Microstructure and mechanical properties of open-cell porous Ti-6Al-4V fabricated by selective laser melting

The open-cell porous Ti-6Al-4V structure, intended to be applied as replacement for human cortical and cancellous bone, are fabricated by selective laser melting (SLM). The computer aided design (CAD) was used to design porous structures in various porosity levels from 40% to 80% and with pore sizes from 600 to 1000 μm, in order to fit the bone-tissue in-growth. The SLM porous samples with 40% to 70% porosity matched well with the CAD structure, but the 80% porosity one was found to be difficult to achieve the design. In comparison with the CAD structures and the SLM samples, there are minor discrepancies in terms of pore size and ligament width, mainly a result of laser beam broadening. To achieve more precise SLM porous morphologies, further reduction of powder size and laser beam diameter would be necessary. The measured data on the Young's modulus and yield strength of the SLM porous samples can be roughly estimated by the Gibson and Ashby model. The sample with 67% porosity was found to match best with human bone, with Young's modulus of 15 GPa and yield stress of 129 MPa, preventing from the risk of stress shielding effect.