Volume 106, Issue 5

Phase diagram and thermodynamic data of the complete binary Ti–O system are assessed using the Calphad method. The main focus is on the proper description of high temperature titanium monoxide TiO x phase using the common compound energy formalism. The structural data of this complex solid solution phase could be successfully modeled together with the phase equilibrium and thermodynamic data, embedded in the comprehensive Ti–O assessment. The presentation of all original phase equilibrium data in the entire system indicates the well or less well established regions in comparison with the calculated phase diagram.

Phase equilibria in the ‘Cu 2 O’–‘Fe 2 O 3 ’–MgO–SiO 2 system in equilibrium with copper alloy have been investigated at temperatures between 1 100 and 1 250 °C. A high-temperature equilibration/quenching/electron probe micro-analysis technique has been used to accurately determine the liquid and solid compositions. The standard methodology has been modified to accurately determine the phase equilibria and liquidus in this particular chemical system. Results on phase equilibria in the tridymite primary phase field, including the tridymite–pyroxene, tridymite–spinel and tridymite–pyroxene–spinel phase boundaries, are reported. The study demonstrates the validity of the method and provides new data on the effect of MgO on the tridymite liquidus temperatures. Increasing MgO concentration was found to decrease the tridymite liquidus.

The phase equilibria of the V–Si–Ho ternary system at 973 K were experimentally investigated by using X-ray powder diffraction and backscattered electron imaging with energy dispersive X-ray analysis. The existence of nine binary compounds, namely, V 5 Si 3 , V 6 Si 5 , VSi 2 , V 3 Si, HoSi 2− b , HoSi 2− a , HoSi, Ho 5 Si 3 and Ho 5 Si 4 was confirmed. The phases of HoSi (FeB) and Ho 4 Si 5 were not found at 973 K. No binary compound was found in the V–Ho binary system. No ternary compound was found at 973 K in this system. The homogeneity range of V 3 Si was determined to be from 22 at.% to 25 at.% Si. The maximum solid solubility of Si in V is about 4 at.%.

The phase equilibria of the 700 °C isothermal section of the Al–Si–Fe–Cr quaternary system with Al fixed at 90 at.%, and the related Al-rich ternary systems, have been determined experimentally with scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffractometry. Eight four-phase regions and a new quaternary compound named ζ are found in the 700 °C isothermal section of Al–Si–Fe–Cr quaternary system. The ζ phase is found to be in equilibrium with all phases in the section including the FeAl 3 , τ 5 , τ 6 , (Si), τ 1 , Al 4 Cr, Al 45 Cr 7 and H phases, as well as the liquid phase.

In order to determine the effect of quench–ageing treatment on the microstructure and properties of Zn-15Al-3Cu alloy, it was prepared by permanent mould casting and then solution treated at a temperature of 330 °C, quenched and aged at 180 °C. The changes in the microstructure, length, hardness, strength and ductility of the quenched alloy were monitored during ageing. The microstructure of the alloy in the as-cast condition consisted of β dendrites and α, η and ∊ phases. However, solution treatment followed by quenching removed the lamellar microstructure of the alloy and produced a supersaturated β solid solution. Subsequent ageing resulted in transformation of β solid solution to α and η phases and conversion of metastable ∊ phase to stable T′ compound. Appropriate ageing times for T6 and T7 heat treatments of this alloy have been determined according to the experimental results.

Using the melt spinning technique, a nanocrystalline (NC) Fe–B single-phase solid solution was prepared at a disk speed of 7 000 rpm. After treatment by isothermal annealing at 700 °C for the NC solid solution, the grain growth behavior was investigated using the dimensionless parabolic growth model, the dimensionless purely kinetic model, and a recently proposed dimensionless thermo-kinetic model. Neither the parabolic growth model nor the purely kinetic growth model with solute drag was in agreement with the experimental results, although the grain growth rate was partially inhibited. However, the thermo-kinetic model was consistent with the experimental results, which confirmed that the main stabilizing mechanism is a reduction in the grain boundary energy and an increase in the interface activation energy.

The dependence of properties of sintered Fe–Mn steels, produced with commercial ferromanganese and ferrosilicon, on processing parameters are examined. By controlling the local “microclimate”, using a semiclosed container/getter/activator combination, Fe-3.2Mn-1.4Si-0.5C steel was successfully sintered in flowing technical nitrogen or 95 vol.% N 2 /5 vol.% H 2 furnace atmosphere. The getters were naphthalene and ferromanganese. The necessary reducing reactions involving manganese vapour and nascent carbon with water vapour and manganese and silicon oxides took place in the dry “microatmosphere” within and around the specimens. The resultant average values of ultimate tensile strength, 0.2% offset yield stress and elongation were 871 MPa, 561 MPa, and 2.21%, respectively, not significantly different from literature values for steels produced on the basis of Fe–Si–Mn ferroalloys sintered in dry hydrogen.

A nanostructured composite powder formed from 75 wt.% NiSb and 25 wt.% Sb was obtained by mechanical alloying binary mixtures of elemental Ni and Sb powders in the composition NiSb 2 for 39 hours. The structural evolution was followed by X-ray diffraction measurements and Rietveld structural refinement. At the end of milling, the crystallites of Sb and NiSb reached a mean size of 17 and 15 nm, respectively. Differential scanning calorimetry measurement showed two exothermic processes at 263 °C and 309 °C. Variable temperature powder X-ray diffraction measurements at 25, 100, 200 and 300 °C showed that the sample is structurally stable until 100 °C. The beginning of the transition NiSb + Sb → NiSb 2 was observed at 200 °C and the nucleation of Sb 2 O 3 was observed at 300 °C in accordance with differential scanning calorimetry measurement. Raman spectroscopy measurements showed neither NiSb nor NiSb 2 compounds produce significant Raman signals when compared with Sb and Sb 2 O 3 .

Using three elementary substances, Mo, Ni, and amorphous B as raw materials, four series of Mo 2 NiB 2 -based cermets with the Mo/B atomic ratio ranging from 0.9 to 1.2 were successfully prepared via reaction sintering. The effect of Mo/B atomic ratio on the microstructure and properties was studied for the cermets. The results indicate that there is a strong correlation between the Mo/B atomic ratio and properties. The transverse rupture strength of the cermets increases with an increase in Mo/B ratio and shows a maximum value of 1 872 MPa at an Mo/B atomic ratio of 1.1 and then decreases with increasing Mo/B atomic ratio. The hardness and the corrosion resistance of the cermets increase monotonically with an increase in Mo/B atomic ratio. In Mo-rich cermets with an atomic ratio of Mo/B above 1.1, a small amount Ni–Mo intermetallic compound is found precipitated at the interface of Mo 2 NiB 2 grains.

High quality alumina thin films were deposited on glass substrate by reactive radio-frequency sputtering. The deposition process and rate were controlled by radio-frequency power and reactive gas (oxygen) flow rate. The relationships between O/Al ratio contents and the structural, electrical resistivity and optical parameters of the films were investigated. The O/Al of the films varied with change in oxygen flow ratio, power density and post deposition annealing. The structure and phase of the films were unaltered as the deposition parameters and post deposition annealing up to 573 K were varied. O/Al of 1.5 was obtained at oxygen flow ratio of 11%, radio-frequency power of 250 W and post deposition annealing of 573 K. The sheet resistance of the films were all very high but the same within experimental uncertainties. The optical parameters (transmittance, refractive index and extinction coefficient) of the films varied considerably and depended on the films' stoichiometry.

The bio-mechanics of skin and bone play a crucial role in dexterous object manipulations and artificial robotic gripper design. Establishing a quantitative relationship between imposed loads and contact factors is necessary to understand the governing mechanics behind it. Towards this goal, experimental investigations on the contact parameters of a sandwich soft fingertip comprising a soft layer and solid core are presented. The influence of soft layer stratum and material grades on the power law equation is investigated by introducing a new dimensionless parameter – Power Factor. The results clearly indicate that the power index “ γ ” is dependent on the material as well as shell thickness and in addition the proportionality constant “ C ” is dependent on the geometry. Also, the magnitude of both the constants increases with power factor and saturates at a value of ≈1.25. Numerical simulation is performed to support the experimental results. Finally, an optimum ratio of power factor is determined and the number ≈1.25 is critical in designing the artificial robotic sandwich fingertip.

Of the five steps in powder injection molding, namely feedstock formulation, mixing, injection, debinding and sintering, the one which markedly demands more time is debinding. Studying the effect of specimen thickness on debinding time in the current study, 316L stainless steel feedstock was exploited as the material for fabrication cylindrical specimens with varying thicknesses ranging from 2 to 10 mm. The thicker the specimen, the more time-consuming the debinding is. In addition, a novel method has been presented to produce thick components with large sections by powder injection molding, using preformed inserts in the injection stage. By using a wrought insert on which the feedstock is injected, the thickness of the injected section in need of debinding decreased while the whole thickness of the component was still large. Finally, defect-free specimens with diameter of 20 mm have been fabricated using inserts with different sizes, which resulted in dramatic reduction of debinding time from several days to only some hours. Moreover, it revealed that the interface of the insert and injected section was bonded properly, reaching more than 400 MPa of shear strength, depending on insert/part diameter ratio.

Ag nanoparticles were synthesized using microwave irradiation. Oleylamine was used as a stabilizer and capping agent, dimethylformamide as a reducing agent, and deionized water as a solvent. The subsequent use of functionalized Ag nanoparticles for microwave irradiation obtained Ag@SiO 2 core–shell nanoparticles. UV–Vis spectroscopy shows a characteristic plasmon peak at 407 nm and 430 nm for Ag nanoparticles and Ag@SiO 2 core–shells. Transmission electron microscope images show that Ag nanoparticles have an average size of 15 nm. It is also shown that the core–shell structure was formed with an average size of 100 nm for Ag core and 25 nm SiO 2 shell thickness.

We report our investigations on structural, thermal and electrical behavior of 10 mol.% dysprosia stabilized zirconia (DySZr) and 2 mol.% Bi 2 O 3 -doped dysprosia stabilized zirconia (2BiDySZr) prepared via a solid state ceramic route. Addition of 2 mol.% of Bi 2 O 3 decreased the sintering temperature of DySZr, promoted the growth of zirconia grains and also improved the density. This also supports stabilizing the cubic phase at room temperature. The electrical conductivity was found to increase on account of bismuth doping in DySZr. The activation energies for conduction in DySZr and 2BiDySZr systems were found to be 1.11 and 1.15 eV, respectively in the measured temperature range, indicating the oxygen ion conductivity in the system. The thermal expansion coefficient of the Bi 2 O 3 -doped DySZr system was found to match with the other component materials for solid oxide fuel cells.