Publications
440 results found
Khanchandani H, Gault B, 2023, Atomic scale understanding of the role of hydrogen and oxygen segregation in the embrittlement of grain boundaries in a twinning induced plasticity steel, SCRIPTA MATERIALIA, Vol: 234, ISSN: 1359-6462
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- Citations: 1
El-Zoka AA, Stephenson LT, Kim S-H, et al., 2023, The fate of water in hydrogen-based iron oxide reduction, Advanced Science, Vol: 10, ISSN: 2198-3844
Gas–solid reactions are important for many redox processes that underpin the energy and sustainability transition. The specific case of hydrogen-based iron oxide reduction is the foundation to render the global steel industry fossil-free, an essential target as iron production is the largest single industrial emitter of carbon dioxide. This perception of gas–solid reactions has not only been limited by the availability of state-of-the-art techniques which can delve into the structure and chemistry of reacted solids, but one continues to miss an important reaction partner that defines the thermodynamics and kinetics of gas phase reactions: the gas molecules. In this investigation, cryogenic-atom probe tomography is used to study the quasi in situ evolution of iron oxide in the solid and gas phases of the direct reduction of iron oxide by deuterium gas at 700°C. So far several unknown atomic-scale characteristics are observed, including, D2 accumulation at the reaction interface; formation of a core (wüstite)-shell (iron) structure; inbound diffusion of D through the iron layer and partitioning of D among phases and defects; outbound diffusion of oxygen through the wüstite and/or through the iron to the next free available inner/outer surface; and the internal formation of heavy nano-water droplets at nano-pores.
Yoo S-H, Aota LS, Shin S, et al., 2023, Dopant evolution in electrocatalysts after hydrogen oxidation reaction in an alkaline environment, ACS Energy Letters, Vol: 8, Pages: 3381-3386, ISSN: 2380-8195
Introduction of interstitial dopants has opened a new pathway to optimize nanoparticle catalytic activity for, e.g., hydrogen evolution/oxidation and other reactions. Here, we discuss the stability of a property-enhancing dopant, B, introduced through the controlled synthesis of an electrocatalyst Pd aerogel. We observe significant removal of B after the hydrogen oxidation reaction. Ab initio calculations show that the high stability of subsurface B in Pd is substantially reduced when H is adsorbed/absorbed on the surface, favoring its departure from the host nanostructure. The destabilization of subsurface B is more pronounced, as more H occupies surface sites and empty interstitial sites. We hence demonstrate that the H2 fuel itself favors the microstructural degradation of the electrocatalyst and an associated drop in activity.
Douglas JO, El-Zoka A, Conroy M, et al., 2023, Development of site specific cryogenic specimen preparation and transfer of frozen liquids for complementary high-resolution analysis by scanning transmission electron microscopy and atom probe tomography, Microscopy and Microanalysis, Vol: 29, Pages: 1700-1701, ISSN: 1083-0375
Chen X, Mianroodi JR, Liu C, et al., 2023, Investigation of vacancy trapping by solutes during quenching in aluminum alloys, ACTA MATERIALIA, Vol: 254, ISSN: 1359-6454
Antonov S, Prithiv TS, Zhou X, et al., 2023, Phase transformations in the alumina-forming austenitic stainless-steel Fe-20Cr-30Ni-2Nb-5Al during creep at 750°C 45 MPa, MATERIALIA, Vol: 30, ISSN: 2589-1529
Pedrazzini S, Pek ME, Ackerman AK, et al., 2023, Effect of substrate bed temperature on solute segregation and mechanical properties in Ti–6Al–4V produced by laser powder bed fusion, Metallurgical and Materials Transactions A, Vol: 54, Pages: 3069-3085, ISSN: 1073-5623
Titanium alloys are particularly sensitive to temperature during additive manufacturing processes, due to their dual phase microstructure and sensitivity to oxygen uptake. In this paper, laser powder bed fusion (LPBF) was used in conjunction with a heated substrate bed at 100 °C, 570 °C and 770 °C to produce specimens of Ti–6Al–4V, to investigate the change in mechanical properties and segregation of alloying elements. An initial increase in ductility was observed when increasing the temperature from 100 °C to 570 °C, followed by a significant loss in ductility when samples were produced at 770 °C. A suite of multi-scale characterisation techniques revealed that the as-printed microstructure was drastically different across the range of temperatures. At 100 °C, α + α′ phases were identified. Deformation twinning was extensively observed in the a phase, with Al and V segregating at the twin interfaces. At 570 °C (the most ductile sample), α′, α and nano-particles of β were observed, with networks of entangled dislocations showing V segregation. At 770 °C, no martensitic α′ was identified. The microstructure was an α + β microstructure and an increased volume fraction of tangled dislocations with localised V segregation. Thermodynamic modelling based on the Gibbs-free energy of formation showed that the increased V concentration at dislocations was insufficient to locally nucleate β phase. However, b-phase nucleation at grain boundaries (not dislocations) caused pinning of grain boundaries, impeding slip and leading to a reduction in ductility. It is likely that the increased O-content within specimens printed at increased temperatures also played a key role in high-temperature embrittlement. Building operations are therefore best performed below sub-transus temperatures, to encourage the growth of strengthening phases via so
Vurpillot F, Rousseau L, Hatzoglou C, et al., 2023, Beyond Atom Mapping in Atom Probe Tomography Using Field Evaporation Energy Loss Spectroscopy., Microsc Microanal, Vol: 29, Pages: 605-606
Morgado FF, Bhatt S, Stephenson L, et al., 2023, Role of Simulations and Experiments in Analytical Field Ion Microscopy., Microsc Microanal, Vol: 29
Schwarz TM, Yu W, Zhan H, et al., 2023, Uncovering Ce-rich clusters and their role in precipitation strengthening of an AE44 alloy, Scripta Materialia, Vol: 232, ISSN: 1359-6462
The peak-aged (250°C for 4 h) magnesium-aluminum-rare earth (Mg-Al-RE) alloy AE44-2 produced using high-pressure die casting, exhibits a 10 % increase in yield strength attributed to the formation of nanoscale AlMn precipitates. Here, in the as cast state, we show by atom probe tomography Ce-rich clusters in the dendritic and not in the inter-dendritic α-Mg, despite a higher RE concentration. Their formation hence depends mainly on solidification kinetics and not on the concentration. The Ce-rich clusters within the dendritic region, act as heterogeneous nucleation sites for the formation of Al10Mn7RE2 nanoscale precipitates during the T5 heat treatment. No changes in the Al11RE3 lamella phase were observed, including to the concentration of segregated Si at the Al11RE3/α-Mg interface. Understanding the precipitate formation pathways, specifically the influence of low concentrations of Ce in the dendritic matrix, provides a pathway for tailoring mechanical properties by manipulating these clusters and consequently precipitation.
Ahmadian A, Scheiber D, Zhou X, et al., 2023, Interstitial segregation has the potential to mitigate liquid metal embrittlement in iron., Advanced Materials, Vol: 35, Pages: 1-11, ISSN: 0935-9648
The embrittlement of metallic alloys by liquid metals leads to catastrophic material failure and severely impacts their structural integrity. The weakening of grain boundaries (GBs) by the ingress of liquid metal and preceding segregation in the solid are thought to promote early fracture. However, the potential of balancing between the segregation of cohesion-enhancing interstitial solutes and embrittling elements inducing GB de-cohesion is not understood. Here, the mechanisms of how boron segregation mitigates the detrimental effects of the prime embrittler, zinc, in a Σ5 [001] tilt GB in α-Fe (4 at.% Al) is unveiled. Zinc forms nanoscale segregation patterns inducing structurally and compositionally complex GB states. Ab initio simulations reveal that boron hinders zinc segregation and compensates for the zinc-induced loss in GB cohesion. The work sheds new light on how interstitial solutes intimately modify GBs, thereby opening pathways to use them as dopants for preventing disastrous material failure.
Prithiv TS, Gault B, Li Y, et al., 2023, Austenite grain boundary segregation and precipitation of boron in low-C steels and their role on the heterogeneous nucleation of ferrite, ACTA MATERIALIA, Vol: 252, ISSN: 1359-6454
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- Citations: 1
Zhou X, Ahmadian A, Gault B, et al., 2023, Atomic motifs govern the decoration of grain boundaries by interstitial solutes, NATURE COMMUNICATIONS, Vol: 14
Morgado FF, Stephenson L, Rousseau L, et al., 2023, Improving Spatial and Elemental Associations in Analytical Field Ion Microscopy, MICROSCOPY AND MICROANALYSIS, Vol: 29, Pages: 1077-1086, ISSN: 1431-9276
Kim S-H, Stephenson LT, Schwarz T, et al., 2023, Chemical Analysis for Alkali Ion-exchanged Glass Using Atom Probe Tomography, MICROSCOPY AND MICROANALYSIS, Vol: 29, Pages: 890-899, ISSN: 1431-9276
Aota LS, Jung C, Zhang S, et al., 2023, Revealing Compositional Evolution of PdAu Electrocatalyst by Atom Probe Tomography, ACS ENERGY LETTERS, Vol: 8, Pages: 2824-2830, ISSN: 2380-8195
Douglas JO, Conroy M, Giuliani F, et al., 2023, In-situ sputtering from the micromanipulator to enable cryogenic preparation of specimens for atom probe tomography by focused-ion beam, Microscopy and Microanalysis, Vol: 29, Pages: 1009-1017, ISSN: 1083-0375
Workflows have been developed in the past decade to enable atom probe tomography analysis at cryogenic temperatures. The inability to control the local deposition of the metallic precursor from the gas-injection system (GIS) at cryogenic temperatures makes the preparation of site-specific specimens by using lift-out extremely challenging in the focused-ion beam. Schreiber et al. exploited redeposition to weld the lifted-out sample to a support. Here, we build on their approach to attach the region-of-interest and additionally strengthen the interface with locally sputtered metal from the micromanipulator. Following standard focused-ion beam annular milling, we demonstrate atom probe analysis of Si in both laser pulsing and voltage mode, with comparable analytical performance as a presharpened microtip coupon. Our welding approach is versatile, as various metals could be used for sputtering, and allows similar flexibility as the GIS in principle.
Gault B, Khanchandani H, Prithiv TS, et al., 2023, Transmission Kikuchi diffraction mapping induces structural damage in atom probe specimens, Microscopy and Microanalysis, Vol: 29, Pages: 1026-1036, ISSN: 1083-0375
Measuring local chemistry of specific crystallographic features by atom probe tomography (APT) is facilitated by using transmission Kikuchi diffraction (TKD) to help position them sufficiently close to the apex of the needle-shaped specimen. However, possible structural damage associated to the energetic electrons used to perform TKD is rarely considered and is hence not well-understood. Here, in two case studies, we evidence damage in APT specimens from TKD mapping. First, we analyze a solid solution, metastable β-Ti-12Mo alloy, in which the Mo is expected to be homogenously distributed. Following TKD, APT reveals a planar segregation of Mo among other elements. Second, specimens were prepared near Σ3 twin boundaries in a high manganese twinning-induced plasticity steel, and subsequently charged with deuterium gas. Beyond a similar planar segregation, voids containing a high concentration of deuterium, i.e., bubbles, are detected in the specimen on which TKD was performed. Both examples showcase damage from TKD mapping leading to artefacts in the distribution of solutes. We propose that the structural damage is created by surface species, including H and C, subjected to recoil from incoming energetic electrons during mapping, thereby getting implanted and causing cascades of structural damage in the sample.
Ma Y, Bae JW, Kim S-H, et al., 2023, Reducing Iron Oxide with Ammonia: A Sustainable Path to Green Steel, ADVANCED SCIENCE, Vol: 10
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- Citations: 2
Douglas JO, Conroy M, Giuliani F, et al., 2023, In situ sputtering from the micromanipulator to enable cryogenic preparation of specimens for atom probe tomography by focused-ion beam, Microscopy and Microanalysis, Vol: 29, Pages: 1009-1017, ISSN: 1083-0375
Workflows have been developed in the past decade to enable atom probe tomography analysis at cryogenic temperatures. The inability to control the local deposition of the metallic precursor from the gas-injection system (GIS) at cryogenic temperatures makes the preparation of site-specific specimens by using lift-out extremely challenging in the focused-ion beam. Schreiber et al. exploited redeposition to weld the lifted-out sample to a support. Here, we build on their approach to attach the region-of-interest and additionally strengthen the interface with locally sputtered metal from the micromanipulator. Following standard focused-ion beam annular milling, we demonstrate atom probe analysis of Si in both laser pulsing and voltage mode, with comparable analytical performance as a presharpened microtip coupon. Our welding approach is versatile, as various metals could be used for sputtering, and allows similar flexibility as the GIS in principle.
Bishara H, Langenohl L, Zhou X, et al., 2023, Decoupling the electrical resistivity contribution of grain boundaries in dilute Fe-alloyed Cu thin films, SCRIPTA MATERIALIA, Vol: 230, ISSN: 1359-6462
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- Citations: 2
Rousseau L, Normand A, Morgado FF, et al., 2023, Introducing field evaporation energy loss spectroscopy, COMMUNICATIONS PHYSICS, Vol: 6, ISSN: 2399-3650
Khanchandani H, Ponge D, Zaefferer S, et al., 2023, Hydrogen-induced hardening of a high-manganese twinning induced plasticity steel, Materialia, Vol: 28
High-manganese twinning-induced plasticity (TWIP) steels exhibit high strain hardening, high tensile strength, and high ductility, which make them attractive for structural applications. At low tensile strain rates, TWIP steels are prone to hydrogen embrittlement (HE). Here though, we study the hardening and strengthening resulting from electrochemical hydrogen-charging of a surface layer of a Fe-26.9Mn-0.28C (wt.%) TWIP steel. We observed a 20% increase in yield strength following the electrochemical hydrogen-charging, accompanied by a reduction in ductility from 75% to 10% at a tensile strain rate of 10−3s−1. The microstructural evolution during tensile deformation was examined at strain levels of 3%, 5% and 7% by electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) to study the dislocation structure of the hardened region. As expected, the microstructure of the hydrogen-hardened and the uncharged regions of the material evolve differently. The uncharged areas show entangled dislocation structures, indicating slip from a limited number of potentially coplanar slip systems. In contrast, hydrogen segregated to the grain boundaries, revealed by the deuterium-labelled atom probe tomography, delays the dislocation nucleation by blocking dislocation sources at the grain boundaries. The charged areas hence first show the formation of cells, indicating dislocation entanglement from more non-coplanar slip systems. With increasing strain, these cells dissolve, and stacking faults and strain-induced ε-martensite are formed, promoted by the presence of hydrogen. The influence of hydrogen on dislocation structures and the overall deformation mechanism is discussed in details.
Villoro RB, Wood M, Luo T, et al., 2023, Fe segregation as a tool to enhance electrical conductivity of grain boundaries in Ti(Co,Fe)Sb half Heusler thermoelectrics, ACTA MATERIALIA, Vol: 249, ISSN: 1359-6454
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- Citations: 2
Belkacemi LT, Gault B, Esin VA, et al., 2023, Ga-induced delithiation of grain boundaries in a Li containing Al-based alloy, MATERIALS CHARACTERIZATION, Vol: 199, ISSN: 1044-5803
Kim S-H, Shin K, Zhou X, et al., 2023, Atom probe analysis of BaTiO3 enabled by metallic shielding, Scripta Materialia, Vol: 229, Pages: 1-5, ISSN: 1359-6462
Atom probe tomography has been raising in prominence as a microscopy and microanalysis technique to gain sub-nanoscale information from technologically-relevant materials. However, the analysis of some functional ceramics, particularly perovskites, has remained challenging with extremely low yield and success rate. This seems particularly problematic for materials with high piezoelectric activity, which may be difficult to express at the low temperatures necessary for satisfactory atom probe analysis. Here, we demonstrate the analysis of commercial BaTiO3 particles embedded in a metallic matrix. Density-functional theory shows that a metallic coating prevents charge penetration of the electrostatic field, and thereby suppresses the associated volume change linked to the piezoelectric effect.
Zhou X, Bai Y, El-Zoka AA, et al., 2023, Effect of pore formation on redox-driven phase transformation, Physical Review Letters, Vol: 130, ISSN: 0031-9007
When solid-state redox-driven phase transformations are associated with mass loss, vacancies areproduced that develop into pores. These pores can influence the kinetics of certain redox and phasetransformation steps. We investigated the structural and chemical mechanisms in and at pores in acombined experimental-theoretical study, using the reduction of iron oxide by hydrogen as a model system.The redox product (water) accumulates inside the pores and shifts the local equilibrium at the alreadyreduced material back toward reoxidation into cubic Fe1-xO (where x refers to Fe deficiency, space groupFm3¯m). This effect helps us to understand the sluggish reduction of cubic Fe1-xO by hydrogen, a keyprocess for future sustainable steelmaking
Khanchandani H, Rolli R, Schneider H-C, et al., 2023, Hydrogen embrittlement of twinning-induced plasticity steels: contribution of segregation to twin boundaries, Scripta Materialia, Vol: 225, Pages: 1-5, ISSN: 1359-6462
Metallic materials, especially steel, underpin transportation technologies. High-manganese twinning induced plasticity (TWIP) austenitic steels exhibit exceptional strength and ductility from twins, low-energy microstructural defects that form during plastic loading. Their high-strength could help light-weighting vehicles, and hence cut carbon emissions. TWIP steels are however very sensitive to hydrogen embrittlement that causes dramatic losses of ductility and toughness leading to catastrophic failure of engineering parts. Here, we examine the atomic-scale chemistry and interaction of hydrogen with twin boundaries in a model TWIP steel by using isotope-labelled atom probe tomography, using tritium to avoid overlap with residual hydrogen. We reveal co-segregation of tritium and, unexpectedly, oxygen to coherent twin boundaries, and discuss their combined role in the embrittlement of these promising steels.
Dubosq R, Woods E, Gault B, et al., 2023, Electron microscope loading and in situ nanoindentation of water ice at cryogenic temperatures, PLoS One, Vol: 18, Pages: 1-11, ISSN: 1932-6203
Interest in the technique of low temperature environmental nanoindentation has gained momentum in recent years. Low temperature indentation apparatuses can, for instance, be used for systematic measurements of the mechanical properties of ice in the laboratory, in order to accurately determine the inputs for the constitutive equations describing the rheologic behaviour of natural ice (i.e., the Glen flow law). These properties are essential to predict the movement of glaciers and ice sheets over time as a response to a changing climate. Herein, we introduce a new experimental setup and protocol for electron microscope loading and in situ nanoindentation of water ice. Preliminary testing on pure water ice yield elastic modulus and hardness measurements of 4.1 GPa and 176 MPa, respectively, which fall within the range of previously published values. Our approach demonstrates the potential of low temperature, in situ, instrumented nanoindentation of ice under controlled conditions in the SEM, opening the possibility for investigating individual structural elements and systematic studies across species and concentration of impurities to refine to constitutive equations for natural ice.
Wang S, Douglas JO, Lovell E, et al., 2023, Near-atomic scale chemical analysis of interfaces in a La(Fe,Mn,Si)13-based magnetocaloric material, Scripta Materialia, Vol: 224, Pages: 1-6, ISSN: 1359-6462
La(Fe,Mn,Si)13-based magnetocaloric materials are one of the most promising material families for the realisation of near-room temperature magnetic refrigeration. The functional and mechanical properties of these materials crucially depend on their chemistry, which is difficult to control at interfaces between microstructural units. Atom probe tomography was employed to reveal the local elemental distribution at the α-Fe/1:13 phase boundary and the 1:13/1:13 grain boundary. Strong Mn segregation (and Fe depletion) at the α-Fe/1:13 phase boundary suggests the potential effect of phase boundary area on the Curie temperature of the material. A local off-1:13 stoichiometry layer at the 1:13/1:13 grain boundary may adversely affect the magnetocaloric performance. Routes to mitigate the negative effects of interfaces on the functional and mechanical performance of these materials are discussed, in order to achieve durable and efficient operation of magnetic cooling devices.
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