On the Anisotropic Mechanical Properties of Selective Laser-Melted Stainless Steel

Abstract

The thorough description of the peculiarities of additively manufactured (AM) structures represents a current challenge for aspiring freeform fabrication methods, such as selective laser melting (SLM). These methods have an immense advantage in the fast fabrication (no special tooling or moulds required) of components, geometrical flexibility in their design, and efficiency when only small quantities are required. However, designs demand precise knowledge of the material properties, which in the case of additively manufactured structures are anisotropic and, under certain circumstances, inhomogeneous in nature. Furthermore, these characteristics are highly dependent on the fabrication settings. In this study, the anisotropic tensile properties of selective laser-melted stainless steel (1.4404, 316L) are investigated: the Young’s modulus ranged from 148 to 227 GPa, the ultimate tensile strength from 512 to 699 MPa, and the breaking elongation ranged, respectively, from 12% to 43%. The results were compared to related studies in order to classify the influence of the fabrication settings. Furthermore, the influence of the chosen raw material was addressed by comparing deviations on the directional dependencies reasoned from differing microstructural developments during manufacture. Stainless steel was found to possess its maximum strength at a 45° layer versus loading offset, which is precisely where AlSi10Mg was previously reported to be at its weakest.

A Review of Metal Fabricated with Laser‐ and Powder‐Bed Based Additive Manufacturing Techniques: Process, Nomenclature, Materials, Achievable Properties, and its Utilization in the Medical Sector

“…For example, for a safe dimensioning, which entirely neglects all these irregularities, the knowledge of the minimal strength and ductility is the crucial information. [127][128][129] To illustrate the necessity of a proper description of the material characteristics, differing material properties are attributed to where and when a specific section of the component was manufactured during the build job. This leads to the necessity to describe the material properties in relation to a specific direction and overall location.…”

“…Mechanical strength and ductility, for most cases less emphasised as the polar angle dependency [1,63,129,230,237] Polar angle (Φ)…”

“…In this case, the polar angle serves as the only rotational parameter accounting for directional dependencies. [127][128][129] To illustrate the necessity of a proper description of the material characteristics, differing material properties are attributed to where and when a specific section of the component was manufactured during the build job. For example, it has been reported that age-hardenable alloys, like AlSi10Mg, undergo a precipitation hardening during fabrication, the emphasis of which is related to the dwell time at elevated temperatures and results in deviations along the z-coordinate.…”

Compressive behaviour of additively manufactured AlSi10Mg

“…In the as-fabricated condition, the single aluminium-grains are surrounded by silicon-segregations, which hinder the aluminiumgrains from growing further [6][7][8][9]. However, left untreated, these silicon-enrichments represent brittle areas and predetermined points of fracture, i. e. a drop in tensile strength of AlSi10Mg at a 458 angle offset between the layer and the loading direction, which is attributed to the brittle shear fracture along these silicon-rich areas [10,11]. The grain stabilization effect prevents secondary grain growth via subsequent heat input, i. e. fabrication of neighbouring scan tracks and subsequent layers, or due to the preheating temperature of the build chamber.…”

Thermographic analysis of the building height impact on the properties of tool steel in selective laser beam melting

“…However, there are challenges through many influencing factors. One of the possible influences can be the orientations in the building chamber, which causes location-related surface qualities, or anisotropic properties [2][3][4]. Another challenge is the occurrence of thermal stresses, caused by the melting and remelting in the selective laser beam process [5].…”