Effects of Powder Attributes and Laser Powder Bed Fusion (L-PBF) Process Conditions on the Densification and Mechanical Properties of 17-4 PH Stainless Steel

Irrinki, Harish; Dexter, Michael; Barmore, Brenton; Enneti, Ravi K.; Pasebani, Somayeh; Badwe, Sunil; Stitzel, Jason; Malhotra, Rajiv; Atre, Sundar V.

doi:10.1007/s11837-015-1770-4

Cited by 70 publications

(37 citation statements)

References 17 publications

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“…[1][2][3][4][5][6][7][8][9][10] In general, the above processing conditions along with powder characteristics such as size, shape, and purity significantly determine the density, microstructures, and properties obtained from L-PBF parts. [6][7][8][11][12][13][14][15][16][17] In our former work, 18,19 a comprehensive study was performed to understand the role powder characteristics such as powder type, shape, and size along with L-PBF processing conditions on densification, mechanical properties, and microstructure of 17-4 PH stainless steel L-PBF parts. It was found that the % theoretical density, ultimate tensile strength, and hardness of L-PBF parts are sensitive to L-PBF processing conditions and starting powder shape, size, and type.…”

Section: Introductionmentioning

confidence: 99%

Microstructures, properties, and applications of laser sintered 17‐4PH stainless steel

Irrinki

Nath

Alhofors³

et al. 2019

J Am Ceram Soc

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The effects of hot isostatic pressing (HIP) on the densification, mechanical properties, and microstructures of laser‐powder bed fusion (L‐PBF) 17‐4 PH stainless steel parts were studied using gas‐ and water‐atomized powders. The % theoretical density, ultimate tensile strength, yield strength, elongation, and hardness of as‐printed and HIP‐ed L‐PBF parts were sensitive to energy density and starting powder shape, size, and type. At low‐energy densities of 64 and 80 J/mm3, densification was significant for water‐atomized L‐PBF parts when subjected to HIP treatment and density increased from 90% to 97%. For all the energy densities, the gas‐atomized L‐PBF parts after the HIP treatment showed significantly higher tensile strength, yield strength, and hardness when compared to water‐atomized L‐PBF parts properties. At low‐energy densities of 64 and 80 J/mm3, long columnar grains in the as‐printed L‐PBF parts did not change significantly after the HIP treatment whereas the columnar grains present in as‐printed gas‐atomized L‐PBF parts completely disappeared when subjected to HIP treatment. However, at high‐energy densities of 84 and 104 J/mm3, the columnar grains in as‐printed L‐PBF gas‐ and water‐atomized L‐PBF parts were changed to equiaxed grains and showed a higher level of homogenization when subjected to HIP treatment. This variation in grains and grain size had significantly affected the yield strength and elongation of HIP‐treated gas‐ and water‐atomized L‐PBF parts.

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Section: Introductionmentioning

confidence: 99%

Microstructures, properties, and applications of laser sintered 17‐4PH stainless steel

Irrinki

Nath

Alhofors³

et al. 2019

J Am Ceram Soc

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“…PH stainless-steel AM samples exhibit columnar bcc grains with strong overall [118] texture and small equi-axed fcc grains at molten pool boundaries, as shown in Figure 4. Previous work on as-built PH SS AM components revealed a non-equilibrium microstructure, as well as strong differences in texture parallel and perpendicular to the build direction, due to the very high cooling rates [17,99,[104][105][106][107]115]. Some of the literature claimed that the as-built microstructure via L-PBF contains martensite and retained austenite (metastable phase at room temperature) [26,27,95,98,[119][120][121][122], completely different from that of a wrought 17-4 PH stainless steel, which is fully martensitic.…”

Section: Microstructure In As L-pbfed Statementioning

confidence: 99%

“…Various combinations of these parameters result in parts experiencing a unique and complex thermal history, which results in a mixture of microstructures during the fabrication. For example, Irrinki et al [115] studied the mechanical properties of L-PBF 17-4 PH stainless steel using gas-versus water-atomized powders. It was found that specimens built by gas-atomized powder had superior densification (87% to 97%), elongation (7% to 23%), and ultimate tensile strength (470 MPa to 850 MPa) at a laser energy density of 64 J/mm 3 .…”

Section: Introductionmentioning

confidence: 99%

Laser Powder Bed Fusion of Precipitation-Hardened Martensitic Stainless Steels: A Review

Zai

Zhang

Wang

et al. 2020

Metals

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Martensitic stainless steels are widely used in industries due to their high strength and good corrosion resistance performance. Precipitation-hardened (PH) martensitic stainless steels feature very high strength compared with other stainless steels, around 3-4 times the strength of austenitic stainless steels such as 304 and 316. However, the poor workability due to the high strength and hardness induced by precipitation hardening limits the extensive utilization of PH stainless steels as structural components of complex shapes. Laser powder bed fusion (L-PBF) is an attractive additive manufacturing technology, which not only exhibits the advantages of producing complex and precise parts with a short lead time, but also avoids or reduces the subsequent machining process. In this review, the microstructures of martensitic stainless steels in the as-built state, as well as the effects of process parameters, building atmosphere, and heat treatments on the microstructures, are reviewed. Then, the characteristics of defects in the as-built state and the causes are specifically analyzed. Afterward, the effect of process parameters and heat treatment conditions on mechanical properties are summarized and reviewed. Finally, the remaining issues and suggestions on future research on L-PBF of martensitic precipitation-hardened stainless steels are put forward.Metals 2020, 10, 255 2 of 25 types of microstructures can be obtained with different heat treatment processes [9]. The typical temperature range for aging heat treatment for this alloy is 480-620 • C [1]. Under the H900 condition (aging temperature: 482 • C, time: 1 h), the precipitation in 17-4 PH stainless steel begins with Cu-rich precipitates (bcc, body center cubic) that maintain a coherent relationship with the matrix, which would lead to an increase in tensile strength and toughness [4]. These precipitates can transform into non-coherent Cu-rich particles (fcc, face center cubic) after extended aging at 400 • C [5]. After experiencing over-aging, the precipitates are coarsened. The number of precipitates is reduced, and the coherence relationship is also destroyed [6,10]. These changes together lead to a decrease in mechanical strength, but an increase in ductility and impact toughness.PH stainless steels are widely used in the aerospace industry [11,12], the marine industry [13], nuclear reactor components [14], chemical process equipment [15], and medical apparatus due to their high tensile strength, impact strength, fracture toughness, and corrosion resistance at typical service temperatures below 300 • C [15,16]. Most of these parts are important load-bearing components of heavy machinery in a demanding service environment. However, PH stainless steels have poor workability and machinability due to their high strength and high hardness, which result in a long production cycle and difficulties in obtaining desired shapes through conventional machining and forming processes [17].Due to the high strength and high hardness of PH steels, they are difficult to b...

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“…Another hinderance is represented by the very low viscosity of molten aluminum that significantly reduces the size of the feasible melt pool. In fact, if the viscosity is low, the molten metal is likely to show better wettability, which is expected to enhance powder densification [12]. Nonetheless, if the viscosity is too low, the melt pool is not stable anymore and balling phenomena are likely to occur [13].…”

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confidence: 99%

Fatigue Behavior of As-Built L-PBF A357.0 Parts

Bassoli

Denti

Comin

et al. 2018

Metals

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Laser-based powder bed fusion (L-PBF) is nowadays the preeminent additive manufacturing (AM) technique to produce metal parts. Nonetheless, relatively few metal powders are currently available for industrial L-PBF, especially if aluminum-based feedstocks are involved. In order to fill the existing gap, A357.0 (also known as A357 or A13570) powders are here processed by L-PBF and, for the first time, the fatigue behavior is investigated in the as-built state to verify the net-shaping potentiality of AM. Both the low-cycle and high-cycle fatigue areas are analyzed to draw the complete Wohler diagram. The infinite lifetime limit is set to 2 × 10 6 stress cycles and the staircase method is applied to calculate a mean fatigue strength of 60 MPa. This value is slightly lower but still comparable to the published data for AlSi10Mg parts manufactured by L-PBF, even if the A357.0 samples considered here have not received any post-processing treatment.Keywords: additive manufacturing; laser-based powder bed fusion; aluminum; fatigue strength present in AM parts, which may impact the mechanical behavior of finished constructs [3].Originally developed for rapid prototyping, AM is now growing very rapidly in terms of production numbers and economic importance. According to recent estimations, the sale of AM products and services is expected to grow from US $5.2 billion in 2015 to over US $26.5 billion by 2021. If metal AM is considered, according to statistics, 1768 AM systems were sold in 2017, compared to 983 systems in 2016, thus scoring an impressive increase of nearly 80% [4].Standard ISO/ASTM 52900-15 [5], which defines general principles and terminology for AM, groups AM techniques into seven categories, all of which are compatible with polymer feedstocks. However, only three of these processes, including powder bed fusion, direct energy deposition, and sheet lamination, also apply to metals. Among them, powder bed fusion (PBF) is emerging as the most promising one, on account of its flexibility in terms of part design and feedstock availability.In PBF, thermal energy is used to selectively consolidate specific areas of the powder bed, which is a relatively thin layer of fresh powder (typically below 100 µm) evenly distributed on top of the previously consolidated powder layers. The heat input may be supplied by an electron beam, in electron beam melting (EBM), or by a laser beam, in laser-based powder bed fusion (L-PBF). In the latter case, consolidation may rely upon sintering (direct laser sintering, DLS, also known as selective laser sintering, SLS) or complete melting-solidification mechanisms (selective laser melting, SLM) [6]. As a rule, the energy conveyed to the powder bed is enough to affect not only the new powder layer, but also the material underneath, so as to provide interlayer bonding [7].At present, in spite of the increasingly widespread diffusion of AM in the industry, there is still a lack of understanding of the mechanical behavior of materials processed by L-PBF, especially aluminum and its alloys...

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Effects of Powder Attributes and Laser Powder Bed Fusion (L-PBF) Process Conditions on the Densification and Mechanical Properties of 17-4 PH Stainless Steel

Cited by 70 publications

References 17 publications

Microstructures, properties, and applications of laser sintered 17‐4PH stainless steel

Microstructures, properties, and applications of laser sintered 17‐4PH stainless steel

Laser Powder Bed Fusion of Precipitation-Hardened Martensitic Stainless Steels: A Review

Fatigue Behavior of As-Built L-PBF A357.0 Parts

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