Thermal behavior of Nickel deformed to ultra-high strain by high pressure torsion

Publication: Research - peer-reviewConference article – Annual report year: 2012

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Polycrystalline Ni (99.5 %) has been deformed to an ultra-high strain of εvM=100 (εvM, von Mises strain) by high pressure torsion (HPT) at room temperature. The deformed sample is nanostructured with an average boundary spacing of 90 nm, a high density of dislocations of >1015m-2 and a large fraction of high angle boundaries (>15°) 68% as determined by transmission electron microscopy and 80% as determined by electron backscatter diffraction. The thermal behavior of this nanostructued sample has been investigated by isochronal annealing for 1h at temperatures from 100 to 600°C, and the evolution of the structural parameters (boundary spacing, average boundary misorientation angle and the fraction of high angle boundaries), crystallographic texture and hardness have been determined. Based on microstructural parameters the stored energy in the deformed state has been estimated to be 24 MPa. The isochronal annealing leads to a hardness drop in three stages: a relatively small decrease at low temperatures (recovery) followed by a rapid decrease at intermediate temperatures (discontinuous recrystallization) and a slow decrease at high temperatures (grain growth). Due to the presence of a small amount of impurity elements, the recovery and recrystallization are strongly retarded in comparison with Ni of high purity (99.967%). This finding emphasizes the importance of alloying in delaying the process of recovery and recrystallization, which enables a tailoring of the microstructure and properties through an optimized annealing treatment. © (2012) Trans Tech Publications, Switzerland.
Original languageEnglish
JournalMaterials Science Forum
Publication date2012
Volume715-716
Pages387-392
ISSN0255-5476
DOIs
StatePublished

Conference

Conference4th International Conference on Recrystallization and Grain Growth
CountryUnited Kingdom
CitySheffield
Period04/07/1009/07/10
CitationsWeb of Science® Times Cited: 0

Keywords

  • Annealing, Compressible flow, Grain growth, Hardness, Nickel, Plastic deformation, Torsional stress, Transmission electron microscopy, Recrystallization (metallurgy)
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