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

Abstract

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 mill-annealing of Ti–6Al–4V alloys. The results have shown that the SLMed and EBMed samples possess very fine acicular α′ martensite while the conventional mill-annealed ones have granular α phase. The SLMed samples exhibit the highest tensile and yield strength resulted from the combined effects of refined α’ 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. • EBMed samples possess more type- II pores and uncertain mechanical properties. • SLMed samples have the highest strength due to refined α′ and residual micro stress. • Mill-annealed have the largest elongation due to dense structure and favorable texture.