353 research outputs found
Mechanical alloying of Cu and Fe induced by severe plastic deformation of a Cu-Fe composite
A filamentary composite elaborated by cold drawing was processed by High
Pressure Torsion (HPT). The nanostructure resulting from this severe plastic
deformation (SPD) was investigated thanks to scanning electron microscopy,
transmission electron microscopy, X-ray diffraction and 3D atom probe. Although
the mutual solubility of Cu and Fe is extremely low at room temperature in
equilibrium conditions, it is shown that nanoscaled Fe clusters dissolve in the
Cu matrix. The non-equilibrium copper supersaturated solid solutions contain up
to 20at.% Fe. The driving force of the dissolution is attributed to capillary
pressures and mechanisms which could enhanced the atomic mobility during HPT
are discussed. We conclude that the interdiffusion is the result of a dramatic
increase of the vacancy concentration during SPD.Comment: 20 page
Atomic scale characterization of the nucleation and growth of SnO2 particles in oxidized CuSn alloys
The internal oxidation of Sn was investigated to understand the oxidation
kinetics of monophase CuSn alloys. SnO2 particles were characterized by
analytical transmission electron microscopy. The orientation relationship
between SnO2 and Cu was determined with a special emphasis on the atomic scale
structure of Cu/SnO2 interfaces (misfit dislocations and chemical structure).
Habit planes with a pure oxygen plane terminating the SnO2 phase are greatly
favored and large misfits promote the growth of plate shaped precipitates
On the origin of extremely high strength of ultrafine-grained Al alloys produced by severe plastic deformation
Ultrafine-grained Al alloys produced by high pressure torsion are found to
exhibit a very high strength, considerably exceeding the Hall-Petch predictions
for the ultrafine grains. The phenomena can be attributed to the unique
combination of ultrafine structure and deformation-induced segregations of
solute elements along grain boundaries, which may affect the emission and
mobility of intragranular dislocations
Nanostructure of a cold drawn tempered martensitic steel
The carbon atom distribution in a tempered martensitic steel processed by
cold drawing was investigated with a three-dimensional atom probe. Data clearly
show that cementite starts to decompose at the early stage of deformation. This
indicates that the driving force of cementite decomposition during plastic
deformation is not related to a strong increase of the interfacial energy.
Carbon atmospheres were also analysed. They probably result from pipe diffusion
of carbon atoms along dislocations pined by Fe3C carbides.Comment: 12 page
Grain boundary segregation in UFG alloys processed by severe plastic deformation
Grain boundary segregations were investigated by Atom Probe Tomography in an
Al-Mg alloy, a carbon steel and Armco\trademark Fe processed by severe plastic
deformation (SPD). In the non-deformed state, the GBs of the aluminium alloy
are Mg depleted, but after SPD some local enrichment up to 20 at.% was
detected. In the Fe-based alloys, large carbon concentrations were also
exhibited along GBs after SPD. These experimental observations are attributed
to the specific structure of GBs often described as "non-equilibrum" in ultra
fine grained materials processed by SPD. The grain boundary segregation
mechanisms are discussed and compared in the case of substitutional (Mg in fcc
Al) and interstitial (C in bcc Fe) solute atoms
Non-equilibrium intermixing and phase transformation in severely deformed Al/Ni multilayers
Al/Ni multilayers have been prepared by repeated folding and cold rolling
(F&R) of elemental foils. The thickness of Al and Ni foils is reduced down to
less than 50 nm after fifty F&R cycles. Three-dimensional atom probe analyses
clearly reveal the presence of supersaturated solid solutions and give the
evidence of deformation-induced intermixing. The formation of the solid
solutions and their transformation into the Al3Ni phase upon annealing is
discussed.Comment: 4 page
Drones in the Desert: Augmenting HMA and Socio-Economic Activities in Chad
Funded by the Belgian Directorate-General for Development and led by Humanity & Inclusion (HI) under the auspices of the National Mine Action Centre, Haut Commissariat National au DĂ©minage (HCND) in Chad, the Odyssey2025 Project explores ways to accelerate land release for the local population with the combined use of small consumer drones, new survey methods, and mobile data collection. Project partners include Mobility Robotics, Dynergie, InZentive, and Third Element Aviation. A practical, field-driven approach is being undertaken together with partners in the PRODECO project, Mines Advisory Group (MAG), and Fondation Suisse de DĂ©minage (FSD)
Achieving highly strengthened Al-Cu-Mg alloy by grain refinement and grain boundary segregation
An age-hardenable Al-Cu-Mg alloy (A2024) was processed by high-pressure
torsion (HPT) for producing an ultrafine-grained structure. The alloy was
further aged for extra strengthening. The tensile strength then reached a value
as high as ~1 GPa. The microstructures were analyzed by transmission electron
microscopy and atom probe tomography. The mechanism for the high strength was
clarified in terms of solid-solution hardening, cluster hardening, work
hardening, dispersion hardening and grain boundary hardening. It is shown that
the segregation of solute atoms at grain boundaries including subgrain
boundaries plays a significant role for the enhancement of the tensile
strength
Understanding the role of Ca segregation on thermal stability, electrical resistivity and mechanical strength of nanostructured aluminum
Achieving a combination of high mechanical strength and high electrical
conductivity in low-weight Al alloys requires a full understanding of the
relationships between nanoscaled features and physical properties. Grain
boundary strengthening through grain size reduction offers some interesting
possibilities but is limited by thermal stability issues. Zener pinning by
stable nanoscaled particles or grain boundary segregation are well-known
strategies for stabilizing grain boundaries. In this study, the Al-Ca system
has been selected to investigate the way segregation affects the combination of
mechanical strength and electrical resistivity. For this purpose, an Al-Ca
composite material was severely deformed by high-pressure torsion to achieve a
nanoscaled structure with a mean grain size of only 25 nm. X-ray diffraction,
transmission electron microscopy and atom probe tomography data revealed that
the fcc Ca phase was dissolved for large levels of plastic deformation leading
mainly to Ca segregations along crystalline defects. The resulting
microhardness of about 300 HV is much higher than predictions based on Hall and
Petch Law and is attributed to limited grain boundary mediated plasticity due
to Ca segregation. The electrical resistivity is also much higher than that
expected for nanostructured Al. The main contribution comes from Ca
segregations that lead to a fraction of electrons reflected or trapped by grain
boundaries twice larger than in pure Al. The two-phase state was investigated
by in-situ and ex-situ microscopy after annealing at 200{\textdegree}C for 30
min, where precipitation of nanoscaled Al4Ca particles occurred and the mean
grain size reached 35 nm. Annealing also significantly decreased electrical
resistivity, but it remained much higher than that of nanostructured pure Al,
due to Al/Al4Ca interfaces that reflect or trap more than 85% of electrons
Proof: How Small Drones Can Find Buried Landmines in the Desert Using Airborne IR Thermography
Hypotheses and speculation have circulated for at least three decades regarding how IR thermography could be viable as a technique for locating buried landmines in arid environments. However, there has been a lack of proof under actual field conditions. Addressing many overall questions regarding small drones in HMA, the Odyssey2025 Project—led by HI and Mobility Robotics— closely collaborated with the national mine action center in Chad, the Haut Commissariat National au Déminage (HCND), to complete activities and objectives. As part of a holistic approach, the primary objective was to determine how small drones could add value in HMA field operations and augment other assets at both simple and advanced perspectives. This research is from an advanced perspective, following on from the work previously published in The Journal of Conventional Weapons Destruction outlining how low-cost consumer drones can augment HMA operations at a simple level using visual imagery and GIS/cartography/photogrammetry. This article aims to advance the field’s understanding of drones and their ability to indicate the location of buried objects
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