Enhanced oxidation resistance at 1700 °C of Cf-ZrB2/SiC composites via NbB2/NbC layered coatings

Carbon fibre reinforced ZrB 2 /SiC composites, produced via slurry infiltration and hot pressing, were coated with metallic niobium by means of magnetron sputtering. The coated substrates revealed an average coating thickness of ∼13 µm (as-coated specimens). Vacuum annealing at 1800 °C in a graphite vacuum furnace induced the transformation of the coating to a layered NbC-NbB 2 system (annealed specimens). Oxidation experiments were carried out at 1500 °C and 1700 °C in controlled dry air with baseline material, as-coated, and annealed specimens. The results revealed the beneficial effect of the Nb coating in stabilizing and preserving B 2 O 3 even at 1700 °C, considerably slowing oxidation kinetics of the ZrB 2 /SiC matrix material and the incorporated carbon fibres. Thanks to the chemical compatibility between the coating and the UHTC substrate, and the good adhesion of the coating, these materials do not suffer from typical CMCs-related issues, such as coating spallation. The oxidation mechanisms were discussed in detail. • NbB 2 /NbC layered coatings were produced via magnetron sputtering on C f -ZrB 2 /SiC composites. • The annealing step is essential in guaranteeing the perfect adhesion between the coating and substrate. • The oxidation behaviour was similar at 1500°C but diverged significantly at 1700°C. • The coating promoted the formation of a compact Nb 2 Zr 6 O 17 mixed oxide and B 2 O 3 retention up to 1700°C.