Understanding the impact of texture on the micromechanical anisotropy of laser powder bed fused Inconel 718

Abstract

The manufacturability of metallic alloys using laser-based additive manufacturing methods such as laser powder bed fusion has substantially improved within the last decade. However, local melting and solidification cause hierarchically structured and crystallographically textured microstructures possessing large residual stress. Such microstructures are not only the origin of mechanical anisotropy but also pose metrological challenges for the diffraction-based residual stress determination. Here we demonstrate the influence of the build orientation and the texture on the microstructure and consequently the mechanical anisotropy of as-built Inconel 718. For this purpose, we manufactured specimens with [001]/[011]-, [001]- and [011]/[$$\overline{1} {\text{11}}$$ 1 ¯ 11 ]-type textures along their loading direction. In addition to changes in the Young’s moduli, the differences in the crystallographic textures result in variations of the yield and ultimate tensile strengths. With this in mind, we studied the anisotropy on the micromechanical scale by subjecting the specimens to tensile loads along the different texture directions during in situ neutron diffraction experiments. In this context, the response of multiple lattice planes up to a tensile strain of 10% displayed differences in the load partitioning and the residual strain accumulation for the specimen with [011]/[$$\overline{1} {\text{11}}$$ 1 ¯ 11 ]-type texture. However, the relative behavior of the specimens possessing an [001]/[011]- and [001]-type texture remained qualitatively similar. The consequences on the metrology of residual stress determination methods are discussed.

Tensile and Low‐Cycle Fatigue Behavior of Laser Powder Bed Fused Inconel 718 at Room and High Temperature

“…[6] Therefore, the adaptation and optimization of possible heat treatments for AM materials are further and more current research topics. [6,[10][11][12] Comprehensive studies on the mechanical properties, in particular the LCF behavior at high temperatures on heat-treated AM variants, are still lacking. This is also the case for IN718 manufactured by PBF-LB/M.…”

Texture-based residual stress analysis of laser powder bed fused Inconel 718 parts

“…The bulk texture measurements were performed at the KOWARI strain scanner located at the Australian Nuclear Science and Technology Organisation (ANSTO) in Lucas Heights. For the measurements, cylinders with a diameter and a height of 8 mm were extracted from the center of the threaded region of the H 0 and H 45 tensile specimens (see Schro ¨der et al, 2022). The neutron wavelength of 1.4 A ˚was selected from the 400 reflection of the Si monochromator.…”

“…However, another consequence of the localized melting and solidification during the PBF-LB process is the columnar grain growth as reviewed by Volpato et al (2022). In such cases, it has been experimentally shown that the Reuss model represents the materials behavior for PBF-LB/M/IN718 more accurately (Schro ¨der et al, 2022;. In fact, the usage of DECs based on the Kro ¨ner model may lead to RS exceeding the yield strength of as-built PBF-LB/M/IN718 (Pant et al, 2020;.…”

“…In this article the strain and RS distribution in as-built PBF-LB/ M/IN718 prisms (manufactured with two different scan strategies) will be determined using a combined approach of laboratory X-ray, high-energy synchrotron and neutron diffraction. These investigations are carried out on material identical to that used in the in situ loading studies reported by Schro ¨der et al (2022). Hence for the isotropic case, the DECs are known to be well predicted by Reuss for the 311 reflection, which mitigates one of the key unknowns for the accurate RS determination.…”

The 2022 Robert W. Cahn best paper award

“…The runners-up are: ''Phase transformation and incompatibility at grain boundaries in zirconia-based shape memory ceramics: a micromechanics-based simulation study'' by Zhiyi Wang, Alan Lai, Christopher A. Schuh, and Rau ´l Radovitzky [4] and ''Understanding the impact of texture on the micromechanical anisotropy of laser powder bed fused Inconel 718'' by Jakob Schro ¨der, Alexander Evans, Efthymios Polatidis, Jan Capek, Gunther Mohr, Itziar Serrano-Munoz, and Giovanni Bruno [5]. The paper by Zhiyi Wang et alis a collaboration between several groups at the Massachusetts Institute of Technology.…”