National Institute Of Materials Physics - Romania

Mixtures of B4C, alpha-AlB12 and B powders were reactively spark plasma sintered at 1800 degrees C. Crystalline and amorphous boron powders were used. Samples were tested for their impact behavior by the Split Hopkinson Pressure Bar method. When the ratio R = B4C/alpha-AlB12 >= 1.3 for a constant B-amount, the major phase in the samples was the orthorhombic AlB24C4, and when R < 1 the amount of AlB24C4 significantly decreased. Predictions that AlB24C4 has the best mechanical impact properties since it is the most compact and close to the ideal cubic packing among the Al-B-C phases containing B-12-type icosahedra were partially confirmed. Namely, the highest values of the Vickers hardness (32.4 GPa), dynamic strength (1323 MPa), strain and toughness were determined for the samples with R = 1.3, i.e., for the samples with a high amount of AlB24C4. However, the existence of a maximum, detectable especially in the dynamic strength vs. R, indicated the additional influence of the phases and the composite's microstructure in the samples. The type of boron does not influence the dependencies of the indicated mechanical parameters with R, but the curves are shifted to slightly higher values for the samples in which amorphous boron was used.

Indium-doped zinc oxide (IZO) and aluminium-doped zinc oxide (AZO) thin films were grown by radio-frequency (RF) magnetron sputtering onto optical glass substrates and their structural, morphological, and optical properties were discussed in terms of varying the sputtering power as 40 W, 60 W, 80 W, and 100 W. No heating substrate or any post-thermal treatment was performed. The structural features were analyzed by grazing incidence X-ray diffraction and revealed the amorphous phase for IZO samples, while the AZO thin films inherited the Wurtzite structure of zinc oxide. The morphological properties were investigated by atomic force microscopy (AFM), in tapping mode and scanning electronmicroscopy (SEM). The AFM images showed relatively uniform and smooth surfaces for all prepared structures. The optical transmission spectra proved the excellent theoretical values of transparency for metallic oxides in the visible region of the electromagnetic spectrum, i.e. similar to 60% for IZO and similar to 70% for AZO. The obtained results showed that even without any thermal treatment the structural, morphological, and optical properties of IZO and AZO thin films prepared by RF magnetron sputtering are similar with those for samples subjected to medium or high temperatures.

MgB2 green bodies were prepared by magnetic field slip casting in ethyl alcohol with added polyethyleneimine dispersing agent under a high magnetic field, mu H-0(0) = 12 T. Samples were further processed by spark plasma sintering (SPS) and characterized for superconducting properties. Slip casting provides texturing of MgB2 (the degree of c-axis orientation is approximately 3.5%), which is further increased significantly (to about 21%) in the SPSed sample. The critical current density (J(c)) displays anisotropy relative to the orientation of the measuring magnetic field. Specific features of J(c)(H, T) and of the pinning force extracted from magnetic measurements with the field parallel and perpendicular to H-0 are discussed.

The work is dedicated to the investigation of optical, structural, magnetic and magneto-optical properties of an aluminophosphate glass doped with Dy3+ ions, for specific applications as Faraday rotators in the visible spectral domain. The vitreous material belongs to the 16Li(2)O-8Al(2)O(3)-6BaO center dot 60P(2)O(5)-10Dy(2)O(3) system. Optical homogeneity measured by a polariscopic method, as well as by polarimetry and interferometry revealed an optical quality glass. Time dependent electrical conductance measurements have shown a high chemical strength of the glass. Optical absorption of the doped glass in the visible domain evidenced the specific absorption lines of dysprosium ions, whereas structural investigations made by FTIR and Raman spectroscopy put in evidence the vitreous network forming role of phosphorous pentoxide. Magnetic and magneto-optical measurements demonstrated paramagnetic features of the doped glass, as well as a Verdet constant of about -0.05 min/Oe/cm at 600 nm wavelength.

Copper (Cu) and dysprosium (Dy) co-doped zinc oxide (ZnO) thin films were fabricated by radio frequency magnetron sputtering (RF-magnetron sputtering) using a homemade target having the atomic percentage of Cu and Dy of 1%, onto optical glass substrates and quartz substrates. The structural, morphological, optical, and electrical properties of fabricated ZnO:(Cu, Dy) structures were analyzed and discussed. It was found that all samples have hexagonal Wurtzite structure. Optical transmission measurements indicate values larger than 75% in the 400-2500 nm ranges. The current-voltage characteristics of hybrid heterojunctions based on ZnO:(Cu, Dy) and poly(3-hexylthiophene-2.5-diyl) (P3HT) or copper (II) phthalocyanine (CuPc) thin films were acquired in the dark, in ambient atmosphere, and they exhibit the typical diode behavior, almost free of electrical hysteresis.

In the case of DEMO fusion reactor, the divertor should be able to extract a steady heat flux of about 10 MW/m(2). A promising concept is the W-monoblock which should be connected to a CuCrZr or an advanced Cu ODS alloy pipe passing through the W component. Taking into account the optimum operating temperature windows for W and existing Cu-based alloys and the thermal expansion coefficients mismatch of these two materials, a "thermal barrier" interface material is inserted in between in order to mitigate the thermal stresses and to optimize the heat flow through divertor components. In this work we investigate the feasibility to realize such divertor components using materials produced by FAST (field assisted sintering technology). This powder metallurgy technique was used firstly to produce W or W-based composites and the thermal barriers in an almost final shape and then to join the materials in realistic divertor mock-ups. The thermal barrier materials are various Cu-based composites which are included both as single material or as functionally graded components. The interface quality between different materials is investigated by scanning electron microscopy and the heat flow through components is evaluated using simulations.

In this study, CuxCrFeTiV (x = 0.21, 0.44, 1 and 1.7 M ratio) high entropy alloys have been devised for thermal barriers between the plasma facing tungsten tiles and the copper-based heat sink in the first wall of nuclear fusion reactors. The high entropy alloys were produced by ball milling the elemental powders, followed by consolidation with spark plasma sintering. Irradiation of the equiatomic CuCrFeTiV sample was carried out at room temperature with Ai(+) (300 keV) beams with a fluence of 3 x 10(20) at/m(2). Structural changes prior and after irradiation were investigated by scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy, X-ray diffraction and thermal diffusivity. Preliminary results showed the presence of heterogenous and multiphasic microstructures in all samples. Moreover, with the increase of the Cu content it is possible to observe the formation of Cu-rich structures. The diffractogram of the CuCrFeTiV sample revealed major peaks of a BCC crystal structure and minor peaks of a FCC crystal structure. In addition, after irradiation no modifications in the CuCrFeTiV microstructure or in the diffractogram were observed.

We reported on three-dimensional (3D) superparamagnetic scaffolds that enhanced the mineralization of magnetic nanoparticle-free osteoblast cells. The scaffolds were fabricated with submicronic resolution by laser direct writing via two photons polymerization of Ormocore/magnetic nanoparticles (MNPs) composites and possessed complex and reproducible architectures. MNPs with a diameter of 4.9 +/- 1.5 nm and saturation magnetization of 30 emu/g were added to Ormocore, in concentrations of 0, 2 and 4 mg/mL. The homogenous distribution and the concentration of the MNPs from the unpolymerized Ormocore/MNPs composite were preserved after the photopolymerization process. The MNPs in the scaffolds retained their superparamagnetic behavior. The specific magnetizations of the scaffolds with 2 and 4 mg/mL MNPs concentrations were of 14 emu/g and 17 emu/g, respectively. The MNPs reduced the shrinkage of the structures from 80.2 +/- 5.3% for scaffolds without MNPs to 20.7 +/- 4.7% for scaffolds with 4 mg/mL MNPs. Osteoblast cells seeded on scaffolds exposed to static magnetic field of 1.3 T deformed the regular architecture of the scaffolds and evoked faster mineralization in comparison to unstimulated samples. Scaffolds deformation and extracellular matrix mineralization under static magnetic field (SMF) exposure increased with increasing MNPs concentration. The results are discussed in the frame of gradient magnetic fields of similar to 3 x 10(-4) T/m generated by MNPs over the cells bodies.

W-laminates are multi layered composites realized from alternately stacked W and a second metal foils. Such materials are promising candidates for W-based structural materials for fusion reactors like DEMO or beyond concepts, due to the fact that cold-rolled ultrafine-grained thin W foils show exceptional properties in terms of ductility, toughness and ductile to brittle transition (DBT), in contrast to classic bulk W materials. Therefore, different routes to transfer the W foils properties to bulk materials have been investigated. In this work we present the results obtained for W-Cu laminates produced via a FAST (Field Assisted Sintering Technique) joining route. The main advantages of FAST resides in the short processing time, with subsequent lower recrystallization detrimental effects. Structural and thermophysical properties show that the best materials are obtained for about 100 mu m thick W foils and 50-100 mu m thick Cu foils, while tensile and Charpy impact tests results show that the FAST processed W-Cu laminates are similar to the W-Cu laminates obtained by diffusion bonding.

Oxide dispersion-strengthened ferritic steels (ODSFSs) are promising structural materials for applications in fusion and fission power reactors, but further improvement in their (high-temperature) mechanical properties and ferrite phase stability is required. This work demonstrates that an approach to produce Fe14Cr ODSFSs with a stable ferrite phase and improved strength could involve grain size strengthening by long-term milling with a tiny amount of nitrogen. Fe-14Cr-3W-0.4Ti-0.25Y(2)O(3) powders were ball-milled up to 170 hours under an argon atmosphere. In addition to X-ray diffraction, the change in product quality during milling and upon heating was thoroughly investigated by more sensitive magnetic and thermal analysis by measuring the saturation magnetization sigma(s), coercivity H-c, Curie temperature T-c, and temperature of ferrite-austenite (alpha ->gamma) transition T-alpha ->gamma. A pronounced modification of magnetic and microstructure parameters was observed when milling over 70 hours and upon heating above 800 degrees C and was found to be generated by long-term milling with a tiny amount of nitrogen. Upon heating, the nitrogen, incorporated during milling, developed a transition region, with the decomposition of nitrides precipitated at the earlier stage of heating followed by austenite decomposition, nitrogen degassing, and microstructure refinement to a grain size of a few tenths of a nm (e.g., 28 nm by heating at 910 degrees C of 100-hour milled powder). The resulting ferrite phase with refined grains is highly stable to (further) heating. The powders milled for 70 and 100 hours containing 0.175 and 0.500 wt pct nitrogen, respectively, were consolidated at 1100 degrees C with subsequent annealing at 1050 degrees C and subjected to Vickers hardness and 3-point bending tests. The steel produced from the powder milled for 70 hours shows lower hardness, higher density (close to the theoretical value of 7.8 g/cm(3)), and fracture strain. The ductility of this ODS alloy (0.075 fracture strain) is comparable with Eurofer97 (0.075 fracture strain), whereas its strength (2070 MPa ultimate stress) is significantly higher than that of Eurofer97 (1222 MPa ultimate stress). This improvement was attributed to grain size strengthening-the refined grains (promoted by milling with nitrogen) could be effectively pinned by Y-Ti-O dispersoids.