Imperial College London

ProfessorBaptisteGault

Faculty of EngineeringDepartment of Materials

Professor of Atomic-Scale Characterization
 
 
 
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Contact

 

b.gault

 
 
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Location

 

Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

375 results found

Wu Y, Skokov KP, Schäfer L, Maccari F, Aubert A, Rao Z, Schweinar K, Gault B, Xu H, Jiang C, Gutfleisch Oet al., 2022, A comparative study of Nd<inf>15</inf>Fe<inf>78</inf>B<inf>7</inf> and Nd<inf>15</inf>Co<inf>78</inf>B<inf>7</inf> systems: phase formations and coercivity mechanisms, Acta Materialia, Vol: 240, ISSN: 1359-6454

Both Nd-Fe-B and Nd-Co-B nanocrystalline magnets exhibit coercivity above 1 T. While the microstructure and mechanism of the coercive force of Nd-Fe-B magnets are well known, the Nd-Co-B system is much less studied, and the microstructure and origin of the high coercive state in this material is not well understood. In this work, we selected Nd15Fe78B7 and Nd15Co78B7 alloys with simple and stable stoichiometries to reveal the similarities and differences between these two systems. For this study, melt-spun nanocrystalline ribbons, hot-compacted magnets and bulk materials crystallized from the amorphous precursor were used. The coercivity of Nd15Fe18B7 alloy is in the range of 0.9–1.7 T, while for Nd15Co18B7 it was of 0.5–1.0 T. Electron microscopy and atom probe tomography analyses indicate that, in contrast to conventional Nd15Fe78B7, where the ferromagnetic Nd2Fe14B phase is the dominant matrix phase and the Nd-rich phase distributes along the grain boundaries providing magnetic decoupling, the Nd15Co18B7 alloys comprise of three randomly redistributed exchange-coupled ferromagnetic phases: Nd2Co14B, NdCo5 and NdCo4B. Single crystals of all constituent phases were grown and their spontaneous magnetization Ms and anisotropy constant K1 were determined. Using these measured intrinsic parameters and real nanostructure of Nd15Fe78B7 and Nd15Co78B7 alloys, micromagnetic simulations were carried out in order to reveal the differences in the coercivity mechanisms in these two distinctly different systems.

Journal article

Saksena A, Kubacka D, Gault B, Spiecker E, Kontis Pet al., 2022, The effect of gamma matrix channel width on the compositional evolution in a multi-component nickel-based superalloy, SCRIPTA MATERIALIA, Vol: 219, ISSN: 1359-6462

Journal article

Kim S-H, Dong K, Zhao H, El-Zoka AA, Zhou X, Woods EV, Giuliani F, Manke I, Raabe D, Gault Bet al., 2022, Understanding the degradation of a model si anode in a li-ion battery at the atomic scale., Journal of Physical Chemistry Letters, Vol: 36, Pages: 8416-8421, ISSN: 1948-7185

To advance the understanding of the degradation of the liquid electrolyte and Si electrode, and their interface, we exploit the latest developments in cryo-atom probe tomography. We evidence Si anode corrosion from the decomposition of the Li salt before charge-discharge cycles even begin. Volume shrinkage during delithiation leads to the development of nanograins from recrystallization in regions left amorphous by the lithiation. The newly created grain boundaries facilitate pulverization of nanoscale Si fragments, and one is found floating in the electrolyte. P is segregated to these grain boundaries, which confirms the decomposition of the electrolyte. As structural defects are bound to assist the nucleation of Li-rich phases in subsequent lithiations and accelerate the electrolyte's decomposition, these insights into the developed nanoscale microstructure interacting with the electrolyte contribute to understanding the self-catalyzed/accelerated degradation Si anodes and can inform new battery designs unaffected by these life-limiting factors.

Journal article

Xu Y, Toda H, Shimizu K, Wang Y, Gault B, Li W, Hirayama K, Fujihara H, Jin X, Takeuchi A, Uesugi Met al., 2022, Suppressed hydrogen embrittlement of high-strength Al alloys by Mn-rich intermetallic compound particles, ACTA MATERIALIA, Vol: 236, ISSN: 1359-6454

Journal article

Gault B, Schweinar K, Zhang S, Lahn L, Scheu C, Kim S-H, Kasian Oet al., 2022, Correlating atom probe tomography with x-ray and electron spectroscopies to understand microstructure-activity relationships in electrocatalysts, MRS BULLETIN, ISSN: 0883-7694

Journal article

Dubosq R, Schneider DA, Zhou X, Gault B, Langelier B, Plese Pet al., 2022, Bubbles and atom clusters in rock melts: A chicken and egg problem, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 428, ISSN: 0377-0273

Journal article

Gomell L, Tsai SP, Roscher M, Bueno Villoro R, Konijnenberg P, Zaefferer S, Scheu C, Gault Bet al., 2022, In situ nitriding of Fe2VAl during laser surface remelting to manipulate microstructure and crystalline defects, Physical Review Materials, Vol: 6

Tailoring the physical properties of complex materials for targeted applications requires optimizing the microstructure and crystalline defects that influence electrical and thermal transport and mechanical properties. Laser surface remelting can be used to modify the subsurface microstructure of bulk materials and hence manipulate their properties locally. Here, we introduce an approach to perform remelting in a reactive nitrogen atmosphere to form nitrides and induce segregation of nitrogen to structural defects. These defects arise from the fast solidification of the full-Heusler Fe2VAl compound that is a promising thermoelectric material. Advanced scanning electron microscopy, including electron channeling contrast imaging and three-dimensional electron backscatter diffraction, is complemented by atom probe tomography to study the distribution of crystalline defects and their local chemical composition. We reveal a high density of dislocations, which are stable due to their character as geometrically necessary dislocations. At these dislocations and low-angle grain boundaries, we observe segregation of nitrogen and vanadium, which can be enhanced by repeated remelting in nitrogen atmosphere. We propose that this approach can be generalized to other additive manufacturing processes to promote local segregation and precipitation states, thereby manipulating physical properties.

Journal article

Han L, Maccari F, Souza Filho IR, Peter NJ, Wei Y, Gault B, Gutfleisch O, Li Z, Raabe Det al., 2022, A mechanically strong and ductile soft magnet with extremely low coercivity., Nature, Vol: 608, Pages: 310-316

Soft magnetic materials (SMMs) serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss1. The electrification of transport, households and manufacturing leads to an increase in energy consumption owing to hysteresis losses2. Therefore, minimizing coercivity, which scales these losses, is crucial3. Yet meeting this target alone is not enough: SMMs in electrical engines must withstand severe mechanical loads; that is, the alloys need high strength and ductility4. This is a fundamental design challenge, as most methods that enhance strength introduce stress fields that can pin magnetic domains, thus increasing coercivity and hysteresis losses5. Here we introduce an approach to overcome this dilemma. We have designed a Fe-Co-Ni-Ta-Al multicomponent alloy (MCA) with ferromagnetic matrix and paramagnetic coherent nanoparticles (about 91 nm in size and around 55% volume fraction). They impede dislocation motion, enhancing strength and ductility. Their small size, low coherency stress and small magnetostatic energy create an interaction volume below the magnetic domain wall width, leading to minimal domain wall pinning, thus maintaining the soft magnetic properties. The alloy has a tensile strength of 1,336 MPa at 54% tensile elongation, extremely low coercivity of 78 A m-1 (less than 1 Oe), moderate saturation magnetization of 100 A m2 kg-1 and high electrical resistivity of 103 μΩ cm.

Journal article

Sun Z, Ma Y, Ponge D, Zaefferer S, Jaegle EA, Gault B, Rollett AD, Raabe Det al., 2022, Thermodynamics-guided alloy and process design for additive manufacturing, NATURE COMMUNICATIONS, Vol: 13

Journal article

López Freixes M, Zhou X, Zhao H, Godin H, Peguet L, Warner T, Gault Bet al., 2022, Revisiting stress-corrosion cracking and hydrogen embrittlement in 7xxx-Al alloys at the near-atomic-scale., Nat Commun, Vol: 13

The high-strength 7xxx series aluminium alloys can fulfil the need for light, high strength materials necessary to reduce carbon-emissions, and are extensively used in aerospace for weight reduction purposes. However, as all major high-strength materials, these alloys can be sensitive to stress-corrosion cracking (SCC) through anodic dissolution and hydrogen embrittlement (HE). Here, we study at the near-atomic-scale the intra- and inter-granular microstructure ahead and in the wake of a propagating SCC crack. Moving away from model alloys and non-industry standard tests, we perform a double cantilever beam (DCB) crack growth test on an engineering 7xxx Al-alloy. H is found segregated to planar arrays of dislocations and to grain boundaries that we can associate to the combined effects of hydrogen-enhanced localised plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanisms. We report on a Mg-rich amorphous hydroxide on the corroded crack surface and evidence of Mg-related diffusional processes leading to dissolution of the strengthening η-phase precipitates ahead of the crack.

Journal article

Raabe D, Ponge D, Uggowitzer PJ, Roscher M, Paolantonio M, Liu C, Antrekowitsch H, Kozeschnik E, Seidmann D, Gault B, De Geuser F, Deschamps A, Hutchinson C, Liu C, Li Z, Prangnell P, Robson J, Shanthraj P, Vakili S, Sinclair C, Bourgeois L, Pogatscher Set al., 2022, Making sustainable aluminum by recycling scrap: The science of "dirty " alloys, PROGRESS IN MATERIALS SCIENCE, Vol: 128, ISSN: 0079-6425

Journal article

Wang S, Gavalda-Diaz O, Luo T, Guo L, Lovell E, Wilson N, Gault B, Ryan MP, Giuliani Fet al., 2022, The effect of hydrogen on the multiscale mechanical behaviour of a La(Fe,Mn,Si)13-based magnetocaloric material, Journal of Alloys and Compounds, Vol: 906, Pages: 1-10, ISSN: 0925-8388

Magnetocaloric cooling offers the potential to improve the efficiency of refrigeration devices and hence cut the significant CO2 emissions associated with cooling processes. A critical issue in deployment of this technology is the mechanical degradation of the magnetocaloric material during processing and operation, leading to limited service-life. The mechanical properties of hydrogenated La(Fe,Mn,Si)13-based magnetocaloric material are studied using macroscale bending tests of polycrystalline specimens and in situ micropillar compression tests of single crystal specimens. The impact of hydrogenation on the mechanical properties are quantified. Understanding of the deformation/failure mechanisms is aided by characterization with transmission electron microscopy and atom probe tomography to reveal the arrangement of hydrogen atoms in the crystal lattice. Results indicate that the intrinsic strength of this material is ~3-6 GPa and is dependent on the crystal orientation. Single crystals under compressive load exhibit shearing along specific crystallographic planes. Hydrogen deteriorates the strength of La(Fe,Mn,Si)13 through promotion of transgranular fracture. The weakening effect of hydrogen on single crystals is anisotropic; it is significant upon shearing parallel to the {111} crystallographic planes but is negligible when the shear plane is {001}-oriented. APT analysis suggests that this is associated with the close arrangement of hydrogen atoms on {222} planes.

Journal article

Kim S-H, Yoo S-H, Shin S, El-Zoka AA, Kasian O, Lim J, Jeong J, Scheu C, Neugebauer J, Lee H, Todorova M, Gault Bet al., 2022, Controlled Doping of Electrocatalysts through Engineering Impurities, ADVANCED MATERIALS, Vol: 34, ISSN: 0935-9648

Journal article

Varanasi RS, Gault B, Ponge D, 2022, Effect of Nb micro-alloying on austenite nucleation and growth in a medium manganese steel during intercritical annealing, ACTA MATERIALIA, Vol: 229, ISSN: 1359-6454

Journal article

Ma Y, Filho IRS, Bai Y, Schenk J, Patisson F, Beck A, van Bokhoven JA, Willinger MG, Li K, Xie D, Ponge D, Zaefferer S, Gault B, Mianroodi JR, Raabe Det al., 2022, Hierarchical nature of hydrogen-based direct reduction of iron oxides, SCRIPTA MATERIALIA, Vol: 213, ISSN: 1359-6462

Journal article

Tan Q, Yan Z, Li R, Ren Y, Wang Y, Gault B, Antonov Set al., 2022, In-situ synchrotron-based high energy X-ray diffraction study of the deformation mechanism of delta-hydrides in a commercially pure titanium, SCRIPTA MATERIALIA, Vol: 213, ISSN: 1359-6462

Journal article

Tan Q, Yan Z, Wang H, Dye D, Antonov S, Gault Bet al., 2022, The role of β pockets resulting from Fe impurities in hydride formation in titanium, Scripta Materialia, Vol: 213, Pages: 114640-114640, ISSN: 1359-6462

The corrosion potential of commercially pure titanium in NaCl solutions is dramatically affected by trace Fe additions, which cause the appearance of submicron pockets of β phase at grain boundary triple points. Furthermore, the low solubility of hydrogen in hexagonal close-packed α-Ti makes titanium alloys prone to subsequent hydride-associated failures due to stress corrosion cracking. We analyzed α-α and α-β sections of the abutting grain boundary of a β pocket in a Grade 2 CP-Ti, and the α-β phase boundary. Fe and H partition to β and segregate at the grain boundary, but no segregation is seen at the α-β phase boundary. In contrast, a significant Ni (>1 at%) accumulation is observed at the α-β phase boundary. We propose that the β-pockets act as hydrogen traps and facilitate the nucleation and growth of hydrides along grain boundaries in CP-Ti.

Journal article

da Silva AK, Souza Filho IR, Lu W, Zilnyk KD, Hupalo MF, Alves LM, Ponge D, Gault B, Raabe Det al., 2022, A sustainable ultra-high strength Fe18Mn3Ti maraging steel through controlled solute segregation and alpha-Mn nanoprecipitation, NATURE COMMUNICATIONS, Vol: 13

Journal article

Joseph S, Kontis P, Chang Y, Shi Y, Raabe D, Gault B, Dye Det al., 2022, A cracking oxygen story: a new view of stress corrosion cracking in titanium alloys, Acta Materialia, Vol: 227, Pages: 117687-117687, ISSN: 1359-6454

Titanium alloys can suffer from halide-associated stress corrosion cracking at elevated temperatures e.g., in jet engines, where chlorides and Ti-oxide promote the cracking of water vapour in the gas stream, depositing embrittling species at the crack tip. Here we report, using isotopically-labelled experiments, that crack tips in an industrial Ti-6Al-2Sn-4Zr-6Mo alloy are strongly enriched (>5 at.%) in oxygen from the water vapour, far greater than the amounts (0.25 at.%) required to embrittle the material. Surprisingly, relatively little hydrogen (deuterium) is measured, despite careful preparation and analysis. Therefore, we suggest that a combined effect of O and H leads to cracking, with O playing a vital role, since it is well-known to cause embrittlement of the alloy. In contrast it appears that in α + β Ti alloys, it may be that H may drain away into the bulk owing to its high solubility in β-Ti, rather than being retained in the stress field of the crack tip. Therefore, whilst hydrides may form on the fracture surface, hydrogen ingress might not be the only plausible mechanism of embrittlement of the underlying matrix. This possibility challenges decades of understanding of stress-corrosion cracking as being related solely to the hydrogen enhanced localised plasticity (HELP) mechanism, which explains why H-doped Ti alloys are embrittled. This would change the perspective on stress corrosion embrittlement away from a focus purely on hydrogen to also consider the ingress of O originating from the water vapour, insights critical for designing corrosion resistant materials.

Journal article

Poplawsky JD, Pillai R, Ren Q-Q, Breen AJ, Gault B, Brady MPet al., 2022, Measuring oxygen solubility in Ni grains and boundaries after oxidation using atom probe tomography, SCRIPTA MATERIALIA, Vol: 210, ISSN: 1359-6462

Journal article

Zhou X, Wei Y, Kuehbach M, Zhao H, Vogel F, Kamachali RD, Thompson GB, Raabe D, Gault Bet al., 2022, Revealing in-plane grain boundary composition features through machine learning from atom probe tomography data, ACTA MATERIALIA, Vol: 226, ISSN: 1359-6454

Journal article

Luo T, Mangelinck D, Serrano-Sanchez F, Fu C, Felser C, Gault Bet al., 2022, Grain boundary in NbCo(Pt)Sn half-Heusler compounds: Segregation and solute drag on grain boundary migration, ACTA MATERIALIA, Vol: 226, ISSN: 1359-6454

Journal article

Liu C, Lu W, Xia W, Du C, Rao Z, Best JP, Brinckmann S, Lu J, Gault B, Dehm G, Wu G, Li Z, Raabe Det al., 2022, Massive interstitial solid solution alloys achieve near-theoretical strength, NATURE COMMUNICATIONS, Vol: 13

Journal article

Zhao H, Chakraborty P, Ponge D, Hickel T, Sun B, Wu C-H, Gault B, Raabe Det al., 2022, Hydrogen trapping and embrittlement in high-strength Al alloys, NATURE, Vol: 602, Pages: 437-+, ISSN: 0028-0836

Journal article

Peng Z, Meiners T, Lu Y, Liebscher CH, Kostka A, Raabe D, Gault Bet al., 2022, Quantitative analysis of grain boundary diffusion, segregation and precipitation at a sub-nanometer scale, ACTA MATERIALIA, Vol: 225, ISSN: 1359-6454

Journal article

Khanchandani H, El-Zoka AA, Kim S-H, Tezins U, Vogel D, Sturm A, Raabe D, Gault B, Stephenson LTet al., 2022, Laser-equipped gas reaction chamber for probing environmentally sensitive materials at near atomic scale, PLOS ONE, Vol: 17, ISSN: 1932-6203

Journal article

Kim S-H, Antonov S, Zhou X, Stephenson LT, Jung C, El-Zoka AA, Schreiber DK, Conroy M, Gault Bet al., 2022, Atom probe analysis of electrode materials for Li-ion batteries: challenges and ways forward, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 10, Pages: 4926-4935, ISSN: 2050-7488

Journal article

Kim S-H, Yoo S-H, Chakraborty P, Jeong J, Lim J, El-Zoka AA, Zhou X, Stephenson LT, Hickel T, Neugebauer J, Scheu C, Todorova M, Gault Bet al., 2022, Understanding Alkali Contamination in Colloidal Nanomaterials to Unlock Grain Boundary Impurity Engineering, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 144, Pages: 987-994, ISSN: 0002-7863

Journal article

Stender P, Gault B, Schwarz TM, Woods E, Kim S-H, Ott J, Stephenson LT, Schmitz G, Freysoldt C, Kastner J, El-Zoka AAet al., 2022, Status and Direction of Atom Probe Analysis of Frozen Liquids, MICROSCOPY AND MICROANALYSIS, Vol: 28, Pages: 1150-1167, ISSN: 1431-9276

Journal article

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