Design of novel materials for additive manufacturing - Isotropic microstructure and high defect tolerance

Abstract

Electron Beam Melting (EBM) is a powder-bed additive manufacturing technology enabling the production of complex metallic parts with generally good mechanical properties. However, the performance of powder-bed based additively manufactured materials is governed by multiple factors that are difficult to control. Alloys that solidify in cubic crystal structures are usually affected by strong anisotropy due to the formation of columnar grains of preferred orientation. Moreover, processing induced defects and porosity detrimentally influence static and cyclic mechanical properties. The current study presents results on processing of a metastable austenitic CrMnNi steel by EBM. Due to multiple phase transformations induced by intrinsic heat-treatment in the layer-wise EBM process the material develops a fine-grained microstructure almost without a preferred crystallographic grain orientation. The deformation-induced phase transformation yields high damage tolerance and, thus, excellent mechanical properties less sensitive to process-induced inhomogeneities. Various scan strategies were applied to evaluate the width of an appropriate process window in terms of microstructure evolution, porosity and change of chemical composition.

Effect of Compositional Variation Induced by EBM Processing on Deformation Behavior and Phase Stability of Austenitic Cr-Mn-Ni TRIP Steel

“…It was shown that the material in its as-built condition, i.e., without the necessity of elaborate post-processing, is capable of addressing the aforementioned major current challenges in powder bed-based AM. 35 Firstly, independent of the applied process parameters, the steel is characterized by a homogeneous microstructure with a remarkably weak texture, i.e., approximately 1.6 and 1.4 multiples of uniform distribution (MUD) as determined by electron back-scatter diffraction (EBSD) and x-ray diffraction (XRD). Moreover, relatively fine grains prevail with a mean areaweighted grain size of approximately 20 lm, as derived from EBSD data (cf.…”

Full-Density Fused Deposition Modeling Dimensional Error as a Function of Raster Angle and Build Orientation: Large Dataset for Eleven Materials

“…However, there are some limitations and problems that need to be considered and addressed when using AM, dimensional accuracy [16,17], process and geometric repeatability [18][19][20], and material defects [21][22][23] being the primary considerations. While all are important considerations, the most essential from the perspective of engineering design are the dimensional accuracy and repeatability of the final parts.…”

Full-Density Fused Deposition Modeling Dimensional Error as a Function of Raster Angle and Build Orientation: Large Dataset for Eleven Materials

“…However, there are some limitations and problems that need to be considered and addressed when using AM, dimensional accuracy [13,14], process and geometric repeatability [15][16][17], and material defects [18][19][20] being the primary considerations. While all of these are important to examine, the most important from the perspective of engineering design are the dimensional accuracy and repeatability of the final parts.…”