Band 106, Heft 2

Freestanding films of highly pure iron and gold multilayers were fabricated and characterized for their intended use as biodegradable implant materials. These samples were deposited using magnetron sputtering on unheated substrates. This technology allows the combination of various non-compounding materials. After annealing for 2 h at 685 °C and 850 °C, respectively to homogenize the multilayer, the microstructures were investigated using X-ray diffraction, energy dispersive X-ray spectroscopy and scanning transmission electron microscopy. Due to the annealing, the multilayered microstructure converts into a new multiphase system consisting of an iron matrix and two different kinds of gold morphologies: segregations along grain boundaries and nanosized core–shell like precipitates.

Morphology evolution and coarsening kinetics of γ ’ (Ni 3 Al) precipitates in Ni–Al alloy were investigated quantitatively using the interface diffusion-controlled, the bulk diffusion-controlled, and the interface diffusion-controlled elastic strain models. By calculating the γ ’ phase number density, volume fraction, and particle radius, the effects of diffusion and elastic strain on the γ ’ phase growth and coarsening were clarified. The coarsening rate constants are smaller in the bulk diffusion-controlled and the interface diffusion-controlled elastic strain models than those of the interface diffusion-controlled model, which is due to the long-range diffusion of Al atoms and the retardant effect of coherent strain between the γ ’ and γ phases, respectively. The linear fitting on the cubic exponent shows the comparable associate coefficient that gives no superiority to the different models in Ni–Al alloy.

Investigations regarding structural, morphological, and magnetic changes induced by ball milling of Fe-50 at.% Al alloy have been carried out. The mechanical alloying process induces a progressive dissolution of Al into Fe, resulting in the nucleation and establishment of an elongated nanostructured Fe(Al) solid solution with the bcc structure only after 5 hr of milling. The average crystallite size of components decreased to ~5 nm and the components diffused to the nanograin boundaries during transition to nanostructured composite. Scanning electron microscopy and transmission electron microscopy confirmed the crystallite size determination and Fe(Al) solid solution formation obtained from X-ray diffraction analysis. The corresponding magnetic (Mössbauer and vibration sample magnetometer) studies confirm that there is magnetic behaviour retained in the FeAl alloys samples even after 5 hr of milling but magnetization decreases as the milling time increases. The ball milling process involves the loss of long range order and reduced grain size, which induces a transition from a paramagnetic to ferromagnetic state. The continuous refinement of grains and the antiphase interface grain bounderies play a major part in the observed variation in the magnetic properties.

Spinel type pure and Sr 2+ doped zinc ferrite nanoparticles were prepared by glycine assisted combustion. The resultant nanoparticles were found to be highly crystalline with cubic crystal structure. The structure and the corresponding changes in the tetrahedral and octahedral bond stretching were investigated. The chemical elements and oxidation states of these nanoparticles were determined and the elemental compositions of synthesized nanoparticles established. It was observed that the optical band gap values increased from 2.43 eV to 2.49 eV as Sr 2+ concentration increased. The morphology, chemical elements and composition of the prepared ferrites were examined. The magnetic behavior of these nanoferrites was studied and corresponding changes in the saturation magnetization, coercivity and remanent magnetization were analyzed.

This paper presents experimental results on intermittent electromagnetic radiation during plastic deformation of Cu – Ni alloys under tension and compression modes of deformation. On the basis of the nature of electromagnetic radiation signals, oscillatory or exponential, results show that the compression increases the viscous coefficient of Cu – Ni alloys during plastic deformation. Increasing the percentage of solute atoms in Cu – Ni alloys makes electromagnetic radiation strength higher under tension. The electromagnetic radiation emission occurs at smaller strains under compression showing early onset of plastic deformation. This is attributed to the role of high core region tensile residual stresses in the rolled Cu – Ni alloy specimens in accordance with the Bauschinger effect. The distance between the apexes of the dead metal cones during compression plays a significant role in electromagnetic radiation parameters. The dissociation of edge dislocations into partials and increase in internal stresses with increase in solute percentage in Cu – Ni alloys under compression considerably influences the electromagnetic radiation frequency.

Isothermal quenching methods were applied to high boron steel for improving the impact toughness and wear resistance. The effect of different heat treatment processes on the microstructure and mechanical properties was studied. Each of the specimens was characterized using metallographic techniques, scanning electronic microscope, energy dispersive spectroscopy, X-ray diffraction, toughness and hardness testing. The results indicate that the as-cast high boron steel consists of pearlite matrix and eutectic boride M 2 B and Fe 3 (C, B) type distributing along grain boundaries. After isothermal quenching, the matrix of high boron steel is changed from pearlite to martensite and lower bainite. The impact toughness and wear resistance of high boron steel after isothermal quenching are better than that of high boron steel after water quenching.

The dry sliding wear behaviour of Al/(Al 2 O 3 + ZrB 2 + TiB 2 ) hybrid composite was tested by using a pin-on-disc testing machine at room temperature and 300 °C. Hybrid reinforcement was fabricated by mechanically activated combustion synthesis, and the composites were prepared by hot pressing of aluminium powder and hybrid reinforcement. The effect of sliding distance, hybrid reinforcement content and temperature on the wear properties of the composites has been investigated. For comparison, the same tests were conducted on Al/Al 2 O 3 composite and pure aluminium. Hybrid composites have higher wear resistance than pure aluminium and Al/Al 2 O 3 composites at room temperature and 300 °C. A study of wear surfaces showed that plastic deformation induced wear and adhesive wear are the dominant mechanisms at room and high temperature, respectively.

The aim of this paper was to obtain the regression equation of the bonding strength of sprayed coatings vs. acoustic emission (AE) signal. FeCrBSi coating, Al 2 O 3 -40 wt.% TiO 2 (AT40) coating and Al 2 O 3 coating were prepared using an atmospheric plasma spraying system. The microstructures and properties of the coatings were characterized. The coatings exhibited typical laminate structure with low porosity and good bonding interface. The AE signals during indentation testing were abstracted and investigated. AE energy was more sensitive to the coating cracking failure than AE amplitude. Moreover, the energy of AE burst signal had a close positive relationship with coating bonding strength. The distribution characteristic of AE peak energy was discussed based on the Weibull distribution. The best regression equations for the three coatings were obtained to predict the bonding strengths of sprayed coatings based on AE burst signal energy for similar coating/substrate systems.

Graphene has gained much significance for its potential applications in optics and electronics owing to its unique physical and chemical properties. Nevertheless, its gapless band structure greatly limits its wider application in optoelectronic devices. The present study seeks to explore chemical functionalization as an effective method to tune the properties of graphene. Covalent modification of graphene by aryl diazonium salt of a photosensitive functional group (azobenzene) has been used to achieve this goal. This is based on the fact that graphene is a two-dimensional, atomically thin lattice of sp 2 -bonded carbon atoms, therefore, its properties can be modulated by modifying the underlying dielectric surface with a self-assembled monolayer resulting in doping control. In the study, a clear difference in the rate of electron-transfer reactions with the photosensitive functional group is shown for monolayer graphene supported on SiO 2 /Si substrates and organic molecule functionalized SiO 2 /Si substrates. Graphene supported on SiO 2 / Si is more reactive towards functionalization than graphene on organic molecule functionalized surfaces, as shown by Raman spectroscopy. The transport characteristics of functionalized graphene on conventional SiO 2 /Si substrates as well as substrates modified with organic molecule octadecyltrichlorosilane self-assembled monolayers are also explored and compared.

In this survey, cordierite glass-ceramic was prepared by melting in a platinum crucible at 1 580 ° C. The effects of temperature and heating rate were studied on the nucleation and crystallization. Nucleation and crystallization temperatures were obtained by differential thermal analysis, scanning electron microscopy and X-ray diffraction. The results showed that the optimum nucleation and crystallization occurred at 810 and 1 150 ° C, respectively. According to the X-ray diffraction patterns, cordierite, rutile, quartz and MgTi 2 O 5 phases were obtained in the crystallized glassceramics. The maximum bending strength of 178 MPa was obtained after the chemical strengthening of the crystallized glass ceramic.

The use of self-lubricating materials not only reduces friction coefficients and alleviates effects of wear and tear, but also helps to maintain the mechanical properties of materials. By using coating technology in the application of self-lubricating materials, it is possible to effectively improve the bonding strength between a solid lubricant and substrate material and additionally to protect the solid lubricant against oxidation and decomposition during the sintering process. This study uses the heterogeneous nucleation method, where aluminum hydroxide (Al(OH) 3 ) is coated on the surface of calcium fluoride (CaF 2 ) to prepare a CaF 2 @Al(OH) 3 composite powder. It was observed, through analysis of the preparation process parameters, that the Al 3+ concentration, pH value, and reaction temperature were the factors which most influence coating quality. Optimum process parameters were found to be an Al 3+ concentration of 0.15 mol · L –1 , pH value of 7.5, and reaction temperature of 75 ° C. Comparing and analyzing the micro-morphology of sample composite powders proved the effectiveness and favorable performance of the CaF 2 @Al(OH) 3 composite we produced under optimized process parameters.

The microstructure and properties of cast chromium bronzes with varying Zr contents obtained by different treatment methods were characterized by using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, and X-ray diffraction. In the specimens with the same composition, the precipitated chromium phase particles in specimens treated by quenching and aging were more granular than those in specimens treated by aging. The precipitated Cr phase was clearly refined and segregated when zirconium was added to the melt. With the addition of zirconium, the tensile strength of the alloy increased by about 3 %, but its electrical conductivity decreased by about 9 %.

ZnO nanorods of 25 – 100 nm in diameter and 0.2 – 1 lm in length were fabricated through a citric acid assisted annealing process. The nanorods were characterized by means of X-ray diffraction, field-emission scanning electron microscopy, fourier transform infrared spectroscopy spectrophotometry, ultraviolet visible spectroscopy and photoluminescence spectroscopy. The obtained ZnO nanorods have good crystal quality and excellent optical properties. The effects of addition of citric acid with Chirality Multi-acid Chemistry function on the optical properties of ZnO nanorods have been investigated.