TiB reinforced lattice structures produced by laser powder bed fusion with high elastic admissible strain

Abstract

Triply periodic minimal surface (TPMS) titanium lattice structures produced by laser powder bed fusion (L-PBF) are promising for the future of bone tissue implant applications. However, growing concerns surrounding the cytotoxicity of Ti6Al4V and the high cost and poor wear performance of novel β titanium alloys limits their practical applications. Titanium matrix composites (TMCs) have an improved strength to stiffness ratio and wear resistance making them ideal for biomedical applications. In this work, a TiB reinforced TMC was produced in situ in L-PBF using 2 vol% boron nitride (BN) nanopowder addition with an 80% porous gyroid TPMS geometry. The lattices exhibited strength to stiffness ratio up to 2.5% with a modulus of 2.5 GPa and yield strength of 62.3 MPa, ideal for cancellous bone applications. TMC strengthening is facilitated by the high aspect ratio TiB reinforcement with best properties achieved after post process heat treatment, which increased the TiB aspect ratio and resulted in a quasi-continuous network microstructure with fine alpha Ti grains. Significant attention was given to optimisation of the L-PBF parameters to achieve a high solid density >99.5% and bulk porosity >77% close to the designed 80%. Direct contact cytotoxicity tests showed TMCs have promise as biomaterials, particularly after heat treatment which reacted residual surface BN.