A Comparison of Stress Corrosion Cracking Susceptibility in Additively Manufactured Ti-6Al-4V for Biomedical Applications

Abstract

Additive manufacturing (AM) is quickly becoming a viable alternative to manufacture metallic materials used in the biomedical industry. Since as-built AM materials present different microstructures and show different material properties compared with their wrought counterparts, the assessment of previously well-understood wrought Ti-6Al-4V (TAV) material properties need to be revisited for AM parts. Historically, wrought TAV alloys have shown little, if any, sensitivity to stress corrosion cracking (SCC) in in vitro studies simulating physiological conditions as long as aluminum and oxygen content is kept within standardized limits. For AM materials, the alloy powder is often sieved and reused multiple times. Recent studies have shown that reused powder may contain increased oxygen concentrations compared with new powder. Because increased oxygen concentration was a known predictor of SCC susceptibility in wrought titanium alloys, the SCC susceptibility of AM TAV parts manufactured from new and reused powder batches needed to be assessed. The first objective of this research was to characterize new and reused (e.g., previously used for several laser powder bed fusion fabrication iterations) AM TAV alloy powder batches. A second objective was to build specimens out of each powder type and compare the associated SCC responses of as-built and machined specimens with a physiological saline environment. As-built AM specimens from both powder types showed reduced ductility upon exposure to physiological conditions indicating a potential susceptibility to SCC. Machined AM specimens also showed significantly increased reduction of area values compared with as-built specimens regardless of the powder type utilized.