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% ≈ 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 α-Ti grain size and randomized the α-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. • 0.77 wt% of hexagonal BN nanosheets was added to titanium in laser-based PBF. • The average size of α laths was reduced from 3.1 μm × 1.1 μm–0.46 μm × 0.15 μm. • According to SAXS-WAXS, Ti-BN displayed a randomised texture in the α grains. • Vickers hardness increased from nearly 200 HV to more than 350 HV • Unoptimized printing parameters caused the Ti-BN parts to crack prematurely.