Evaluating the efficacy of alternative small scale test methodologies in deriving the mechanical properties of additive manufactured materials

Abstract

With the continuous drive of the aerospace industry to implement additive manufactured (AM) components into the next generation of aero-engines, to benefit from the near net shape and weight saving potential that the technology has to offer, the requirement to understand their mechanical performance is also rising in parallel. This is further complicated by the highly localised and transient micro/macro structures that AM produced parts typically possess, raising a question mark over the suitability of more traditional mechanical test approaches where the bulk properties are heavily influenced by the presence of a single defect. As such, alternative experimental approaches, capable of establishing the properties of smaller more intricate structures and geometrically representative microstructures and cross sections, needs to be considered for process parameter down-selection. This paper will explore the suitability of several alternative mechanical test methodologies in characterising the mechanical behaviour of a nickel based superalloy, Inconel 718 (IN718), produced by laser powder bed fusion (LPBF), and establish which results correlate most favourably to those generated through more conventional means. For the first time, results will be presented from several mechanical test methodologies including small punch, shear punch, hardness, nano-indentation and profilometry based indentation plastometry experiments; a set of mechanical test approaches that have yet to be directly compared and discussed in a single study on an additively manufactured material. Findings will be supported by advanced microscopy in the form of field emission SEM and crystallographic texture maps produced through electron back-scattered diffraction.