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
Dislocations (crystals)
Electric sparks
Grain boundaries
Grain size and shape
In situ processing
Nickel
Spark plasma sintering
Strain rate
Transmission electron microscopy
Bi-modal microstructures
Bi-modal structures
Deformation mechanism
In-situ TEM
In-situ transmission electron microscopies
Micrometer sized particles
Partial dislocations
Polycrystalline nickels
Deformation