On the spheroidized carbide dissolution and elemental partitioning in a high carbon bearing steel 100Cr6

We report on the characterization of high carbon bearing steel 100Cr6 using electron microscopy and atom probe tomography in combination with multi-component diffusion simulations (DICTRA). Scanning electron micrographs show that around 14 vol.% spheroidized carbides are formed during soft annealing and only 3 vol.% remain after dissolution into the austenitic matrix by austenitization at 1123 K (850 {\deg}C) for 300 s. The spheroidized particles are identified as (Fe, Cr)3C by transmission electron microscopy. Atom probe analyses reveal the redistribution and partitioning behaviors of elements, i.e. C, Si, Mn, Cr, Fe in both, the spheroidized carbides and the bainitic matrix in the sample isothermally heat-treated at 773 K (500 {\deg}C) after austenitization. A homogeneous distribution of C and gradual gradient of Cr was detected within the spheroidized carbides. Due to its limited diffusivity in (Fe, Cr)3C, Cr exhibits a maximum concentration at the surface of spheroidized carbides (16 at.%) and decreases gradually from surface towards the core down to a level of about 2 at.%. The atom probe results also indicate that the partially dissolved spheroidized carbides during austenitization may serve as nucleation sites for intermediate temperature cementite within bainite, which results in a relatively softer surface and harder core in spheroidized particles. This microstructure may contribute to the good wear resistance and fatigue propertie

Tracking the Mn diffusion in the carbon-supported nanoparticles through the collaborative analysis of atom probe and evaporation simulation

Carbon-supported nanoparticles have been used widely as efficient catalysts due to their enhanced surface-to-volume ratio. To investigate their structure-property relationships, acquiring 3D elemental distribution is highly required. Here, the carbon-supported Pt, PtMn alloy, and ordered Pt3Mn nanoparticles are synthesized and analyzed with atom probe tomography as model systems. The significant difference of Mn distribution after the heat-treatment was found. Finally, the field evaporation behavior of the carbon support was discussed and each acquired reconstruction was compared with computational results from the evaporation simulation. This paper provides a guideline for studies using atom probe tomography on the heterogeneous carbon-nanoparticle system that leads to insights toward to a wide application in carbon-supported nano-catalysts

Element-Resolved Corrosion Analysis of Stainless-Type Glass-Forming Steels

Ultrathin passive films effectively prevent the chemical attack of stainless steel grades in corrosive environments; their stability depends on the interplay between structure and chemistry of the constituents iron, chromium, and molybdenum (Fe-Cr-Mo). Carbon (C), and eventually boron (B), are also important constituents of steels, although in small quantities. In particular, nanoscale inhomogeneities along the surface can have an impact on material failure but are still poorly understood. Addressing a stainless-type glass-forming Fe50Cr15Mo14C15B6 alloy and using a combination of complementary high-resolution analytical techniques, we relate near-atomistic insights into increasingly inhomogeneous nanostructures with time- and element-resolved dissolution behavior. The progressive elemental partitioning on the nanoscale determines the degree of passivation. A detrimental transition from Cr-controlled passivity to Mo-controlled breakdown is dissected atom by atom, demonstrating the importance of nanoscale knowledge for understanding corrosionPostprint (published version

Reducing time to discovery : materials and molecular modeling, imaging, informatics, and integration

This work was supported by the KAIST-funded Global Singularity Research Program for 2019 and 2020. J.C.A. acknowledges support from the National Science Foundation under Grant TRIPODS + X:RES-1839234 and the Nano/Human Interfaces Presidential Initiative. S.V.K.’s effort was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division and was performed at the Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), a U.S. Department of Energy, Office of Science User Facility.Multiscale and multimodal imaging of material structures and properties provides solid ground on which materials theory and design can flourish. Recently, KAIST announced 10 flagship research fields, which include KAIST Materials Revolution: Materials and Molecular Modeling, Imaging, Informatics and Integration (M3I3). The M3I3 initiative aims to reduce the time for the discovery, design and development of materials based on elucidating multiscale processing-structure-property relationship and materials hierarchy, which are to be quantified and understood through a combination of machine learning and scientific insights. In this review, we begin by introducing recent progress on related initiatives around the globe, such as the Materials Genome Initiative (U.S.), Materials Informatics (U.S.), the Materials Project (U.S.), the Open Quantum Materials Database (U.S.), Materials Research by Information Integration Initiative (Japan), Novel Materials Discovery (E.U.), the NOMAD repository (E.U.), Materials Scientific Data Sharing Network (China), Vom Materials Zur Innovation (Germany), and Creative Materials Discovery (Korea), and discuss the role of multiscale materials and molecular imaging combined with machine learning in realizing the vision of M3I3. Specifically, microscopies using photons, electrons, and physical probes will be revisited with a focus on the multiscale structural hierarchy, as well as structure-property relationships. Additionally, data mining from the literature combined with machine learning will be shown to be more efficient in finding the future direction of materials structures with improved properties than the classical approach. Examples of materials for applications in energy and information will be reviewed and discussed. A case study on the development of a Ni-Co-Mn cathode materials illustrates M3I3's approach to creating libraries of multiscale structure-property-processing relationships. We end with a future outlook toward recent developments in the field of M3I3.Peer reviewe

Investigations of grain boundary segregation in nanocrystalline Al-Cu- and Co-P alloys by means of 3d-atom probe tomography

Gegenstand dieser Arbeit ist die Charakterisierung nanokristalliner Al-Cu- und Co-P-Legierungen mit Hilfe der tomographischen Atomsonde (TAP) und weiterer Charakterisierungsmethoden. Von besonderem Interesse ist dabei die Verteilung der gelösten Komponenten, Cu und P, auf Subnanometer-Skala. Auf diese werden die technisch interessanten, makroskopischen Eigenschaften von Al-Cu und Co-P zurückgeführt. Nanokristalline Al-Cu-Schichten wurden durch Ar-Ionen-Sputtern mit einer starken Cu-Übersättigung auf Wolfram-Substratspitzen deponiert. Dabei wurde in den Schichten ein Gefüge aus kolumnar gewachsenen Körnern gefunden. Nach thermischer Behandlung wurde innerhalb der Al-Matrix eine Abnahme der Cu-Konzentration durch eine Korngrenzensegregation von Cu-Atomen nachgewiesen. Aufgrund der kolumnar gewachsenen Körner war jedoch die Detektion einer ausreichend hohen Anzahl von Korngrenzen nicht möglich. Als weiteres System wurde eine durch elektrolytische Abscheidung hergestellte Co-1,2 at.% P-Legierung untersucht. Dabei wurde bereits im Abscheidezustand eine P-Segregation in den Korngrenzen gemessen. Das nanokristalline Gefüge bleibt bis zu einer Temperatur von 400°C thermisch stabil, wobei sich in den Korngrenzen eine Sättigungssegregation von P-Atomen einstellt. Nach Auslagerung bei 480°C werden in den Korngrenzen P-Ausscheidungen detektiert und eine Abnahme des P-Exzesses gemessen. Damit verbunden ist eine merkliche Kornvergröberung, die ebenfalls bei dieser Temperatur beobachtet wird. Die thermische Stabilität der untersuchten Co-P-Legierung steht somit im direkten Zusammenhang mit der Sättigungssegregation von P. Anhand der experimentellen Daten lässt sich die Stabilisierung des nanokristallinen Gefüges auf eine starke Absenkung der Korngrenzenenergie und nicht auf den Solute-Drag-Effekt zurückführen

Oxidation behavior of AlN/CrN multilayered hard coatings

Abstract We report on the oxidation behavior of AlN/CrN multilayers at 900 °C, deposited by radio frequency magnetron sputtering. It is shown that oxidation in this system is controlled by diffusion of Cr towards the surface and formation of Cr2O3. Cr diffusion is found to mainly occur along grain boundaries. Thus, coherent cubic AlN/CrN multilayer regions with coarse columnar grain structures are found to be oxidation resistant, whereas regions decomposed into hexagonal AlN/cubic CrN are prone to oxidation

Microstructural evolution and hot cracking prevention in direct-laser-deposited Ni-based superalloy through Hf addition

Additive manufacturing (AM) is an emerging new paradigm in the production of industrial parts since it allows the fabrication of near-net shape products directly from designs, which is impossible with conventional manufacturing techniques. However, hot cracking phenomena in AM are a critical issue with non-weldable alloys, rendering manufactured parts unusable. There are solutions to this problem, such as alloying Hf with non-weldable Ni-based superalloys to improve cracking resistibility. Although this solution was proposed a few decades ago, the mechanisms of how Hf could prevent hot cracking in Ni-based superalloys have not been clarified in detail, until now. In this study, we revealed the Hf-driven microstructural changes in direct-laser-deposited Ni-based superalloys using various characterization techniques and phase-field simulations. Moreover, the calculated thermal strain and cracking susceptibility decreased with the Hf addition. The results demonstrated that Hf induced specific solidifying processes and resulting microstructural changes that are advantageous to the prevention of hot cracking