In-situ laser additive manufacturing of Ti6Al4V matrix composites by gas-liquid reaction in dilute nitrogen gas atmospheres

Processing titanium(Ti)-basedmaterials in high-concentration nitrogen gas (N-2) atmosphere is creditedwith reducing ductility/plasticity arising from the excessive formation of brittle agglomerated TiN. However processing these materials in dilute N-2 may reduce the risk. In this study, a novel method is developed for laser additive manufacturing of in-situ synthesized TiN and AlN co-reinforced Ti6Al4V matrix composites (NTMCs) by the gas-liquid reaction in low-concentration N-2 atmospheres. The manufacturing process of the NTMCs involves melting Ti6Al4V powders followed by laser-induced pyrolysis of N-2 near the melt pool. The process is facilitated by the reaction between the decomposed nitrogen and molten Ti6Al4V, dissolution and precipitation of nitrides, and formation of the composites layer-by-layer. The formation of the nitride precipitates was verified by XRD, SEM, EDS, and HR-TEM. Such in-situ synthesized nanoscale reinforcements exhibited good dispersion and strong interfacial bonding with thematrix alloy in the composites. Themicrohardness, 0.2% compressive yield strength, and ultimate compressive strength of the NTMCs significantly increased with increasing N-2 concentration in additive manufacturing; their maxima were 511 HV, 1721 MPa, and 2010 MPa, respectively, increased by 36.3%, 67.9%, and 16.8% from those of the Ti6Al4V alloy. The formation and strengthening mechanisms of the NTMCs were elucidated. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

A novel method for laser additive manufacturing of in-situ synthesized TiN and AlN co-reinforced Ti6Al4V matrix composites in low-concentration N-2 atmospheres is developed in this study. The formation of the composites involves reactions between decomposed nitrogen, molten Ti6Al4V, and nitrides layer-by-layer. The resulting nanoscale reinforcements exhibit good dispersion and strong interfacial bonding, leading to significantly increased microhardness and compressive strength of the composites.