Additive manufacturing of metallic components – Process, structure and properties

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test...

Metal Additive Manufacturing: A Review of Mechanical Properties

Materials for additive manufacturing

Inconel 718 superalloy has been fabricated by selective laser melting technology (SLM). Its microstructure and mechanical properties were studied under solution+aging (SA) standard heat treatment, homogenization+solution+aging (HSA) standard heat treatment and as-fabricated conditions. Precipitated phases and microstructures were examined using OM, SEM, TEM and X-ray analysis methods. The fine dendrite structures with an average dendrite arm spacing of approximately 698 nm accompanying some interdendritic Laves phases and carbide particles can be observed in the as-fabricated materials. After standard heat treatments, dendrite microstructures are substituted by recrystallization grains, and Laves phases also dissolve into the matrix to precipitate strengthening phases and δ particles. The test values of all specimens meet Aerospace Material Specification for cast Inconel 718 alloy, and the transgranular ductile fracture mode exists for the three conditions. The strength and hardness of heat-treated SLM materials increase and are comparable with wrought Inconel 718 alloy, whereas their ductility decreases significantly compared with the as-fabricated material. This is because of the precipitation of fine γˊ and γ〞strengthening phases and needle-like δ phases. For the as-fabricated alloy, the formation of finer dislocated cellular structures that develop into a ductile dimple fracture shows excellent ductility. Due to dislocation pinning from γˊ and γ〞strengthening phases and the impediment of dislocation motion caused by the needle-like δ phases, the ductility of the SA materials decreases and causes a transgranular fracture, compared with the as-fabricated samples.

Effect of standard heat treatment on the microstructure and mechanical properties of selective laser melting manufactured Inconel 718 superalloy

Simultaneous enhancements of strength and toughness in an Al-12Si alloy synthesized using selective laser melting

Nickel-based IN738LC samples were built by selective laser melting (SLM). To evaluate the anisotropic mechanical behavior of IN738LC material due to layer-wise build up, specimens were built with their cylinder axis (loading direction) oriented either parallel to the building direction, or perpendicular to the building direction and at 45° to the laser scanning direction. After building up the specimens by SLM, they were investigated either under the ‘as-built’ condition or after heat treatment and compared to IN738LC cast material. The analysis of microstructural anisotropy in SLM made IN738LC specimens was done by using EBSD, EDX and X-ray texture analysis methods, and then correlated with anisotropic material behavior observed during tensile and creep testing at room temperature and 850 °C. All SLM samples possess the same general texture, with the majority of grains forming one single component of a cube texture with one of the cubic axes parallel to the building direction, and another cubic axis parallel to the laser scanning direction. The Young׳s modulus determined during tensile testing is significantly lower parallel to the building direction than perpendicular to the building direction, with the values for cast IN738LC material in between. Creep behavior of specimens with loading parallel to the building direction is superior compared to specimens with loading axis normal to the building direction. The anisotropy of Young׳s modulus was modeled based on the single crystal elastic tensor and the measured crystallographic preferred orientations, and compares well with the data from tensile tests.

Texture, anisotropy in microstructure and mechanical properties of IN738LC alloy processed by selective laser melting (SLM)

Selective laser melting (SLM) is an emerging technology of additive manufacturing, which is used to directly produce metallic parts from thin powder layers. This study aims at correlating laser scanning strategies with the resulting textures and corresponding anisotropy of the elastic behavior of bulk materials. Tensile test specimens made of the γ’-containing Ni-base superalloy IN738LC were built with the loading direction oriented either parallel (z-specimens) or perpendicular to the build-up direction (xy-specimens). Their bulk mechanical properties were determined at room temperature and at 850 °C. Specimens were investigated in the ‘as-built’ condition and after recrystallization heat treatment. SEM-based electron backscatter diffraction (EBSD) was applied to measure their crystallographic preferred orientations (texture) and to correlate the anisotropy of Young's modulus with the texture of the material. It is shown that the applied laser scanning strategies allow to tailor the crystallographic texture locally. The possibility to switch from transverse anisotropic to transverse isotropic properties and reverse is demonstrated for triple layered tensile samples. A recrystallization heat treatment reduces the degree of crystallographic texture and thus the elastic anisotropy by abundant annealing twinning. Predictions of Young's modulus calculated from the measured textures compare well with the data from tensile tests.

Tailoring the texture of IN738LC processed by selective laser melting (SLM) by specific scanning strategies

The invention refers to a method for manufacturing a three-dimensional metallic article/component (11) entirely or partly, comprising the steps of a) successively building up said article /component (11) from a metallic base material (12) by means of an additive manufacturing process by scanning with an energy beam (14), thereby b) establishing a controlled grain orientation in primary and in secondary direction of the article /component (11), c) wherein the secondary grain orientation is realized by applying a specific scanning pattern of the energy beam (14), which is aligned to the cross section profile of said article /component (14), or with characteristic load conditions of the article/component (11).

Method for manufacturing a metallic component by additive laser manufacturing

The invention relates to a method for additively manufacturing an article (10) made of a difficult-to-weld highly-precipitation-strengthened Ni-base super alloy that comprises Al and Ti in the sum of more than 5 wt. -% or a difficult-to weld carbide/solution-strengthened cobalt (Co)-base super alloy, whereby a metal particle mixture (14) of at least a first phase (11) and a second phase (12) is provided as a starting material, said first phase of the mixture being a base material and said second phase of the mixture being a material which is a derivative of the first material and has relative to said material of said first phase an improved weldability, and whereby the metal particle mixture (14) is processed by means of an additive manufacturing process which is one of selective laser melting (SLM), selective laser sintering (SLS), electron beam melting (EBM), laser metal forming (LMF), laser engineered net shape (LENS), or direct metal deposition (DMD).

Method for additively manufacturing an article made of a difficult-to-weld material

Selective Laser Melting (SLM) is an additive manufacturing technology used to directly produce metallic parts from thin powder layers. To evaluate the anisotropic mechanical properties, tensile test specimens of the Ni-base alloy Hastelloy X were built with the loading direction oriented either parallel (z-specimens) or perpendicular to the build-up direction (xy- specimens). Specimens were investigated in the "as-built" condition and after high temperature heat treatment. Tensile tests at room temperature and at 850°C of "as-built" material have shown different mechanical properties for z- and xy-specimens. The anisotropy is reflected in the Young's modulus, with lower values measured parallel to the build-up direction. It is shown that the anisotropy is significantly reduced by a subsequent recrystallization heat treatment. The characterization of microstructural and textural anisotropy was done by Electron Back Scatter Diffraction (EBSD) analysis. Predictions of Young's modulus calculated from the measured textures compare well with the data from tensile tests.

https://iopscience.iop.org/article/10.1088/1757-899X/82/1/012097/pdf

Thomas Etter

Papers

Texture, anisotropy in microstructure and mechanical properties of IN738LC alloy processed by selective laser melting (SLM)

Tailoring the texture of IN738LC processed by selective laser melting (SLM) by specific scanning strategies

Method for manufacturing a metallic component by additive laser manufacturing

Method for additively manufacturing an article made of a difficult-to-weld material

Reduction in mechanical anisotropy through high temperature heat treatment of Hastelloy X processed by Selective Laser Melting (SLM)