We propose an innovative process coupling powder bed additive manufacturing by Electron Beam Melting (EBM) with Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) to develop 3D Ti-6Al-4V structures covered with AlN coating. Despite of the high reactivity of Ti-6Al-4V with nitrogen, thick ( 10 µm) and conformal AlN films are deposited by CVD on Ti-6Al-4V substrates with high surface roughness. An AlN under-layer deposited by ALD is necessary to mitigate the reaction between Ti-6Al-4V and the nitrogen precursor NH 3(g) and to limit the formation of brittle titanium nitride phases. We have thus achieved an adherent coating without any modification of the Ti-6Al-4V microstructure at the core of the substrate. We show that a 7 µm thick AlN coating is efficient in protecting Ti-6Al-4V against cyclic oxidation at 650°C for at least 650 h. This study opens new opportunities for the design of coated 3D Ti-6Al-4V structures for use in high temperature oxidizing environments.

No abstract