Forming properties of additively manufactured monolithic Hastelloy X sheets

Abstract

Additive manufacturing (AM) of semi-finished sheets for a subsequent forming operation has not been investigated yet. The potentials in resource efficiency and effective use of build-chamber-volumes, by combining laser powder bed fusion of metals and forming technology are demonstrated. The overarching aim of this process chain are time savings of up to 50% and the benefit of material strengthening by work hardening. The scope of this paper is the understanding and characterization of the flow behavior of additively manufactured semi-finished parts for the use in a subsequent forming application of the nickel-based superalloy, Hastelloy X. Characterization methods used in sheet metal forming are applied to monolithic additively manufactured tensile, compression and in-plane torsion specimens. The resulting characterization and yield criteria can be used to predict the forming behavior of additively manufactured semi finished parts with integrated functions like cooling channels that are formed in its final geometry. A correction function is introduced to consider the surface roughness in the stress-strain diagrams. The material shows a high anisotropic yield stress with a nearly isotropic hardening behavior in the as-build condition. The heat treatment reveals a homogenization of the material accompanied with an isotropic initial yield stress but anisotropic yield behavior. To numerically model those effects, different yield surfaces based on the preceding material characterization are discussed. It turns out, that the additively manufactured Hastelloy X shows high potential in terms of formability combined with high tensile strengths.