| 1. |
- Gustafsson, Stefan, 1976, et al.
(författare)
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Development of microstructure during creep of polycrystalline mullite and a nanocomposite mullite/5 vol.% SiC
- 2009
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 29:4, s. 539-550
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Tidskriftsartikel (refereegranskat)abstract
- The microstructures of as-sintered and creep tested polycrystalline mullite and mullite reinforced with 5 vol.% nano-sized SiC particles have been characterized by scanning and transmission electron microscopy. The dislocation densities after tensile creep testing at 1300 and 1400 °C were virtually unchanged as compared to the as-sintered materials which indicates diffusion-controlled deformation. Mullite matrix grain boundaries bending around intergranular SiC particles suggest that grain boundary pinning, in addition to a reduced mullite grain size, contributed to the increased creep resistance of the mullite/5 vol.% SiC nanocomposite. Both materials showed pronounced cavitation at multi-grain junctions after creep testing at 1400 °C which suggests that unaccommodated grain boundary sliding, facilitated by softening of the intergranular glass, occurred at this temperature. This is consistent with the higher stress exponents at 1400 °C. © 2008 Elsevier Ltd. All rights reserved.
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| 2. |
- Pitchford, J. E., et al.
(författare)
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The effect of particle migration on the creep-rate of nanocomposites
- 2006
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Ingår i: Key Engineering Materials. - : Trans Tech Publications, Ltd.. - 1013-9826 .- 1662-9795. ; 317-318, s. 445-448
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Tidskriftsartikel (refereegranskat)abstract
- The tensile creep behaviour of a mullite-SiC nanocomposite containing 5 vol% of SiC particles deformed under stresses from 4 to 50 MPa at 1400°C has been studied. After grain-size effects had been accounted for, the creep-rate of the nanocomposite was found to be approximately 30× less than that of the monolithic mullite. It is suggested that this reduction is caused not by a threshold stress but by the extra work required to drive diffusion in the low diffusivity SiC particles so that they can move with the grain boundaries during creep. A model is presented which predicts the rate of creep under these conditions and gives reasonable agreement with the experiments at low stresses.
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| 3. |
- Rantakyrö, F.T., et al.
(författare)
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50 μas resolution VLBI images of AGN’s at λ3 mm
- 1998
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Ingår i: Astronomy and Astrophysics. - Berlin : Springer-Verlag. - 0004-6361 .- 1432-0746. ; 131, s. 451-467
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Tidskriftsartikel (refereegranskat)abstract
- We present 15 images from the global mm-VLBI sessions in 1990 April at 100 GHz and 1993 April at 86 GHz. These observations probe the central engines of the 16 observed AGN's with up to 50 mu as resolution. Among other sources previously observed with lambda 3 mm VLBI we present the first lambda 3 mm maps of 0735+178, 0748+126, 1055+018, 2145+067, and CTA102, in total we have been able to image 13 out of the 16 observed sources. 6 out of the 13 imaged sources observed exhibit curvature and rapid structural changes, although the low dynamic range in two thirds of the maps limits the detection of weak features. Most of the sources have unresolved cores even at this high resolution. There is substantial evidence that the observed sources can be grouped into two general groups: A misaligned population with parsec scale jets in the form of low pitch helices and an aligned population with straight jets with small changes in PA due to intrinsic bends.
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