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  • 11
    Electronic Resource
    Electronic Resource
    Magnetic Properties and Microstructure of a FeCo Ferritic Steel after Severe Plastic Deformation (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 503-504 (Jan. 2006), p. 299-304 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A commercial FeCo ferritic steel with an initial grain size of 10 μm was subjected to Severe Plastic Deformation in a temperature range between 293 K (0.16Tm, Tm: melting temperature in K) and 723 K (0.4Tm) up to strain levels where a saturation of the microstructural refinement is observed. The microstructure of the severely deformed state is analyzed by Back Scattered Electrons micrographs captured in a SEM. The magnetic properties were characterized by means of SQUID-magnetometer providing information about the magnetization behavior of the material in the as processed state. Depending on the deformation temperature mean microstructural sizes in the steady state of 50 nm and 270 nm were observed after SPD at 293 K and 723 K, respectively. These small microstructural sizes influences significantly the magnetic properties of the material: it shifts the behavior from soft-magnetic in the initial coarse grained state towards a hard-magnetic with decreasing size of the crystallites. For sizes of the crystallites smaller than about 100 nm the magnetic properties become again more soft-magnetic
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/11/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.503-504.299.pdf
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  • 12
    Electronic Resource
    Electronic Resource
    Differences in Structural Evolution in Single- and Dual-Phase Materials during Severe Plastic Deformation (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 503-504 (Jan. 2006), p. 407-412 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Severe plastic deformation (SPD) has been applied to two classes of metallic materials, single phase and dual phase materials. The applied shear strain has been varied between 1 and 1000 and the homologous temperature between 0.08 and 0.4. The deformation experiments are performed by high pressure torsion (HPT). The resulting microstructures were investigated by backscattered electron imaging, orientation image microscopy, and in selected cases by transmission electron microscopy. It will be shown that the behavior of single phase material is relatively uniform. With increasing strain, the size of the structural elements decreases and reaches a saturation between a shear strain of 10 to 100. The temperature and the alloying are the main parameters, which controls the saturation size of the structural elements (grains). The behavior in the dual phase materials is more complex, it varies from simple homogenisation, fragmentation of one phase, to desintegration and supersaturation of the phases
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/11/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.503-504.407.pdf
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  • 13
    Electronic Resource
    Electronic Resource
    High Pressure Torsion of Rail Steels (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 503-504 (Jan. 2006), p. 455-460 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: To study the influence of shear deformation on the evolution of the microstructure and the mechanical strength in rail steels, three steels with different microstructure (two pearlitic, one bainitic) were deformed by High Pressure Torsion (HPT). In order to evaluate in addition the effect of the strain path, a cyclic form of HPT was applied. The mechanical strength was determined by means of in-situ measurement of the flow stress and microhardness measurements. The differences of the mechanical strengths between the monotonic and cyclic deformed samples clearly indicate that a monotonic deformation promotes higher dislocation densities and leads to the assumption that dissolution of the cementite takes place more pronounced
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/11/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.503-504.455.pdf
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  • 14
    Electronic Resource
    Electronic Resource
    Microstructure and Indentation Size-Effect in Pure Niobium Subjected to SPD via ECAP and HPT (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 215-220 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A commercially pure niobium has been subjected to SPD at room temperature ( ~0.11TM) via ECAP (90º, route BC) up to 16 passes and via HPT up to shear strains γ =1000. ECAP-edsamples show an equiaxed structure after 8 and 16 passes with a decreasing average grain size. Theresults show that both the microstructure and mechanical properties of ECAP-ed samples do notreach a steady state up to at least 16 passes. HPT samples show at outer region a finer structural sizebut similar hardness values at similar equivalent strains. The nanoindentation results show anevident indentation size-effect even for the most deformed samples. The hardness values at the nanolevel converge for the recrystallized, the ECAP-ed and the HPT samples. This implies that, at thenano level, when the geometrically necessary dislocation density overcomes significantly the(initial) statistically stored dislocation density, hardness depends mainly on the physical intrinsicproperties of the material (Burgers modulus, bulk modulus...) and the contribution of bulkmechanical properties (i.e., bulk yield strength) to hardness is smoothed down. Strain-ratesensitivity (SRS) of plastic strength has been also measured by means of rate-jump nanoindentationtests. The SRS is proportional to the inverse of hardness
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.215.pdf
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  • 15
    Electronic Resource
    Electronic Resource
    Athermal and Thermal Limits of the Grain Refinement by SPD (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 938-943 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Severe plastic deformation, SPD, enables the grain refinement of bulk materials.However, at strains larger than a critical value, no further microstructural refinement can beobserved. This regime is denoted as saturation region of the microstructural size. It will be shownthat this regime can be divided into a thermal and an athermal part. The transition between thesetwo regimes was examined in an Al-3wt.%Mg alloy. The single phase alloy was deformed by highpressure torsion (HPT) at various temperatures and different rotational speeds. During the HPTdeformationthe flow stress was measured by a torque cell in a temperature range between -196°C(evaporation temperature of the liquid nitrogen) and 450°C. The temperature and the strain ratedependent behavior reveal a shift of the onset of the thermal activated regime towards highertemperatures by an increase of the strain rate
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.938.pdf
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  • 16
    Electronic Resource
    Electronic Resource
    Severe Plastic Deformation of a Bainitic Rail Steel (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 655-660 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Severe Plastic Deformation (SPD) is known to be an effective method of producingnanocrystalline materials, for instance by HPT and ECAP. These techniques are also capable ofreproducing microstructures which arise naturally when high pressure and friction is involved, forexample in wheel-rail contact problems. The resulting deformation layers build the origin point forfatigue cracks. For that reason the knowledge of the mechanical properties of these deformationlayers are of vital importance. In the framework of this study a baintic rail steel quality wasdeformed by High Pressure Torsion up to distinctive equivalent strains at a nominal pressure of 6GPa up to a final equivalent strain of 16. Afterwards the evolution of the resulting microstructurewas investigated by Scanning Electron Microscopy, by microhardness measurements and X-raydiffraction. The bainitic structure showed a strong alignment and fragmentation into the sheardirection with increasing strain, which was accompanied by an increase in hardness as well. X-raydiffraction measurements showed that the amount of retained austenite decreases dramatically aftersmall amounts of strain, which indicates that retained austenite cannot be stabilized by highpressures. Torque measurements during deformation showed after strong hardening at thebeginning, a saturation behaviour for higher strains, whereas for instance pearlitic rail steel qualitiesshow further hardening
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.655.pdf
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  • 17
    Electronic Resource
    Electronic Resource
    Tailoring the Magnetic Properties of Ferritic Alloys by HPT (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 923-928 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Industrial available FeSi, FeCo and FeNi alloys with an initial grain size of 20-50 [removed info]m weresubjected to Severe Plastic Deformation (SPD) up to strain levels where a saturation of themicrostructural refinement is observed. For both SPD conditions, ambient temperature (293 K) andliquid nitrogen temperature (77 K), the microstructure of the severely deformed state is analysed byBack Scattered Electrons (BSE) micrographs captured in a SEM. Additionally, samples that weredeformed at 77 K are examined in a Transmission Electron Microscope (TEM). The magneticproperties were characterised by means of SQUID-magnetography providing information about themagnetization behaviour of the material in the as-processed state. Depending on the SPD conditionsthe mean microstructural sizes in the steady state are about 100-150 nm and 30-80 nm at 293 K and77 K, respectively. The small microstructural sizes influence significantly the magnetic propertiesof these ferritic alloys. The initial soft-magnetic behaviour of the coarse grained state shifts towardsa hard-magnetic with decreasing crystallite size. For crystallite sizes smaller than ~80 nm themagnetic properties become again more soft-magnetic. The experiments show that very lowcoercitivity can be obtained by SPD if the grain size is smaller than ~50 nm
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.923.pdf
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  • 18
    Electronic Resource
    Electronic Resource
    TEM Study of Local Disordering: A Structural Phase Change Induced by High-Pressure Torsion (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 422-427 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Long-range ordered intermetallic alloys with L12 (Ni3Al, Cu3Au) and B2 (FeAl)structures were deformed by high-pressure torsion at room temperature up to high grades ofdeformation. Transmission electron microscopy shows that disordering caused by the deformationoccurs on a very local scale within coarse grains along glide planes (Cu3Au, Ni3Al) and in the formof well defined local regions (Ni3Al, FeAl). The latter leads to a duplex structure consisting of anordered coarse-grained structure and a disordered nanocrystalline structure. The differentmechanisms that can lead to disordering during severe plastic deformation are discussed on thebasis of the different ordering energies and on the basis of antiphase boundaries associated withgliding dislocations. The results indicate that in intermetallic alloys the formation of ananocrystalline structure by severe plastic deformation is facilitated by the loss of order
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.422.pdf
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  • 19
    Electronic Resource
    Electronic Resource
    Strengthening of Nickel Deformed by High Pressure Torsion (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 417-421 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The strength of a deformed metal depends on the content of high angle boundaries, lowangle dislocation boundaries and the dislocations between the boundaries. High angle boundariescontribute by Hall-Petch strengthening, whereas for the low angle dislocation boundaries anddislocations between boundaries the strengthening is proportional to the square root of the dislocationdensity. Based on an assumption of additivity of these contributions, the flow stresses of metalsdeformed by cold rolling have been calculated successfully. In the present investigation pure Ni(99.9%) has been deformed by high pressure torsion (HPT) to von Mises strains of 0.9, 1.7, 8.7 and 12.The strength of the HPT Ni has been determined by Vickers microhardness (HV) measurements andthe microstructural parameters have been determined by transmission electron microscope (TEM) inthe longitudinal section. HPT has been compared with deformation by cold rolling and torsion basedon the structural evolution with strain and the stress-structure relationship. Based on an assumption ofa linear additivity of boundary strengthening and dislocation strengthening, good agreement has beenfound between the calculated and the experimental flow stress
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.417.pdf
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  • 20
    Electronic Resource
    Electronic Resource
    The J-integral at Dugdale cracks perpendicular to interfaces of materials with dissimilar yield stresses (2000)
    Springer
    International journal of fracture 103 (2000), S. 397-418 
    Details
    ISSN: 1573-2673
    Keywords: Bimaterial ; J-integral ; plastic Mismatch ; strengthening mechanism.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The J-integral is applied to a Dugdale crack perpendicular to an interface of materials with equal elastic properties but different yield stresses. It is shown that the integral is path independend with certain limitations to the integration path. Three essentially different paths can be distinguished. The first integration path is totally within the first material, it provides the local crack driving force. Performing the integral around the plastic zone in both materials gives the global crack driving force. An interface force can be defined by evaluating the integral along both sides of the plastically deformed region of the interface. A comparison of these three integrals reveals that the global crack driving force is equal to the sum of the local crack driving force and of the interface force. The derived expression for the J-integral are compared with the crack tip opening displacement published recently. This reveals that the local J describes the plastic deformation at the crack tip. Therefore it represents the crack driving force in bimaterials as it does the conventional J-integral in case of homogeneous materials. The analyses are also extended to cyclic plasticity, where an out-of-phase effect is observed. Finally it is discussed how these results can be used to explain fatigue tests at bimaterial specimens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007605224764
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