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Your search keyword '"Couque, H."' showing total 4 results
Start Over Author "Couque, H." Topic ductility
4 results on '"Couque, H."'

3. Powder metallurgy processing and deformation characteristics of bulk multimodal nickel.

Author

Farbaniec, L., Dirras, G., Krawczynska, A., Mompiou, F., Couque, H., Naimi, F., Bernard, F., and Tingaud, D.

Subjects
*POWDER metallurgy, *DEFORMATIONS (Mechanics), *NICKEL alloys, *METAL microstructure, *PARTICLE size distribution, *DUCTILITY, *METALS, *INTERFACES (Physical sciences)
Abstract

Abstract: Spark plasma sintering was used to process bulk nickel samples from a blend of three powder types. The resulting multimodal microstructure was made of coarse (average size ~135μm) spherical microcrystalline entities (the core) surrounded by a fine-grained matrix (average grain size ~1.5μm) or a thick rim (the shell) distinguishable from the matrix. Tensile tests revealed yield strength of ~470MPa that was accompanied by limited ductility (~2.8% plastic strain). Microstructure observation after testing showed debonding at interfaces between the matrix and the coarse entities, but in many instances, shallow dimples within the rim were observed indicating local ductile events in the shell. Dislocation emission and annihilation at grain boundaries and twinning at crack tip were the main deformation mechanisms taking place within the fine-grained matrix as revealed by in-situ transmission electron microscopy. Estimation of the stress from loop's curvature and dislocation pile-up indicates that dislocation emission from grain boundaries and grain boundary overcoming largely contributes to the flow stress. [Copyright &y& Elsevier]

Published
2014
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4. Effect of strain rate on the hydrogen embrittlement of a DP steel

Author

Ahmed Elmahdy, Tom Depover, Kim Verbeken, Patricia Verleysen, Florian Vercruysse, Buzaud, E, Cosculluela, A, Couque, H, and Cadoni, E

Subjects
010302 applied physics, Technology and Engineering, Strain (chemistry), Physics, QC1-999, 02 engineering and technology, Strain rate, 021001 nanoscience & nanotechnology, 01 natural sciences, INDUCED MECHANICAL DEGRADATION, INDUCED CRACKING, INDUCED DUCTILITY LOSS, 0103 physical sciences, Ultimate tensile strength, Composite material, Deformation (engineering), 0210 nano-technology, Ductility, Embrittlement, Hydrogen embrittlement, Stress concentration
Abstract

Advanced high strength steels (HSSs), such as dual phase steels, are widely used in the automotive industry due to their excellent combination of strength and ductility. In certain applications, they might be exposed to hydrogen (H) which is known to be detrimental for the deformation. H embrittlement (HE) is still not fully understood. It might drastically reduce the energy absorbed in a crash event and limits the use of HSSs in car bodies. Although H diffusion is a highly time dependent phenomenon, so far, the combined effect of dynamic strain rates and electrochemical H pre-charging has not been studied. Therefore, a reproducible methodology has been developed. Tensile specimens were electrochemically H pre-charged and immediately tested in a split Hopkinson tensile bar setup. To distinguish between the effect of strain rate and HE, static tests have been conducted using the same procedure. Results show that the HE resistance decreased due to higher H amounts in the sample for all strain rates. The HE increased when slower strain rates were applied due to higher probability of H to diffuse to regions of stress concentration ahead of a crack tip and as such accelerating failure. At the highest strain rate considered (900 s-1), the material still lost about 10% of its ductility.

Published
2018

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