Laser Powder Bed Fusion (LPBF) processed Ti and Ti-hBN metal matrix composite: Microstructure evolution, Mechanical and Corrosion behavior

The hexagonal boron nitride (hBN) reinforcement was employed to enhance microstructural isotropy and the mechanical and electrochemical characteristics of pristine Ti. The ball-milling followed by the laser powder bed fusion (LPBF) process was investigated, and the optimal processing parameter window was identified to fabricate defect-free samples. The SEM analysis revealed the formation of a distinct boride network around the grain boundary and within the grain, influenced by hBN addition. SEM and EBSD analyses demonstrated pronounced microstructural anisotropy in the pure Ti sample along the scanning and build directions, with columnar and oriented grains that nearly transitioned to equiaxed grains in Ti-hBN, attributed to in-situ TiB 2 formation. TEM analysis further confirmed the localized detection of B and Ti traces, with an SAED pattern indexed to hexagonal TiB 2 along the [0001] zone axis. In contrast, the uniform distribution of N within the Ti matrix indicates the formation of an α(Ti-N) solid solution. The mechanical property evolution revealed higher hardness and strength in Ti-hBN than in Ti, accompanied by improved isotropy. Parallel to the mechanical properties, the lower corrosion rate from the Tafel fit and the higher polarisation resistance from the Nyquist plot highlight the improved corrosion resistance of the Ti-hBN. The boosted strength of the Ti-hBN composite is primarily governed by precipitation and solid-solution strengthening, supplemented by grain refinement and dislocation strengthening. These findings highlight the potential of LPBF-processed Ti-hBN composites as promising materials for advanced structural applications