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  • 1
    Digitale Medien
    Digitale Medien
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: An improvement for the application of computer-assisted stereophotogrammetry to ceramics is presented. To compensate for the lack of contrast in the fracture facets in scanning electron microscopy fractographs, a special decoration technique has been developed. The structure of the fracture facets is enhanced via heat treatment of a sputtered gold layer. This procedure enables the measurement of the three-dimensional location of more than 10 000 points on the fracture surface by means of automatic stereophotogrammetry.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 426-432 (Aug. 2003), p. 2747-2752 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 467-470 (Oct. 2004), p. 1277-1282 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Notizen: At present, the possibility of the formation of high-angle grain boundaries upon severe cold deformation, in particular, equal-channel angular (ECA) pressing is reliably proved. The structure formation upon multi-cycle ECA pressing substantially depends on the route determining the shear plane in the sample upon repeated passes. The route is defined by the rotation of the sample around its axis upon the multi-cycle ECA pressing. There are four main routes: route A, in which the sample is deformed by many passes without any rotations; route Ba, in which the sampleis rotated by ± 90°; route Bc, in which the sample is sequentially rotated in the same direction by 90°and route C, in which the sample is rotated by 180° about its axis before each subsequent pass. By the methods of SEM, TEM and EBSD analysis it was shown that the fraction of high-angle boundaries in a-Fe upon cold ECA pressing with an angle of 90° between the channels and N=4 depends on the deformation route and increases according to the route sequence: Ba-C-Bc
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 215-220 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Notizen: 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
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 422-427 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Notizen: 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
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 417-421 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Notizen: 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
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 923-928 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Notizen: 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
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 938-943 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Notizen: 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
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 655-660 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Notizen: 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
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 550 (July 2007), p. 277-282 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Notizen: By using techniques of severe plastic deformation a metallic material can be subjected toan enormous strain that is not achievable by conventional methods of deformation. In this studynickel single crystals with different crystallographic orientation and nickel polycrystals weredeformed by high pressure torsion. All nickel samples were processed up to the evolution of asaturation microstructure where no further hardening of the material can be observed. In this regionall samples develop a similar microstructure and micro-texture. The differences in the fragmentationof the microstructure and the micro-texture development between the single crystals and thepolycrystalline aggregate were examined using EBSD. A major difference between single crystalsand polycrystals was not only the microstructure evolution at low equivalent strains, but also thedevelopment of a stable micro-texture, which is achieved earlier by the use of a polycrystallineaggregate
    Materialart: Digitale Medien
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