| 1. |
- Bernard-Granger, Guillaume, et al.
(författare)
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Phenomenological analysis of densification mechanism during spark plasma sintering of MgAl2O4
- 2009
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 24:6, s. 2011-2020
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Tidskriftsartikel (refereegranskat)abstract
- Spark plasma sintering (SPS) of MgAl2O4 powder was investigated at temperatures between 1200 and 1300 degrees C. A significant grain growth was observed during densification. The densification rate always exhibits at least one strong minimum, and resumes after an incubation period. Transmission electron microscopy investigations performed on sintered samples never revealed extensive dislocation activity in the elemental grains. The densification mechanism involved during SPS was determined by anisothermal (investigation of the heating stage of a SPS run) and isothermal methods (investigation at given soak temperatures). Grain-boundary sliding, accommodated by an in-series {interface-reaction/lattice diffusion of the O-2(-) anions} mechanism controlled by the interface-reaction step, governs densification. The zero-densification-rate period, detected for all soak temperatures, arise from the difficulty of annealing vacancies, necessary for the densification to proceed. The detection of atomic ledges at grain boundaries and the modification of the stoichiometry of spinel during SPS could be related to the difficulty to anneal vacancies at temperature soaks.
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| 2. |
- Chen, Xiang, et al.
(författare)
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In situ x-ray observation of bainitic transformation of austempered silicon alloyed steel
- 2009
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 24:4, s. 1559-1566
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Tidskriftsartikel (refereegranskat)abstract
- The in situ x-ray diffraction observations of the bainitic transformation were conducted by using the high-temperature x-ray diffraction technique. The volume fraction and carbon content of austenite depend on the transformation temperature. The d{110} value of bainitic ferrite decreases with increasing austempering temperature, which is related to the decrease of carbon concentration in bainitic ferrite. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation at any austempering temperatures. This asymmetry diffraction peak after the formation of bainitic ferrite could be attributed to a heterogeneous distribution of carbon in different regions of austenite and show that two types of austenite with different carbon contents, low-carbon austenite (?LC) and the high-carbon austenite (?HC), exist during the transformation. The microstructure after cooling down to room temperature is presented to show the effectiveness of the x-ray diffraction analysis.
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| 3. |
- Emmerlich, Jens, et al.
(författare)
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Electrical resistivity of Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films
- 2007
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 22:8, s. 2279-2287
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electrical resistivity of (0001)-oriented Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films deposited by magnetron sputtering onto Al2O3(0001) substrates at temperatures ranging from 500 to 950 °C. Four-point-probe measurements show that all films are good conductors with resistivity values of ∼21–51 μΩ cm for Ti–Si–C films, ∼15–50 μΩ cm for Ti–Ge–C films, and ∼46 μΩ cm for Ti2SnC. We find a general trend of decreasing resistivity with decreasing n for the Ti–Si–C and Ti–Ge–C systems due to the increased metallicity obtained with increasing density of A-element layers. We also show that crystalline quality and competitive growth of impurity phases affect the measured resistivity values. The effect of a given impurity phase largely depends on its location in the sample. Specifically, a TiCx layer in the center of the film constricts the current flow and results in an increased measured resistivity value. However, TiCx transition or seed layers at the substrate–film interface as well as surface segregation of Ge and Ti5Ge3Cx (for Ti–Ge–C) have only little effect on the measured resistivity values. For the Ti–Sn–C system, the resistivity is mainly influenced by the segregation of metallic Sn, yielding a wide spread in the measured values ranging from 20–46 μΩ cm, in the order of increased film purity.
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| 4. |
- Flink, Axel, et al.
(författare)
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The location and effects of Si in (Ti1-xSix)N-y thin films
- 2009
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Ingår i: JOURNAL OF MATERIALS RESEARCH. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 24:8, s. 2483-2498
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Tidskriftsartikel (refereegranskat)abstract
- (Ti1-xSix)N-y (0 andlt;= x andlt;= 0.20; 0.99 andlt;= y(x) andlt;= 1.13) thin films deposited by arc evaporation have been investigated by analytical transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and nanoindentation. Films with x andlt;= 0.09 are single-phase cubic (Ti,Si)N solid solutions with a dense columnar microstructure. Films with x andgt; 0.09 haven a featherlike microstructure consisting of cubic TiN:Si nanocrystallite bundles separated by metastable SiNz with coherent-to-semicoherent interfaces and a dislocation density of as much as 10(14) cm(-2) is present. The films exhibit retained composition and hardness between 31 and 42 GPa in annealing experiments to 1000 degrees C due to segregation of SiN, to the grain boundaries. During annealing at 1100-1200 degrees C, this tissue phase thickens and transforms to amorphous SiNz. At the same time, Si and N diffuse out of the films via the grain boundaries and TiN recrystallize.
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| 5. |
- Ghafoor, Naureen, et al.
(författare)
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Effects of O and N impurities on the nanostructural evolution during growth of Cr/Sc multilayers
- 2009
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 24:1, s. 79-95
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal multilayers are prime candidates for high reflectivity soft x-ray multilayer mirrors. In particular, Cr/Sc multilayers in the amorphous state have proven to give the highest reflectivity in the water window. We have investigated the influence of impurities N and O as residual gas elements on the growth, structure, and optical performance of Cr/Sc multilayers deposited in high vacuum conditions by a dual cathode direct current magnetron sputter deposition. Multilayer structures with the modulation periods in the range of 0.9–4.5 nm and Cr layer to bilayer thickness ratios in the range of 0.17–0.83 were deposited with an intentionally raised base pressure (pB), ranging from 2 × 10-7 to 2 × 10-5 Torr. Compositional depth profiles were obtained by elastic recoil detection analysis and Rutherford backscattering spectroscopy, while the structural investigations of the multilayers were carried out using hard x-ray reflectivity and transmission electron microscopy. By investigating stacked multilayers, i.e., several multilayers with different designs of the modulation periods, stacked on top of each other in the samples, we have been able to conclude that both N and O are incorporated preferentially in the interior of the Sc layers. At pB = 2 × 10-6 Torr, typically <3 at.% of N and <1.5 at.% of O was found, which did not influence the amorphous nanostructure of the layers. Multilayers deposited with a high pB ~2 × 10-5 Torr, a N content as high as ~37 at.% was measured by elastic recoil detection analysis. These multilayers mainly consist of understoichiometric face-centered cubic CrN x /ScN y nanocrystalline layers, which could be grown as thin at 0.3 nm and is explained by a stabilizing effect on the ScN y layers during growth. It is also shown that by adding a background pressure of as little as 5 × 10-6 Torr of pure N2 the soft x-ray reflectivity (? = 3.11 nm) can be enhanced by more than 100% by N incorporation into the multilayer structures, whereas pure O2 at the same background pressure had no effect.
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| 6. |
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| 7. |
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| 8. |
- Högberg, Hans, 1968-, et al.
(författare)
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Epitaxial Ti2GeC, Ti3GeC2, and Ti4GeC3 MAX-phase thin films grown by magnetron sputtering
- 2005
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 20:4, s. 779-782
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Tidskriftsartikel (refereegranskat)abstract
- We have grown single-crystal thin films of Ti2GeC and Ti3GeC2 and a new phase Ti4GeC3, as well as two new intergrown MAX-structures, Ti5Ge2C3 and Ti7Ge2C5. Epitaxial films were grown on Al2O3(0001) substrates at 1000 °C using direct current magnetron sputtering. X-ray diffraction shows that Ti–Ge–C MAX-phases require higher deposition temperatures in a narrower window than their Ti–Si–C correspondences do, while there are similarities in phase distribution. Nanoindentation reveals a Young’s modulus of 300 GPa, lower than that of Ti3SiC2. Four-point probe measurements yield resistivity values of 50–200 μΩcm. The lowest value is obtained for phase-pure Ti3GeC2(0001) films.
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| 9. |
- Jayamani, Jayaraj, et al.
(författare)
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Synthesis and characterization of nanometer-sized Ti-based amorphous powders
- 2007
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Ingår i: Journal of Materials Research. - : Cambridge University Press. - 0884-2914 .- 2044-5326. ; 22:6
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Tidskriftsartikel (refereegranskat)abstract
- We present a simple method for preparing nanometer-sized, Ti-based amorphous powders from the Y28Ti28Al24Co20and Y36Ti20Al24Co20two-phase amorphous alloys. The initial microstructure of these rapidly quenched alloys is composed of Ti-based, amorphous, spherical, nanometer-sized particles embedded in a Y-based amorphous matrix, with particle size dependent on the alloy composition. The Ti-based powders were extracted from the two-phase amorphous alloys through selective dissolution of the Y-rich matrix in a 0.1 M HNO3solution. The powders of size ranging between 20 and 200 nm have smooth and spherical morphology, and exhibit different magnetic behavior than the bulk alloy of identical composition.
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| 10. |
- Lassen, B, et al.
(författare)
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Electronic structure of free-standing InP and InAs nanowires
- 2006
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Ingår i: Journal of Materials Research. - 0884-2914. ; 21:11, s. 2927-2935
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Tidskriftsartikel (refereegranskat)abstract
- An eight-band k.p theory that does not suffer from the spurious solution problem is demonstrated. It is applied to studying the electronic properties of InP and InAs free-standing nanowires. Band gaps and effective masses are reported as a function of size, shape, and orientation of the nanowires. We compare our results with experimental work and with other calculations.
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| 11. |
- Mao, Huahai, et al.
(författare)
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Thermodynamic assessment of the MgO-AL(2)O(3)-SiO2 system
- 2005
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 20:4, s. 975-986
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Tidskriftsartikel (refereegranskat)abstract
- Thermodynamic properties of the phases in the MgO-Al2O3-SiO2 system were assessed, resulting in a set of self-consistent thermodynamic data. The two ternary Compounds, cordierite and sapphirine, were optimized from subsolidus reactions. The liquid phase was described by the ionic two-sublattice model with a new species AlO2-1 yielding the formula (Al+3,Mg+2)(p)(AlO2-1 O-2,SiO4-4,SiO2o)(Q). Projection of the liquidus surface was calculated. Various isothermal and isoplethal sections were compared with the experimental data.
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| 12. |
- Pohl, Annika, et al.
(författare)
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Sol-gel derived Nd1/3La1/3Ca1/3MnO3 : Phase evolution and preparation of films and nanopowders
- 2007
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 22:6, s. 1737-1743
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Tidskriftsartikel (refereegranskat)abstract
- An all-alkoxide sol-gel route to the formation of Nd1/3La1/3Ca1/3MnO3 thin films and powders has been developed. The microstructural evolution on heat treatment of the gel to yield the perovskite oxide was monitored by means of thermogravimetric analysis-differential scanning calorimetry, powder x-ray diffraction (XRD), Fourier transform infrared spectroscopy, and transmission electron microscopy (TEM)-energy dispersive spectroscopy (EDS). It was found that the amorphous gel consists of hydrated oxo-carbonate without organic residues, and on heating it decomposes in several steps, finally forming single-phase perovskite at 680 degrees C. Further heating results in only slight changes in the cell parameters and crystal growth. Films were prepared by spin coating, followed by heat treatment in air to a temperature of 800 degrees C, and studied by scanning electron microscopy, TEM-EDS, and XRD. Films on Al2O3 were more porous, while films on Pt-TiO2-SiO2-Si were rather dense and consisted of areas with different crystal orientations.
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| 13. |
- Rubino, Stefano, 1978-, et al.
(författare)
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Energy-loss magnetic chiral dichroism (EMCD) : Magnetic chiral dichroism in the electron microscope
- 2008
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 23:10, s. 2582-2590
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Forskningsöversikt (refereegranskat)abstract
- A new technique called energy-loss magnetic chiral dichroism (EMCD) has recently been developed [P. Schattschneider, et al. Nature 441, 486 (2006)] to measure magnetic circular dichroism in the transmission electron microscope (TEM) with a spatial resolution of 10 nm. This novel technique is the TEM counterpart of x-ray magnetic circular dichroism, which is widely used for the characterization of magnetic materials with synchrotron radiation. In this paper we describe several experimental methods that can be used to measure the EMCD signal [P. Schattschneider, et al. Nature 441, 486 (2006); C. Hébert, et al. Ultramicroscopy 108(3), 277 (2008); B. Warot-Fonrose, et al. Ultramicroscopy 108(5), 393 (2008); L. Calmels, et al. Phys. Rev. B 76, 060409 (2007); P. van Aken, et al. Microsc. Microanal. 13(3), 426 (2007)] and give a review of the recent improvements of this new investigation tool. The dependence of the EMCD on several experimental conditions (such as thickness, relative orientation of beam and sample, collection and convergence angle) is investigated in the transition metals iron, cobalt, and nickel. Different scattering geometries are illustrated; their advantages and disadvantages are detailed, together with current limitations. The next realistic perspectives of this technique consist of measuring atomic specific magnetic moments, using suitable spin and orbital sum rules, [L. Calmels, et al. Phys. Rev. B 76, 060409 (2007); J. Rusz, et al. Phys. Rev. B 76, 060408 (2007)] with a resolution down to 2 to 3 nm.
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| 14. |
- Scudino, Sergio, et al.
(författare)
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High-strength Al87Ni8La5 bulk alloy produced by spark plasma sintering of gas atomized powders
- 2009
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Ingår i: Journal of Materials Research. - : Cambridge University Press. - 0884-2914 .- 2044-5326. ; 24:9, s. 2909-2916
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Tidskriftsartikel (refereegranskat)abstract
- In situ devitrification and consolidation of gas atomized Al87Ni8La5 glassy powders into highly dense bulk specimens was carried out by spark plasma sintering. Room temperature compression tests of the consolidated bulk material reveal remarkable mechanical properties, namely, high compression strength of 930 MPa combined with plastic strain exceeding 25%. These findings demonstrate that the combined devitrification and consolidation of glassy precursors by spark plasma sintering is a suitable method for the production of Al-based materials characterized by high strength and considerable plastic deformation.
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| 15. |
- Seipel, B., et al.
(författare)
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Structural and ferromagnetic properties of Cu-doped GaN
- 2007
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 22:5, s. 1396-1405
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Tidskriftsartikel (refereegranskat)abstract
- The wurtzite polymorph of GaN was calcined with CuO in flowing nitrogen. As a result of this processing, both superconducting quantum interference device magnetometry and ferromagnetic resonance studies showed ferromagnetism in these samples at room temperature. These magnetic results are qualitatively consistent with very recent first-principle calculations [Wu et al., Appl. Phys. Lett. 89, 062505 (2006)] that predict ferromagnetism in Cu-doped GaN. We focus in this paper on analyzing changes in the GaN atomic and electronic structure due to calcination with CuO using multiple analytical methods. Quantitative powder x-ray diffraction (XRD) showed changes in the lattice constants of the GaN due to the incorporation of copper (and possibly oxygen). Energy-dispersive x-ray spectroscopy proved the incorporation of copper into the GaN crystal structure. Electron-gun monochromated electron energy loss spectroscopy showed CuO calcinations-induced GaN band gap changes and indicated changes in the atomic arrangements due to the calcination process. The fine structure of the N K-edge showed differences in the peak ratios with respect to higher nominal CuO contents, corresponding to an increase in the c-lattice constant as confirmed by XRD.
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| 16. |
- Söderberg, Hans, et al.
(författare)
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Growth and characterization of TiN/SiN(001)superlattice films
- 2007
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 22:11, s. 3255-3264
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Tidskriftsartikel (refereegranskat)abstract
- We report the layer structure and composition in recently discovered TiN/SiN(001) superlattices deposited by dual-reactive magnetron sputtering on MgO(001) substrates. High-resolution transmission electron microscopy combined with Z-contrast scanning transmission electron microscopy, x-ray reflection, diffraction, and reciprocal-space mapping shows the formation of high-quality superlattices with coherently strained cubic TiN and SiN layers for SiN thickness below 7-10 Å. For increasing SiN layer thicknesses, a transformation from epitaxial to amorphous SiNx (x 1) occurs during growth. Elastic recoil detection analysis revealed an increase in nitrogen and argon content in SiNx layers during the phase transformation. The oxygen, carbon, and hydrogen contents in the multilayers were around the detection limit (∼0.1 at.%) with no indication of segregation to the layer interfaces. Nanoindentation experiments confirmed superlattice hardening in the films. The highest hardness of 40.4 ± 0.8 GPa was obtained for 20-Å TiN with 5-Å-thick SiN(001) interlayers, compared to monolithic TiN at 20.2 ± 0.9 GPa.
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| 17. |
- Teleki, A, et al.
(författare)
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Flame-coating of titania particles with silica
- 2005
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Ingår i: Journal of Materials Research. - Swiss Fed Inst Technol, Particle Technol Lab, Inst Proc Engn, Dept Mech & Proc Engn, CH-8092 Zurich, Switzerland. Swiss Fed Inst Technol, Dept Chem & Appl Biosci, Inorgan Chem Lab, CH-8093 Zurich, Switzerland.. - 0884-2914 .- 2044-5326. ; 20:5, s. 1336-1347
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Tidskriftsartikel (refereegranskat)abstract
- Silica/titania composite particles were prepared by co-oxidation of titanium-tetra-isopropoxide and hexamethyldisiloxane in a co-flow diffusion flame reactor. The influence of precursor composition on product powder characteristics was studied by x-ray diffraction, nitrogen adsorption, electron microscopy, elemental mapping, and energy-dispersive x-ray analysis. The flame temperature was measured by Fourier transform infrared spectroscopy. The evolution of composite particle morphology from ramified agglomerates to spot- or fully coated particles was investigated by thermophoretic sampling and transmission/scanning electron microscopy. At 40-60 wt% TiO2, particles with segregated regions of silica and titania were formed, while at 80 wt% TiO2 rough silica coatings were obtained. Rapid flame-quenching with a critical flow nozzle at 5 cm above the burner nearly halved the product particle size, changed its crystallinity from pure anatase to mostly rutile and resulted in smooth silica coatings on particles containing 80 wt% TiO2.
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| 18. |
- Tilliander, Ulrika, et al.
(författare)
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Morphology studies of a W/Cu alloy synthesized by hydrogen reduction
- 2006
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 21:6, s. 1467-1475
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Tidskriftsartikel (refereegranskat)abstract
- Because of the applications for W/Cu composite materials in high technology, the advantages of synthesizing this alloy by the hydrogen reduction route were investigated, with special attention to the properties of the product that was formed. Kinetic studies of reduction indicated that the mechanism changes significantly at 923 K, and the product had unusual properties. In the present work, morphological studies of the W/Cu alloy with 20 wt% Cu, produced at 923 K, were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. The structural studies performed by XRD indicated that, at 923 K, Cu dissolved in W, forming a metastable solid solution in the nanocrystalline state. The samples produced at higher as well as lower temperatures, on the other hand, showed the presence of two phases, pure W and pure Cu. The SEM results were in agreement with the XRD analysis and confirmed the formation of W/Cu alloy. TEM analysis results confirmed the above observations and showed that the particle sizes were about 20 nm. The structure of the W/Cu alloy produced in the present work was compared with those for pure Cu, produced from Cu2O produced by hydrogen reduction under similar conditions. This indicated that the presence of W hinders the coalescence of Cu particles, and the alloy retains its nano-grain structure. The present results open up an interesting process route toward the production of intermetallic phases and composite materials under optimized conditions.
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| 19. |
- Wang, Lianjun, et al.
(författare)
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Formation of a unique glass by spark plasma sintering of a zeolite
- 2009
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 24:10, s. 3241-3245
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Tidskriftsartikel (refereegranskat)abstract
- A simple approach, order–disorder transition (ODT), has been developed to synthesize a novel glass using ZSM-5 as starting materials. In this process, the ZSM-5 powders were pressed uniaxially in a graphite die and rapidly sintered using spark plasma sintering (SPS). High-resolution transmission electron microscopic images revealed that a few crystalline zeolite fragments were still preserved locally inside the SPS consolidated sample. Vickers microhardness and fracture toughness of this as-prepared transparent glass sample at room temperature reaches 7.3 ± 0.2 GPa and 2.0 ± 0.3MPa·m1/2, respectively. It is very interesting that these novel bulk transparent glasses exhibit ultraviolet photoluminescence (PL) properties at about ∼360 nm.
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| 20. |
- Wang, Y.D., et al.
(författare)
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Textures and compressive properties of ferromagnetic shape-memory alloy Ni48Mn25Ga22Co5 prepared by isothermal forging process
- 2006
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 21:3, s. 691-697
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Tidskriftsartikel (refereegranskat)abstract
- A ferromagnetic shape-memory alloy Ni48Mn25 Ga22CO5 was prepared by the induction melting and isothermal forging process. Dynamic recrystallization occurs during the isothermal forging. The deformation texture was studied by the neutron diffraction technique. The main texture components consist of (110) [11¯2] and (001) [100], which suggested that in-plane plastic flow anisotropy should be expected in the as-forged condition. The uniaxial compression fracture strain in the forged alloy reaches over 9.5%. The final room-temperature fracture of the polycrystalline Ni48Mn25Ga22CO5 is controlled mainly by intergranular mode.
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| 21. |
- Willmann, Herbert, et al.
(författare)
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Hardness evolution of Al-Cr-N coatings under thermal load
- 2008
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 23:11, s. 2880-2885
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure and hardness evolution of arc-evaporated single-phase Cubic Al0.56Cr0.44N and Al0.68Cr0.32N coatings have been investigated after thermal treatment in Ar atmosphere. Based on a combination of differential scanning calorimetry and x-ray diffraction studies, We Can Conclude that Al0.56Cr0.44N undergoes only small structural changes without any decomposition for annealing temperatures T-a <= 900 degrees C. Consequently, the hardness decreases only marginally from the as-deposited value of 30.0 +/- 1.1 GPa to 29.4 +/- 0.9 GPa with T-a increasing to 900 degrees C, respectively. The film with higher Al content (Al0.68Cr0.32N) exhibits formation of hexagonal (h) AlN at T-a >= 700 degrees C, which occurs preferably at grain boundaries as identified by analytical transmission electron microscopy. Hence, the hardness increases from the as-deposited value of 30.1 +/- 1.3 GPa to 31.6 +/- 1.4 GPa with T-a = 725 degrees C. At higher temperatures, where the size and volume fraction of the h-AlN phase increases, the hardness decreases to 27.5 +/- 1.0 GPa with T-a = 900 degrees C.
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