Volume 108, Issue 10

The study of diffusion of hydrogen atoms in the crystal lattice of fcc metals Pd, Ni, Al, Ag was performed by the method of molecular dynamics. The diffusion characteristics of hydrogen impurity (activation energy of hydrogen atom migration and pre-exponential factor in the Arrhenius equation) in the considered metals were calculated. It is shown that the prevailing mechanism of the over-barrier hydrogen diffusion in fcc metals consists of successive migration through octahedral and tetrahedral pores. During migration, as a rule, the hydrogen atom is not delayed in tetrahedral pores.

The diffusion coefficient of nickel in cold-worked Type 316 austenitic steel was determined by the diffusion couple method in the temperature range between 360 and 500 °C. A diffusion couple was prepared by electroless nickel plating on the surface of a 20 % cold-worked Type 316 austenitic steel specimen. The growth in width of the interdiffusion zone was proportional to the square root of diffusion time until 14 055 h. The diffusion coefficient of nickel ( D Ni ) in cold-worked Type 316 austenitic steel was determined by extrapolating the concentration-dependent interdiffusion coefficient to 11 at.% of nickel. The value of D Ni at 360 °C was about 5 000 times higher than the lattice diffusion coefficient of nickel in Type 316 austenitic steel. The determined activation energy 117 kJ mol −1 was 46.6 % of the activation energy 251 kJ mol −1 for the lattice diffusion of nickel in Type 316 austenitic steel.

The surface structuring process micro-milling introduces small grooves, which act as geometrical notches and influence the mechanical properties of the component, into the surface. The mechanical behaviour depends on the relation of the notch size to the grain size. Micro-milling processes were applied to improve the functional properties of component surfaces. They are used in mechanically loaded environments as well as in biotechnological applications. Therefore, commercially-pure-titanium is a favoured material of investigation. To determine the effect of the notches, a detailed analysis of the deformation behaviour of the structured material is indispensable. In the present work, structured specimens were tested under quasi-static loading. The testing was interrupted at different strain values. The micro-sections of the specimens were characterized by means of electron backscatter diffraction analysis to obtain information about the first indication of plastic deformation and the development of the deformation features. The results show inhomogeneous deformation behaviour of the material. The deformation mechanisms, the development of small angle and high angle grain boundaries as well as twinning are shown.

The isothermal section of the Zr–Si–B ternary system (Zr–Si–ZrB 2 region) at 1 173 K has been experimentally determined. All equilibrated alloys were characterized via X-ray powder diffraction and scanning electron microscopy equipped with energy-dispersive X-ray analysis. A ternary phase Zr 5 (Si 0.86 B 0.14 ) 3 was found at 1 173 K. The experimental results show that the isothermal section consists of 11 single-phase regions, 26 two-phase regions and 13 three-phase regions. The existence of eight compounds, i. e. ZrSi 2 , ZrSi, Zr 5 Si 4 , Zr 3 Si 2 , Zr 2 Si, ZrB, ZrB 2 and Zr 5 (Si 0.86 B 0.14 ) 3 in this system has been confirmed in the Zr–Si–ZrB 2 region at 1 173 K.

The relationship between the density and temperature in hypereutectic Al–Si alloys was measured in the temperature range from 800 K to ( T l + 30) K using the indirect Archimedean method. This method eliminates the effects of surface tension on the densities of salts and alloys and reduces the error in estimating the density and solidification shrinkage of Al–Si alloys. Eutectic LiCl–KCl salt was used as a reference liquid. The results indicate that the density vs. temperature curve has three transformation points: the liquidus temperature, eutectic transformation temperature and completely finished eutectic transformation temperature. The obtained densities of solid and liquid hypereutectic Al–Si alloys are in agreement with those reported in earlier investigations. The solidification shrinkage decreases from 2.5 % for the Al–Si alloy containing 15 % Si to −0.4 % for the alloy with 25 % Si.

A modified phase-field model was proposed for the incorporation of magnetic energy contributions in the ferromagnetic alloys including Zeeman energy, magnetocrystalline anisotropy energy and demagnetizing field energy. To verify the accuracy of this model, the Mn–Bi system was taken as an example, and the effects of different magnetic energy contributions on the microstructural evolution during the non-equilibrium peritectic reaction (Liquid + Mn 1.08 Bi → MnBi) were investigated. The simulation results demonstrated that the formation of ferromagnetic MnBi was promoted by the introduction of the Zeeman energy, and the magnetic moments of the MnBi phase tended to align along the orientation of the easy axis due to the effect of magnetocrystalline anisotropy energy. It was also indicated that the MnBi grain would be elongated along the direction of the external magnetic field when the demagnetizing field is considered.

We investigate the influence of the quality of precursor amorphous silicon (a-Si) films on the quality of flash-lamp-crystallized (FLC) polycrystalline Si (poly-Si) films by tuning the conditions of a-Si deposition by catalytic chemical vapor deposition. Electron spin resonance measurement reveals that the defect density of FLC poly-Si films is affected by the defect density of a-Si films, and FLC poly-Si films with lower defect density can be formed by using precursor a-Si films with lower defect density. The same tendency is also confirmed through μ-PCD measurement. Improvement in the characteristics of thin-film crystalline Si (c-Si) solar cells can be expected by using high-quality FLC poly-Si films formed from a-Si films with low defect density.

Thermite welding of Cu–Nb microcomposite wires was investigated. Suitable compositions of thermite material and slag were determined from the equation of the exothermic combustion synthesis reaction. The phase compositions of the thermite mixture and slag determined by X-ray diffraction analysis correspond to those assessed from the equation. According to non-destructive radiographic testing, the joint structure does not have welding defects. Microstructural examination of the joint cross-section with scanning electron microscopy showed that the Cu–Nb wire retained its shape and microstructure and only a thin surface layer of wire was melted during welding. The difference in electrical resistances of the conductor and welded joint was below 20 %. The thermite joint can withstand a maximum load equal to 62.5 % of the load-bearing capacity of microcomposite conductor.

The microstructure and mechanical properties of Al–Zn–Mg/3 wt.% Al 2 O 3 composite were modified through a thermomechanical processing technique. The powders were cold pressed and solid state sintered for 90 min under argon atmosphere. Thermomechanical processing was then applied to the solid state sintered samples, which consisted of cold pressing followed by partial remelting for 30 min under argon atmosphere. Four different loads in the thermomechanical processing were used to investigate the effects of compressive loads on the microstructures and the mechanical properties. The results revealed modifications in the microstructure of the thermomechanically processed samples with the optimum combination of properties in the sample modified by applying the load of 250 MPa. Increasing the thermomechanical processing load decreased the amounts of porosity by about 7 %, decreased the average grain size to about 4 μm, enhanced the compressive yield strength to about 295 MPa, and increased the microhardness values from 250 HV to 600 HV. In addition, the energy absorption capacity increased by about three times.

The microstructure and indentation behavior of magnesium nanocomposites containing a high volume fraction (up to 15 vol.%) of nanometer-sized SiC was studied using X-ray diffraction, electron microscopy, and microindentation techniques. The indentation hardness and contact stiffness were found to increase with increasing volume fraction of the nanometer-sized SiC particles up to 10 vol.%. The magnesium nanocomposites with 15 vol.% SiC had a lower indentation hardness than that of 10 vol.% SiC. The strain rate sensitivity exponent of the Mg–SiC nanocomposites increased with increasing volume fraction of SiC. The decrease of the indentation hardness suggested that the deformation mechanism of the magnesium nanocomposites was likely altered when the critical volume percent of SiC nanoparticles was achieved, estimated at 10 vol.%.

In this study, NiO–yttria stabilized zirconia (YSZ) composite anodes were prepared by using ball-milling followed by a sintering process. For this purpose, two different weight percent ratios of NiO and YSZ powders (50 : 50 and 60 : 40) were mixed by the cost-effective ball-milling method. The morphology and particle size distribution of the mixed powders were investigated using scanning electron microscopy and dynamic light scattering methods, respectively. The powders were then uniaxially pressed to form pellets with a thickness and diameter of around 1 and 22 mm, respectively. Sintering of the pellets was conducted at 1 100 °C and the microstructure and porosity, as well as phase analysis of bulk composites, were then investigated using scanning electron microscopy and X-ray diffraction, respectively. More importantly, the microhardnesses of the prepared pellets were obtained and compared with literature values to evaluate the accuracy of the sintering process. The results showed that the open porosity of the samples varied between 30 to 40 percent, which makes them suitable for anode application in solid oxide fuel cells. The prepared NiO–YSZ composites with a uniform distribution of Ni particles showed a value of microhardness above 0.5 GPa, and these results were discussed in detail.