Volume 103, Issue 12

The effect of crystallographic texture on grain growth was studied in two samples from an interstitial-free steel sheet with two different primary recrystallization textures, one with a pronounced {111} fiber texture and the other with an almost random texture. Upon grain growth annealing, the sample with the random texture showed slow continuous grain growth. In the strongly textured material discontinuous grain growth prevailed at a higher growth rate. The effect of texture on the rate of grain growth is discussed in terms of the motion of the grain boundary triple junctions in the two samples with different distributions of grain-to-grain misorientations. Numerical simulations with a 2D vertex model confirmed the influence of the triple junctions on the development of microstructure and texture observed during grain growth in the two differently textured steel samples.

Depending on the processing method, pseudoelastic NiTi alloys can have small, lenticular Ni 4 Ti 3 precipitates; however, the mechanical properties of these precipitates are not well understood. By performing nanoindentation with a spherical indenter, Ni 4 Ti 3 precipitates within a pseudoelastic NiTi alloy were examined. Scanning electron microscopy was used to examine the indents after nanoindentation. After unloading, the hardness and remnant depth ratios of the indents in the Ni 4 Ti 3 precipitates, the NiTi matrix, and the “average” NiTi alloy were compared. To decouple the effects of elasticity from those of pseudoelasticity, similar nanoindentation experiments were performed on an NiAl sample and compared with results from the NiTi sample.

FeSi samples with 7.5 mass.% Si were cold deformed with a thickness reduction of 16% and isochronally annealed for one hour at different temperatures. Their microstructure was characterised using positron annihilation lifetime spectroscopy and electron backscatter diffraction. Positron annihilation mean lifetime values (τ mean ) decreased slightly with the increase in annealing temperature (20 to 600°C), a process related to recovery. In addition, τ mean decreased significantly in the 700–900°C temperature range. The measured value of τ mean is 106 ps, which is similar to the pure undeformed Fe after annealing at 900°C. Thus, the material is virtually free of defects at 900°C. Microscopy and diffraction studies showed a high amount of shear bands for the deformed sample. In the temperature range of 20–600°C, no recrystallisation was observed. According to the electron backscatter diffraction data, the recrystallisation starts after 700°C, and it is completed at 900°C.

Three models to describe the relationship between the green porosity of compacts and the applied external pressure during the compaction of metal powders are proposed in order of growing complexity. Only in the third model do all of the parameters have a clear physical meaning and become measurable. These parameters are related to the plastic behaviour of the powder particle material, the friction coefficient between the powder and die walls, as well as the interparticle friction. The three proposed models include a parameter representing a certain value related to the initial porosity of the powder mass; however, only in the third model is this value clearly defined by the tap porosity of the powders. The proposed models have been experimentally verified by compressibility curves obtained from metal powders of different types. The agreements between the second and third models and the experimental data are reasonable over the tested pressure range.

The surface tension and density of Sn-Ag-Cu alloys, lying along two cross-sections of silver to copper molar ratios equal to 1 and 7/3, were studied. Sessile drop measurements were carried out over a broad temperature range. It was found that both surface tension and density decrease with increasing concentration of Sn. With the increase in temperature, the density decreases linearly for all compositions, whereas the surface tension shows linear and curvilinear dependence for different compositions. The results are compared with literature data obtained with a different technique and the results of model calculations. Relatively good agreement is observed between the models and experimental data.

The thermodynamic properties of liquid Au–Sb–Sn are discussed with regard to the energetics of the system. The analysis in terms of the partial excess Gibbs energies and the partial enthalpies of mixing indicates that the presence of Sb in the alloys is energetically unfavourable. In addition, this is found also to be reflected by the concentration–concentration correlations in the long-wavelength limit, S cc ij , which are representative of the fluctuations in local composition occuring in the system. It is suggested that the analysis of the partial quantities in the system might give an extremely helpful contribution to understanding the energetics of multi-component systems.

Sub-solidus phase relations in the ZrO 2 -Sm 2 O 3 -Y 2 O 3 and Sm 2 O 3 -Al 2 O 3 -Y 2 O 3 systems were experimentally studied at 1523-1873 K and thermodynamic databases for these systems were developed. Analysis of phase equilibria in the Sm 2 O 3 -Y 2 O 3 -Al 2 O 3 system indicated that REAM phase (Sm,Y) 4 Al 2 O 9 is not stable in the Sm 2 O 3 rich-composition. Therefore, the stability limit of the Sm 4 Al 2 O 9 phase was established experimentally and thermodynamic parameters of the Sm 2 O 3 -Al 2 O 3 system were re-optimised. The eutectic melting in the Sm 2 O 3 -Y 2 O 3 -Al 2 O 3 system was investigated using differential thermal analysis and scanning electron microscopy. The results obtained were used to assess the mixing parameter of the liquid phase. A new description of binary system was introduced into the database of the ZrO 2 -Sm 2 O 3 -Al 2 O 3 system and phase diagrams were re-calculated. The obtained thermodynamic databases were combined with literature data for the ZrO 2 -Y 2 O 3 -Al 2 O 3 system and a thermodynamic database for the ZrO 2 -Sm 2 O 3 -Y 2 O 3 -Al 2 O 3 system was developed.

The phase composition and defect structure of the system Li 2 O–MgO was investigated in terms of the long term stability of Li/MgO catalysts. The Li content was varied from 0 to 7 mol.%. Pure Li · MgO solid solutions were prepared via a special washing procedure. Li contents below 0.04 wt.% were stabilized within the MgO host lattice, whereas higher Li contents were found to segregate as Li 2 O and Li 2 CO 3 phases. The catalytic activity in the oxidative coupling of methane was found to decay for all catalysts over a period of 19 h on stream, accompanied by a loss of Li as LiOH. Li in the Li · MgO solid solution was found to be more stable in the lattice than in the surface region of the solid. However, impedance measurements on transition metal stabilized Li/MgO catalysts indicated that even the Li ions within the Li · MgO solid solution are not sufficiently stabilized. Thus, neither the Li compounds nor the dissolved Li ions within the Li/MgO solution seem to be truly stable at 750°C under catalytic conditions.

In order to examine the existence of different phase transitions, the ultrasonic longitudinal modulus ( L ) and its first (Δ L /Δ T ) and second (Δ 2 L /Δ 2 T ) differentials have been established for two different perovskite manganites over a wide range of temperatures, La 0.67 Sr 0.33 MnO 3 from 460 to 300 K and Nd 0.67 Sr 0.33 MnO 3 300 to 150 K. The anomalies in L and its differentials at T C (≈378 K) in La 0.67 Sr 0.33 MnO 3 are due to the ferromagnetic metal transition; the changes at T C (≈234 K), T CO (≈194 K) in Nd 0.67 Sr 0.33 MnO 3 represent the ferromagnetic transition and charge ordering transition respectively. The existing phase transitions are due to a strong electron-phonon interaction arising from the Jahn-Teller effect and spin-phonon interaction from the linear magnetostriction effect. The first (Δ L /Δ T ) and second (Δ 2 L /Δ 2 T ) differentials of L are identified as an effective approach for the clear identification/detection of different phase transitions in the above systems over a wide range of temperatures.

The aim of this study was to develop Au-Pt-Pd-Si alloys with metal-resin bonding properties optimized for dental restorations. The amount of silicon added ranged from 0.00-0.54 wt.%. The Au-Pt-Pd-Si alloys were manufactured using an arc melting furnace. They were homogenized at 800°C in air and cold rolled to a 1 mm thickness. The changes in the surface morphology and oxide layer formation were analyzed using scanning electron microscopy, energy dispersive X-ray spectroscopy, electron probe microanalysis and X-ray photoelectron spectroscopy before and after oxidation treatment. The mechanical properties of the alloys were evaluated using micro-hardness and shear bonding tests. The surface oxide layer was mostly composed of silicon dioxide and metallic gold. The micro-hardness of the Au-Pt-Pd-Si alloys increased as a function of the silicon concentration. The shear bonding strength was significantly higher (9.30 MPa) at 0.54 wt.% silicon ( p < 0.05).

The high temperature stability of γ-Al 2 O 3 films deposited using filtered cathodic arc and plasma assisted chemical vapor deposition on Ti 0.33 Al 0.67 N coated WC–Co cutting inserts is investigated. X-ray diffractometry reveals that filtered cathodic arc deposited films transform partially into the thermodynamically stable α-Al 2 O 3 phase at a temperature of 1000°C. The γ to α-Al 2 O 3 transformation for plasma assisted chemical vapor deposition grown films is observed at 900°C. These results are in qualitative agreement with differential scanning calorimetry measurements. Transmission electron microscopy on filtered cathodic arc and plasma assisted chemical vapor deposition films annealed at 900°C reveals the existence of hexagonal AlN in the Ti 0.33 Al 0.67 N interlayer, as well as Al depletion at the Al 2 O 3 /Ti 0.33 Al 0.67 N interface. After annealing the plasma assisted chemical vapor deposition sample at 900°C, α-Al 2 O 3 grains with a size of ∼100 nm are observed inside the γ-Al 2 O 3 matrix, while for filtered cathodic arc samples only the γ-phase is identified. Transmission electron microscopy analysis on both filtered cathodic arc and plasma assisted chemical vapor deposition samples annealed at 1000°C shows that the original Al 2 O 3 /Ti 0.33 Al 0.67 N/WC–Co layer architecture is no longer intact. The formation of TiO 2 is detected along the growth direction of the Al 2 O 3 films. The present study suggests that not only the morphology and the impurities incorporated into γ-Al 2 O 3 but also stability of the Ti 0.33 Al 0.67 N interlayer determine the high temperature stability of γ-Al 2 O 3 /Ti 0.33 Al 0.67 N coated hardmetal.

The influence of composition and annealing temperature on the magnetic properties of (Nd 0.5 Pr 0.5 ) 6 + x Nb 1.5 Fe 88.5 – x – y B 4 + y ( x = 0–6, y = 0–10) nanocomposites prepared via melt-spinning and subsequent annealing was investigated systematically to obtain their optimal compositions and fabrication conditions. The results show that each of the rare earth concentrations has an appropriate ratio of Fe/B to reveal the best performance of the material. The optimal annealing temperature decreases from 750 to 675°C when concentration of rare earth is increased from 6 to 12 at.%. Coercivity, H c , and maximum energy product, ( BH ) max , of these nanocomposites can be regulated up to 14.5 kOe and 16 MGOe, respectively, by suitably choosing their composition.

Nanoparticles of Cd 1- x Zn x S ( x = 0–0.8) were prepared in neat 1-ethyl-3-methylimidazolium ethyl sulfate, a halide-free and low-cost room-temperature ionic liquid (RTIL) via a simple heating method. The nanoparticles were investigated by means of powder X-ray diffraction, scanning electron microscopy, and UV-Vis diffuse reflectance spectroscopy techniques. The diffraction patterns demonstrate that the prepared nanoparticles in the RTIL have smaller size relative to the samples prepared in water. The photocatalytic activities of the nanoparticles towards photodegradation of methylene blue were evaluated under UV and visible irradiation. The results indicate that the nanoparticles prepared in the RTIL have greater photocatalytic activity relative to the samples prepared in water. The reaction rate constant under visible light irradiation on the nanoparticles prepared in the RTIL is at least six times greater than for the samples prepared in water.

In this work, WO 3 films have been grown using spray pyrolysis of ammonium tungstate precursor on glass substrates. The obtained WO 3 films have been subjected to sulfurization under vacuum at 550°C. The structural properties of the obtained films were investigated using X-ray diffraction, atomic force microscopy and scanning electronic microscopy. The results showed that the sulfurized films contained only WS 2 . The c -axis preferential orientation of the WS 2 films has been verified by several means. The deposition technique is simple and less expensive than several recently proposed ones.

Al-Zn-In anodes show better performance due to the beneficial effects of Zn and In on prevention of aluminum passivity and producing a homogeneous structure for uniform corrosion of the anodes. However, there are different views about the optimum concentration of each element in the anode. In this study, the anodic behavior of Al-Zn-In alloy with different concentrations of zinc from 1 to 6 wt.% and indium from 0.01 to 0.05 wt.% are studied. The NACE efficiency test and polarization are used in 3 wt.% NaCl solution for corrosion characterization. The results showed that zinc and indium change the anode potential to more active potentials and improve the microstructure uniformity of anodes. The latter leads to more uniform corrosion. Optimum concentrations of zinc (5 wt.%) and indium (0.02 wt.%) were found in this respect.

The effect of molybdenum addition on the fracture toughness and micro-hardness of Fe 2 B in Fe-B-C alloy was investigated. The results indicate that, with the increase in molybdenum addition, the micro-hardness of Fe 2 B increases and its fracture toughness first increases and then decreases. Compared with the fracture toughness (3.8 MPa · m 1/2 ) of Fe 2 B without molybdenum addition, its toughness at 2.14 wt.% molybdenum addition can be nearly doubled, achieving 7.4 MPa · m 1/2 . The wear result indicates that increasing the toughness of Fe 2 B may distinctly improve the wear resistance of Fe-B-C alloy and the wear resistance is improved by around 35% in this experimental condition.