Laser powder bed fusion of Ni-based Hastelloy X superalloy: Microstructure, anisotropic mechanical properties and strengthening mechanisms

The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like microstructure with <100>//build direction (BD) (<100>-SCM), single crystalline-like microstructure with <110>//BD (<110>-SCM), crystallographic lamellar microstructure (CLM), or polycrystalline microstructure (PCM). These four crystallographic textures were realized in Hastelloy-X for the first time here to the best of our knowledge. The mechanical properties of the samples varied depending on their texture. The tensile properties were affected not only by the Schmid factor but also by the grain size and the presence of lamellar boundaries (grain boundaries). The lamellar boundaries at the interface between the <110>//BD oriented main layers and the <100>//BD-oriented sub-layers of CLM contributed to the resistance to slip transmission and the increased proof stress. It was possible to control a wide range of crystallographic microstructures via the LPBF process parameters, which determines the melt pool morphology and solidification behavior.

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Determination of Anisotropic Mechanical Properties for Materials Processed by Laser Powder Bed Fusion

Advances in Materials Science and Engineering ◽

10.1155/2018/7650303 ◽

2018 ◽

Vol 2018 ◽

pp. 1-20 ◽

Cited By ~ 6

Author(s):

Even W. Hovig ◽

Amin S. Azar ◽

Frode Grytten ◽

Knut Sørby ◽

Erik Andreassen

Keyword(s):

Mechanical Properties ◽

Transversely Isotropic ◽

Tensile Tests ◽

Image Correlation ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Inconel 718 Alloy ◽

Powder Bed ◽

Anisotropic Mechanical Properties ◽

Anisotropic Elastic

Improving the success rate in additive manufacturing and designing highly optimized structures require proper understanding of material behaviour. This study proposes a novel experimental method by which anisotropic mechanical properties of additively manufactured materials can be assessed. The procedure is based on tensile testing of flat specimens, manufactured by laser powder bed fusion (LPBF) at different orientations relative to the build plate. In this study, the procedure was applied to the Inconel 718 alloy. Three identical specimen sets were built, each of which received complementary postprocessing treatments. The tensile tests were carried out on specimens with as-built surface finish. Digital image correlation was used to record the strain field evolution on two perpendicular surfaces of the tensile specimens under loading. An optimization algorithm is also proposed for determining the anisotropic elastic constants using only a few tensile test results. It was observed that both build orientation and postprocessing have strong influence on the anisotropic mechanical properties of the material. The effect of microstructure was also investigated and characterised. Consequently, three transversely isotropic compliance matrices were constructed, representing the effect of the different processing conditions.

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