Volume 104, Issue 1

An AA 7075 aluminium alloy with an ultra-fine grained structure was prepared through equal channel angular pressing (ECAP) at pressing temperatures T ECAP of 120, 170, and 220 °C. A decrease in T ECAP from 220 to 120 °C was found to lead to a more pronounced refinement of the microstructure and to worse stability of the microstructure – the onset of grain coarsening was displaced to lower temperatures. The material pressed with the highest T ECAP exhibited superplastic behaviour at temperatures close to 400 °C and grain boundary sliding was identified as the dominant operating deformation mechanism. The materials prepared with both of the lower T ECAP exhibited only enhanced ductility of about 200 %, however this behaviour was observed at temperatures as low as 200 °C. It was found that this “low temperature superplasticity” resulted from a combined operation of grain boundary sliding at selected grain boundaries and glide of lattice dislocations.

Variations in strain and work output in two Ti-47 at.%Ni-3 at.%Cu and Ti-51.5 at.%Ni alloys during thermal cycling in the mode of fixed stress acting on cooling and heating were studied. It was found that in the Ti 50 Ni 47 Cu 3 alloy with a low level of yield stress, the values of transformation plasti city and shape memory effect and work output were changing during thermal cycling. It was observed that the mechanical behavior and work performance of Ti-51.5 at.%Ni alloy with a high level of yield stress was stable on thermal cycling irrespective the value of stress acting on cooling and heating. It was found that under the same stress conditions the value of work output in Ti-51.5 at.% Ni alloy was four times lower than in the Ti-47 at.%Ni-3 at.%Cu alloy. Moreover, the accumulated residual strain was approximately 40 times lower than in Ti 50 Ni 47 Cu 3 alloy with a low level of yield stress.

In this paper, the AlMg4.5Mn alloy has been welded using tungsten inert gas (TIG) and metal inert gas (MIG) processes with different gas shielding atmospheres. Tensile strength, hardness, impact and fracture toughness, fatigue crack growth parameters (Δ K th , d a /d N ), as well as microstructure were determined. By comparing results for different gas mixtures, the main conclusion for TIG welding was that increased helium content has an important effect on toughness and fatigue crack growth parameters, whereas its effect on other mechanical properties is not significant. On the other hand, in the case of MIG welding, adding helium does not affect mechanical properties, except the fatigue crack growth rate. It was also established that adding nitrogen (TIG welding) and oxygen (MIG welding) reduces toughness and increases crack growth rate, so their use in shielding mixtures is not recommended.

The results of comparative thermodynamic analysis and phase diagram prediction of the Ga – Sn – Zn system are presented in this work. The thermodynamic study was done experimentally – using Oelsen calorimetry, for the section Ga – SnZn eut , and analytically – according to the general solution model, for the whole system. Main thermodynamic quantities – integral and partial molar Gibbs excess energies, activities and activity coefficients were calculated over a wide temperature range. Additionally, the phase diagram of the section Ga – SnZn eut was investigated using differential thermal analysis and predicted using the CALPHAD method. Comparison with available literature data showed reasonable agreement. The liquidus projection of the ternary Ga – Sn – Zn was also calculated.

The Zn-rich corner of the 450°C isothermal section of the Zn-Fe-Co-Si quaternary system with the Zn content being fixed at 93 at.% was determined experimentally using the equilibrated alloy approach. The specimens were investigated by means of scanning electronic microscopy coupled with wave dispersive X-ray spectroscopy, and X-ray powder diffraction. It was found that 2 four-phase regions, i. e. L+(Fe,Co)Si+FeSi2+Si and L+(Fe,Co)Si+CoSi2+Si, exist in the section. The Si solubility in ζ-FeZn13 phase is rather limited, with Co dissolving in this compound, the solubility of Si is up to 0.82 at.%. The Fe solubility in CoSi2 is no more than 1.21 at.%, whereas the Co solubility in FeSi2 is high up to 7.81 at.%. The maximum solubility of Zn in (Fe,Co)Si, FeSi2, and CoSi2 is 1.92, 1.49, 2.93 at.%, respectively. No true quaternary compound was found in the present study.

The enthalpies of mixing in liquid alloys in the binary Ce-Sb and ternary Ce-Co-Sb systems were determined over a wide range of composition by means of isoperibolic calorimetry in the temperature range 1 600-1 723 K. The minimum value of the integral enthalpy of mixing (Δ H min ) in the Ce-Sb system was evaluated to be −123 kJ mol -1 at x Ce = 0.55. The enthalpies of mixing in liquid ternary alloys were found to increase smoothly from the binary boundary systems Co-Ce and Co-Sb towards the Ce-Sb system reaching the value of approximately −123 kJ mol -1 in the vicinity of the phase CeSb.

The Ni – Sn system was critically re-assessed by means of the CALPHAD technique. The excess Gibbs energies of the solution phases (liquid, fcc (Ni) and bct (Sn)) were modeled with the Redlich–Kister equation. Five intermetallic compounds, Ni 3 Sn_HT (which is stable at high temperature), Ni 3 Sn_LT (which is stable at low temperature), Ni 3 Sn 2 _HT, Ni 3 Sn 2 _LT and Ni 3 Sn 4 in the Ni – Sn system were treated as the formula (Ni,Sn) 1/4 (Ni,Sn) 1/4 (Ni) 1/2 , (Ni,Sn) 3/4 (Ni,Sn) 1/4 , (Ni) 1/3 (Ni,Sn) 1/3 (Sn) 1/3 , (Sn) 1/5 (Ni,Sn) 2/5  · (Ni) 2/5 , and (Ni) 1/4 (Ni,Sn) 1/4 (Ni) 1/2 , respectively. A set of self-consistent thermodynamic parameters of the Ni – Sn system was obtained.

The aim of the work was to study the creation of micro- and macro-segregation of iridium in low-alloyed molybdenum single crystals after electron beam zone melting (floating zone technique) depending on various conditions of crystallization. In order to evaluate relations between the chemical inhomogeneity and structural defects and their influence on properties of single crystals, the dependence of concentration and character of distribution of admixtures under various crystallization conditions on the origin of concentration undercooling and dislocation substructure of molybdenum single crystals prepared by electron beam floating zone melting was experimentally investigated.

(Y 2 O 3  + TiC)/Ti-4.5Si composites have been in-situ synthesized using arc-melting technology. Y 2 O 3 and TiC particles grow in near-equiaxed and dendritic shapes, which are distributed uniformly in Ti-4.5Si matrix including the network Ti + Ti 5 Si 3 eutectic cells. From hardness and compressive tests at room temperature, (Y 2 O 3  + TiC)/Ti-4.5Si composites show the higher hardness and compressive strength compared with the unreinforced and single TiC reinforced Ti-4.5Si matrix. The introduction of in-situ Y 2 O 3 and TiC particles influenced the oxidation behavior of the matrix. The excellent oxidation resistance of Y 2 O 3 and TiC particle reinforced composites is attributed to lower growth rate, dense oxide scale and stronger adherence of oxide scale.

In this paper we report the synthesis of molybdenum trioxide (MoO 3 ) microstructures via acidification of sodium molybdate (Na 2 MoO 4 ). The structure and morphology of the products were characterized by means of X-ray powder diffraction, Raman spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. It is found that as-synthesized micro-belts were pure orthorhombic structured MoO 3 grown along [010], with length up to more than 10 μm and width ranging from 200 to 500 nm. On the basis of the experimental facts, a mechanism for the growth of the MoO 3 belts is proposed.

We report a simple low cost method at room temperature and normal pressure for the synthesis of mono-dispersed spherical rutile titania nanoparticles using the water in oil microemulsion process. The as-synthesized and calcined TiO 2 nanoparticles were characterized by means of X-ray diffractometry, Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analysis, Brunauer–Emmett–Teller surface area analysis, scanning electron microscopy and transmission electron microscopy. The effect of calcination temperature on the crystalline phase, particle size, specific surface area and surfactant concentration was studied in detail. As-synthesized rutile TiO 2 nanoparticles showed remarkable photocatalytic activity for the degradation of methyl orange dye as a model pollutant. The reaction was found to follow first order kinetics. Chemical oxygen demand results show substantial degradation and mineralization of targeted dye.

Polymer nanocomposites were prepared by mixing Epoxy resin with 2, 5 and 7 wt.% of organically modified montmorillonite clay using a high shear mixer. Microstructural analysis of the nanocomposites was performed with transmission electron microscopy and X-ray diffraction. The effects of voltage, frequency, temperature and seawater ageing on electrical conductivity and impedance of the nanocomposites were evaluated. The transmission electron microscopy and X-ray diffraction results indicate that montmorillonite clay nanoparticles were uniformly dispersed in the Epoxy matrix. Experimental results show higher conductivity and lower impedance with the addition of 2 wt.% montmorillonite clay in the Epoxy matrix with respect to frequency, temperature and seawater ageing. On the other hand, with further increase in filler loading (5 and 7 wt.%) a reverse trend was observed with respect to conductivity and impedance. The obtained values of capacitance and resistance were found to be well correlated.

Porous quartz ceramics were produced using river sand from the Yangtze River in China as the raw material by the use of sponge absorption methods. We found that sintering conditions clearly affected the porous structure and other properties. With increasing sintering temperature, the microstructure of the samples changed accordingly and the density increased while the porosity decreased, the micropore edges gradually became smooth. The density of the porous quartz ceramics increased at a holding time of up to 60 min but the porosity decreased. Optimum sintering of the porous quartz ceramics was obtained at 1 100 °C over 60 min as determined by an analysis of the performance–price ratio of the porous quartz ceramics, the density is 1.25 g cm –3 , the porosity is 49.5 %, the outside shape is regular, the micropore structure is smooth.

First principles calculations for rare earth compounds PrSb and PrBi in NaCl(B1), CsCl(B2), ZB(B3), WC(Bh) and CuAu(L1 o ) structures have been performed using density functional theory within the generalized gradient approximation. For the total-energy calculation, the projected augmented plane-wave implementation of the Vienna ab-initio simulation package has been used. Our structural results are consistent with the available experimental and other theoretical data. The phonon dispersion curves and corresponding one-phonon density of states (DOS) for both compounds are also computed in NaCl(B1) structure which is energetically more stable than the other structures. In addition to these properties, the temperature/pressure variation of the volume, thermal expansion coefficient, heat capacity are calculated in over wide pressure and temperature ranges.

Quantum mechanics calculations were performed on fluorinated oligoacenes, with and without 2-thienyl attached. Reorganization energies between the switch of neutral molecules and anion radicals, and the electron-transfer coupling matrix were obtained. By using the Marcus theory and the Einstein relation, the electron hopping rates and mobilities were predicted for the title compounds. The mobility of 3b2 was predicted to be 3.03 cm 2 V – 1 s – 1 , which is the largest value among the title compounds. This indicates that the 2-thienyl considerably facilitates electronic mobility for n - type organic semiconductors when attached to oligoacenes at an appropriate position.