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Fracture and fracture toughness of nanopolycrystalline metals produced by severe plastic deformation.

Hohenwarter A, Pippan R - Philos Trans A Math Phys Eng Sci (2015)

Bottom Line: Nowadays, novel techniques provide access to much smaller grain sizes, where severe plastic deformation (SPD) is one of the most significant techniques.This opens the door to extend basic research in fracture mechanics to the nanocrystalline (NC) grain size regime.Here, an overview of recent results on the fracture behaviour of several different ultrafine-grained (d<1 μm) and NC (d<100 nm) metals and alloys covering examples of body- and face-centred cubic structures produced by SPD will be given.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Physics, Montanuniversität Leoben, Jahnstrasse 12, 8700 Leoben, Austria anton.hohenwarter@unileoben.ac.at.

ABSTRACT
The knowledge of the fracture of bulk metallic materials developed in the last 50 years is mostly based on materials having grain sizes, d, in the range of some micrometres up to several hundred micrometres regarding the possibilities of classical metallurgical methods. Nowadays, novel techniques provide access to much smaller grain sizes, where severe plastic deformation (SPD) is one of the most significant techniques. This opens the door to extend basic research in fracture mechanics to the nanocrystalline (NC) grain size regime. From the technological point of view, there is also the necessity to evaluate standard fracture mechanics data of these new materials, such as the fracture toughness, in order to allow their implementation in engineering applications. Here, an overview of recent results on the fracture behaviour of several different ultrafine-grained (d<1 μm) and NC (d<100 nm) metals and alloys covering examples of body- and face-centred cubic structures produced by SPD will be given.

No MeSH data available.


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Example of an UFG Ni microstructure after strains of (a) 1600 and (b) 3200%. A cessation of grain refinement is recognizable. (Online version in colour.)
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RSTA20140366F2: Example of an UFG Ni microstructure after strains of (a) 1600 and (b) 3200%. A cessation of grain refinement is recognizable. (Online version in colour.)

Mentions: In order to understand the fracture behaviour of metals produced by HPT, it is important to mention some basic microstructural features. Since it would go far beyond the scope of this article, details of the fragmentation process are excluded here and can be found for example in [13,15]. Only one example of microstructures after very large strains is presented in figure 2. Here, the microstructure of nickel after strains of 1600% and 3200% are shown. It is evident that there is principally no difference in the grain size, even if the strain is doubled. That means that the grain size during the refinement process must stabilize and a saturation of grain fragmentation evolves indicating that an increase of strain does not change the structure any further and an equilibrium between grain fragmenting and grain coarsening processes establishes. This lower limit of grain fragmentation is mainly dependent on the purity of the material, the alloying content, deformation temperature and strain rate. So it is possible to tailor the microstructure in a wide grain size range. Finally, this saturation behaviour also means that after applying a sufficiently high number of rotations the lower limit of grain refinement can be reached at very small disc radii of the sample. So, a fairly homogeneous microstructure can be introduced in the samples even if the applied strain is inhomogeneous along the radius. The majority of results presented in this overview are determined on samples having a saturation microstructure obtained after room-temperature deformation.Figure 2.


Fracture and fracture toughness of nanopolycrystalline metals produced by severe plastic deformation.

Hohenwarter A, Pippan R - Philos Trans A Math Phys Eng Sci (2015)

Example of an UFG Ni microstructure after strains of (a) 1600 and (b) 3200%. A cessation of grain refinement is recognizable. (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4342981&req=5

RSTA20140366F2: Example of an UFG Ni microstructure after strains of (a) 1600 and (b) 3200%. A cessation of grain refinement is recognizable. (Online version in colour.)
Mentions: In order to understand the fracture behaviour of metals produced by HPT, it is important to mention some basic microstructural features. Since it would go far beyond the scope of this article, details of the fragmentation process are excluded here and can be found for example in [13,15]. Only one example of microstructures after very large strains is presented in figure 2. Here, the microstructure of nickel after strains of 1600% and 3200% are shown. It is evident that there is principally no difference in the grain size, even if the strain is doubled. That means that the grain size during the refinement process must stabilize and a saturation of grain fragmentation evolves indicating that an increase of strain does not change the structure any further and an equilibrium between grain fragmenting and grain coarsening processes establishes. This lower limit of grain fragmentation is mainly dependent on the purity of the material, the alloying content, deformation temperature and strain rate. So it is possible to tailor the microstructure in a wide grain size range. Finally, this saturation behaviour also means that after applying a sufficiently high number of rotations the lower limit of grain refinement can be reached at very small disc radii of the sample. So, a fairly homogeneous microstructure can be introduced in the samples even if the applied strain is inhomogeneous along the radius. The majority of results presented in this overview are determined on samples having a saturation microstructure obtained after room-temperature deformation.Figure 2.

Bottom Line: Nowadays, novel techniques provide access to much smaller grain sizes, where severe plastic deformation (SPD) is one of the most significant techniques.This opens the door to extend basic research in fracture mechanics to the nanocrystalline (NC) grain size regime.Here, an overview of recent results on the fracture behaviour of several different ultrafine-grained (d<1 μm) and NC (d<100 nm) metals and alloys covering examples of body- and face-centred cubic structures produced by SPD will be given.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Physics, Montanuniversität Leoben, Jahnstrasse 12, 8700 Leoben, Austria anton.hohenwarter@unileoben.ac.at.

ABSTRACT
The knowledge of the fracture of bulk metallic materials developed in the last 50 years is mostly based on materials having grain sizes, d, in the range of some micrometres up to several hundred micrometres regarding the possibilities of classical metallurgical methods. Nowadays, novel techniques provide access to much smaller grain sizes, where severe plastic deformation (SPD) is one of the most significant techniques. This opens the door to extend basic research in fracture mechanics to the nanocrystalline (NC) grain size regime. From the technological point of view, there is also the necessity to evaluate standard fracture mechanics data of these new materials, such as the fracture toughness, in order to allow their implementation in engineering applications. Here, an overview of recent results on the fracture behaviour of several different ultrafine-grained (d<1 μm) and NC (d<100 nm) metals and alloys covering examples of body- and face-centred cubic structures produced by SPD will be given.

No MeSH data available.


Related in: MedlinePlus