Investigation of deformation micro-mechanisms in nickel consolidated from a bimodal powder by spark plasma sintering
Résumé
Bulk polycrystalline nickel compact was processed by spark plasma sintering from heterogeneous powder consisting of a mixture of nanometer and micrometer sized particles. The consolidated samples inherited the bimodal structure of the starting powder and was composed of ∼55 vol.% coarse-grained (with the grain size larger than 1 innodatamum) and ∼45 vol.% ultrafine-grained (with an average grain size of ∼550 nm) components. The deformation mechanisms were established by EBSD, X-ray line pro file analysis and in-situ TEM observations. In the ultrafine-grained volume, the deformation occurred mainly through the activation of dislocation sources emitting full or partial dislocation either from grain interior or grain boundaries. Besides dislocation activity, rolling and sliding of nanograins were also observed during deformation by in-situ transmission electron microscopy, which have a considerable contribution to the observed high strain rate sensitivity of the bimodal microstructure. The cracks formed during deformation easily propagated in the nanograin regions due to the weaker particle bonding caused by the relatively high fraction of native oxide layer on the surface of the initial nanoparticles.
Mots clés
- Strain rate
- Dislocations (crystals)
- Electric sparks
- Grain boundaries
- Grain size and shape
- In situ processing
- Nickel
- Spark plasma sintering
- Bi-modal microstructures
- Transmission electron microscopy
- Deformation
- Polycrystalline nickels
- Partial dislocations
- Micrometer sized particles
- In-situ transmission electron microscopies
- In-situ TEM
- Deformation mechanism
- Bi-modal structures