Band 112, Heft 2

Negative creep using precision dilatation experiments is investigated on a broad variety of single, dual and multiphase nickel-based superalloys. Pure nickel and dilute binary nickel-based alloys show no signs of negative creep. However, with higher contents of Cr and Al and in highly alloyed ternary and multicomponent nickel-based alloys negative creep is observed. Short range ordering of Cr and/ or Al are identified to cause negative creep at 550 °C. Carbon additions leading to retarded carbide precipitation or transformation can enhance negative creep.

The present study elucidates the influence of Mo content on the microstructure – toughness relationship in the coarsegrained heat-affected zone of high-strength low-alloy steels. The low-Mo and high-Mo steels were subjected to 100 kJ cm –1 heat input welding thermal cycling. The results indicated that (Ti,Mo)-carbonitrides were formed in high-Mo steel, whereas (Ti,Nb)-carbonitrides were formed in low-Mo steel. The finer and dispersed precipitates in high-Mo steel refined the prior austenite grain in the coarse-grained heat-affected zone based on the grain boundary pinning effect. However, the smaller prior austenite grain and excessive Mo content induced the formation of an entirely bainitic microstructure in high-Mo steel. Furthermore, a higher fraction of martensite –austenite constituents was observed in high-Mo steel. These results could be responsible for the deterioration of the toughness in the coarse-grained heat-affected zone of high-Mo steel.

The relationship between microstructure and mechanical properties is studied for eutectoid Zn-22Al (wt.%) alloys modified with Cu and Ag. Three alloys with a Cu content of 2 wt.% and varying amounts of Ag were cast and hot-extruded. Different microstructural characteristics were induced by heat treatments: natural aging, artificial aging and furnace cooling. Structural and microstructural characterizations were carried out with X-ray diffraction and scanning electron microscopy. Mechanical properties were determined by tensile testing. Dilatometry was used for determining the effects of composition on the transformation points. The addition of Ag increased the ε phase fraction and provided solid solution strengthening, improving the mechanical strength and reducing ductility. Ag additions also displaced the eutectoid reaction to higher temperatures. The microstructure of the matrix has proven to have a strong impact on mechanical properties. The naturally aged specimens presented the highest ductility and tensile strength; however, these properties are severely affected by aging. Lamellar microstructures present the lowest ductility and values of tensile strength between those of the natural and artificially-aged specimens.

In this investigation, copper–TiB 2 metal matrix composites were fabricated by spark plasma sintering. The effect of TiB 2 (2.5, 5, 7.5, and 10 wt.%) additions on the microstructural, electrical, and mechanical properties of the composites was investigated. There was a remarkable reduction in processing time and temperature by this process as compared to conventional sintering. Scanning electron microscopy with energy dispersive X-ray spectroscopy elemental maps revealed a homogeneous distribution of TiB 2 in the copper matrix. The hardness of the composites exhibited no consistent trend with the addition of TiB 2 . An improvement in tensile strength was observed at the expense of ductility. Electrical conductivity showed a decreasing trend. Morphology of the fracture surfaces was analyzed to predict the nature of failure under tensile load.

The Cu-12.5Ni-5Sn- x Fe alloys were prepared using powder metallurgy. The effect of the amount of Fe addition on the microstructure and mechanical characteristics of Cu-12.5Ni-5Sn- x Fe alloys was investigated. The microstructure and morphology of alloys were examined by means of X-ray diffraction, scanning electron microscopy and cold field emission scanning electron microscope. Results indicate that the hardness and yield strength of the Cu-12.5Ni-5Sn alloy are improved by addition of trace amounts of Fe. The lamellar precipitates of Cu-12.5Ni-5Sn- x Fe alloys are more and finer compared to those of Cu-12.5Ni-5Sn alloy. Fe can facilitate the aging process and strengthen the effect of aging-hardening.

The effects of additions of Co and Ni to the FeNbBCu alloys on the glass forming ability (GFA), soft magnetic properties and electrical resistivity of Fe-based amorphous alloys were studied by means of X-ray diffraction, differential scanning calorimetry, vibrating sample magnetometry and four-probe testing. The Fe 80– x – y Nb 5 B 14 Cu 1 Co x Ni y alloys exhibit high thermal stability and excellent GFA with T x1 ≥ 735 K and T x1 / T m ≥ 0.539. They also show excellent soft magnetic properties with high saturation magnetization of 93– 101 emu g –1 and low coercivity of 0.04 –2.37 Oe. The electrical resistivity of these alloys ranges from 121 μΩ cm to 163 μΩ cm. The newly developed FeNbBCu-CoNi glassy alloys not only possess good GFA and high thermal stability, but also have excellent magnetic properties, high electrical resistivity and low cost. With such promising properties, these alloys have potential for industrial applications.

The electrochemical behavior of nickel at different pH values in industrial electrolyte was investigated by means of cyclic voltammetry, chronoamperometry and scanning electron microscopy. The results show that the cathodic reaction of nickel ions on glassy carbon electrode surface in industrial electrolyte is a quasi-reversible nucleation and growth process controlled by diffusion. The process is carried out in a three-dimensional instantaneous nucleation and growth mode, and pH values only influence the growth process. The grain size decreased, the deposition rate increased and the density of deposition layer on electrode surface increased with the increase in pH . When the electrolyte pH is 4.8, the grains are uniformly distributed on the electrode surface in a spherical shape with the size of 80 nm, which is the optimum pH value for preparing fine-grained nano-nickel.

In this work, optical properties of undoped zinc oxide (ZnO) and chromium (Cr) doped ZnO prepared at different concentrations of Cr (2, 3, and 5 wt.%) on glass substrates by a spray pyrolysis method are reported. The structural properties investigated by X-ray diffraction revealed the hexagonal wurtzite structure, noting that the crystallite size of the films decreases with increasing Cr content. The optical characterization of the samples was carried out using spectral transmittance. The refractive index, energy gap, and extinction coefficient of pure and Cr-doped ZnO thin films have been calculated. The single oscillator model of Wemple–DiDomenico was used to study the dispersion of the refractive index. The oscillator parameters, the single oscillator energy, the dispersion energy, and the static refractive index were determined. The linear optical susceptibility and non-linear optical susceptibility were also studied and discussed. These promising results achieved by Cr-doping of ZnO exhibited an important behavior for technological applications in electronic, optoelectronic devices and non-linear optical applications.

The nanotribological properties of Zn 0.75 Mg 0.25 O grown on R-plane sapphire using metal-organic vapor-phase epitaxy at different substrate temperatures (RT, 600, 700 and 800 °C) were investigated. A slight sliding track was observed at ramped loads of 250 μN, and an obvious bulge edge surrounding the groove was observed at ramped loads of 1 000 μN. Because of the annealing treatment, all the Zn 0.75 Mg 0.25 O coatings showed a reconstruction phenomenon of crystallites. The volumes of the bulge edges were as high as 30% in the annealed specimens and were larger than the volumes of the RT-treated specimens when ramped loads of 1 000 μN were applied. Under frictional loading, atomic force microscopy examination of scratch-tested films indicated lower bonding forces on R-plane sapphire than M-plane sapphire.

Aerogels are ultra-light solids with extremely low thermal conductivity (even lower than air), thanks to which they have a huge potential in a wide range of applications. The purpose of this publication is to present the state-of-the art knowledge of the possibility of using aerogels to increase the thermal insulation properties of clothing materials intended for use in both cold and hot environments. Various methods of aerogels application to textile materials (non-woven, woven and knitted fabrics) are discussed, indicating their advantages and limitations. Numerous research studies confirm that aerogels significantly improve the thermal insulation properties of materials, but due to their delicate and brittle structure and their tendency to dusting, their application still poses considerable problems.