Highly Anisotropic Steel Processed by Selective Laser Melting

Abstract

For additive manufacturing of metals, selective laser melting can be employed. The microstructure evolution is directly influenced by processing parameters. Employing a high energy laser system, samples made from austenitic stainless steel were manufactured. The microstructure obtained is characterized by an extremely high degree of anisotropy featuring coarse elongated grains and a h001i texture alongside the build direction during processing. Eventually, the anisotropy of the microstructure drastically affects the monotonic properties of the current material. Recently, techniques allowing for additive manufacturing of highly complex components have been gaining significant attention in both industry and academic research. [1][2][3] As no tools are required for processing, small to medium batches can be produced very efficiently. Polymers and metals can be processed depending on the technique employed; for processing of metals, wire-based techniques are available, but techniques employing a powder bed have the higher impact. Electron beam melting and selective laser melting (SLM Ò ), both melting the powder locally accordingly to data provided by a model stemming from computer-aided design, are widely used nowadays. [1][2][3] From the academic point of view, the high degree of design freedom allowing for an extreme lightweight design and the aspect of microstructural design are very attractive. [4,5] The latter aspect is mainly influenced by process-related parameters such as scanning strategy and energy input. As has been shown by Thijs et al. for an aluminum alloy processed by selective laser melting in a very recent paper, the thermal gradient during cooling and the direction of heat flow are key parameters for microstructure evolution and design, respectively.[4] Numerous metals and alloys have been processed by SLM Ò ; aluminum and titanium alloys, nickel-based alloys, and stainless steels have been the subjects of recent work. [1][2][3][4][5][6][7][8] Focusing on materials such as nickel-based alloys and austenitic steels, high-temperature applications are of interest. For such applications, a coarse-grained anisotropic microstructure is highly attractive.[9] The current paper addresses this topic and introduces a highly anisotropic austenitic alloy 316L directly obtained from powder processed by SLM Ò . The conditions for obtaining such kind of microstructure are discussed in light of the processing parameters.The material employed in the current study was facecentered cubic (fcc) 316L stainless steel. The initial powder with a mean particle size of 40 lm was supplied by SLM Solutions GmbH. For fabrication of cubical and tension specimens, a SLM Ò -280 HL selective laser melting system in combination with MTT AutoFab software (Marcam Engineering GmbH) was used. The tensile specimens were built in the z-direction; thus, the loading axis was parallel to the built direction. Two Yttrium fiber lasers are employed in the current SLM Ò system, featuring maximum beam energies of 400 W and 1000 W, respectively. ...

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

“…The purpose at that early phase was mainly to understanding the SLM process [120][121][122], and with the development of SLM process the focuses and aims gradually shift to exploring the possibilities of manufacturing high-value added components. The most commonly reported SLM iron-base alloys include 316L stainless steel [123][124][125][126][127][128].…”

On the Anisotropic Mechanical Properties of Selective Laser Melted Stainless Steel

“…due to the neighbouring scan track or subsequent layer being generated, the grains of the already solidified materials become altered by the secondary heat input [38]. This behaviour is commonly referred to as epitaxial grain growth, describing the tendency of needle-like grain growth towards the heat source [41,42]. Due to this tendency, the grains of 1.4404 grew through the individual layers (in direction of the heat source), causing an interlocking of the individual layers ( Figure 9).…”

Density of additively-manufactured, 316L SS parts using laser powder-bed fusion at powers up to 400 W

“…However, as the studies in Table 1 powers <225W. Recently, metal additive-manufacturing machines have become available with powers up to 1000W, as described in the work of Niendorf et al (2013) on the microstructure and mechanical properties of 316L stainless steel at powers of 400W and 1000W.…”