Low cycle fatigue behavior of the beta-type titanium cellular structures fabricated by electron beam melting

Titanium alloy cellular structures possess a low elastic modulus comparable to that of human bone, while their interconnected pores facilitate bone ingrowth. These combined properties make them highly suitable as implant materials. For the long-term and safe application as human implants, it is crucial to thoroughly understand their fatigue properties. In this study, cellular structures of a β-type titanium alloy were fabricated using electron beam melting (EBM) with two different unit cell designs: rhombic dodecahedron (RD) and topology-optimized (TO). The aim was to fundamentally examine the effect of the cell geometry on the compressive and strain-controlled low cycle fatigue (LCF) properties. The results showed that the RD structure exhibited lower compressive yield strength but higher strain-controlled LCF properties compared with the TO structure. This difference is attributed to the varying contributions of buckling and bending in the struts of the cellular/porous structures. Specifically, a higher bending component was associated with reduced compressive yield strength but improved fatigue resistance under strain-controlled conditions. The RD structure demonstrated higher strain-controlled LCF performance due to its ability to sustain larger recoverable elastic strains at constant applied strain. Moreover, under comparable fabrication conditions (EBM), the β-type titanium alloy with RD unit cells exhibited better strain-controlled fatigue properties than the Ti-6Al-4V (α+β) alloy. The study highlights that both the cell shape and nature of the material significantly affect the LCF properties, and provide an important guide for the design of lightweight metallic cellular components with high LCF strength.