Narrow Results

The present study was focussed on investigating the corrosion properties of plasma-oxidized and -nitrided CoCrMo alloys under different conditions. The structural properties of untreated and treated samples were examined by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Corrosion behavior of samples was mainly investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid solution. The results showed that corrosion resistance of the oxidized layers was better than that of the nitrided ones. The corrosion resistance of the alloys increased as the plasma oxidation process temperature and time increased. However, the corrosion resistance of the alloys reduced with increase in the process temperature and time after plasma nitriding process.

Particle coalescence has wide applications in nature and industry. In this study, molecular dynamics (MDs) simulations were employed to examine the sintering of Cu and Au nanoparticles, as well as two other systems, namely, Cu nanoparticles and Au nanoparticles. The results suggested that, the Au atoms diffused through the outer area of the sintering neck before the nanoparticles were fused into one sphere. The possible reason was that the Au atoms resembled fluid, which could be ascribed to the local thermal energy at the contact area. Typically, the change in energy per atom from 300 K to the contact temperature denoted that less energy was required for the atoms in the pure Cu system to contact with each other than those in the other two systems.

Using a density functional approach calculation, the structural and electronic properties of Mg₈Ni₅, Mg₈Ni₄Al, Mg₈Ni₄Ca and Mg₈Ni₄Mn clusters are investigated. The Al-, Ca-, Mn-doping in MgNi clusters lengthen $d_{\mathrm{\text{(Mg–Ni)}}}$, also increase the Mulliken charge, and improve magnetic moment on most shell atoms, so that the doping is helpful for hydrogen storage. The reaction heats of hydrogenation, the enthalpies of formation, the desorption energies show that the Mg₈Ni₄Mn, Mg₈Ni₅, Mg₈Ni₄Al clusters have a good property of hydrogen storage materials with relatively higher reaction heat of hydrogenation, and that their hydrides have a smaller desorption energy. So the Mg₈Ni₄M (M = Ni, Al, Ca, Mn) clusters are some preferred candidates of H storage. These results indicate the advantage of small size and suitable metal-doped MgNi clusters on hydrogenation and dehydrogenation.

The MCrAlY bonding layer alloy was prepared by vacuum melting, and the alloy composition was NiCoCrAlY and NiCoCrAlYHfTa. The high-temperature cyclic oxidation experiment was carried out in air at 1050^∘C until it failed. The results show that Hf and Ta have a significant influence on the oxidation resistance of the alloy. The doped specimens have longer oxidation lifetimes compared to the undoped samples. The study also found that the Hf would diffuse out and combine with O to form HfO₂ in the thermally grown oxide (TGO) layer, which would improve the adhesion and reduce the wrinkles of the oxide layer. Ta in the doped specimens hinders the diffusion of Al and reduces the oxidation rate, while improving the thermal mismatch. Therefore, the specimens doped with both Hf and Ta have the highest oxidation lifetimes, though the oxidation lifetime was 10 times longer than that of the undoped specimens. It is indicated that the doping of Hf and Ta is an important method to improve the oxidation lifetime of thermal barrier coatings (TBCs).

The electronic packaging and systems are very important topics as the limitation of miniaturization approaches in semiconductor industry. Regarding the optimal materials microstructure for these applications, we studied different alloys such as Sn-3.0Ag-0.5Cu (wt.%)/organic solderability preservative (SAC305/OSP) Cu and SAC305–0.05Ni/OSP Cu solder joints. We implemented the fractal dimension characterization and microstructure morphology reconstruction. This is the first time that we applied fractals on such alloys. The morphology reconstruction is important for predicting and designing the optimal microstructure for the advanced desirable properties these alloys. These analyzed parameters are important for the hand-held devices and systems especially for the exploitation. The fractal reconstruction was applied on the prepared microstructures with five different magnifications. The results confirmed successful application of fractals in this area of materials science considering the grains and shapes reconstructions.

The oxidation of the single crystal stepped Pt₃Ti(510) surface at oxygen pressures below 10^-5 mbar and at a temperature of 770 K was studied by means of X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS) and low energy electron diffraction (LEED). Scanning tunneling microscopy (STM) was used to follow the evolution of the surface morphology on the atomic scale. The clean surface studied in ultrahigh vacuum conditions was found by LEIS to be composed of platinum only in the outermost surface plane. LEED and STM indicate that the clean Pt₃Ti(510) surface consists of (100) terraces separated by double atomic steps. The exposure of the clean surface to oxygen at pressures in the range of 10^-7–10^-5 mbar leads to the growth of a titanium oxide layer (with a composition close to TiO) which covers completely the substrate surface. The TiO film has long range order and exhibits complex LEED patterns. The STM measurements indicate that the ordered array of steps is kept in the early stages of the oxide film growth, whereas a change of the step morphology and step orientation is observed during the oxidation process.

Unlike synthesis of nanowires (1D nano-objects) the synthesis of nanoplatelets (2D nano-objects) has not been performed frequently. Herein, we report on the synthesis of Cu–Ge based on nanoplatelets with a high surface-to-volume ratio prepared by low pressure chemical vapor deposition (LPCVD) of Ge₂Me₆ and a mixture of Ge₂Me₆/PbEt₄. Nanostructured deposits are composed of Cu_1-xGe_x nanoplatelets, Ge nanowires and Ge nanoparticles. The nanoplatelets, which have the lateral size up to several tens of micrometers and thickness of 100–400 nm, belong to the cubic α phase of Cu₉₁Ge₉ alloy (Ge admixture in cubic Cu) and hexagonal ζ phase of Cu₈₅Ge₁₅ alloy. Nanowires composed of cubic Ge have a diameter of about 30 nm and length of several tens of micrometers. Lead does not enter any of these phases due to Pb–Cu and Pb–Ge immiscibility; therefore, it was observed as separate nanoparticles.