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Nanosecond timescale plasticity in shock-compressed polycrystalline MgO: evidence for transition in mechanism above 100 GPa
Authors:
A. Chakraborti,
H. Ginestet,
F. Bertrand,
J. Chantel,
S. Merkel,
M. Harmand,
S. Pandolfi,
A. Amouretti,
M. Andrzejewski,
K. Appel,
E. Barraud,
A. B. Belonoshko,
E. Brambrink,
K. Buakor,
C. Camarda,
O. Castelnau,
D. M. Cheshire,
G. Collins,
T. E. Cowan,
C. Crépisson,
J. Deng,
X. Fang,
M. Fitzgerald,
A. Gleason,
F. Hanby
, et al. (58 additional authors not shown)
Abstract:
The mechanical properties of ceramics under extreme conditions directly impact applications ranging from shielding spacecrafts, designing plasma facing materials in nuclear fusion to understanding the rheology of deep planetary interiors. Here, we use polycrystalline MgO as a model ceramic to understand the high-pressure-temperature mechanical behaviour of such materials under extreme strain rates…
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The mechanical properties of ceramics under extreme conditions directly impact applications ranging from shielding spacecrafts, designing plasma facing materials in nuclear fusion to understanding the rheology of deep planetary interiors. Here, we use polycrystalline MgO as a model ceramic to understand the high-pressure-temperature mechanical behaviour of such materials under extreme strain rates. We use laser-driven shock compression up to 175(15) GPa on the principal Hugoniot along with ultrafast diagnostics at the European X-ray Free Electron Laser to probe the dominant deformation mechanisms with changing P -T conditions. These near-instantaneous time-resolved snapshots, coupled with elasto-viscoplastic self-consistent (EVPSC) simulations, strongly suggest that MgO attains plastic regime in the nanoseconds scale accompanied by a pressure-mediated change in dominant slip system between 95 and 175 GPa. This work provides a new direct window into the deformation dynamics of polycrystalline ceramics under high-velocity impacts.
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Submitted 5 August, 2026;
originally announced August 2026.
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Grain boundary diffusion in CoCrFeMnNi high entropy alloy: kinetic hints towards a phase decomposition
Authors:
Marcel Glienke,
Mayur Vaidya,
K. Gururaj,
Lydia Daum,
Bengü Tas,
Lukasz Rogal,
K. G. Pradeep,
Sergiy V. Divinski,
Gerhard Wilde
Abstract:
Grain boundary self-diffusion of $^{57}$Co, $^{51}$Cr, $^{59}$Fe and $^{54}$Mn in a coarse-grained, single-phase fcc CoCrFeMnNi high entropy alloy is measured in a wide temperature range of 643 to 1273~K in both C- and B-type kinetic regimes after Harrison's classification. The results suggest that the product of the pertinent segregation factors, $s$, and the grain boundary width, $δ$, is about 0…
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Grain boundary self-diffusion of $^{57}$Co, $^{51}$Cr, $^{59}$Fe and $^{54}$Mn in a coarse-grained, single-phase fcc CoCrFeMnNi high entropy alloy is measured in a wide temperature range of 643 to 1273~K in both C- and B-type kinetic regimes after Harrison's classification. The results suggest that the product of the pertinent segregation factors, $s$, and the grain boundary width, $δ$, is about 0.5~nm for all elements at temperatures $T>800$~K. Whereas one short-circuit contribution is observed at higher temperatures above 800~K, the penetration profiles in the C-type kinetic regime (643 -- 703~K) reveal two distinct contributions that hint towards a phase decomposition at a fraction of high-angle grain boundaries at these temperatures. A correlative microscopy combining transmission Kikuchi diffraction and atom probe tomography manifests formation of neighbouring Ni-Mn-rich and Cr-rich precipitates at a segment of high angle grain boundaries. Transmission electron microscopy revealed an increased dislocation density in the vicinity of such interfaces which is suggested to be a reason of the enhanced diffusion rates at low temperatures for such short circuits.
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Submitted 2 April, 2020; v1 submitted 23 March, 2020;
originally announced March 2020.
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Experimental and theoretical study of tracer diffusion in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloys
Authors:
Josua Kottke,
Daniel Utt,
Mathilde Laurent-Brocq,
Adnan Fareed,
Daniel Gaertner,
Loic Perriere,
Lukasz Rogal,
Alexander Stukowski,
Karsten Albe,
Sergiy V. Divinski,
Gerhard Wilde
Abstract:
Tracer diffusion of all constituting elements is studied at various temperatures in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloys with compositions ranging from pure Ni to the equiatomic CoCrFeMnNi high-entropy alloy. At a given homologous temperature, the measured tracer diffusion coefficients change non-monotonically along the transition from pure Ni to the concentrated alloys and finally to the…
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Tracer diffusion of all constituting elements is studied at various temperatures in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloys with compositions ranging from pure Ni to the equiatomic CoCrFeMnNi high-entropy alloy. At a given homologous temperature, the measured tracer diffusion coefficients change non-monotonically along the transition from pure Ni to the concentrated alloys and finally to the equiatomic CoCrFeMnNi alloy. This is explained by atomistic Monte-Carlo simulations based on a modified embedded-atom potentials, which reveal that local heterogeneities of the atomic configurations around a vacancy cause correlation effects and induce significant deviations from predictions of the random alloy model.
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Submitted 20 March, 2020;
originally announced March 2020.
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Computational engineering of sublattice ordering in a hexagonal AlHfScTiZr high entropy alloy
Authors:
Lukasz Rogal,
Piotr Bobrowski,
Fritz Koermann,
Sergiy Divinski,
Frank Stein,
Blazej Grabowski
Abstract:
Multi-principle element alloys have enormous potential, but their exploration suffers from the tremendously large range of configurations. In the last decade such alloys have been designed with a focus on random solid solutions. Here we apply an experimentally verified, combined thermodynamic and first-principles design strategy to reverse the traditional approach and to generate a new type of hcp…
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Multi-principle element alloys have enormous potential, but their exploration suffers from the tremendously large range of configurations. In the last decade such alloys have been designed with a focus on random solid solutions. Here we apply an experimentally verified, combined thermodynamic and first-principles design strategy to reverse the traditional approach and to generate a new type of hcp Al-Hf-Sc-Ti-Zr high entropy alloy with a hitherto unique structure. A phase diagram analysis narrows down the large compositional space to a well-defined set of candidates. First-principles calculations demonstrate the energetic preference of an ordered superstructure over the competing disordered solid solutions. The chief ingredient is the Al concentration, which can be tuned to achieve a D019 ordering of the hexagonal lattice. The computationally designed D019 superstructure is experimentally confirmed by transmission electron microscopy and X-ray studies. Our scheme enables the exploration of a new class of high entropy alloys.
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Submitted 13 February, 2017;
originally announced February 2017.