Microstructure and Mechanical Behavior of 17-4 Precipitation Hardenable Steel Processed by Selective Laser Melting

Rafi, H. Khalid; Pal, Devendra; Patil, Nachiket; Starr, Thomas L.; Stucker, Brent

doi:10.1007/s11665-014-1226-y

Cited by 237 publications

(99 citation statements)

References 34 publications

(2 reference statements)

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“…Other steels, e.g., M2 tool steel [96,[129][130][131] and 17-4 PH stainless steel [132][133][134][135][136] have also been reported.…”

Section: Materials Manufactured With Slmmentioning

confidence: 99%

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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Linköping 2018Cover image: A fracture surface of EBM IN718 after tensile test at room temperature.During the course of research underlying this thesis, Dunyong Deng was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2018 © Dunyong Deng AbstractAdditive manufacturing (AM), also known as 3D printing, has gained significant interest in aerospace, energy, automotive and medical industries due to its capabilities of manufacturing components that are either prohibitively costly or impossible to manufacture by conventional processes. Among the various additive manufacturing processes for metallic components, electron beam melting (EBM) and selective laser melting (SLM) are two of the most widely used powder bed based processes, and have shown great potential for manufacturing high-end critical components, such as turbine blades and customized medical implants. The futures of the EBM and SLM are doubtlessly promising, but to fully realize their potentials there are still many challenges to overcome.Inconel 718 (IN718) is a nickel-base superalloy and has impressive combination of good mechanical properties and low cost. Though IN718 is being mostly used as a turbine disk material now, the initial introduction of IN718 was to overcome the poor weldability of superalloys in 1960s, since sluggish precipitation of strengthening phases γ ′ /γ ′′ enables good resistance to strain-age cracking during welding or post weld heat treatment. Given the similarity between AM and welding processes, IN718 has been widely applied to the metallic AM field to facilitate the understandings of process-microstructure-property relationships.The work presented in this licentiate thesis aims to better understand microstructures and mechanical properties EBM and SLM IN718, which have not been systematically investigated. Microstructures of EBM and SLM IN718 have been characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and correlated with the process conditions. Monotonic mechanical properties (e.g., Vickers microhardness and tensile properties) have also been measured and rationalized with regards to the microstructure evolutions before and after heat treatments.For EBM IN718, the results show the microstructure is not homogeneous but dependant on the location in the components, and the anisotropic mechanical properties are probably attributed to alignment of porosities rather than texture.iii Post heat treatment can slightly increase the mechanical strength compared to the as-manufactured condition but does not alter the anisotropy. SLM IN718 shows significantly different microstructure and mechanical properties to EBM IN718. The as-manufactured SLM IN718 has very fine dendritic microstructure and Laves phases in the interdendrites, and is "work-hardened" by the residual strains and dislocations present in the material. Mechanical properties are different between horizontally and vertically built samples, and heat treatment can m...

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“…Other steels, e.g., M2 tool steel [96,[129][130][131] and 17-4 PH stainless steel [132][133][134][135][136] have also been reported.…”

Section: Materials Manufactured With Slmmentioning

confidence: 99%

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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“…However, although the mechanical properties have become close to those of bulk materials [3][4][5][6][7][8][9][10][11][12][13][14], SLM has some inherent drawbacks such as warping, cracking and detrimental tensile residual stresses (TRS). A large degree of shrinkage occurs during liquid -solid transformation, thus accumulating considerable tensile residual stresses on the surface of the SLM produced components.…”

Section: Introductionmentioning

confidence: 99%

Tailoring residual stress profile of Selective Laser Melted parts by Laser Shock Peening

Kalentics

Boillat

Peyre

et al. 2017

Additive Manufacturing

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Selective laser melting Laser shock peening 3D Laser shock peening Residual stress profile 15-5 PH stainless steel 316L stainless steel a b s t r a c t The paper describes a new approach in controlling and tailoring residual stress profile of parts made by Selective Laser Melting (SLM). SLM parts are well known for the high tensile stresses in the as -built state in the surface or subsurface region. These stresses have a detrimental effect on the mechanical properties and especially on the fatigue life. Laser Shock Peening (LSP) as a surface treatment method was applied on SLM parts and residual stress measurements with the hole -drilling method were performed. Two different grades of stainless steel were used: a martensitic 15-5 precipitation hardenable PH1 and an austenitic 316L. Different LSP parameters were used, varying laser energy, shot overlap, laser spot size and treatments with and without an ablative medium. For both materials the as-built (AB) residual stress state was changed to a more beneficial compressive state. The value and the depth of the compressive stress was analyzed and showed a clear dependence on the LSP processing parameters. Application of LSP on SLM parts showed promising results, and a novel method that would combine these two processes is proposed. The use of LSP during the building phase of SLM as a "3D LSP" method would possibly give the advantage of further increasing the depth and volume of compressive residual stresses, and selectively treating key areas of the part, thereby further increasing fatigue life.

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“…The microstructures of powder-bed AM processed samples can be affected significantly by various factors including beam energy density, beam speed, local heat transfer conditions, and scan strategy. In a study by Reafi et al on AM parts prepared by Selective Laser Melting (SLM) using 17-4 precipitation hardenable (PH) stainless steel, it was reported that a nonequilibrium microstructure developed [1]. This microstructure exhibited a strong difference in texture components parallel and perpendicular to the build direction resulting from the very high cooling rates.…”

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confidence: 99%

Microstructural Study of the Heat-treated 17-4PH Stainless Steel Parts Prepared by Selective Laser Melting

2017

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Metal powder-bed additive manufacturing (AM) processes are very different from the conventional subtractive manufacturing methods, resulting in non-uniform microstructures and highly anisotropic material properties for the as-built parts. The microstructures of powder-bed AM processed samples can be affected significantly by various factors including beam energy density, beam speed, local heat transfer conditions, and scan strategy. In a study by Reafi et al. on AM parts prepared by Selective Laser Melting (SLM) using 17-4 precipitation hardenable (PH) stainless steel, it was reported that a nonequilibrium microstructure developed [1]. This microstructure exhibited a strong difference in texture components parallel and perpendicular to the build direction resulting from the very high cooling rates. The SLM-prepared as-built part also contained a substantial fraction of retained austenite, in contrast to wrought 17-4PH materials, which have a fully martensitic structure strengthened by fine Cu-rich precipitates. In recent work by Cheruvathur et al., post-build heat treatments were applied to AM 17-4PH materials to obtain a more uniform microstructure and promote the precipitation of the Cu-rich phase [2]. It is clearly important to understand the microstructural development during AM processing and during subsequent heat treatment. In this study, the effect of post-build heat treatments on SLM prepared 17-4PH as-built parts is studied in comparison to that of conventionally processed 17-4PH.A 3DSystems ProX-300 laser powder bed AM machine was used to fabricate the test specimens. The microstructures of as-built and solution-treated (annealed at 1040°C for 4 hours and air cooled) 17-4PH AM parts and solution-treated 17-4PH bar stock were studied. SEM and EBSD analyses were performed using a FEI Teneo-LoVac FEG-SEM equipped with an EDAX TEAM TM EBSD system. The acquired EBSD orientation map was further processed using the TSL OIM analysis software.EBSD orientation maps of 17-4PH as-built and solution-treated samples are shown in Figure 1a and 1b. A non-uniform microstructure is exhibited for the as-built sample composed of elongated coarse martensite laths, up to 100 µm in length and aligned roughly parallel to the build direction, and fine equiaxed grains along the martensite lath boundaries. The corresponding EBSD phase map indicates that the retained austenite grains are all located in the fine-grained regions. The solution-treated 17-4PH AM sample exhibits a much more uniform martensitic microstructure. The martensite grain size measured by EBSD is refined from ~22 µm in the as-built sample to ~2.8 µm in the solution-treated sample. EBSD orientation maps from solution-treated conventional 17-4PH samples also exhibit a uniform martensite microstructure, as shown in Figure 1c. However, the martensite laths are much coarser than those in the solution-treated AM sample. It is well known that the martensite transformation occurs within the prior austenite grains, and so the size of these grains has a significant inf...

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Microstructure and Mechanical Behavior of 17-4 Precipitation Hardenable Steel Processed by Selective Laser Melting

Cited by 237 publications

References 34 publications

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Tailoring residual stress profile of Selective Laser Melted parts by Laser Shock Peening

Microstructural Study of the Heat-treated 17-4PH Stainless Steel Parts Prepared by Selective Laser Melting

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