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

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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Surface conditions and the fatigue behavior of nodular cast iron

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propagation of long fatigue cracks in ti6al4v alloy produced by direct metal laser sintering

Abstract The growth of long fatigue cracks in Ti6Al4V alloy manufactured by direct metal laser sintering was experimentally determined on CT specimens. The crack propagation was investigated in three different orientations with regard to the building direction. The as-built CT specimens were heat treated at temperatures 380, 740 and 900 °C. The crack growth curves with the threshold values of the stress intensity factor ΔKth were determined. The measurement was carried out in laboratory air at room temperature and stress ratios R = 0.1 and 0.8. It was found that the crack growth rate in the Paris region is identical for all three heat treatments for the same R ratio. For the particular stress intensity factor range ∆K the crack growth rates at R = 0.1 and 0.8 differs by factor of two. Contrary to the Paris region there is a clear effect of the heat treatment in the near threshold region. For the material heat treated at 380 °C and loaded at R = 0.1 the threshold is 3.7 MPam1/2, for 740 °C 2.7 MPam1/2 and for 900 °C 3.5 MPam1/2. The explanation of the observed dependence of the threshold on the post processing heat treatment is discussed in terms of microstructure and residual stresses

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

Microstructure vs. Near-threshold Fatigue Crack Growth Behavior of an Heat-treated Ductile Iron

<p>Perferritic isothermal ductile iron (IDI®) is an intermediate grade between the low-strength grades of austempered ductile iron (ADI) and pearlitic ductile iron (DI) recently developed by Zanardi Fonderie Italy. IDI is produced by heat-treating an unalloyed nodular cast iron. The specific matrix microstructure is called “Perferritic” and consists predominantly of ferrite and pearlite. Compared to the pearlitic grades of nodular ductile iron, IDI combines similar strength with higher toughness as a result of the isothermal heat treatment.</p> In this contribution the fatigue crack growth resistance and <em>K_ath</em> of IDI are investigated and correlated to mechanical properties and microstructural features. The threshold <em>K_a</em> was determined using the load shedding technique as per ASTM Standard E-647 using CT specimens extracted from a cast block. Tensile specimens were extracted from the broken CT halves and used to determine the static mechanical properties. A metallographic investigation was carried out to correlate structural features and mechanical properties.<p>DOI: <a href="http://dx.doi.org/10.5755/j01.ms.18.1.1336">http://dx.doi.org/10.5755/j01.ms.18.1.1336</a></p

Influence of microstructure and defect population on the fatigue performance of cast A356-T6 automotive components

In the paper fatigue specimens are extracted from different regions of cast aluminum cylinder heads produced by two foundries. A high strength region and a low strength region were identified within the cylinder head and the A356-T6 material locally characterized in terms of microstructure and defect population. High cycle fatigue testing according to a reduced staircase method was performed to determine the local fatigue strength at 107 cycles in the cylinder heads of the two foundries. The implications of the experimental observations are discussed. © (2014) Trans Tech Publications, Switzerland

Nodular cast iron fatigue lifetime in cyclic plane bending

<em>The fatigue behavior of a component is strongly dependent on the material and its surface condition. Therefore, the manner in which the surface is prepared during component manufacturing (surface roughness, residual stresses etc.) has a decisive role in dictating the initiation time for fatigue cracks. The fatigue behavior of the same material, a nodular cast iron, with three different surface conditions (fine ground, sand blast and as-cast) has been investigated under cyclic plane bending. The results show differences in fatigue strength, which are associated with the surface conditions. The characteristics of the surface layers of the different test specimens were examined by metallography</em>