Revealing relationships between porosity, microstructure and mechanical properties of laser powder bed fusion 316L stainless steel through heat treatment

Rønneberg, Tobias; Davies, Catrin M.; Hooper, Paul A.

doi:10.1016/j.matdes.2020.108481

Cited by 219 publications

(103 citation statements)

References 39 publications

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“…Samples manufactured by SLM with metallic powder have a higher elastic modulus in the in-plane direction compared with the cross-plane direction [11]. In the manufacturing process, thermal stress accumulates as a result of rapid heating and cooling [34], or flat pores are generated because of the low energy density [35,36] between layers. These defects result in a higher elastic modulus in the in-plane direction than in the cross-plane direction [11,14].…”

Section: Resultsmentioning

confidence: 99%

Anisotropic Thermal Conductivity of Nickel-Based Superalloy CM247LC Fabricated via Selective Laser Melting

et al. 2021

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Efforts to enhance thermal efficiency of turbines by increasing the turbine inlet temperature have been further accelerated by the introduction of 3D printing to turbine components as complex cooling geometry can be implemented using this technique. However, as opposed to the properties of materials fabricated by conventional methods, the properties of materials manufactured by 3D printing are not isotropic. In this study, we analyzed the anisotropic thermal conductivity of nickel-based superalloy CM247LC manufactured by selective laser melting (SLM). We found that as the density decreases, so does the thermal conductivity. In addition, the anisotropy in thermal conductivity is more pronounced at lower densities. It was confirmed that the samples manufactured with low energy density have the same electron thermal conductivity with respect to the orientation, but the lattice thermal conductivity was about 16.5% higher in the in-plane direction than in the cross-plane direction. This difference in anisotropic lattice thermal conductivity is proportional to the difference in square root of elastic modulus. We found that ellipsoidal pores contributed to a direction-dependent elastic modulus, resulting in anisotropy in thermal conductivity. The results of this study should be beneficial not only for designing next-generation gas turbines, but also for any system produced by 3D printing.

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Section: Resultsmentioning

confidence: 99%

Anisotropic Thermal Conductivity of Nickel-Based Superalloy CM247LC Fabricated via Selective Laser Melting

et al. 2021

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“…The revealed coupled thermomechanical behavior was similar to the trends observed during heat treatment of the additively manufactured stainless steel specimens that, in horizontal orientation of the printed structure, exhibited a decrease in yield stress and increase in elongation at break with the increasing heat treatment temperature. [ 12 ]…”

Section: Methodsmentioning

confidence: 99%

“…Relationships between porosity, microstructure, and mechanical properties of additively manufactured stainless steel were investigated by Ronneberg et al through heat treatment. [ 12 ] Heat treatment of the additively manufactured austenitic steel is considered as a suitable approach to modify and improve the mechanical properties of the as‐built material.…”

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confidence: 99%

Impact Behavior of Additively Manufactured Stainless Steel Auxetic Structures at Elevated and Reduced Temperatures

et al. 2020

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Metamaterials produced using additive manufacturing represent advanced structures with tunable properties and deformation characteristics. However, the manufacturing process, imperfections in geometry, properties of the base material as well as the ambient and operating conditions often result in complex multiparametric dependence of the mechanical response. As the lattice structures are metamaterials that can be tailored for energy absorption applications and impact protection, the investigation of the coupled thermomechanical response and ambient temperature‐dependent properties is particularly important. Herein, the 2D re‐entrant honeycomb auxetic lattice structures additively manufactured from powdered stainless steel are subjected to high strain rate uniaxial compression using split Hopkinson pressure bar (SHPB) at two different strain rates and three different temperatures. An in‐house developed cooling and heating stages are used to control the temperature of the specimen subjected to high strain rate impact loading. Thermal imaging and high‐speed cameras are used to inspect the specimens during the impact. It is shown that the stress–strain response as well as the crushing behavior of the investigated lattice structures are strongly dependent on both initial temperature and strain rate.

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“…Contrary to the as-built microstructures, melt-pool boundaries and overlapping melt-pool boundaries are hardly visible after preheat treatment at 320 °C. Heat treatments tend to homogenise microstructures and may have accounted for melt-pool dissolution at 320 °C [ 33 , 34 ]. SEM of 320 °C micrographs shown in Figure 6 c,d at different magnification levels show a microstructure with a variety of rod-like precipitates in the matrix, as well as globular-like phases which are seen as bright spots and appear to be Cu-rich.…”

Section: Resultsmentioning

confidence: 99%

Characterising the Microstructure of an Additively Built Al-Cu-Li Alloy

et al. 2020

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Al-Cu-Li alloys are famous for their high strength, ductility and weight-saving properties, and have for many years been the aerospace alloy of choice. Depending on the alloy composition, this multi-phase system may give rise to several phases, including the major strengthening T1 (Al2CuLi) phase. Microstructure investigations have extensively been reported for conventionally processed alloys with little focus on their Additive Manufacturing (AM) characterised microstructures. In this work, the Laser Powder Bed Fusion (LPBF) built microstructures of an AA2099 Al-Cu-Li alloy are characterised in the as-built (no preheating) and preheat-treated (320 °C, 500 °C) conditions using various analytical techniques, including Synchrotron High-Energy X-ray Diffraction (S-HEXRD). The observed dislocations in the AM as-built condition with no detected T1 precipitates confirm the conventional view of the difficulty of T1 to nucleate on dislocations without appropriate heat treatments. Two main phases, T1 (Al2CuLi) and TB (Al7.5Cu4Li), were detected using S-HEXRD at both preheat-treated temperatures. Higher volume fraction of T1 measured in the 500 °C (75.2 HV0.1) sample resulted in a higher microhardness compared to the 320 °C (58.7 HV0.1) sample. Higher TB volume fraction measured in the 320 °C sample had a minimal strength effect.

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Revealing relationships between porosity, microstructure and mechanical properties of laser powder bed fusion 316L stainless steel through heat treatment

Cited by 219 publications

References 39 publications

Anisotropic Thermal Conductivity of Nickel-Based Superalloy CM247LC Fabricated via Selective Laser Melting

Anisotropic Thermal Conductivity of Nickel-Based Superalloy CM247LC Fabricated via Selective Laser Melting

Impact Behavior of Additively Manufactured Stainless Steel Auxetic Structures at Elevated and Reduced Temperatures

Characterising the Microstructure of an Additively Built Al-Cu-Li Alloy

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