Tensile properties, strain rate sensitivity, and activation volume of additively manufactured 316L stainless steels

Li, Zan; Voisin, Thomas; McKeown, Joseph T.; Ye, Jianchao; Braun, Tom; Kamath, Chandrika; King, Wayne E.; Wang, Y. Morris

doi:10.1016/j.ijplas.2019.05.009

Cited by 184 publications

(64 citation statements)

References 72 publications

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“…[67,69] Thus, the values of m are estimated from the gradient of a double logarithmic plot of H/3 versusε and shown as inset in Figure 9, whereas the evolution of The values of m for the as-received disk are estimated as %0.041 (center) and %0.040 (edge), which are of one order higher than 0.0061 obtained for coarse-grained 316L SS [70] and other typical coarse-grained FCC metals, e.g., %0.004 for high-purity Cu, [71] %0.0028 for pure Ni, [72] and %0.004 for Al 99.5. [73] However, these values are consistent with the m values for AM 316L SS as explained by Li et al, [74] ranging from 0.02 to 0.03, when measured by tensile tests at different strain rates and strain rate jump tests. In fact, the high values of m obtained for the as-received SLM-fabricated 316L SS in this study are close to or higher than those of CM FCC metals having nanosized grains, e.g., m ¼ 0.015-0.034 for pure Ni with grain sizes <100 nm.…”

Section: Discussionsupporting

confidence: 87%

“…[80,81] However, it is closer to the value of 22-28b 3 reported by Li et al for AM 316L SS. [74] This discrepancy can be attributed to the difference in the testing method used to determine m, with tensile and strain rate jump tests used in the study by Li et al [74] and nanoindentation in this study. Nevertheless, the rather low V * p value in AM 316L SS compared with CM coarse-grained 316L SS and other FCC metals suggests the abundance of barriers to dislocation for deformation via plastic flow, including a mix of high-angle and low-angle GBs, pre-existing dislocations, nanoprecipitates, cellular structure networks, numerous fusion boundaries from solidified melt pools, and localized misorientations.…”

Section: Discussionmentioning

confidence: 72%

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Micromechanical Response of Additively Manufactured 316L Stainless Steel Processed by High‐Pressure Torsion

et al. 2020

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Numerous studies have reported attractive properties in ultrafinegrained (UFG) and nanograined (NG) metals and alloys compared with their coarse-grained (CG) counterparts, including significantly higher yields and tensile strengths, [1-3] enhanced wear and corrosion resistance, [4-6] and superplasticity at room temperature (RT). [7,8] It is now accepted that UFG and NG materials are defined as those having grain sizes in the range of 0.1-1 μm and <100 nm, respectively. Such remarkable properties are largely attributed to grain refinement and the generation of large amounts of dislocations in these grain scales, highlighting the benefit of fine grain microstructure. [9,10] To date, severe plastic deformation (SPD) processing has emerged as one of the most popular techniques that can produce bulk metals with UFG and NG microstructures, including equal-channel angular pressing (ECAP), high-pressure torsion (HPT), and accumulative roll bonding (ARB). From these techniques, HPT has been shown as the most effective method to produce true NG structures with large amounts of highangle grain boundaries (GBs) via the application of concurrent compressive force and torsional straining on HPT-processed samples. [11] In contrast, additive manufacturing (AM) has now been utilized to fabricate metallic components for niche engineering applications, e.g., automotive, biomedical, and aerospace, due to its attractive features of design flexibility, time and cost savings, and minimal material waste. [12] Selective laser melting (SLM) is one of the most widely used AM methods in the laser powder bed fusion (LPBF) category. As its name implies, SLM uses laser as the heat source to selectively consolidate layers of the powder bed into a complete 3D structure according to the initial computer-aided design (CAD) data. To date, a wide range of alloys have been used to fabricate metallic components using SLM, including 316L stainless steel (316L SS), Inconel 718 (IN 718), AlSi 10 Mg, and Ti6Al4V. [13,14] So far, research on metal AM has focused on optimizing processing parameters to achieve the highest densification levels with minimal porosity or defect contents. [15-28] To minimize

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Section: Discussionsupporting

confidence: 87%

Section: Discussionmentioning

confidence: 72%

Micromechanical Response of Additively Manufactured 316L Stainless Steel Processed by High‐Pressure Torsion

et al. 2020

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“…A high work hardening rate is essential for good uniform elongation because it can help delay the localized deformation stress (necking) under tension 38 . The strain hardening exponent (n) of the cast and SLM samples was calculated using the Holloman-Ludwig equation 39 ; however, it is difficult to obtain a single power law fit, which was also found for other additive manufactured materials 14 . Values of~0.20 and 0.28 are obtained for the SLM sample at strains of 0.012-0.05 and 0.05-0.17, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…The SLM sample has a higher value of n than the cast sample, which can be explained by the presence of a high density of internal defects, disconnected precipitates, and a hierarchical microstructure (giving back stress) 14,15 , which significantly influence the strain-hardening behavior. An interaction between the nanotwining and the disconnected precipitates is also observed and may contribute to the strain hardening.…”

Section: Resultsmentioning

confidence: 99%

“…The premature failure is due to the presence of external defects (pores and unmelted particles) that act as sites for crack initiation; the cracks then propagate through the grain boundaries and/or cellular boundaries. Materials fabricated by selective laser melting typically have a unique metastable cellular microstructure, such as Al-12Si, AlSi10Mg, CoCrMo, and 316L [12][13][14][15] . The cellular boundaries usually constitute a nearly connected layer 12 that can accelerate crack propagation.…”

Section: Introductionmentioning

confidence: 99%

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Premature failure of an additively manufactured material

et al. 2020

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Additively manufactured metallic materials exhibit excellent mechanical strength. However, they often fail prematurely owing to external defects (pores and unmelted particles) that act as sites for crack initiation. Cracks then propagate through grain boundaries and/or cellular boundaries that contain continuous brittle second phases. In this work, the premature failure mechanisms in selective laser melted (SLM) materials were studied. A submicron structure was introduced in a SLM Ag-Cu-Ge alloy that showed semicoherent precipitates distributed in a discontinuous but periodic fashion along the cellular boundaries. This structure led to a remarkable strength of 410 ± 3 MPa with 16 ± 0.5% uniform elongation, well surpassing the strength-ductility combination of their cast and annealed counterparts. The hierarchical SLM microstructure with a periodic arrangement of precipitates and a high density of internal defects led to a high strain hardening rate and strong strengthening, as evidenced by the fact that the precipitates were twinned and encircled by a high density of internal defects, such as dislocations, stacking faults and twins. However, the samples fractured before necking owing to the crack acceleration along the external defects. This work provides an approach for additively manufacturing materials with an ultrahigh strength combined with a high ductility provided that premature failure is alleviated.

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Strengthening Mechanisms and Strain Hardening Behavior of 316L Stainless Steel Manufactured by Laser‐Based Powder Bed Fusion

Taghipour

Mazaheri

McDavid³

et al. 2022

Adv Eng Mater

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The microstructure–properties relations and strengthening mechanisms of additively manufactured 316L stainless steel are comprehensively investigated in this work. The orientation dependency and the strain hardening are studied by tensile testing of as‐built specimens fabricated by laser‐based powder bed fusion (LPBF) in different directions. The results are compared with those obtained for wrought material. The microstructure of the wrought and the LPBF materials are also comprehensively investigated. Equiaxed grains with random orientation and relatively uniform size (≈30 μm) are observed in the wrought material, where the LPBF samples show columnar grains inside as well as fine equiaxed grains in the bottom of the molten pool. A bimodal grain size distribution, higher values of geometrically necessary dislocations density (≈25–32%), and lower fractions of high‐angle grain boundaries (≈24–28%) are observed in LPBF 316L. A significant yield strength and considerable ultimate strength improvement without remarkable elongation decrease are obtained for the LPBF tensile specimens, resulting in a high strength‐elongation balance (up to 26 122 MPa%). Two‐stage strain hardening is depicted in both wrought and LPBF samples. This is successfully predicted with two‐stage Hollomon analysis. However, the LPBF samples illustrate lower strain hardening exponents in comparison with the wrought ones.

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Tensile properties, strain rate sensitivity, and activation volume of additively manufactured 316L stainless steels

Cited by 184 publications

References 72 publications

Micromechanical Response of Additively Manufactured 316L Stainless Steel Processed by High‐Pressure Torsion

Micromechanical Response of Additively Manufactured 316L Stainless Steel Processed by High‐Pressure Torsion

Premature failure of an additively manufactured material

Strengthening Mechanisms and Strain Hardening Behavior of 316L Stainless Steel Manufactured by Laser‐Based Powder Bed Fusion

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