Creep behaviour of inconel 718 processed by laser powder bed fusion

Additive manufacturing lends itself well to the manufacture of aerospace parts due to the high complexity and small volume of many components found in modern aero engines. By exploiting additive manufacturing design freedoms, enhanced part functionality can be achieved and lead time can be reduced. However, the integrity of these parts is a primary concern which often cannot be guaranteed with current generation additive manufacturing methods and materials. Studies on the performance of additively manufactured parts under service conditions are therefore required. In this study, laser powder bed fusion is used to produce specimens for creep testing. To allow this a novel specimen design, i.e. Two Bar Specimen, was applied for creep testing. The performance of these specimens, in the as-build condition, is showed to be largely poor because of surface integrity defects and unfavourable microstructure formation. These are clearly highlighted and explored. Further specimens, subjected to heat treatments, have also been tested. These showed a marked improvement of the microstructure. The lifetime of the heat-treated sample prepared with milling + wire electrical discharge machining was enhanced by as much as four times compared to the as-build specimens. However, this lifetime performance remains 33% below that of samples machined from the equivalent wrought material. This work then proposes manufacturing strategies to significantly enhance the performance of Inconel 718 when processed via laser powder bed fusion and post-heat treatments.