Refined microstructure and ultrahigh mechanical strength of (TiN + TiB)/Ti composites in situ synthesized via laser powder bed fusion

Abstract

• (TiN + TiB)/Ti composites were in-situ synthesized via laser powder bed fusion with a near-full density. • Refined microstructure and ultrahigh mechanical strength were achieved in the printed composite as compared with the pure Ti. • The in-situ synthesis process of TiN/TiB precipitates and underlying strengthening mechanisms were investigated. Titanium matrix composites reinforced by titanium nitride (TiN) and titanium boride (TiB) were in-situ synthesized via laser powder bed fusion (L-PBF) using premixed boron nitride (BN) and titanium powders. The optimal BN content was determined as 0.5 wt%, and a near-full density was achieved with optimized process parameters. The microstructure of the printed composite consisted of α-Ti matrix doped with N, as well as nano-sized TiN and TiB precipitates. The ultimate tensile strength of the printed composite sample was enhanced by ∼85% from ∼590 MPa to ∼1100 MPa as compared with the pure Ti counterpart, whereas the elongation was reduced to ∼3%. This research provides insights into the additive manufacturing of metal composites with near-full density and enhanced mechanical strength.