Origin of dislocation structures in an additively manufactured austenitic stainless steel 316L

Bertsch, K.M.; Bellefon, G. Meric de; Kuehl, Bailey; Thoma, Dan J.

doi:10.1016/j.actamat.2020.07.063

Cited by 491 publications

(110 citation statements)

References 41 publications

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“…part is dominated by the dislocation density. The dislocation density of different alloys in the as-LPBFprocessed state remains a closely consistent value in the order of magnitude of 10 14 /m 2 from a batch of reports [18,176,177] Another approach to validate the consistency of dislocation densities is to deduce the cellular size of the as-LPBF-processed samples. The dislocation density, , in a cellular structure containing materials is related to the reciprocal of the cubic square of cellular size, 2 , and it could be expressed as ∝ 1 2 ⁄…”

Section: )mentioning

confidence: 93%

Alloy Design and Characterization of γ′ Strengthened Nickel-based Superalloys for Additive Manufacturing

2021

Linköping Studies in Science and Technology. Licentiate Thesis

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Nickel-based superalloys, an alloy system bases on nickel as the matrix element with the addition of up to 10 more alloying elements including chromium, aluminum, cobalt, tungsten, molybdenum, titanium, and so on. Through the development and improvement of nickel-based superalloys in the past century, they are well proved to show excellent performance at the elevated service temperature. Owing to the combination of extraordinary high-temperature mechanical properties, such as monotonic and cyclic deformation resistance, fatigue crack propagation resistance; and high-temperature chemical properties, such as corrosion and oxidation resistance, phase stability, nickel-based superalloys are widely used in the critical hot-section components in aerospace and energy generation industries. The success of nickel-based superalloy systems attributes to both the well-tailored microstructures with the assistance of carefully doped alloying elements, and the intently developed manufacturing processes. The microstructure of the modern nickel-based superalloys consists of a two-phase configuration: the intermetallic precipitates (Ni,Co)3(Al,Ti,Ta) known as γ′ phase dispersed into the austenite γ matrix, which is firstly introduced in the 1940s. The recently developed additive manufacturing (AM) techniques, acting as the disruptive manufacturing process, offers a new avenue for producing the nickel-based superalloy components with complicated geometries. However, γ′ strengthened nickel-based superalloys always suffer from the micro-cracking during the AM process, which is barely eliminated by the process optimization. On this basis, the new compositions of γ′ strengthened nickel-based superalloy adapted to the AM process are of great interest and significance. This study sought to design novel γ′ strengthened nickel-based superalloys readily for AM process with limited cracking susceptibility, based on the understanding of the cracking mechanisms. A two-parameter model is developed to predict the additive manufacturability for any given composition of a nickel-based superalloy. One materials index is derived from the comparison of the deformation-resistant capacity between dendritic and interdendritic regions, while another index is derived from the difference of heat resistant capacity of these two spaces. By plotting the additive manufacturability diagram, the superalloys family can be categorized into the easy-to-weld, fairly-weldable, and non-weldable regime with the good agreement of the existed knowledge. To design a novel superalloy, a Cr-Co-MoW -Al-Ti-Ta-Nb-Fe-Ni alloy family is proposed containing 921,600 composition recipes in total. Through the examination of additive manufacturability, undesired phase formation propensity, and the precipitation fraction, one composition of superalloy, MAD542, out of the 921,600 candidates is selected. Validation of additive manufacturability of MAD542 is carried out by laser powder bed fusion (LPBF). By optimizing the LPBF process parameters, the crack-free MAD542 part is achieved. I...

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Section: )mentioning

confidence: 93%

Alloy Design and Characterization of γ′ Strengthened Nickel-based Superalloys for Additive Manufacturing

2021

Linköping Studies in Science and Technology. Licentiate Thesis

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“…In an as-built condition, the dendritic substructure usually goes along with a high dislocation density at the cell boundaries resulting from high thermal stresses. [13] It can be assumed that heat treatments between 800 and 1000 C lead to a reduction in the dislocation density and the residual stresses. [6,39,40] A higher-resolution image (Figure 3b) of the heat-treated condition shows an area where the substructure has vanished and left parallel line patterns (see arrow).…”

Section: Microstructure Of Additively and Conventionally Manufactured Materialsmentioning

confidence: 99%

Temperature‐Dependent Dynamic Strain Aging in Selective Laser Melted 316L

et al. 2021

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to that, superior tensile properties of AM 316L were also obtained at temperatures of 250 [7] and 800 C. [8] For long time exposures under high temperatures, however, unstable dislocation cells can deteriorate the creep properties. [9,10] Saeidi et al. [8] also observed the propagation of Luders bands, which are closely related to dynamic strain aging (DSA), at 800 C. However, no systematic study on the influence of the SLM microstructure on the mechanical properties over the entire temperature regime from room temperature to 900 C has been conducted yet. This is surprising, as AISI 316L is a widely used austenitic stainless steel for applications at elevated temperatures, and it is known from the conventionally produced material that DSA occurs at elevated temperatures. The improvement of the process parameters in recent years with respect to the laser power, hatch distance, scan strategy, etc. allows nowadays the manufacturing of geometrically accurate parts with high strength. [11] The high thermal gradients and high solidification rates in the SLM process lead to a fine columnar dendritic solidification with microsegregation. Rapid local heating and cooling introduce significant stresses in accordance with the temperature gradient mechanism (TGM). [12] Recent results of Bertsch et al. [13] showed that these stresses and strains contribute strongly to the formation of dislocations. Mainly due to the high dislocation density, networks are formed. These dislocation cells typically overlap the microsegregations. Dendritic segregations and dislocation cells are known to be beneficial for the mechanical properties. [1][2][3]5] The main strengthening mechanisms of the austenitic steel 316L are solid solution and Hall-Petch strengthening. In the case of SLM-processed 316L, additional strengthening by the dendritic substructure has to be considered. These substructures consist of segregated elements and entangled dislocations contributing to the strength of the material. [1,14,15] One model to understand the fundamentals of strengthening by cellular dislocation structures was established by Mughrabi. [16][17][18] The socalled composite model describes the stress distribution in the soft cell and hard wall regions and enables the calculation of the total strengthening effect by a modified Taylor equation, using a geometric constant for the heterogeneous composite, α het , depending on the wall thickness and cell diameter. [18] It was also found by Blum and Reppich, [19,20] for cellular dislocation networks developed under static creep loads, that the

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“…A number of studies have been carried out to understand the fundamental strengthening mechanisms and the roles of porosity, dislocation cell size, dislocation density, elemental segregation, and particles in the strength of AM 316L SS [2,4,5,17,27,[29][30][31][32][33]. The lowtemperature high strength and good ductility of AM 316L SS has been attributed to dislocation cell structures formed during printing.…”

Section: Introductionmentioning

confidence: 99%

Location-Dependent Mechanical Property Evaluation on Additively Manufacture Materials

Chen

Zhang

et al. 2021

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This report summarizes research activities conducted at Argonne National Laboratory in support of the development, qualification and certification of additively manufactured (AM) metallic components to allow for innovative reactor design and licensing for the Transformational Challenge Reactor (TCR). Focus is on the evaluation of high temperature mechanical properties including creep and fatigue of 316L stainless steel manufactured by the laser powder bed fusion process. Creep behavior of AM 316L stainless steel was evaluated for rods printed by either or a combination of both lasers of the dual-laser system of a Concept Laser-M2 printer to examine the consistency across the build plate. Creep tests were conducted at temperatures of 550, 575, 600, and 650°C and stresses between 175 and 300 MPa using ASTM standard-sized specimens. The effect of heat treatments at different temperatures on creep properties of AM 316L SS was examined to understand the processing-microstructure-property relationship. Fatigue properties of AM 316L SS were investigated for two print geometries (rod and plate) and in two build orientations of printed plates. Locations of specimens in the build were carefully tracked such that the testing data can be directly related to location-specific in situ data to establish links between printing process, post-printing treatment, microstructure and mechanical properties. The work is to support the development of a digital platform informed approach to AM component qualification and certification for nuclear applications.

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Origin of dislocation structures in an additively manufactured austenitic stainless steel 316L

Cited by 491 publications

References 41 publications

Alloy Design and Characterization of γ′ Strengthened Nickel-based Superalloys for Additive Manufacturing

Alloy Design and Characterization of γ′ Strengthened Nickel-based Superalloys for Additive Manufacturing

Temperature‐Dependent Dynamic Strain Aging in Selective Laser Melted 316L

Location-Dependent Mechanical Property Evaluation on Additively Manufacture Materials

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