排序方式: 共有27条查询结果,搜索用时 15 毫秒
1.
Thronsen Elisabeth Mørkeseth Hanne Marioara Calin D. Minakuchi Kazuhiro Katsumi Tetsuya Marthinsen Knut Matsuda Kenji Holmestad Randi 《Metallurgical and Materials Transactions A》2022,53(9):3296-3310
Metallurgical and Materials Transactions A - The effect of 0.03 and 0.08 at. pct Fe additions on the formation of secondary phases in an Al–1.1Mg–0.5Cu–0.3Si at. pct alloy was... 相似文献
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Wang G Saeterli R Rorvik PM van Helvoort A Holmestad R Grande T Einarsrud MA 《Journal of nanoscience and nanotechnology》2007,7(7):2538-2541
Novel hierarchical self-assembled structures; bur-like PbTiO3 nanostructures were made by self-assembly of PbTiO3 nanocrystals under hydrothermal conditions using sodium dodecylbenzene sulfonate surfactant. The bur-like nanostructures exhibit a unique geometrical shape with cores of agglomerated nanocrystals and outershells of nanorods. The nanorods were between 30 nm and 100 nm in diameter and from several hundred nm up to 2 microm in length. We demonstrate that these nanostructures are formed in a two step process where agglomeration of PbTiO3 nanoparticles into microspheres occurs in a first step, followed by assembly of cube-shaped nanoparticle building blocks into PbTiO3 mesocrystals in a second step. The mesocrystals continuously grow into nanorods from the surface of the microspheres acting as a substrate. 相似文献
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Sigurd Wenner Katsuhiko Nishimura Kenji Matsuda Teiichiro Matsuzaki Dai Tomono Francis L. Pratt Calin D. Marioara Randi Holmestad 《Metallurgical and Materials Transactions A》2014,45(12):5777-5781
The precipitate microstructure and vacancy distribution in Al-Mg-Si alloys with different amounts of solute and different heat treatments were investigated by transmission electron microscopy and muon spin relaxation measurements. A high amount of vacancies is normally present in Al-Mg-Si alloys as these bind to atomic clusters. We observe these vacancies to leave the material not before over-aging at very high temperatures such as 623 K (350 °C), meaning that vacancies do not bind to incoherent over-aged precipitates. For samples only stored at room temperature after solution heat treatment, a reduction of muon trapping was found at a temperature of 140 K (?133 °C) when reducing the amount of solute in the alloy. This might be connected to a lower number density of Cluster (1), which contrary to Cluster (2) do not nucleate precipitates upon further aging of the material. 相似文献
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Tommy Mokkelbost Hilde Lea Lein Per Erik Vullum Randi Holmestad Tor Grande Mari-Ann Einarsrud 《Ceramics International》2009,35(7):2877-2883
Thermal and mechanical properties of polycrystalline La1−xAxNbO4 (x = 0, 0.005, 0.02 and A = Ca, Sr and Ba) are reported. The materials possess a ferroelastic to paraelastic phase transition close to 500 °C, and the linear thermal expansion is significantly lower (8.6 ± 0.5 × 10−6 °C−1) for the paraelastic phase compared to the ferroelastic phase (15 ± 3 × 10−6 °C−1). The hardness was significantly higher for acceptor doped materials (6 GPa) compared to pure LaNbO4 (3 GPa) due to a significantly smaller average grain size. The fracture toughness of La0.98Sr0.02NbO4, measured by single edge V-notched beam method, was 1.7 ± 0.2 MPa m1/2 independent of temperature up to 600 °C. The ferroelastic properties of the materials were confirmed by non-linear relationships between stress and strain during compression/decompression, a remnant strain after decompression and the presence of ferroelastic domains. The mechanical properties of LaNbO4-based materials are discussed with focus on ferroelasticity, microcracking due to crystallographic anisotropy and pinning of ferroelastic domain boundaries. 相似文献
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Atomic Structures of Precipitates in Al–Mg–Si Alloys with Small Additions of Other Elements 下载免费PDF全文
Takeshi Saito Eva A. Mørtsell Sigurd Wenner Calin D. Marioara Sigmund J. Andersen Jesper Friis Kenji Matsuda Randi Holmestad 《Advanced Engineering Materials》2018,20(7)
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Calin D. Marioara Sigmund J. Andersen Jostein Røyset Oddvin Reiso Sverre Gulbrandsen-Dahl Tor-Erik Nicolaisen Inge-Erland Opheim Jan Fredrik Helgaker Randi Holmestad 《Metallurgical and Materials Transactions A》2014,45(7):2938-2949
It is demonstrated that good thermal stability in Al-Mg-Si-Cu aluminum alloys correlates with a high density of fine lath-shaped, Cu-containing, disordered L-precipitates. Alloys optimized for L retained hardness above 90 HV after 3 weeks over-aging at 473 K (200 °C). Further improvement was achieved by substituting Si by Ge in one alloy. High-angle annular dark-field scanning transmission electron microscopy showed that at peak-hardness conditions, L coexists with more common needle-shaped precipitates, often with Cu-enriched interfaces. 相似文献
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C. D. Marioara S. J. Andersen A. Birkeland R. Holmestad 《Journal of Materials Science》2008,43(14):4962-4971
The orientations Si-crystals take in aluminium, in an alloy with composition Al–1.3at%Si, were investigated by transmission
electron microscopy. Hardness was measured for isothermal heat-treatments at 175 °C and 260 °C. Conditions analysed by TEM
were 17 h at 175 °C and an additional 3 h at 260 °C, both containing a high density of small Si-crystals, the finest corresponding
to 175 °C. Two main orientation relationships were found: The first accounted for approximately 60% of Si precipitates in condition 17 h_175 °C. Despite a high number density and
well-aligned interfaces, the Si precipitates have negligible influence on hardness. Findings are consistent with Ge particles
in Al–Ge alloys. 相似文献
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W. M. Tucho H. J. Venvik J. C. Walmsley M. Stange A. Ramachandran R. H. Mathiesen A. Borg R. Bredesen R. Holmestad 《Journal of Materials Science》2009,44(16):4429-4442
The microstructure of self-supported 1.5–10-μm thick Pd/23 wt%Ag membranes grown by magnetron sputtering have been studied
after heat treatment and hydrogen permeation tests using electron microscopy and synchrotron X-ray diffraction. After hydrogen
flux stabilization and permeance measurements at 300 °C, the membranes were annealed in air at 300 °C or in N2/Ar at 300/400/450 °C for 4 days and then tested for hydrogen permeation. The permeation results show that changes in permeability
depend on the treatment atmosphere and temperature, as well as membrane thickness. Air treatment at ~300 °C generally induced
a positive effect on permeation in the thickness range of 1.5–10 μm. Significant microstructural changes, including grain
growth, strain relief, void formation, and growth of nodules occurred in the membranes. The changes in microstructure are
more severe for the thinner membranes, and may be attributed mainly to the oxidation processes at or near the surface. For
samples annealed in N2/Ar, enhanced permeation was only obtained with treatment at ~450 °C for 5 and 10 μm. The changes in the microstructure generally
increased with heat-treatment temperature, and decreased with membrane's thickness. The membrane with enhanced permeation
was accompanied by significant grain growth, strain relief, and surface roughening. For all the membranes, the relative changes
in the microstructure were substantially more prominent on the permeate surface than on the feed surface. Details of the analysis
are presented and discussed. 相似文献
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R. Bjørge C. Dwyer M. Weyland P.N.H. Nakashima C.D. Marioara S.J. Andersen J. Etheridge R. Holmestad 《Acta Materialia》2012,60(6-7):3239-3246
Precipitates in an Al–Mg–Ge alloy similar to the β′ phase in Al–Mg–Si alloys were investigated using qualitative and quantitative aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). The needle-shaped β′-Ge precipitates are coherent with the Al matrix along the needle direction which is parallel to a 〈0 0 1〉Al direction, as well as one direction in the cross-section plane that is parallel to a 〈1 0 0〉Al direction. This is linked to a smaller lattice parameter in the needle cross-section plane than that of coarser, less coherent β′ precipitates in Al–Mg–Si alloys, despite Ge having a larger atomic radius than Si. Quantitative HAADF STEM results show that the nominal Ge columns of the β′-Ge precipitates are not fully occupied by Ge, the intensity of these columns being consistent with an Al concentration of 30 ± 10%, or a vacancy concentration of 20 ± 10%. The coherent interface is atomically smooth, but with matrix columns containing Ge spaced periodically along the interface. 相似文献