Ti6Al4V matrix composites fabricated by laser powder bed fusion in dilute nitrogen

In situ synthesised TiN reinforced Ti6Al4V matrix composites were fabricated via laser powder bed fusion (L-PBF) in an atmosphere of 10vol.-% N 2 and 90vol.-% Ar based on novel gas–liquid reaction between N 2 and Ti6Al4V melt pool. With lower laser energy density (LED), the microstructures of the composites mainly consisted of acicular α′ martensites, while the martensites were shortened and coarsened with increasing LED. The X-ray diffraction analysis demonstrated that the interstitial solid solution of N was formed in the Ti lattice. High-resolution transmission electron microscopy analysis confirmed the generation of TiN. The microhardness, yield strength, ultimate strength and plasticity of the composites initially increased and then decreased with increasing LED. The strengthening mechanisms of the composites were elucidated.