Microstructure and fracture properties of open-cell porous Ti-6A1-4V with high porosity fabricated by electron beam melting

The open-cell porous Ti-6A1-4V structure with high porosity, intended to be applied as replacement for human cancellous bone, were fabricated by electron beam melting (EBM). Computer aided design (CAD) was applied to design porous structures using the same unit cell with different unit cell sizes from 2.5 to 4 mm, different ligament widths from 600 to 900 μm, and different pore sizes from 1200 to 1800 μm, in order to achieve high porosity of 80% in avoiding the stress shielding effect. In comparison with the CAD designs and the EBM samples, there were minor discrepancies in terms of pore size and ligament width, mainly a result of melting pool. The measured data on the Young's modulus and yield strength of the EBM porous samples can be predicted by the Gibson and Ashby model. All samples with high porosity were found to match well with cancellous bone, with Young's modulus of 2 GPa and yield stress of 31 MPa, effective to diminish the risk of stress shielding effect. For porous EBM sample with high 80% porosity, the work of fracture can increase from 15.9 to 47.6 kJ/m² with increasing ligament width from 600 to 900 μm.