Corrosion-fatigue of additively manufactured Ti6Al4V.

Abstract

Additive manufacturing (AM) has been used to process complex one-of-a-kind patient-specific implants, along with on-demand manufacturing with innovative geometries. AM parts are more susceptible to fatigue failure due to inherent porosities than conventionally processed parts. This study investigates the high-cycle rotating bending fatigue behavior of laser powder bed fusion (LPBF) processed Ti6Al4V parts in as-processed and hot isostatically pressed (HIPed) conditions, and compares them to commercially available wrought Ti6Al4V. Ti6Al4V is widely used in orthopedic and dental implants due to its high strength-to-weight ratio, good biocompatibility, and excellent corrosion resistance. To understand the fatigue performance of Ti6Al4V parts, a custom cell was designed to fully immerse the fatigue samples in Dulbecco's Modified Eagle Medium (DMEM) for the duration of the test. The fatigue strength was normalized to the compressive yield strength, and it was found that as-processed samples had the greatest compressive strength but approximately half the relative endurance limit (10⁷ cycles) when compared to wrought and HIPed samples. This inferior fatigue performance of as-processed samples was attributed to porosity defects inherent to the AMed parts. However, it was found through fractography and energy-dispersive spectroscopy (EDS) analyses that these internal defects dominated the fatigue crack initiation in as-processed samples, making DMEM immersion have a minimal effect. The wrought and HIPed samples were susceptible to corrosion fatigue, showing a reduction in endurance limit of 9 % and 6 % in relative strength, respectively. This study highlights the need for in situ corrosion fatigue evaluation of additively manufactured load-bearing implants.