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Mark R. Stoudt

Bio: Mark R. Stoudt is an academic researcher from National Institute of Standards and Technology. The author has contributed to research in topics: Surface roughness & Inconel 625. The author has an hindex of 20, co-authored 55 publications receiving 1018 citations. Previous affiliations of Mark R. Stoudt include United States Department of Commerce.


Papers
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TL;DR: It is demonstrated that a subsequent homogenization heat treatment can effectively homogenize the AM alloy and remove the deleterious δ phase, and the combined experimental and modeling methodology can be extended to elucidate the phase evolution during heat treatments in a broad range of AM materials.

171 citations

Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution of additively manufactured Inconel 625 during a post-build stress-relief anneal of 1-hour at 1143 K (870 K) is investigated.
Abstract: The microstructural evolution of laser powder-bed additively manufactured Inconel 625 during a post-build stress-relief anneal of 1 hour at 1143 K (870 °C) is investigated. It is found that this industry-recommended heat treatment promotes the formation of a significant fraction of the orthorhombic D0a Ni3Nb δ-phase. This phase is known to have a deleterious influence on fracture toughness, ductility, and other mechanical properties in conventional, wrought Inconel 625; and is generally considered detrimental to materials’ performance in service. The δ-phase platelets are found to precipitate within the inter-dendritic regions of the as-built solidification microstructure. These regions are enriched in solute elements, particularly Nb and Mo, due to the micro-segregation that occurs during solidification. The precipitation of δ-phase at 1073 K (800 °C) is found to require up to 4 hours. This indicates a potential alternative stress-relief processing window that mitigates δ-phase formation in this alloy. Ultimately, a homogenization heat treatment is recommended for additively manufactured Inconel 625 because the increased susceptibility to δ-phase precipitation increases the possibility for significant degradation of materials' properties in service.

126 citations

Journal ArticleDOI
TL;DR: In this article, the role of grain orientation effects on critical strain localization was investigated using a scanning laser confocal microscope (SLCM) and electron backscatter diffraction (EBSD).
Abstract: Polycrystalline AA6022 tensile specimens were cut from sheet stock, mechanically polished, and uniaxially strained in situ under a scanning laser confocal microscope (SLCM) using a sub-sized universal testing apparatus. Prior to deformation, electron backscatter diffraction (EBSD) was performed on the gauge sections of one specimen in the rolling direction of the sheet and one in the transverse direction. Maps of the largest displacements in the surface morphology were constructed from the SLCM data and overlaid onto maps derived from the crystallographic orientation data to examine the strength of the influence that grain orientation effects have on critical strain localization. The roles of Taylor factors, grain boundary misorientation, largest Schmid factors, grain sizes, coincident site lattice orientations, and local grain breakup were considered. The largest surface displacements were observed to be concentrated at triple junctions where there is a large difference between the Taylor factors of the individual grains. The high degree of correlation between the density and location of these large surface displacements and the local plasticity conditions indicate that a critical localization event is most likely to initiate in grain boundary regions where unfavorable slip interactions produce the largest plastic strains.

87 citations

Journal ArticleDOI
20 Feb 2018-JOM
TL;DR: In this paper, single-track laser melting experiments and simulations on Inconel-625 were used to estimate the dimensions and microstructure of the resulting melt pool, based on a design-of-experiments approach which uses multiple laser power and scan speed combinations.
Abstract: We use single-track laser melting experiments and simulations on Inconel 625 to estimate the dimensions and microstructure of the resulting melt pool. Our work is based on a design-of-experiments approach which uses multiple laser power and scan speed combinations. Single-track experiments generated melt pools of certain dimensions that showed reasonable agreement with our finite-element calculations. Phase-field simulations were used to predict the size and segregation of the cellular microstructure that formed along the melt-pool boundaries for the solidification conditions that changed as a function of melt-pool dimensions.

71 citations

Journal ArticleDOI
TL;DR: In this paper, the microstructure evolution in Inconel 625 (IN625) manufactured using the additive manufacturing (AM) technique of laser powder-bed fusion is evaluated.
Abstract: The ability to use common computational thermodynamic and kinetic tools to study the microstructure evolution in Inconel 625 (IN625) manufactured using the additive manufacturing (AM) technique of laser powder-bed fusion is evaluated. Solidification simulations indicate that laser melting and re-melting during printing produce highly segregated interdendritic regions. Precipitation simulations for different degrees of segregation show that the larger the segregation, i.e., the richer the interdendritic regions are in Nb and Mo, the faster the δ-phase (Ni3Nb) precipitation. This is in accordance with the accelerated δ precipitation observed experimentally during post-build heat treatments of AM IN625 compared to wrought IN625. The δ-phase may be undesirable since it can lead to detrimental effects on the mechanical properties. The results are presented in the form of a TTT diagram and agreement between the simulated diagram and the experimental TTT diagram demonstrate how these computational tools can be used to guide and optimize post-build treatments of AM materials.

64 citations


Cited by
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TL;DR: Heterostructured materials have been reported as a new class of materials with superior mechanical properties, which was attributed to the development of back stress as discussed by the authors, and there are numerous reports on...
Abstract: Heterostructured materials have been reported as a new class of materials with superior mechanical properties, which was attributed to the development of back stress. There are numerous reports on ...

519 citations

Journal ArticleDOI
TL;DR: In this paper, an overview of the different kinds of steels in use in fusion-based AM processes and present their microstructures, their mechanical and corrosion properties, their heat treatments and their intended applications.
Abstract: Today, a large number of different steels are being processed by Additive Manufacturing (AM) methods. The different matrix microstructure components and phases (austenite, ferrite, martensite) and the various precipitation phases (intermetallic precipitates, carbides) lend a huge variability in microstructure and properties to this class of alloys. This is true for AM-produced steels just as it is for conventionally-produced steels. However, steels are subjected during AM processing to time-temperature profiles which are very different from the ones encountered in conventional process routes, and hence the resulting microstructures differ strongly as well. This includes a very fine and highly morphologically and crystallographically textured microstructure as a result of high solidification rates as well as non-equilibrium phases in the as-processed state. Such a microstructure, in turn, necessitates additional or adapted post-AM heat treatments and alloy design adjustments. In this review, we give an overview over the different kinds of steels in use in fusion-based AM processes and present their microstructures, their mechanical and corrosion properties, their heat treatments and their intended applications. This includes austenitic, duplex, martensitic and precipitation-hardening stainless steels, TRIP/TWIP steels, maraging and carbon-bearing tool steels and ODS steels. We identify areas with missing information in the literature and assess which properties of AM steels exceed those of conventionally-produced ones, or, conversely, which properties fall behind. We close our review with a short summary of iron-base alloys with functional properties and their application perspectives in Additive Manufacturing.

467 citations

Journal ArticleDOI

417 citations

Journal ArticleDOI
TL;DR: In this article, the development, fabrication, microstructures, and properties of MGMCs, including the room-temperature, cryogenictemperature and hightemperature mechanical properties upon quasi-static and dynamic loadings are reviewed.
Abstract: The mechanical properties of ex-situ and in-situ metallic glass matrix composites (MGMCs) have proven to be both scientifically unique and of potentially important for practical applications. However, the underlying deformation mechanisms remain to be studied. In this article, we review the development, fabrication, microstructures, and properties of MGMCs, including the room-temperature, cryogenic-temperature, and high-temperature mechanical properties upon quasi-static and dynamic loadings. In parallel, the deformation mechanisms are experimentally and theoretically explored. Moreover, the fatigue, corrosion, and wear behaviors of MGMCs are discussed. Finally, the potential applications and important unresolved issues are identified and discussed.

409 citations