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Title: Microstructure and mechanical properties of bulk highly faulted fcc/hcp nanostructured cobalt microstructures

Nanostructured cobalt powders with an average particle size of 50 nm were synthesized using a polyol method and subsequently consolidated by spark plasma sintering (SPS). SPS experiments performed at 650 °C with sintering times ranging from 5 to 45 min under a pressure of 100 MPa, yielded to dense bulk nanostructured cobalt (relative density greater than 97%). X-ray diffraction patterns of the as-prepared powders showed only a face centered cubic (fcc) crystalline phase, whereas the consolidated samples exhibited a mixture of both fcc and hexagonal close packed (hcp) phases. Transmission electron microscopy observations revealed a lamellar substructure with a high density of nanotwins and stacking faults in every grain of the sintered samples. Room temperature compression tests, carried out at a strain rate of 10{sup −3} s{sup −1}, yielded to highest strain to fracture values of up to 5% for sample of holding time of 15 min, which exhibited a yield strength of 1440 MPa, an ultimate strength as high as 1740 MPa and a Young's modulus of 205 GPa. The modulus of elasticity obtained from the nanoindentation tests, ranges from 181 to 218 GPa. The lowest modulus value of 181 GPa was obtained for the sample with the highestmore » sintering time (45 min), which could be related to mass density loss as a consequence of trapped gases releasing. - Highlights: • Co nanopowder (50 nm) was prepared by reduction in polyol medium. • SPS was used to process bulk nanostructured Co specimens. • Microstructures were made of intricate fcc/hcp, along with nanotwins and SFs. • High strengths and moderate compressive ductility were obtained. • Deformation mechanisms related to complex interplay of different length scales.« less
Authors:
 [1] ;  [2] ;  [1] ; ; ;  [1]
  1. Université Paris 13, Sorbonne Paris Cité, LSPM CNRS UPR 3407, 93430 Villetaneuse (France)
  2. (Mauritania, Islamic Republic of)
Publication Date:
OSTI Identifier:
22340356
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 91; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COBALT; DUCTILITY; ELASTICITY; FCC LATTICES; FRACTURES; HCP LATTICES; MICROSTRUCTURE; MIXTURES; NANOSTRUCTURES; PARTICLE SIZE; PHASE TRANSFORMATIONS; POWDERS; SINTERING; STACKING FAULTS; TEMPERATURE RANGE 0273-0400 K; TRANSMISSION ELECTRON MICROSCOPY; ULTIMATE STRENGTH; X-RAY DIFFRACTION; YIELD STRENGTH; YOUNG MODULUS