| 1. |
- Almer, Jonathan, et al.
(author)
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Microstructural evolution during tempering of arc-evaporated Cr-N coatings
- 2000
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 18:1, s. 121-130
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Journal article (peer-reviewed)abstract
- Cr-N coatings were arc-deposited at 50 and 300 V. The changes in the coating microstructure and phase content during tempering were monitored. As a result, the phase stability and activation energies for defect diffusion were determined as a function of ion energy.
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| 2. |
- Almer, J, et al.
(author)
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Microstructure and thermal stability of arc-evaporated Cr-C-N coatings
- 2004
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In: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; 84:7, s. 611-630
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Journal article (peer-reviewed)abstract
- The role of C incorporation in the microstructure and thermal stability of arc-evaporated Cr-C-N coatings is explored via reactive growth in a mixed C2H4-N2 environment. C is found to react more readily than N at both the Cr cathode and the coating surfaces, so that a C2H4-to-N2 flow ratio of only 1% yields a C-to-N ratio of approximately 10% within the coatings. The as-deposited microstructures consist primarily of the δ-Cr(C, N) phase and possess high compressive residual stresses, which decrease with increasing C content. Post-deposition annealing up to 700°C results in depletion of lattice defects, and concomitant reductions in stress and coating hardness, together with phase transformations which suggest metastable phase formation during growth. Apparent activation energies for this lattice defect are found to be in the range expected for bulk diffusion of N and C (2.4-2.8 eV). The results suggest that inclusion of small amounts of C in this system offers the ability to reduce internal stresses while maintaining defect-related hardness increases, permitting growth of thicker and thus more wear-resistant coatings.
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| 3. |
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| 4. |
- Almer, J, et al.
(author)
-
Microstructure, stress and mechanical properties of arc-evaporated Cr-C-N coatings
- 2001
-
In: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 385:1-2, s. 190-197
-
Journal article (peer-reviewed)abstract
- The relationships between coating microstructure and properties in the Cr-C-N system have been investigated as a function of composition and post-deposition annealing. Coatings of varying compositions were grown using arc-evaporation, by varying the reactive gas flow ratio fR = f(C2H4)/f(N2) from 0 to 0.2, and were found to consist primarily of the cubic d-Cr(C,N) phase. Changes in both the unstressed lattice parameter, ao, and X-ray diffraction background intensity indicate that both the carbon concentration within the d-phase and amorphous/crystalline content increases with fR. Increasing fR also decreases the magnitude of the compressive biaxial residual stress, from approximately 6 to 1 GPa, while increasing both the inhomogeneous stress and thermal stability. The elastic modulus and hardness of as-deposited coatings were determined from nanoindentation to be 320 and 23 GPa, respectively, for moderate carbon concentrations (fR=0.05). Concurrent variations in microstructure and hardness with post-deposition annealing indicate that the as-deposited hardness is significantly enhanced by the microstructure, primarily by lattice defects and related stresses (microstresses) rather than average stresses (macrostresses).
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| 5. |
- Almer, J., et al.
(author)
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Strain and texture analysis of coatings using high-energy x-rays
- 2003
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 94:1, s. 697-702
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Journal article (peer-reviewed)abstract
- We investigate the internal strain and crystallographic orientation (texture) in physical-vapor deposited metal nitride coatings of TiN and CrN. A high-energy diffraction technique is presented that uses synchrotron x rays and an area detector, and which allows the strain and intensity distributions of multiple crystallographic planes to be measured by a single x-ray exposure. Unique texture states and nonlinear sin2 strain distributions are observed for all coatings investigated. Quantitative analysis indicates that existing micromechanical models can reasonably predict strain and corresponding stress for mixed-hkl reflections but are inadequate for fully describing measured data. Alternative mechanisms involving deposition-induced defects are proposed
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| 6. |
- Gibmeier, Jens, et al.
(author)
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Residual Stress Distributions around Clinched Joints
- 2002
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In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 404-407, s. 617-622
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Journal article (peer-reviewed)abstract
- Clinching is a mechanical press joining method, which has become of growing interest in recent time since it has the potential to replace other conventional joining methods like e.g. spot welding. However, there still exists a lack of knowledge in terms of the mechanical behavior of clinched joints under quasistatic or cyclic loading. For that reason clinching is usually used for applications in structures which are not subjected to external loads. In particular the residual stress distribution in the vicinity of clinched joints and its influence on the mechanical behavior of the joints is unknown. Here diffraction methods are used for the determination of characteristic residual stress distributions in undismantled clinched samples. A combined residual stress determination by X-ray and neutron diffraction has been used to get a well-founded assessment of the residual stress distributions in the immediate vicinity of clinched joints. The residual stress analysis is supplemented by characterizations of the microstructures and the mechanical properties of single clinched joints. Two materials with different strain hardening behavior were used for clinching, a micro alloyed steel (ZStE340) and a non age hardenable aluminum base alloy (AlMg5). In addition two different common clinching techniques were applied - the TOX- [5] and the Eckold-technique [6]. Characteristic residual stress distributions were found for the combinations of clinching techniques and joined sheet materials investigated here. It has been determined that the clinching process induces predominantly compressive residual stresses inside the clinch and in the immediate vicinity of the clinch. The near surface residual stress distributions determined by X-ray diffraction measurements tend to reveal somewhat different residual stresses than measured by neutron diffraction, indicating a possible stress gradient through the sheet thickness. Further evaluation of the FWHM-values of the respective interference profiles shows that for both clinching techniques the largest amount of plastic deformation occurs in the clinch lock region.
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| 7. |
- Gibmeier, Jens, et al.
(author)
-
Residual stress in clinched joints of metals
- 2002
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In: Applied Physics A. - : Springer. - 0947-8396 .- 1432-0630. ; 74:SUPPL.II, s. s1440-s1442
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Journal article (peer-reviewed)abstract
- Diffraction methods are used for the determination of characteristic residual stress (RS) distributions in undismantled clinched samples for the assessment of the influence of RS on the mechanical behaviour of clinched joints. While X-ray diffraction enables merely the determination of near-surface RS distributions, the higher penetration depth of neutron radiation allows the determination of triaxial RS states inside the material. In addition, the complex geometry of clinched joints restricts the application of X-ray RS analysis. Therefore a combined RS determination by X-ray and neutron diffraction has been used to obtain an expressive assessment of the RS distributions in the immediate vicinity of clinched joints. Two different materials with different mechanical behaviour were used for clinching, as well as two different common clinching techniques.
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| 8. |
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| 9. |
- Gorishnyy, T.Z., et al.
(author)
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Optimization of wear-resistant coating architectures using finite element analysis
- 2003
-
In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 21:1, s. 332-339
-
Journal article (peer-reviewed)abstract
- The design of successful wear-resistant coating architectures requires simultaneous consideration of several factors. In particular, coatings which consist of CrN layers of varying thickness separated by thin Cr layers have the highest wear resistance for both aluminum and steel substrate materials, but a methodology was needed to optimize both the overall coating design and the individual layer thicknesses. This paper provides an initial step toward the development of future application specific coating designs and improved coating design methodologies.
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| 10. |
- Hultman, Lars, 1960-, et al.
(author)
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Mechanical and thermal stability of TiN/NbN superlattice thin films
- 2000
-
In: Surface & Coatings Technology. - 0257-8972 .- 1879-3347. ; 133-134, s. 227-233
-
Journal article (peer-reviewed)abstract
- High-temperature stability and mechanical deformation mechanisms of TiN/NbN superlattice structures have been investigated. Single-crystal TiN/NbN superlattices were deposited by reactive dual-cathode unbalanced magnetron sputtering in an Ar/N2 discharge onto MgO(001) substrates held at a temperature of 700 ░C. The thermal stability was studied by X-ray measurements of superlattice satellite peak intensity variation during and after annealing at up to 950 ░C. The apparent activation energy for metal interdiffusion in the TiN-NbN diffusion couple is temperature-dependent, with values ranging from 2.6 to 4.5 eV. Film hardness as measured by nanoindentation was observed to decrease during annealing, as the result of effective alloying of the nitride layers. TiN/NbN superlattices are ductile at room temperature and exhibit dislocation glide limited to within individual layers in scratching experiments.
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| 11. |
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| 12. |
- Hörling, Anders, et al.
(author)
-
Thermal stability of arc evaporated high aluminum-content Ti1−xAlxN thin films
- 2002
-
In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 20:5, s. 1815-1823
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Journal article (peer-reviewed)abstract
- The thermal stability of Ti1−xAlxN films deposited by arc evaporation from Ti–Al cathodes with 67 and 75 at. % aluminum, respectively, has been investigated. The microstructure of as-deposited and isothermally annealed samples were studied using scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The chemical composition and elemental distribution were determined by energy dispersive x ray (EDX), Rutherford backscattering spectrometry, and EDX mapping. Transmission electron micrographs revealed a dense and columnar microstructure in the as-deposited condition. Films deposited from the 67 at. % cathodes were of cubic NaCl-structure phase, whereas films deposited from the 75 at. % cathodes exhibited nanocrystallites of wurzite-structure hexagonal-phase AlN in a cubic (c)-(Ti,Al)N matrix. Both films were stable during annealing at 900 °C/120 min with respect to phase composition and grain size. Annealing at 1100 °C of films deposited from the 67 at. % cathodes resulted in phase separation of c-TiN and h-AlN, via spinodal decomposition of c-TiN and c-AlN. (Ti,Al)N films undergo extensive stress relaxation and defect annihilation at relatively high temperatures, and aspects of these microstructural transformations are discussed.
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| 13. |
- Jensen, J.A.D., et al.
(author)
-
Electrochemically deposited nickel membranes, process-microstructure-property relationships
- 2003
-
In: Surface & Coatings Technology. - 0257-8972 .- 1879-3347. ; 172:1, s. 79-89
-
Journal article (peer-reviewed)abstract
- This paper reports on the manufacturing, surface morphology, internal structure and mechanical properties of Ni-foils used as membranes in reference-microphones. Two types of foils, referred to as S-type and 0-type foils, were electrochemically deposited from a Watts-type electrolyte, with (S-type) or without (0-type) the use of the sulfur-containing additive sodium saccharin. Both types of Ni-foils appeared perfectly smooth when investigated with scanning electron microscopy (SEM), while atomic force microscopy (AFM) and transmission electron microscopy (TEM) revealed differences in the surface morphologies and a smaller grain-size in the S-type foils. X-Ray diffraction showed a <311> texture component in both types of Ni-foils, most pronounced for 0-type foils. A minor <111> texture component observed in both foil types was strongest in the S-type foils. Mechanically 0-type foils proved more ductile than S-type foils during thin film tensile testing, due to microstructural defects caused by sodium saccharin during deposition. Tensile strengths in the order of 700-1000 MPa were observed - highest for the more ductile 0-type foils. A hardness in the order of 6 GPa (590 HV) was found by nanoindentation. © 2003 Elsevier Science B.V. All rights reserved.
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| 14. |
- Johansson, Johan, et al.
(author)
-
Micro- and macrostress evolution in a duplex stainless steel during uniaxial loading
- 2000
-
In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 347-3, s. 603-608, s. 603-608
-
Journal article (peer-reviewed)abstract
- The evolution of micro- and macrostresses in a duplex stainless steel during uniaxial loading has been investigated in situ by X-ray diffraction. Due to differences in the coefficient of thermal expansion between the two phases, compressive residual microstresses were found in the ferritic phase and balancing tensile microstresses in the austenitic phase. The initial microstresses were almost two times higher in the transverse direction compared to the rolling direction. During loading the microstresses increase in the macroscopic elastic regime but starts to decrease slightly with increasing load in the macroscopic plastic regime. During unloading from the plastic regime the microstresses increases by approximately 35 MPa in the direction of applied load but remains constant in the other directions.
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| 15. |
- Johansson (Moverare), Johan, 1973-, et al.
(author)
-
Load sharing between austenite and ferrite in a duplex stainless steel during cyclic loading
- 2000
-
In: Metallurgical and Materials Transactions. A. - : SpringerLink. - 1073-5623 .- 1543-1940. ; 31:6, s. 1557-1570
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Journal article (peer-reviewed)abstract
- The load sharing between phases and the evolution of micro- and macrostresses during cyclic loading has been investigated in a 1.5-mm cold-rolled sheet of the duplex stainless steel SAF 2304. X-ray diffraction (XRD) stress analysis and transmission electron microscopy (TEM) show that even if the hardness and yield strength are higher in the austenitic phase, more plastic deformation will occur in this phase due to the residual microstresses present in the material. The origin of the microstresses is the difference in coefficients of thermal expansion between the two phases, which leads to tensile microstresses in the austenite and compressive microstresses in the ferrite. The microstresses were also found to increase from 50 to 140 MPa in the austenite during the first 100 cycles when cycled in tension fatigue with a maximum load of 500 MPa. The cyclic loading response of the material was, thus, mainly controlled by the plastic properties of the austenitic phase. It was also found that initial compressive macrostresses on the surface increased from −40 to 50 MPa during the first 103 cycles. After the initial increase of microstresses and macrostresses, no fading of residual stresses was found to occur for the following cycles. A good correlation was found between the internal stress state and the microstructure evolution. The change in texture during cyclic fatigue showed a sharpening of the deformation texture in the ferritic phase, while no significant changes were found in the austenitic phase.
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| 16. |
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| 17. |
- Larsson, Cecilia, et al.
(author)
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Hardness profile measurements in functionally graded WC–Co composites
- 2004
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 382:1-2, s. 141-149
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Journal article (peer-reviewed)abstract
- Micro- and nanoindentation were used to determine hardness as a function of depth in two functionally graded WC–Co composites. The gradients were continuous (extended over ∼70 and ∼40 μm, respectively) and consisted of varying WC and Co phase volume fractions. Five comparable homogeneous samples with different Co contents and different average WC grain sizes were also used for direct comparison. A relationship between hardness and Co content was established for both the graded and the homogeneous samples wherein the hardness decreased with increasing Co content. The magnitude of the hardness was the same (for a given Co content) for the functionally graded and the homogeneous materials. The hardness measurements were also correlated with X-ray diffraction studies of thermal residual stresses and the absence of any major influence explained. It is generally concluded that the hardness values are dominated by the local Co content. Additionally, the examination of surface cracks around indents suggests that compositional gradients in WC–Co composites offer increased toughness.
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| 18. |
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| 19. |
- Larsson, Cecilia, 1973-, et al.
(author)
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X-ray diffraction determination of residual stresses in functionally graded WC–Co composites
- 2004
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 22:4-5, s. 177-184
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Journal article (peer-reviewed)abstract
- X-ray diffraction was used to determine the thermal residual stresses that develop in a functionally graded WC–Co composite. Stresses were measured in both WC and Co phases at various depths. Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. For WC, the in-plane compressive residual stresses varied approximately between −300 and −500 MPa with depth below the surface. For the low volume fraction Co phase, the tensile residual stresses were approximately 600 MPa. The microstresses in the graded zone were attributed to the thermal mismatch between the WC and the Co phase during cooling from the liquid phase sintering temperature (1450 °C). The microstresses determined were in reasonable agreement with a prediction using Eshelby theory. The compressive macrostresses were attributed to the compositional gradient, a result further substantiated by the fact that no significant macrostresses were measured in a comparable homogeneous sample, i.e., without the compositional gradient. Thus, varying compositional gradients in WC–Co composites during fabrication can be expected to directly influence the macrostress component of the overall residual stress state.
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| 20. |
- Molina-Aldareguia, J.M., et al.
(author)
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Deformation structures under indentations in TiN/NbN single-crystal multilayers deposited by magnetron sputtering at different bombarding ion energies
- 2002
-
In: Philosophical magazine. A. Physics of condensed matter. Defects and mechanical properties. - 0141-8610. ; 82:10 SPEC., s. 1983-1992
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Journal article (peer-reviewed)abstract
- Work elsewhere has suggested that multilayer films with layer thicknesses of a few nanometres can be much harder than monolithic films, although there is considerable variation in the observed magnitude of this effect. To investigate this, multilayer TiN/NbN films have been deposited by reactive magnetron sputtering on to MgO single crystals. The hardnesses measured were similar to those of the TiN and NbN alone, which is consistent with the observation by transmission electron microscopy (TEM) that deformation across the interfaces was not prevented. Varying the electrical potential at which the film was grown from -10 to -200 V and the corresponding ion energy from 10 to 200 eV increased the hardness from 19 to 25 GPa, further decreases in the potential caused the hardness to decrease. Using TEM, deformation was observed to occur along the apparent columnar boundaries within the films, suggesting that the effect of the electrical potential on the measured hardness was caused by changes in the apparent strength of the columnar boundaries, possibly associated with the variations in the volume fraction of voids that were observed on these boundaries.
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| 21. |
- Moverare, Johan, 1973-, et al.
(author)
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Anisotropic high cycle fatigue behaviour of duplex stainless steels : influence of microstresses
- 2002
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In: International Journal of Materials Research - Zeitschrift für Metallkunde. - : Walter de Gruyter GmbH. - 1862-5282 .- 2195-8556. ; 93:1, s. 7-11
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Journal article (peer-reviewed)abstract
- The anisotropic high cycle fatigue behaviour has been investigated for a duplex stainless steel in as-received and prestrained condition. It was found that the anisotropy of the fatigue limit is different from the anisotropy of yield strength. The main reason for this is the influence of microstresses on fatigue crack initiation. Fatigue cracks are seen to nucleate preferably in the austenite phase, which has tensile microstresses. Prestraining alters the microstresses from being higher in the transverse direction to being higher in the rolling direction. At the same time, the fatigue limit is changed from being higher in the rolling direction to being higher in the transverse direction.
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| 22. |
- Moverare, Johan, 1973-, et al.
(author)
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Deformation behaviour of a prestrained duplex stainless steel
- 2002
-
In: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 337:1-2, s. 25-38
-
Journal article (peer-reviewed)abstract
- The anisotropic flow behaviour due to a change in strain path during uniaxial deformation of a duplex stainless steel has been investigated. The anisotropic flow behaviour of the as-received material could be predicted from the crystallographic texture. However, it was found that prestraining introduces a transient work hardening behaviour during the second stage deformation, which causes an anisotropic flow behaviour immediately after yielding that cannot be described by the crystallographic texture. Samples subjected to a coaxial second stage deformation show a small increase in flow stress and similar work hardening rate as in the monotonic loading. Samples subjected to noncoaxial second stage deformation show a pronounced transient stage characterised by early yielding and a high work hardening rate in the first part of the transient stage. Beyond the earliest stage of deformation a higher flow stress and a lower work hardening rate compared to monotonic loading is observed for the noncoaxial samples. The transient phenomena are discussed based on the measured internal stresses and the differences in dislocation structures in the two different phases.
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| 23. |
- Moverare, Johan, 1973-, et al.
(author)
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Influence of elastic and plastic anisotropy on the flow behavior in a duplex stainless steel
- 2002
-
In: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 33:1, s. 57-71
-
Journal article (peer-reviewed)abstract
- The load partitioning between two phases in a cold-rolled duplex stainless steel has been experimentally studied in situ by X-ray diffraction, for different loading directions. It was found that the load partitioning between the two phases is dependent on the loading direction. For loading in the rolling direction, both phases deform plastically to the same degree, while more plastic deformation occurs in the austenitic phase during loading in the transverse direction. For loading in the 45-deg direction, more plastic deformation occurs in the ferritic phase. The strong crystallographic texture in the ferritic phase makes the material anisotropic, with a higher stiffness and yield strength in the transverse direction compared to the rolling direction. The measured texture was used as input to theoretical predictions of both elastic and plastic anisotropy. The plastic anisotropy was predicted by assuming intragranular slip as the main deformation mechanism. The predicted anisotropic material properties were then used in finite-element simulations to study the flow behavior of the material in different directions. The predicted flow behavior was found to be in good agreement with the experimentally observed load partitioning between the phases for loading in the rolling and transverse directions. However, the yield strength of the ferritic phase during loading in the 45-deg direction was found to be lower than what was predicted. The reason for this is the difference in slip characteristics in different sample directions, because of the morphological texture.
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| 24. |
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| 25. |
- Moverare, Johan, 1973-, et al.
(author)
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Influence of Texture and Anisotropy on Microstresses and Flow Behavior in a Duplex Stainless Steel During Loading
- 2000
-
In: Advances in X-ray Analysis, Vol. 44. ; , s. 229-234
-
Conference paper (other academic/artistic)abstract
- The load partitioning between the two phases in a cold rolled duplex stainless steel sheet have been experimentally studied in situ during loading, via X-ray diffraction, for different loading directions. The microstresses in the two phases were found to decrease when loading in the transverse direction, while they increase during loading in the rolling and 45°-direction. Due to strong crystallographic texture in the ferritic phase the material is anisotropic with a higher stiffness and yield strength in the transverse direction compared to the rolling direction. The texture have been measured and used as input to theoretical predictions of both elastic and plastic anisotropy. The predicted anisotropic material properties have then been used in finite element simulations to study the flow behaviour of the material in different directions. The predicted flow behaviour was found to be in good agreement with the experimentally observed load partitioning between the phases for loading in the rolling and transverse direction. However, the yield strength of the ferritic phase during loading in the 45°-direction was found to be lower than what can be predicted by the crystallographic texture.
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| 26. |
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| 27. |
- Odén, Magnus, 1965-, et al.
(author)
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Growth of single-crystal CrN on MgO(001) : Effects of low-energy ion-irradiation on surface morphological evolution and physical properties
- 2002
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:6, s. 3589-3597
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Journal article (peer-reviewed)abstract
- CrN layers, 0.5 ╡m thick, were grown on MgO(001) at Ts=570-775░C by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition in pure N2 discharges at 20 mTorr. Layers grown at Ts=700░C are stoichiometric single crystals exhibiting cube-on-cube epitaxy: (001)CrN(001)MgO with [100]CrN[100]MgO. At higher temperatures, N2 desorption during deposition results in understoichiometric polycrystalline films with N fractions decreasing to 0.35, 0.28, and 0.07 with Ts=730, 760, and 775░C, respectively. The surface morphologies of epitaxial CrN(001) layers were found to depend strongly on the incident ion-to-metal flux ratio JN2+/JCr which was varied between 1.7 and 14 with the ion energy maintained constant at 12 eV. The surfaces of layers grown with JN2+/JCr=1.7 consist of self-organized square-shaped mounds, due to kinetic roughening, with edges aligned along orthogonal <100> directions. The mounds have an average peak-to-valley height =5.1 nm and an in-plane correlation length of =0.21 ╡m. The combination of atomic shadowing by the mounds with low adatom mobility results in the formation of nanopipes extending along the growth direction. Increasing JN2+/JCr to 14 leads, due to increased adatom mobilities, to much smoother surfaces with =2.5 nm and =0.52 ╡m. Correspondingly, the nanopipe density decreases from 870 to 270 ╡m-2 to <20 ╡m-2 as JN2+/JCr is increased from 1.7 to 6 to 10. The hardness of dense CrN(001) is 28.5▒1 GPa, but decreases to 22.5▒1 GPa for layers containing significant nanopipe densities. The CrN(001) elastic modulus, 405▒15 GPa, room-temperature resistivity, 7.7╫10-2 cm, and relaxed lattice constant, 0.4162▒0.0008 nm, are independent of JN2+/JCr. ⌐ 2002 American Institute of Physics.
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| 28. |
- Odén, Magnus, 1965-, et al.
(author)
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Microstructure-property relationships in arc-evaporated Cr-N coatings
- 2000
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In: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 377-378, s. 407-412
-
Journal article (peer-reviewed)abstract
- Chromium nitride (Cr-N) coatings have received increased attention for tribological applications due to their favorable properties including wear resistance, toughness and oxidation resistance. These properties, in turn, can be strongly influenced by the coating microstructure and residual stress resulting from deposition and subsequent processing operations. In this study these microstructure-property correlations are investigated in Cr-N coatings grown by arc-evaporation. Prominent as-deposited features include formation of metastable amounts of the cubic d-CrN phase, and high levels of compressive residual stress and defect density. During annealing up to 650 ░C the residual stress and defect density decrease substantially, accompanied by a diffusion-based d-CrN to ▀-Cr2N phase transformation and equiaxed grain formation. The effects of these microstructural modifications on the hardness, fracture and wear properties of the coatings are evaluated using a combination of nanoindentation, scratch and pin-on-disk testing. Appreciable changes in these properties are found after annealing, and are correlated to the Cr-N microstructure. As-deposited coating hardness is enhanced by high levels of lattice defect density, with both decreasing concomitantly during annealing. Scratch results show that resistance to cohesive flaking is increased by annealing, suggesting ductility increases via defect annealing and equiaxed grain formation. Finally, the wear rate under dry sliding generally increased with annealing temperature, although wear rates of all Cr-N coatings significantly outperformed TiN tested under identical conditions.
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| 29. |
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| 30. |
- Palmquist, J.-P., et al.
(author)
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Magnetron sputtered W-C films with C60 as carbon source
- 2003
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In: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 444:1-2, s. 29-37
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Journal article (peer-reviewed)abstract
- Thin films in the W–C system were prepared by magnetron sputtering of W with coevaporated C60 as carbon source. Epitaxial deposition of different W–C phases is demonstrated. In addition, nanocrystalline tungsten carbide film growth is also observed. At low C60/W ratios, epitaxial growth of α-W with a solid solution of carbon was obtained on MgO(001) and Al2O3(001) at 400 °C. The carbon content in these films (10–20 at.%) was at least an order of magnitude higher than the maximum equilibrium solubility and gives rise to an extreme hardening effect. Nanoindentation measurements showed that the hardness of these films increased with the carbon content and values as high as 35 GPa were observed. At high C60/W ratios, films of the cubic β-WC1−x (x=0–0.6) phase were deposited with a nanocrystalline microstructure. Films with a grain size <30 Å were obtained and the hardness of these films varied from 14 to 24 GPa. At intermediate C60/W ratios, epitaxial films of hexagonal W2C were deposited on MgO(111) at 400 °C. Polycrystalline phase mixtures were obtained on other substrates and hexagonal WC could be deposited as minority phase at 800 °C.
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| 31. |
- Peng, Ru, 1960-, et al.
(author)
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Characterisation of residual stress distribution in clinching joints of carbon steel by diffraction methods
- 2003
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In: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 19:3, s. 336-342
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Journal article (peer-reviewed)abstract
- Sheet joints of carbon steel fabricated by two different clinching methods, namely TOX and Eckold, have been investigated. The holding force of the joints was determined by shear tension tests and the deformation microstructure was characterised using optical microscopy. The surface residual stress and mean residual stress distributions as a function of increasing distance from the outer diameter of the interlock button were mapped by X-ray and neutron diffractometry, respectively.The Eckold joints showed more severe joint distortion in the form of global sheet bending, but nevertheless possessed higher shear tension strength than the TOX joints. Characteristic residual stress distributions depending on the clinching method were found in both the TOX and Eckold joints. The observed residual stress distributions have been attributed to the different die construction employed by the two methods, which permitted different degrees of plastic deformation during clinching.
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| 32. |
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| 33. |
- Peng, Ru, 1960-, et al.
(author)
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Intergranular strains and plastic deformation of an austenitic stainless steel
- 2002
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In: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 334:1-2, s. 215-222
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Journal article (peer-reviewed)abstract
- Intergranular strains due to tensile plastic deformation were investigated in a sheet material of austenitic stainless steel. The objective was to study the development of residual intergranular strains in samples unloaded from the intermediate and large plastic deformation regimes for which few theoretical and experimental studies were available. By using neutron diffraction, residual lattice strain distribution as a function of sample direction was mapped for a number of crystallographic planes. Deformation microstructures were examined by both transmission electron microscopy and the electron back scattering pattern technique. Residual intergranular strains were observed in samples deformed significantly beyond the elastic limit and the strains varied with sample directions as well as the amount of applied plastic strain. In addition, a different tendency of intergranular strain evolution was observed after large plastic deformation, which could be attributed to the change of dominant plastic deformation mode from slip to mechanical twinning. The results are discussed based on the observed deformation microstructure studies. ⌐ 2002 Elsevier Science B.V. All rights reserved.
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| 34. |
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| 35. |
- Schlauer, Christian, 1975-, et al.
(author)
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Residual Stresses in a Nickel-based Superalloy Introduced by Turning
- 2002
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In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 404-407, s. 173-178, s. 173-178
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Journal article (peer-reviewed)abstract
- Near-surface residual stress distributions in the nickel-based superalloy Inconel 718 that originate from the machining operation turning are studied. The turning process that is used in the experiments is face grooving which gives quasi-orthogonal cutting conditions. Cutting speed and feed have been varied to investigate their effects on the residual stress state. Tensile residual stresses with a maximum of 1300 MPa were found at the surface that turn rapidly into compressive residual stresses of up to -800 MPa. The depth distributions of the residual stresses are presented and discussed with respect to observations made by optical and transmission electron microscopy.
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| 36. |
- Shin, C.-S., et al.
(author)
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Epitaxial NaCl structure d-TaNx(001) : Electronic transport properties, elastic modulus, and hardness versus N/Ta ratio
- 2001
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:6, s. 2879-2885
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Journal article (peer-reviewed)abstract
- While metastable Bl-NaCl-structure d-TaNx. is presently used in a variety of hard coating, wear-resistant, and diffusion barrier applications, it is a complex material exhibiting a wide single-phase field, x?0.94-1.37, and little is known about its fundamental properties. Here, we report physical properties of epitaxial d-TaNx. layers grown as a function of x on MgO(00) by ultrahigh vacuum reactive magnetron sputter deposition. The room-temperature resistivity (? = 225 µO cm), hardness (H = 30.9 GPa), and elastic modulus (E = 455 GPa) of d-TaNx(001) are independent of x over the range 0.94-1.22. However, changes in the electronic structure associated with increasing x>1.22 lead to an increase in ? with a decrease in H and E. All d-TaNx(001) layers exhibit negative temperature coefficients of resistivity between 20 and 400 K due to weak carrier localization. d-TaNx is superconducting with the highest critical temperature, 8.45 K, obtained for layers with the lowest N/Ta ratio, x=0.94. Based upon the above results, combined with the fact that the relaxed lattice constant a0 shows only a very weak dependence on x, we propose that the wide phase field in d-TaNx is due primarily to antisite substitutions of Ta on N (and N on Ta) sites, rather than to cation and anion vacancies. To first order, antisite substitutions in TaNx are isoelectronic and hence have little effect on charge carrier density. At sufficiently high N/Ta ratios, however, simple electron-counting arguments are no longer valid since large deviations from stoichiometry alter the character of the band structure itself. © 2001 American Institute of Physics.
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| 37. |
- Talyzin, AV, et al.
(author)
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In situ x-ray diffraction study of C-60 polymerization at high pressure and temperature
- 2002
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:16
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Journal article (peer-reviewed)abstract
- The C-60 polymerization was studied by x-ray diffraction in situ in the pressure range 13-18 GPa and at temperatures up to 830 K and nonhydrostatic conditions. Quenched samples were studied ex situ by Raman spectroscopy. The results of the high-pressure and high-temperature treatment are strongly dependent on the history of the sample and stress. An inaccurate increase of the pressure leads to the formation of internal stresses in the sample which gives elliptical Debye-Scherrer diffraction rings already at room temperature. During the subsequent heat treatment a soft amorphous phase is formed. At certain conditions no elliptical diffraction patterns were observed at 13 GPa and 830 K. Samples with a relatively low internal stress showed a transformation to a phase with decreased c-cell parameter compared to the known two-dimensional rhombohedral phase. The observed phase can be described as distorted cubic, but a better fit is achieved using a rhombohedral cell. It is suggested that this phase is a three-dimensional polymer with each C-60 molecule bonded to eight neighbors. This phase showed an increased hardness (about 37 GPa) and a Raman spectrum distinctly different from previously known polymeric phases.
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| 38. |
- Talyzin, A V, et al.
(author)
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Superhard and superelastic films of polymeric C60
- 2001
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In: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 10:11, s. 2044-2048
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Journal article (peer-reviewed)abstract
- The C60 thin film deposited on steel substrate was transformed by high pressure-high temperature treatment to a superhard and superclastic material. The films were studied by Raman spectroscopy in situ at 20 GPa after heating at 300░C and ex situ after the quenching. The hardness and elastic properties of the high-pressure phases have been characterized with nanoindentation. The hardness of the films were determined to be 0.5 ▒ 0.1 GPa and 61.9 ▒ 9 GPa for unmodified C60 and HPHT treated films, respectively. The hardness of the pressurized film is higher than for cubic BN but lower than hardness values reported for ultrahard fullerite samples prepared from powders. An interesting observation was that the HPHT treated film showed an extreme elastic response with an elastic recovery of approximately 90%. ⌐ 2001 Elsevier Science B.V. All rights reserved.
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