Abstract
Several nanostructured states of high purity cobalt were achieved by high pressure torsion (HPT) at pressures of 4 and 8 GPa and temperatures of 300 and 77 K. Changes of crystallographic texture, grain sizes and phase transformations as a result of HPT and subsequent annealing have been measured and analyzed. Mechanical properties of nanostructured Co were studied by microhardness measurements at 300 K, and uniaxial compression at temperatures 300, 77 and 4.2 K. Comparison of the strength characteristics, plasticity and strain hardening of the nanostructured and coarse grained Co has been carried out. Micromechanisms of plastic deformation of Co during HPT deformation and uniaxial compression are discussed.
Highlights
In the last years the method of high pressure torsion (HPT), which is one of the most successful methods of severe plastic deformation, was used to produce nanostructured states in hcp metals, such as Ti and Zr [1,2,3,4,5]
Deformation twinning is very active at low temperatures in Co in both coarse grained and nanocrystalline state [6]; HPT of Co at a cryogenic temperature of 77 K can lead to the formation of a considerable quantity of deformation twins, which should contribute to strength and plasticity of the nanostructured Co
As nanocrystalline cobalt with an average grain size 20 nm achieved by electrodeposition method [6] was recently investigated [7], this paper aims to compare the mechanical properties of nanograined Co in different
Summary
In the last years the method of high pressure torsion (HPT), which is one of the most successful methods of severe plastic deformation, was used to produce nanostructured states in hcp metals, such as Ti and Zr [1,2,3,4,5]. The use of cryogenic temperature (77 K) during HPT gives smaller grain sizes (80-100 nm), while applying higher stresses during HPT at both temperatures 77 and 300 K leads to a phase transformation to the ω phase. Deformation twinning is very active at low temperatures in Co in both coarse grained and nanocrystalline state [6]; HPT of Co at a cryogenic temperature of 77 K can lead to the formation of a considerable quantity of deformation twins, which should contribute to strength and plasticity of the nanostructured Co. the aim of this work is (i) to produce nanostructured Co by the HPT method at 300 and 77 K, and (ii) to study its structure and properties. As nanocrystalline cobalt with an average grain size 20 nm achieved by electrodeposition method [6] was recently investigated [7], this paper aims to compare the mechanical properties of nanograined Co in different
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