EVALUATION OF COATED HEAT SINK MATERIALS FOR FUSION-RESEARCH

Coatings applied to copper and graphite have been thermal shock tested up to 7.5 kW/cm2 for pulses up to 1 sec in length, using 10 keV electrons. Plated nickel, iron, gold, and a carbon coating applied with a glow discharge process on copper survived up to approximately the melting point of the copper without debonding. Plasma sprayed tungsten behaves about the same as plated coatings. Both ion vapor deposited carbon and plasma spray deposited boron carbide failed from brittle fracture at comparatively low power densities (4.5 kW/cm2 at 0.25 sec and 0.1 sec respectively). The results show that for thin coatings (Δt < 0.2 mm), failure occurs when the surface temperature exceeds either the melting point of the coating or the substrate. Only a laminated thermal insulating coating can stand off a significant temperature difference (> 500°C) but is subject to brittle failure at much lower heating rates than for uncoated material. Fatigue tests on the glow discharge deposited carbon and plasma sprayed tungsten showed no serious failures for 1000 cycles at > 3.7 kW/cm2 for 0.5 sec pulses on the carbon coating and incipient failure on the tungsten coating. © 1979.