Abstract
The underlying cause of mechanical anisotropy in additively manufactured (AM) parts is not yet fully understood and has been attributed to several different factors like microstructural defects, residual stresses, melt pool boundaries, crystallographic and morphological textures. To better understand the main contributing factor to the mechanical anisotropy of AM stainless steel 316L, bulk specimens were fabricated via laser powder bed fusion (LPBF). Tensile specimens were machined from these AM bulk materials for three different inclinations: 0°, 45°, and 90° relative to the build plate. Dynamic Young’s modulus measurements and tensile tests were used to determine the mechanical anisotropy. Some tensile specimens were also subjected to residual stress measurement via neutron diffraction, porosity determination with X-ray micro-computed tomography (μCT), and texture analysis with electron backscatter diffraction (EBSD). These investigations revealed that the specimens exhibited near full density and the detected defects were spherical. Furthermore, the residual stresses in the loading direction were between −74±24MPa and 137±20MPa, and the EBSD measurements showed a preferential 〈110〉 orientation parallel to the build direction. A crystal plasticity model was used to analyze the elastic anisotropy and the anisotropic yield behavior of the AM specimens, and it was able to capture and predict the experimental behavior accurately. Overall, it was shown that the mechanical anisotropy of the tested specimens was mainly influenced by the crystallographic texture.
Highlights
Additive manufacturing describes layerwise production processes that incrementally build structures from a feedstock material
Stainless steel 316L specimens produced via laser powder bed fusion (LPBF316L) usually have a layered morphology, which consists of many different features on a broad range of length scales [6,7]
These representative volume element (RVE) equal the statistical properties of the grain morphology and crystallographic texture, which were extracted from the electron backscatter diffraction (EBSD) scans of the specimens
Summary
Additive manufacturing describes layerwise production processes that incrementally build structures from a feedstock material. Despite the technological improvements made in recent years, metal additive manufacturing, known as metal 3D printing, still faces many different challenges such as microstructural defects, residual stresses (RSs), mechanical anisotropy and in general lack of understanding of process-property-performance relationship [2,3,4]. The authors of [13, 17,19,31,32] consider the combination of crystallographic texture and different deformation mechanisms, mainly dislocation slip and twinning, responsible for the directional dependency of material behavior. The authors of [26] investigated the mechanical anisotropy of LPBF316L and compared the results with previous studies They reported that the observations concerning the orientation dependency of the material behavior differed significantly and even contradictory. The dependency of ultimate tensile strength on loading direction showed no clear tendency [26]
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