Band 104, Heft 10

The isochronal transformation behavior from martensite (α′) to austenite (γ) of modified high Cr ferritic heat-resistant steel was analyzed using the kinetic information extracted from differential thermal analysis results. The thus obtained α′→γ transformation kinetic process has been described by a JMAK-like model including three overlapping processes: site saturation nucleation, diffusion-controlled growth, and impingement correction for random distribution of nuclei. It is found that both the diffusion of alloying components and the inhibition of carbide precipitates strongly affect the α′→γ transformation kinetic processes. The α′→γ transformation (at relatively low heating rates) is of diffusion-controlled nature, and the obstruction of carbides during the migration of the α′/γ interface leads to a decrease in the pre-exponential factor of diffusion coefficient.

Ageing textures of three alloys, namely, Ti-8Nb, Ti-12Nb and Ti-16Nb have been studied in β STWQ and α + β STWQ specimens at three different temperatures. Ageing treatments in the present study are associated with phase transformation as well as the growth of orientations of the transformation products. The development of an ideal c-type texture depends on alloy composition, solution treatment and ageing treatment temperatures. The 450°C aged specimens of the alloys Ti-8Nb (β STWQ and α + β STWQ) and Ti-12Nb (α + β STWQ) possessed c-type texture. The presence of β phase weakens the basal component and strengthens non-basal components in {0002} pole figure. The resultant texture of 550°C aged specimens appears to be independent of the texture of the starting material.

Thixocast ZA27 alloy and particulate ZA27/SiC p composites were subjected to artificial aging at 80, 120 and 160°C (T5 regime). Composites with 5 and 10 vol.% SiC particles were produced via the compocasting method. The influence of the aging was investigated using different techniques. Differential scanning calorimetry was performed to reveal the presence of phases created in the thixocast ZA27 alloy and the composites. Microstructures and fracture behavior were examined by means of optical microscopy, scanning electron microscopy and X-ray diffraction. Aging processes in the matrix alloy and composites were followed using hardness measurements. A decrease in the hardness values was noticed with the increase in the aging temperature. At higher temperatures diffusion of zinc atoms from supersaturated phases in the matrix alloy was enhanced, which resulted in faster changes in the hardness. Aging processes in the composites were significantly accelerated compared to the matrix alloy, due to the presence of particulate reinforcements. The maximum in hardness was achieved for shorter time in the ZA27/SiC p composite with higher volume fraction of SiC particles.

Low cycle fatigue experiments under asymmetric loading on differently prepared AZ31 alloys show that the alloy with fine grains exhibits higher stress amplitudes than those of the alloy with coarse grains at the same strain amplitudes. The elastic strain in the tensile process is higher than that in the compressive process for both alloys, but the difference is much smaller for the alloy with fine grains. The microstructure with fine grains exhibits a symmetrical hysteresis loop and cyclic strain softening at the early fatigue stage at low strain amplitude.

Aluminum was extruded via the KOBO method with direct and lateral outflow at ambient temperature with an extrusion ratio of λ = 100, keeping constant extrusion force all the time. Despite the far different metal flow geometries, in both cases products were obtained with very good quality (die shape reflection and surface state) and a slight variation in mechanical properties. It was also found that higher torsion angle of extruded metal lowers their levels. The results show both the real possibilities of conducting the extrusion process with lateral outflow, as well as a successive argument supporting the concept of superplastic flow of metal in the KOBO process.

The hot compression deformation of an Mg–2.54Nd–0.26Zn–0.32Zr cast alloy was investigated in the 25–400°C temperature range at initial strain rates from 10 −4 s −1 to 10 −2 s −1 . It was found that strain rate has little effect on true stress when the material was compressed below 250°C. Above this temperature, high strain rates resulted in an increased true stress. The average strain rate sensitivity exponent at higher temperature (300–400°C) was determined to be 0.24 and the calculated activation energy was 185 kJ · mol −1 , which is higher than that of lattice self diffusion of pure Mg. The constitutive equation was established and the Zener-Hollomon parameter was calculated as a function of peak stress. The microstructure of a sample tested at 300°C was analyzed by optical microscopy.

The friction and wear performance of cast polyamide, unfilled poly-oxy-methylene, 10 wt.% graphite filled polyamide 6, 10 wt.% graphite filled poly-oxy-methylene, and 10 wt.% graphite plus 6% wax filled polyamide 6 sliding against stainless steel under dry sliding conditions were studied. The aim was to evaluate the tribological behavior of the above materials which enables suggesting alternative material for costly cast polyamide polymer in industrial applications. Tribological tests were carried out using a pin-on-disk arrangement at a sliding speed of 0.5–2.0 m s −1 and under applied loads of 50 to 150 N. The results showed that the friction coefficient of the tested materials decreases with the increase in applied load as well as with the decrease in sliding speed values. Furthermore, the lowest wear rate is 2.24 −15 m 2 N −1 for 10 wt.% graphite filled polyamide 6 composite. This suggests its use instead of cast polyamide polymer. Finally, it is concluded that the wear mechanism includes transfer film and deformation.

The evolution of the passive films on AISI 204Cu and AISI 304 stainless steels in simulated pore solution for steel reinforcements in concrete, and with and without the addition of chloride, was studied using cyclic voltammetry and potentiodynamic measurements. The passive layers were studied at open-circuit potential by means of X-ray photoelectron spectroscopy. The passive films on both materials predominantly contained Cr-oxides, whereas the Fe-species were markedly depleted. Mn-enrichment was also observed. The addition of chloride ions did not have a significant influence on the composition of the passive layers. The surface morphology of the products formed on the surface of both investigated materials at open-circuit potential and at high over-potentials in the presence of chloride was studied using scanning electron microscopy.

The corrosion behavior of nanograined (NG) IF-steel was compared with its coarse-grained (CG) counterpart. The corrosion tests were carried out using different solutions of NaCl and H 2 SO 4 . The results show that the nanostructured IF steel exhibited higher corrosion resistance ( E corr ) and lower corrosion rate ( i corr ). According to the corroded microstructures, extensive cracking was observed in the case of CG subjected to both chloride and acidic media, as well as localized corrosion with signs of severe pitting. The results also show that NaCl can act as an inhibitor when added to H 2 SO 4 -containg solution leading to a decrease in the detrimental effect of H 2 SO 4 .

In the present study, the corrosion resistance behavior of untreated and laser treated Hastelloy was examined. The electrochemical tests including potentiodynamic polarization, Tafel analysis, and linear polarization resistance were carried out in deaerated 0.5% NaCl aqueous solution at room temperature. Surface roughness was measured to correlate it with corrosion resistance properties of the materials. Surface morphology of the samples after corrosion tests was examined using scanning electron microscopy and energy dispersive X-ray spectroscopy. Results showed that laser treated surface exhibited better corrosion resistance properties as compared to untreated surface.

Si-doped zinc oxide (SZO, Si 3%) thin films were deposited on glass substrates by means of direct current magnetron sputtering under different pressures. The influence of sputtering pressure on structure, morphology, optical and electrical properties of SZO thin films was investigated. The results reveal that the sputtering pressures have a significant impact on the growth rate, crystal quality and electrical properties of the films, but have little impact on the optical properties of the films. SZO thin film samples grown on glasses are polycrystalline with a hexagonal wurtzite structure and have a preferred orientation along the c-axis perpendicular to the substrate. When the sputtering pressure increases from 2 to 8 Pa, the film surface becomes compact and smooth, the degree of crystallization of the films increases, and the resistivity of films decreases. However, when the sputtering pressure continues to increase from 8 to 10 Pa, the degree of crystallization of the films decreases, the grain size decreases, and the resistivity of the films increases. SZO(3%) thin film deposited at a sputtering pressure of 8 Pa shows the largest carrier concentration, the largest mobility, the lowest resistivity of 3.0 × 10 −4 Ω cm and a high overall transmission of 93.3% in the visible range.

In this paper, we report the production of Cu 2 SnS 3 thin films with high phase purity via successive ionic layer adsorption and reaction method on soda lime glass substrates. Structural, morphological, compositional, optical and electrical investigations were carried out. The X-ray diffraction patterns of the samples matched very well with the reference pattern and proved the polycrystalline nature of the films. As a secondary phase, one weak peak indicating covallite Cu 2–x S phase was observed in the pattern of the sample deposited by using equimolar Cu and Sn. The surface morphologies of the films were found to be continuous and composed of homogeneously distributed large grains. From the reflectance and transmittance data, the optical absorption coefficient values of the films were found to be about 10 4 cm −1 and the films were found to be almost opaque in the wavelengths from 200 to 600 nm with a small reflectivity of about 10%. Band gap values of the films decreased from 1.45 to 1.35 eV with decreasing Cu content. Electrical characterization showed that the films were p-type semiconductor. Two different impurity levels for each film were found via resistivity-temperature characteristics.

Nanocrystalline ceria powders have been synthesised via the gel combustion route, using for the first time urea formaldehyde as fuel for doping of dysprosium oxide. This synthesis route can produce well-crystallised powder within a one step combustion process, eliminating the need for further calcinations. The formation sequences have been described through differential scanning calorimetry-thermo gravimetric analysis study and the crystallinity of the powder was examined using X-ray diffraction, selected area electron diffraction and high resolution patterns. Lattice parameter was found to increase with doping concentration. Very fine grains in the size range of 3–5 nm are found to occur in the form of large and soft agglomerates (50–130 nm). The optical band gap suggests that those powders with low dopant concentration may have useful applications in UV-shielding and in transparent conducting film.

The purpose of the present study is to prepare ZrB 2 -based nanocomposites with limited or no obvious grain growth. For ZrB 2 nanoparticles, the densification on-set temperature was about 1300°C, whereas the obvious grain growth on-set temperature for ZrB 2 nanoparticles was found to be about 1500°C. Therefore, there was a temperature “window” 1300–1500°C where ZrB 2 nanoparticles could be densified with limited or no grain growth. In this study, densification of ZrB 2 -based nanocomposite was finally realized by means of low-temperature hot-pressing at 1450°C for 60 min under a uniaxial pressure of 30 MPa using Cu as a sintering additive. After hot-pressing, the grain growth of ZrB 2 nanoparticles was greatly suppressed, and the average grain size for ZrB 2 was only 310 nm. The microstructure and mechanical properties were examined, and the flexural strength and fracture toughness were 472.8 ± 36.4 MPa and 12.4 ± 0.5 MPa · m 1/2 , respectively. We believe this paper can lay the foundation for the preparation of ZrB 2 -based nanocomposites.

Ti/S/C powders were used as raw material for the combustion synthesis of Ti 2 SC. The results showed that Ti 2 SC was the main phase of the product of the 2Ti/S/C powders used for the synthesis. Furthermore, certain amounts of TiC and Ti 3 S 4 were found in the product. Excess S addition improved the synthesis of Ti 2 SC. Scanning electron microscopy indicates that the lamellar Ti 2 SC grains had lengths ranging from 20 µm to 30 µm.