EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Additive Manufacturing (AM) has clear advantages over conventional manufacturing methods, such as design freedom and manufacturability of hard-to-machine superalloys. A limiting factor, however, is the lack of understanding of microstructural and mechanical performance of AM materials, particularly for high value applications. Laser Powder Bed Fusion (LPBF), which is mainly used to fabricate metals, results in unfavourable microstructures with process induced defects, such as pores, precipitate formation, lack of fusion and suboptimal grain size and morphology. In turn, the mechanical properties, which are sometimes poorer than wrought equivalents, are anisotropic and not fully understood, particularly for high temperatures applications. In this work, LPBF alloy 718 parts were built with 3 different build orientations and with 2 different scan strategies to understand the effects of the LPBF process parameters on the microstructure and on the creep behaviour of the material. Heat treating the LPBF samples resulted in a creep life 5 times longer than its as-built equivalent. Additionally, the build orientation greatly affected the creep life, rate and failure mode. The creep life for the Meander scan strategy was 58% longer than the Stripe strategy, due to the higher number of laser overlapping areas in the latter. Finally, compared to wrought alloy 718, one strategy, resulted in a 24% increase in creep life, showing that it is possible for LPBF components to surpass wrought material properties with further work. It is therefore possible, as a result of this work, to propose build strategies for high temperature creep applications.