Grain refining in additively manufactured titanium using boron nitride nanosheets

The functionalization of additive manufacturing (AM) powders with nucleating particles has the potential to alter the grain structure, and hence the mechanical properties of 3D printed structures. We have investigated use of hexagonal boron nitride (BN) nanosheets to modify the microstructure of Ti parts produced by laser-based powder bed fusion (PBF-LB). The components were 3D printed from commercially pure titanium (cp-Ti) powders coated with small amounts (1.5 vol% approximate to 0.77 wt%) of BN nanosheets. As a comparison, pure cp-Ti parts were also built under the same processing conditions. Small- and wide-angle X-ray scattering (SAXS-WAXS) analysis of the 3D printed test structures revealed that BN addition significantly refined the alpha-Ti grain size and randomized the alpha-Ti texture. It was observed that grain-refined Ti-BN samples were harder and more brittle than their pure cp-Ti counterparts. This research provides new insights for grain refining using functional powder feedstocks with relatively simple powder pre-processing, and may be applied more broadly in laser-based metal AM.