Abstract
In order to investigate the behaviour of B 4C coatings under thermal loading, a variety of substrates (fine grain graphite, carbon-carbon composite and the molybdenum alloy TZM) was covered with a coating of B 4C by low pressure plasma spray in an inert gas atmosphere. The thickness of the coating was varied between 125 and 250 μm. Mechanical tests proved good adhesion of the B 4C layer on all substrates. Tiles of the coated materials, 50 × 50 mm 2 and 50 × 25 mm 2 in size, were then exposed to high thermal fluxes in an ion beam test facility. The power densities applied on the specimens was varied between 3 and 10.5 MW/m 2 at pulse lengths up to 10 s (passively cooled specimens only). During thermal loading the surface temperature of the specimens was registered by means of optical pyrometers. Additionally, surface modifications of the specimens were observed with a video camera, and each pulse was recorded on tape. The results showed that already at surface temperatures below 2000°C crack formation in the B 4C coating and delamination occurred in particular for thick coatings (approximately 250 μm in thickness). On graphite substrates no melting of the B 4C-layer was observed up to more than 2100°C (melting temperature of B 4C ≈ 2400°C).
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