Coupling powder bed additive manufacturing and vapor phase deposition methods for elaboration of coated 3D Ti-6Al-4V architectures with enhanced surface properties

Abstract

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 NH3(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.