Papers by Keyword: Nickel Ni

Abstract: Ni/Si multilayer contact structures to 4H-SiC after subsequent annealing steps are investigated with electron microscopy methods. After high temperature annealing step, specific defects in the contact structures are observed. The influence of phase transformations during annealings on the morphology on the contacts is discussed and the explanation of formation mechanism of voids within contact layer is proposed.

Abstract: Micro-porous nickel foams with an open cell structure were fabricated by the space-holding sintering. The average pore size of the micro-porous nickel specimens ranged from 30 μm to 150 μm, and the porosity ranged from 60 % to 80 %. The porous characteristics of the nickel specimens were observed using scanning electron microscopy (SEM). The mechanical properties were studied using compressive tests. For comparison, macro-porous nickel foams prepared by the chemical vapour deposition method with pore sizes of 800 μm and 1300 μm and porosity of 95 % were also presented. Results indicated that the ratio value of 6 and higher for the specimen length to cell size (L/d) is satisfying for obtaining stable compressive properties. The micro-porous nickel specimens exhibited different deformation behaviour and dramatically increased mechanical properties, compared to those of the macro-porous nickel specimens.

Abstract: Cemented tungsten carbides are industrially one of the most used composite materials as cutting tools, wear parts and replacements of standard materials for tools, dies and machine components. This work focuses on various aspects of diffusion bonding of tungsten carbide to AISI 304 stainless steel using a Ni-foil interlayer. WC/Ni/AISI 304 combinations were diffusion bonded at 1000°C using different holding times under argon atmosphere. The microstructure characterization of the resulting interfaces was carried out by SEM and EPMA. The results show that successful joining between WC and AISI 304 steel is achieved by the formation of a diffusion zone at both ends of the Ni foil. All WC/Ni/AISI 304 samples have been joined with no severe interfacial cracking or porosity at the interface. The joint strength is determined by four-point bending testing, a maximum of 210 MPa for samples joined at 1000 °C for 60 minutes has been achieved. These results indicate that there is a strong relationship between the thickness of the diffusion interface and the mechanical strength of the joints.

Abstract: The effectiveness of phosphorus diffusion gettering (PDG) and related segregation coefficients for different metal impurities were measured applying thermal treatments in the temperature range 800-950 °C for different times. We used multi-crystalline and mono-crystalline CZ p-type wafers with different boron concentrations and different levels of dislocations and bulk micro-defects (BMD). In all sample types, for Cu and Ni we found complete gettering in the temperature range investigated. In the case of Fe, the segregation coefficient increases with both increase in temperature and extension of time. The increase is qualitatively changing when going above 900 °C. At 950 °C the segregation coefficient increases faster at shorter diffusion time but at extended diffusion time it increases slower as compared to diffusion at 900 °C. At the same temperature and time of phosphorus diffusion the segregation coefficient is found to be independent of the metal impurity concentration in the range of 1012-1015 cm-3 investigated. We have shown that the presence of BMD and dislocations in bulk silicon does not impede the ability of PDG to completely remove Fe, Ni and Cu metal impurities from the bulk. Further analysis suggests that the PDG has the same gettering efficiency for mono-crystalline silicon and multi-crystalline silicon. We conclude that if any bulk precipitation of Fe, Ni and Cu impurities is present in multi-crystalline silicon it cannot seriously compete with PDG. However we found that increasing the boron concentration in the samples reduces the segregation coefficient of Fe, and this reduction is more severe at lower temperatures. Finally, by applying a post anneal ramp down from 900 °C to 700 °C after phosphorus diffusion, we found that the Fe segregation coefficient increases by a factor of 36 for lightly B doped samples, from 53 to 1919, leading to a significant reduction of Fe in the bulk after 2 hours ramp down anneal.

Abstract: The impact of nickel on minority carrier recombination lifetime has been studied in ptype CZ silicon using SPV and μ-PCD techniques. The results show that small oxide precipitates can be used to improve drastically the detection limit of nickel. This is explained by the decoration of oxide precipitates by nickel, which results in the enhanced recombination activity. In the absence of oxide precipitates or other related bulk microdefects nickel precipitates preferably to wafer surfaces, which does not have such a high impact on the measured recombination lifetime, at least on a low concentration level. Low temperature anneal at 180°C or light illumination of the wafers after nickel in-diffusion did not reveal any further change in lifetime in any of the wafers, which may indicate that nickel precipitates efficiently during air-cooling from high temperature.

Abstract: In the present study, the BaTiO3/Ni composites were prepared by using the pressureless sintering technique. The ferroelectric and ferromagnetic properties of the composites are measured. The composites exhibit ferroelectric properties only when the Ni content is as low as 1 vol.%. Nevertheless, the saturated magnetization of the BaTiO3/Ni composites increases with the increase of Ni content. The BaTiO3/Ni composites exhibit multiferroic characteristics.

Abstract: Barium orthotitanate ceramics (Ba2TiO4) with ≧0.4wt% Nickel shows highly reproducible CO2 absorption - desorption when they are annealed under cyclic temperature conditions. Addition of Ni powder prohibited the grain growth of the Ba2TiO4 ceramic.

Abstract: 3N nickel has been deformed by equal channel angular pressing (ECAP) at 400°C up to 3 passes using route A. The texture with respect to position in the deformed billet, i.e. from top to bottom, has been measured with high-energy synchrotron radiation. It is characterized by texture components typical for simple shear in the intersection plane of the square-shaped 90° bent channel. Besides, an oblique cube component is observed. Orientation imaging microscopy clearly shows that this component is due to partial recrystallization. Intensities of the texture components as well as deviations from their ideal shear positions vary from the top to the bottom of the billet and with the number of passes. The change of the intensity of texture components and the texture gradient investigated is discussed. Special emphasis is put on the influence of dynamic recrystallization on texture and microstructure formation during ECAP of fcc metals.

Abstract: The effect of crystal orientation on the recovery and recrystallization of cold-rolled Ni (99.96% purity) has been investigated. Particular attention was paid to the annealing response of regions with either the Copper (C), Brass (B) or S rolling texture orientations. Samples with an initial average grain size of approx. 500μm were deformed to strains of up to εvM = 4.5. As a result of the large initial grain size, even after high rolling reductions it is possible to find sufficiently large regions of material with similar crystal orientation to analyze the recovery and recrystallization behaviour as a function of crystal orientation. Microstructural investigations were carried out in the scanning electron microscope using both electron channeling contrast and electron backscatter diffraction orientation mapping. Both the S and C orientation regions exhibit a heterogeneous microstructure containing bands of localized deformation. The presence of volumes surrounded by high angle boundaries in these regions strongly influences both the recovery and recrystallization behaviour of the material. Twinning was observed also to play an important role in the generation of recrystallized grains, with twin chains of up to 3 generations being observed.

Abstract: The anodic aluminum oxide (AAO) templates were prepared by a two step anodization process in a mixture phosphoric acid, sulfuric acid and chromic acid and oxalic acid. The pore of anodic aluminum oxide templates were hexagonal arranged pore domains. Oredred Nickel nanowires were prepared in this porous anodic aluminum oxide templates from Watt solution and additives by an electrodeposition. The diameter of Nickel nanowires in the array were about 80 nm and the length is about 800 nm with the aspect ratio of about 10. The ordered Nickel nanowires were characterized by X-ray diffractometer, scanning electron microscopy and magnetometer.