Comparative study of selective laser melted and spark plasma sintered Ti-6Al-4V with LaB6 addition

This study comparatively investigates the effects of lanthanum hexaboride (LaB 6 ) addition on the microstructure and mechanical properties of Ti-6Al-4V components fabricated by spark plasma sintering (SPS) and selective laser melting (SLM). Gas-atomized spherical Ti-6Al-4V powders were mixed with irregular LaB 6 powders (1.0 wt%) and consolidated using SPS and SLM, respectively. In both processes, LaB 6 partially decomposed into La 2 O 3 and titanium borides, including TiB and TiB 2 . The SPS-processed Ti-6Al-4V, with or without LaB 6 , exhibits a lamellar α+β structure. In contrast, the SLM-fabricated Ti-6Al-4V shows a fully acicular α′ martensitic structure, while the addition of LaB 6 transforms it into a mixed microstructure consisting of α′ martensite and α plates. Owing to the refined structure resulting from the high cooling rate inherent to the SLM process, the SLM-processed Ti-6Al-4V exhibits a higher ultimate compressive strength (1920 MPa) than its SPS counterpart (1540 MPa). The in-situ formation of La 2 O 3 and titanium borides effectively increases the yield strength of both SPS- and SLM-processed Ti-6Al-4V. However, the addition of LaB 6 also leads to a deterioration in ultimate compressive strength, attributed to the reduced plasticity caused by weak interfaces between undissolved LaB 6 particles and the Ti-6Al-4V matrix.