode—ESB detector (d) and mapping of the distribution of Hf and Si atoms (e). Yellow arrows show examples of spherical bulges indicative of gassing processes.

Figure 6

Microstructure of the oxidized surface of sample 2 in the central region according to SEM data: SE2 detector (a–c) in the medium atomic number contrast mode—ESB detector (d). Yellow arrows indicate cracks between particles, green arrows indicate bulges.

Figure 7

Microstructure of the oxidized surface at the edge of sample 2 from SEM data: SE2 detector (a–c) in average atomic number contrast mode with the ESB detector (d). Yellow arrows indicate vertically protruding HfO₂ particles.

Figure 8

Cross-sectional microstructure of sample 1 (central region) according to SEM data: in-lens detector (a,d,g), SE2 detector (b,c,e,h), in contrast mode by average atomic number—ESB detector (f,i), acceleration voltage 1 kV (a,c–i), 20 kV (b).

Figure 9

Cross-sectional microstructure of sample 1 (periphery) from SEM data: in-lens detector (a,e), SE2 detector (b,d), in contrast mode by mean atomic number—ESB detector (c,f), acceleration voltage 1 kV (b–f), 20 kV (a).

Figure 10

Mapping of Hf, Si, O and C distribution in the cross section of sample 1 in the central (top) and peripheral regions (bottom) (a), as well as Raman spectra in the indicated local regions (points 1–5) of chipped samples from the central (b) and peripheral parts of the sample (c).

Figure 11

Cross-sectional microstructure of sample 2 in the central region according to SEM data: in-lens detector (a,b), SE2 detector (c–e), in medium atomic number contrast mode—ESB detector (f), acceleration voltage 1 kV (b–f), 20 kV (a).

Figure 12

Cross-sectional microstructure of sample 2 (periphery) from SEM data (in-lens detector), with an acceleration voltage of 1 kV (b–f) and 20 kV (a).

Figure 13

Mapping of Hf, Si, O and C distribution in the cross section of sample 2 in the central (top) and peripheral regions (bottom) (a), as well as Raman spectra in the indicated local regions (points 1–5) of the chipped samples from the central (b) and peripheral parts of the sample (c).