A comparative study on mechanical properties of Ti-6Al-4V alloy processed by additive manufacturing vs. traditional processing

The unique thermal history of different metal additive manufacturing processes would have profound impacts on the resulting microstructure and material properties. However, few have conducted benchmark research on the impacts. This work provides a comprehensive benchmark comparison on microstructure, mechanical properties, and their underlying mechanisms in selective laser melting (SLM), electron beam melting (EBM), and millannealing of Ti-6Al-4V alloys. The results have shown that the SLMed and EBMed samples possess very fine acicular alpha ' martensite while the conventional mill-annealed ones have granular alpha phase. The SLMed samples exhibit the highest tensile and yield strength resulted from the combined effects of refined alpha' martensite and high microscale residual stress. The lowest tensile and yield strength and intermediate elongation of the EBMed samples are attributed to the relatively high number of type-II pores and in-situ annealing for residual stress relief during the printing process. The mill-annealed samples have the highest elongation due to the fully dense structure, the negligible microscale residual stress, and favorable grain orientation. It is expected to improve the ductility of SLMed samples via appropriate post-annealing and enhance the strength of EBMed samples by reducing the number of type-II pores through process optimization. The fundamental differences in microstructure and properties are attributed to the unique thermal histories of the concerned processes.