a novel test method for the fatigue characterization of metal powder bed fused alloys

Abstract This research addresses the conflicting factors of high costs of fatigue testing and large number of influencing factors that need to be investigated for PBF material and process qualification. Metal powders are remarkably expensive, the PBF production process requires expensive systems and fatigue testing requires multiple specimens (depending the required degree of confidence) to characterize a single material/process combination. In this paper a novel fatigue test method aimed at the peculiar needs of PBF technology is initially presented and fatigue data obtained on Direct Metal Laser Sintering Ti6Al4V are validated against standard rotating bending test results. Then, the link between microstructure and directional fatigue behavior is demonstrated using the present methodology and SLM Inconel 718: namely, the stress direction parallel to build direction is the most severe. Finally, the new test method is applied to the investigation of the fatigue notch sensitivity of DMLS Ti6Al4V in relation to the notch fabrication process. Round notches in specimens with opposite fabrication orientations (i.e. up-skin vs down-skin) resulted in two notch fatigue factors and the up-skin notch has a better fatigue strength than the down-skin notch

efficient determination of influence factors in fatigue of additive manufactured metals

Abstract The additive manufacturing (AM) technology transforms metal powder, layer by layer, into structural components. Sectors such as aerospace and motor racing require: i) in-depth knowledge of mechanical behavior, especially fatigue, of these metals; ii) fatigue data for component design. In the recent years the industrial expectations about metal AM technology have exploded with a focus now on materials and components qualification. Material and AM process qualification costs are high because metal powder and AM system processing time are expensive. The approach adopted in this paper to efficiently generate knowledge on influencing factors of the fatigue behavior of DMLS Ti-6Al4V alloy utilizes non-standard (i.e. miniature) specimens and simple plane bending test machines. After validation of the proposed methodology against test results for the same material obtained with standard specimens, the merit of the innovative approach is demonstrated by presenting original data on the influence of surface quality, heat treatment, coupled material directionality and notch effects on fatigue behaviour of DMLS Ti-6Al4V

on the link between as built surface quality and fatigue behavior of additively manufactured inconel 718

Abstract Inconel 718 is widely used in challenging structural applications because of its excellent high temperature mechanical properties. Selective Laser Melting (SLM) of Inconel 718 powder is increasingly used to fabricate customized parts for jet engines. The surface quality of SLM parts is influenced by powder characteristics, process parameters and the layer-wise fabrication. The as-built fatigue behavior is negatively affected by the inferior surface quality of SLM parts compared to machined version. Here the fatigue behavior of SLM Inconel 718 is investigated using specimens fabricated with two different SLM systems and different directions of applied stress with respect to build direction. Fatigue test results are interpreted in the light of metallographic and fractographic investigations

Surface conditions and the fatigue behavior of nodular cast iron

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notch fatigue behavior of inconel 718 produced by selective laser melting

Abstract Inconel 718 is widely used in hot structures of jet engines because of its excellent mechanical properties at high temperatures. Recently, customized parts of complex geometry are increasingly fabricated by Selective Laser Melting (SLM) of Inconel 718 powder. This contribution investigates the still largely unexplored topic of the combined influence of notches and as-built surfaces on the fatigue strength of SLM Inconel 718 parts. An innovative fatigue test method using miniature notched specimens tested in cyclic plane bending is adopted. Four sets of specimens, each with a different orientation of the notch surface with respect to the build axis, are fabricated with a commercial SLM system, heat treated and fatigue tested. The fatigue results show the directional nature of the as-built notch effect. The link between surface quality of the notched specimens and their layer-wise fabrication is determined by a metallographic investigation

X-ray computed tomography vs. metallography for pore sizing and fatigue of cast Al-alloys

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influence of as built surfaces on the fatigue behavior of alsi10mg parts obtained by laser powder bed fusion

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microstructure and fatigue performance of slm fabricated ti6al4v alloy after different stress relief heat treatments

Abstract The main interest in Additive Manufacturing (AM) technology relates to its ability to produce complex components with relatively reduced weight that are difficult to produce or cannot be produced by other conventional technologies. Selective laser melting (SLM) is extensively used, as one of the AM technologies to fabricate metallic parts. This advanced method allows to produce various parts with complex geometries with high three-dimensional (3D) accuracy from fusion powders in a layer-by-layer style. Ti6Al4V alloy is a widely used material for structural applications in aerospace and biomedical due to high specific fatigue strength. SLM processing makes this alloy attractive when weight reduction is a design objective. The SLM Ti6Al4V microstructure is influenced by process parameters and build orientation. The localized high energy input during very short interaction times leads to the formation of very fine structures and to the generation of internal stresses. Therefore, the SLM parts are heat treated to decrease or completely remove residual stresses. The present study aims at evaluating the effect of stress-relief heat treatments on the microstructure, the mechanical properties and the fatigue performance of SLM Ti6Al4V alloy. Ti6Al4V alloy specimens were manufactured according to the SLM process with an EOS M290 system. Post fabrications heat treatments at different temperatures (i.e. 740˚C vs. 900˚C) resulted in different structure and mechanical properties that were identified and measured. Fatigue testing of specimens with as-built surfaces was performed at room temperature on modified Schenk-type fatigue testing machine applying a pulsating plane bending (load cycle ratio R = 0) to the specimens at a frequency f = 15 Hz

Microstructure and directional fatigue behavior of Inconel 718 produced by selective laser melting

Abstract Recent research efforts in additive manufacturing have focused on developing parts made of Inconel 718 (IN 718), a nickel-based superalloy, which is an attractive material for aerospace and energy high-temperature applications. Here the selective laser melting (SLM) process is used to transform alloy powder into a solid IN 718 parts followed by optimal stress-relief and subsequent precipitation hardening treatment. Two main aspects were investigated. The IN 718 microstructure generated by the SLM process was characterized using metallographic techniques and found to be distinctly directional because it is a result of a layer-by-layer material build-up typical of the SLM process. The high cycle fatigue behavior of SLM IN 718 was determined using a novel test method designed to determine and quantify the directional material behavior, which is important information for part design and process optimization. The fatigue S-N data show that the direction parallel to the build direction is associated with the lowest fatigue strength. The role of the as-produced surface characteristics on fatigue crack initiation is discussed

As‐built surface quality and fatigue resistance of Inconel 718 obtained by additive manufacturing

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