Band 98, Heft 1

Predominantly single phase Zr 3 Al 3 C 5 powders were synthesized in an Ar atmosphere using Zr – Al intermetallics and graphite as starting materials. The reaction path of Zr 3 Al 3 C 5 synthesis was discussed based on differential scanning calorimetry and X-ray diffraction results. Lattice parameters of Zr 3 Al 3 C 5 determined using the Rietveld method are a = 3.347 Å and c = 27.642 Å. In addition, the oxidation of Zr 3 Al 3 C 5 powders was tested by using thermogravimetry – differential scanning calorimetry. The starting and complete oxidation temperatures are 400 °C and 1200 °C, respectively. These temperatures are much higher than those for ZrC, suggesting that Zr 3 Al 3 C 5 has better oxidation resistance than ZrC. On the other hand, the oxidation degree of Zr 3 Al 3 C 5 , defined for the complete carbide – oxide transformation, overshot 100 % during oxidation. This overshooting is attributed to the formation of amorphous carbon. The phase evolution during the oxidation of Zr 3 Al 3 C 5 was also investigated.

The thermodynamic properties of Zn 17 Y 2 and Zn 12 Y were investigated by calorimetry. The standard entropies of formation at 298 K, were determined from measuring the heat capacities, C p , from near absolute zero (2 K) to 300 K by the relaxation method. The standard enthalpies of formation at 298 K, were determined by solution calorimetry in hydrochloric acid solution. The standard Gibbs energies of formation at 298 K, were determined from these data. The results obtained are: (Zn 17 Y 2 ) = – 23.53 ± 1.4 kJ · (mol of atoms) −1 ; (Zn 17 Y 2 ) = – 3.05 ± 0.39 J · K −1 · (mol of atoms) −1 ; (Zn 17 Y 2 ) = – 22.62 ± 1.4 kJ · (mol of atoms) −1 ; (Zn 12 Y) = – 23.89 ± 1.8 kJ · (mol of atoms) −1 ; (Zn 12 Y) = – 0.78 ± 0.41 J · K −1 · (mol of atoms) −1 ; (Zn 12 Y) = – 23.66 ± 1.8 kJ · (mol of atoms) −1 . The electronic contribution to the heat capacity of Zn 17 Y 2 and Zn 12 Y is found to be similar to pure zinc, indicating that the valence electrons of yttrium in the compound are trapped by the density of states for zinc.

The 450 °C isothermal section of the Zn – Fe – S phase diagram has been constructed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. In addition to the ternary extensions of the binary Zn – Fe intermediate compounds of ς, δ, Γ 1 , and Γ, the extensions of the ZnS, FeS and FeS 2 compounds were also determined. The solubility of Fe in ZnS is about 20.2 at.%. The solubility of sulfur in all Fe – Zn intermetallic compounds is negligible. The zinc contents of Fe sulfides were not detectable.

Aluminium oxide nanoparticles were synthesized by a chemical vapor condensation process using aluminium acetylacetonate as a precursor in the temperature range of 700 – 1000 °C. From X-ray diffraction results, it was found that the δ-Al 2 O 3 phase was obtained at 900 °C and 1000 °C. Transmission electron microscopy observation revealed that δ-Al 2 O 3 nanoparticles 10 – 15 nm in diameter consisted of a hollow structure with shells 2 – 3 nm in thickness. The sequential decomposition of acetylacetonate groups observed in thermogravimetry analysis showed that the formation of a hollow structure depends on the characteristics of the metal – organic precursor. Also, a decrease in the transmittance of δ-Al 2 O 3 nanoparticles was found in the wavelength range of 300 – 900 nm by UV-Visible spectrophotometry, which is expected to occur by scattering and absorption of light depending on particle size and hollow structure.

This paper presents low-cycle fatigue (LCF) behaviour and damage mechanisms of uncoated and coated specimens of a single crystal nickel-base superalloy SCB tested at 500 °C and 900 °C. Four coatings were deposited on the base material, an overlay coating AMDRY997, a platinum-modified aluminide diffusion coating RT22 and two innovative coatings called IC1 and IC3 with a NiW diffusion barrier in the interface. AMDRY997 and RT22 were used as reference coatings. The LCF tests were performed at three strain amplitudes, 1.0, 1.2 and 1.4 %, with, in laboratory air and without any dwell time. The LCF life of the specimens is determined by crack initiation and propagation. Crack data are presented for different classes of crack size in the form of crack density, that is, the number of cracks normalised to the investigated interface length. Micrographs of damage of the coatings are also shown. The effect of the coatings on the LCF life of the superalloy was dependent on the test temperature and deposited coating. At 500 °C all coatings had a detrimental effect on the LCF life of the superalloy. At 900 °C both AMDRY997 and IC1 prolonged the fatigue life of the superalloy by factors ranging between 1.5 and 4 while RT22 and IC3 shortened the life of the coating – substrate system. Specimens coated with RT22 exhibited generally more damage than other tested coatings at 900 °C. Most of the cracks observed initiated at the coating surface and a majority were arrested in the interdiffusion zone between the base material and the coating. No topologically close-packed phases were found. Delamination was only found in AMDRY997 at higher strains. Surface roughness or rumpling was found in the overlay coating AMDRY997 with some cracks initiating from the rumples. The failure morphology at 900 °C reflected the role of oxidation in the fatigue life, the crack initiation and propagation of the coated specimens. The wake of the cracks grown into the substrate was severely oxidised leading to the loss of Al and Ti to the oxide and resulting in the formation of a γ′ depleted zone. The cracks grew more or less perpendicular to the load axis in a Stage II manner.

The fluidity of Mg – Al – Ca alloys under high-pressure die casting conditions was studied using fluidity tests with spiral specimens. The flow behavior analyses suggest that flow with zero superheat plays a more important role under high-pressure die casting conditions than gravity casting. This can be attributed to the difference between the two kinds of casting process. Fluidity results with a degree of superheat were interpreted on the basis of the effects of calcium on (1) latent heat, (2) viscosity and (3) solidification characteristics. The latent heat and phase accumulation formed by high pressure are the important factors influencing the fluidity of magnesium alloys in the high-pressure die casting process.

Compound-extruded unidirectionally reinforced lightweight profiles are a novel class of materials for the construction of load-bearing structures. In this paper, investigations of the reinforcing effect of ropes in compound-extruded aluminium profiles tested under quasistatic loading conditions are presented. In particular, the investigations lead to a characterisation of the interface between matrix and reinforcing element, as the compound's internal load transfer is a crucial factor in the overall mechanical properties. It could be shown that – in addition to a form fit – a diffusional bond evolves. Both Young's modulus and tensile strength could be increased by using a rope reinforcement. Furthermore, the results attained are compared to a theoretical model which was adapted to the deformation behaviour of compounds containing a single reinforcement.

To improve impact and flexure properties of ultrahigh carbon steel (UHCS-1.3 wt.% C), a multilayer laminate consisting of 20 layers of the same UHCS has been processed by hot rolling. Two different rolling conditions gave rise to “soft” and “severe” laminates. The toughness of the “soft” laminate, measured by impact test absorbed energy, was more than forty times higher than that of the monolithic UHCS and three times higher than that of mild steels. In contrast, the “severe” laminate showed no increase in toughness with respect to the monolithic UHCS. This large difference in behaviour was studied by means of shear and bend tests, which gave valuable information on bond quality and delamination.

Extruded bars of AA6061 alloy were heat treated above the solidus temperature to produce wrought aluminium feedstock for thixoforming. The extruded material recrystallized during heating to the semi-solid state, producing nearly equiaxed polygonal grains with high-angle boundaries. Melting started at triple junctions during subsequent isothermal heating and progressed along grain boundaries. The low melting point eutectic phase and the high-angle grain boundaries introduced by recrystallization both promoted the grain boundary melting process. The desired feedstock characteristics, comprising complete grain boundary wetting, a perfectly cylindrical slug shape and an average grain size below 100 microns were obtained after 5 min at 640 °C and 635 °C for extrusion ratios of 14: 1 and 5: 1, respectively.

The aim of the present work is to contribute to the identification of indium – selenium phases. Infrared absorption spectra were obtained from some indium – selenium compounds (In 4 Se 3 , InSe, In 6 Se 7 , α-In 2 Se 3 ). X-ray diffractograms of the recently found phase In 9 Se 11 and of InSe are also reported. Both kinds of data can be used for identification of the respective compounds. It is confirmed that α-In 2 Se 3 is stable at room temperature. The stability of the hexagonal InSe modification is also proved and its lattice parameters are recalculated.

In the present paper the Gibbs energy of formation of MgAlON was evaluated, and on this basis the phase stability diagram of Mg – Al – O – N – B was established. Dense magnesium aluminium oxynitride – boron nitride (MgAlON – BN) composites with 0 – 30 vol.% BN were synthesized by hot pressing in the temperature range 1750 – 1850 °C in the phase stability region. The phase compositions of the composites analyzed by X-ray diffraction indicated that the main phases were MgAlON and h-BN and no impurities were found. The microstructures of the composites analyzed by transmission electron microscopy, scanning electron microscopy, and high-resolution electron microscopy showed that the MgAlON did not react with BN, and the latter was distributed on the grain boundary of MgAlON homogeneously. Excessive BN (> 20 vol.%) resulted in a discontinuous microstructure for MgAlON. A matrix-flushing method was employed in the quantitative X-ray diffraction analysis for the multi-component MgAlON – BN composites. The results showed that the relative MgAlON content decreased in the process of sintering MgAlON – BN composites. Thermodynamic analysis showed that some Al 2 O 3 , AlN, and MgO escaped under the reaction conditions. The lattice parameters of MgAlON in the composites have also been evaluated.

The effect of the elastic and plastic anisotropy has been investigated in a welded pipe for nuclear applications (AISI 347) and in a welded plate for conventional power plants (Uni-Fe510D). The analysis has been performed exploiting neutron conventional and reverse time-of-flight spectra and comparing the single peak fit of some set of lattice planes with the Rietveld average. The results show that only some crystallographic directions (namely the 〈311〉 and the 〈111〉 for γ-Fe and 〈211〉 and the 〈110〉 for α-Fe) are in agreement with the average inherent in the Rietveld refinement. Those peaks are therefore recommended for residual stress analysis at steady state sources. The other peaks yield more scattered data (with higher statistical error), but allow spotting the influence of plastic anisotropy. The latter has a greater influence on all single peak data if the macroscopic stress exceeds the bulk yield strength.