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.
Highlights
MethodsSpecimens have been manufactured by Electron Beam Melting (EBM) using an Arcam A2X machine (Arcam AB, Sweden) under 2 × 10−3 mbar vacuum atmosphere operating at an acceleration voltage of 60 kV
A) It has been demonstrated that this particular alloy system is remarkably well suited for layer-wise AM technologies like EBM
B) This novel microstructure development is explained by the specific phase diagram of the CrMnNi steel that is characterized by a high temperature fcc → bcc + fcc phase transformation
Summary
Specimens have been manufactured by Electron Beam Melting (EBM) using an Arcam A2X machine (Arcam AB, Sweden) under 2 × 10−3 mbar vacuum atmosphere operating at an acceleration voltage of 60 kV. It has been determined by X-ray fluorescence spectroscopy, inductively coupled plasma spectroscopy and combustion gas analysis, respectively. The chemical composition of tensile specimens has been analyzed by energy-dispersive X-ray spectroscopy (EDS) and spark emission spectroscopy (Foundry Master, Oxford Instruments plc, UK). For investigation of the phase fractions, phase and element distribution, crystallographic orientations and fractography two scanning electron microscopes have been employed, i.e. a CamScan MV2300 (Electron Optic Services, Inc., Canada) and a high-resolution field emission gun scanning electron microscope (SEM) MIRA 3 XMU (TESCAN, Czech Republic) operating at 20 kV equipped with secondary electron (SE), backscatter-electron (BSE), electron backscatter diffraction (EBSD) and EDS detectors
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