Fatigue behavior of porous biomaterials manufactured using selective laser melting

• Fatigue behavior of porous titanium made with additive manufacturing was studied.
• The strain vs. cycle number showed the three-stage pattern typical of porous metals.
• Higher porosity resulted in shorter fatigue life.
• Normalized S–N curves of materials were overlapping and conforming to a power law.

Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S–N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S–N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S–N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S–N curves. It is shown that the measured data points conform to the fitted power law very well, R2 = 0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (< 0.2) is lower than that of corresponding solid material (c.a. 0.4).