Strain localization in Ti-6Al-4V Widmanstätten microstructures produced by additive manufacturing

Abstract

Although Additive Manufacturing (AM) offers numerous performance advantages over existing methods, AM structures are not being utilized for critical aerospace and mechanical applications due to uncertainties in their structural integrity as a result of microstructural variations and defects arising from the AM process itself. With strain localization serving as a precursor for material failure, the impact of microstructural variations in Direct Metal Laser Sintering (DMLS) produced Ti-6Al-4V on strain localization is investigated through high resolution digital image correlation as a result of monotonic and cyclic loading for both stress relieved and mill annealed specimens. From the experimental characterizations, it was observed that the former β phase boundaries that enclose separate microtextured regions and the α lathe's major axis orientations play a critical role in the localization of strain with respect to the Widmanstätten microstructures exhibited by DMLS Ti-6Al-4V. The results show a potential opportunity to improve the performance of DMLS produced Ti-6Al-4V by decreasing the size of the β grains during the solidification process through higher cooling rates and a build strategy that avoids the reheating of solidified material as much as possible to prevent β grain growth.