Enhanced Fatigue Characteristics of Topologically Optimized Biomedical Titanium Porous Structure by Selective Laser Melting

Abstract

Fatigue property is a critical consideration in the porous structures and most existing porous samples have unsatisfactory performance due to lack of structural optimization. This work finds that a topologically optimized structure of α-type commercial-purity titanium (CP-Ti) produced by selective laser melting presents excellent fatigue properties with an ultra-high normalized fatigue life of ~0.65 at 106 cycles at a low density of 1.3 g/cm3. All factors affecting fatigue have been studied, including material microstructure and porous structure stress analysis. The topologically optimized structure can effectively increase the fatigue life by reducing stress concentrations. The cyclic ratcheting effect plays a dominant role in fatigue crack initiation for the topologically optimized structure. As a results of twinning occurred during the fatigue process, the porous CP-Ti sample exhibits a higher ductility than the Ti-6Al-4V sample with the same structure, which delayed the fatigue crack initiation and therefore produced a higher fatigue life. In addition, the fatigue crack propagation rate was reduced significantly because of the large plastic zone ahead of the fatigue crack tip and the effect of fatigue crack deflection and bifurcation.