Volume 105, Issue 2

The mechanical response of polycrystalline metallic materials is heavily influenced by the orientations of their grains. To predict polycrystalline behavior more accurately, crystal plasticity models account for grain orientations and also, sometimes, for interactions between neighboring grains. However, these models often lack sound experimental input or validation. Furthermore, experimental studies themselves rarely tackle simply the concept of representativity in terms of texture; neither do they try to analyze up to what range neighbor interactions appear to be significant. In this article, we address both aforementioned issues in a single and easily implementable framework by performing extensive statistical analyses of discrete raw orientation and misorientation data respectively, obtained by means of electron back-scattered diffraction on thousand-grain microstructures. First, we show that the analysis of orientation statistics helps determine whether an experimental dataset can be considered as a microstructurally representative volume element in terms of texture. Second, we explain how the statistical processing of misorientations can shed some light on the range of neighbors that have a significant weight in the misorientation distributions and possibly on the grain interactions.

Advanced microstructure simulation models can predict solute segregation in 2D and 3D space, which often leads to outputs of large arrays of concentration values with a multitude of detailed information that hinders straightforward evaluations. The target of this study is to establish a common evaluation method for both simulation results and experimental data as a standard for quantitative comparison and validation. For this purpose, a methodology is adopted from experimental segregation analysis to transform the multi-dimensional data into meaningful 1D segregation profiles, which can easily be plotted and discussed. As an application example, a directional solidification experiment on an AZ31 magnesium alloy is selected and the solidification process is simulated using the phase-field method. The subsequently obtained 1D segregation profiles are compared to measured segregation profiles. As part of the study, two common sorting methods are evaluated with respect to their applicability to recover the general segregation behavior and the solidification path, as well as to handle numerical noise.

In this study, we employed the nanoindentation technique to evaluate the pop-in events of Si–Ge multilayers under extra-low forces. X-ray diffraction revealed a shift of the peaks of the Ge atoms from 68.70 to 68.50°, due to gradual mixing of previously isolated Si and Ge atoms into an SiGe compound, upon increasing the annealing temperature. Atomic force microscopy images of the vicinity near the triangular indentation mark revealed that the primarily plastic deformation, the pop-in event observed in the load–displacement curve, was based on slightly active dislocation nucleation and propagation during treatment with the artificial indenter. The samples annealed at RT , 400, 500, and 600°C exhibited hardnesses ( H ) of 18.6 ± 1.2, 17.9 ± 1.1, 18.9 ± 1.2, and 15.0 ± 0.8 GPa, respectively, and elastic moduli ( E ) of 220.0 ± 5.2, 224.9 ± 5.4, 220.7 ± 4.5, and 186.7 ± 3.8 GPa, respectively. These values reveal that elastic/plastic contact translation of the Si–Ge multilayer occurred to various extents depending upon the annealing conditions; in addition, the values of h f / h max for the samples annealed at RT , 400, 500, and 600°C were 0.449, 0.416, 0.412, and 0.470, respectively. In a crystal structure, release of the indentation load reflects the directly compressed volume; the total penetration depth into the film was approximately 30 nm with a peak load of 500 μN. Accordingly, the annealed samples can exhibit pop-in after indentation earlier than samples treated merely at RT .

With friction stir welding it is possible to join light metals in the solid state. However joints between dissimilar metals are a special challenge. At the Institute of Materials Science and Engineering of the University of Kaiserslautern the friction stir weldability of magnesium–aluminium-joints was investigated. For the realization of high strength joints between these materials the knowledge of the developing microstructure in the welding zone is of especially high interest. Therefore, light microscopic and scanning electron microscopic investigations were carried out and the results compared with phase diagrams and phase fractions for the bonding zone which were calculated at Institute of Metallurgy of the University of Clausthal.

In the present work we perform a detailed investigation of ingot metallurgy processing routes of Ti-30Ta, a shape memory alloy with a good potential for applications at higher temperatures. There is currently considerable interest in high temperature shape memory alloys, both in industry (automotive and aerospace applications) and in academia. By means of scanning electron microscopy, we provide recommendations on the number of remelting cycles in the vacuum arc melting process, and on annealing temperatures/times in order to obtain chemical homogeneity. It is also shown that this is required to obtain well defined differential scanning calorimeter charts, which facilitates characterization and investigations of martensitic transformation in this alloy. Areas in need of further work are identified.

The microstructural evolution of Al–Cu alloys during the downward directional solidification process was investigated. At the planar-to-cellular transformation point, the planar liquid/solid (L/S) interface broke down at the centre. This was contrasted with the behaviour in the liquid metal cooling process, where the interface broke down at the periphery. The critical withdrawal rate at this point was higher than the theoretical value. In addition to this, the variation in the primary dendrite arm spacing ( λ 1 ) as a function of the withdrawal rate ( V ) at constant G L for the Al-2.0 wt.% Cu alloy agreed with the conventional processes. The comparison of λ 1 in our experiment to the calculated value λ 1 using the Kurz–Fisher, Ma and Trivedi models showed that λ 1 , calculated by these models, overvalued our experimental results. However, the λ 1 calculated from the Hunt model agreed well with the experimental values of λ 1 . When we reduced the diameter of the sample from 13 mm to 9 mm and maintained the other parameters constant, the L/S interface retained a planar shape. This indicated that the L/S interface was more stable in the smaller sample than that in the larger. This result contrasted with the result in the liquid metal cooling process.

The cementation of indium on an aluminum plate in indium-bearing concentrated hydrochloric acid solutions has been performed over a period of 2 hr at 278, 298, 318, 328 and 338 K. Aluminum was selected for two reasons: (1) aluminum has significantly higher oxidation potential compared to indium and (2) the leaching of waste plasma display panels produces a significant concentration of aluminum ions in solution. The effect of the cementation variables was comprehensively investigated, and a preliminary kinetic analysis was made using first order kinetics with pertinent Arrhenius-type plots. The cementation process was highly temperature sensitive for the range of 298–338 K, and more than 96% of the indium was recovered at 338 K. For morphology and purity analysis, indium powders obtained from the cementation process were examined using various analytical tools, such as X-ray diffraction and scanning electron microscopy–energy dispersive X-ray spectrometry.

A systematic study on the development of a set of Sn–Cu–Sb alloys and their characteristics, such as phases evolved, mechanical properties, physical properties, and microstructures, that are commonly sought for making pewter is presented. Alloys with various nominal compositions of Sn–Cu (1–3%)–Sb (3–6%) were prepared and they were die cast for complete characterization. The samples were characterized for hardness, malleability, density, microstructure, and phase identification. The study is expected to help in selecting the right composition of the alloys for making pewter with appropriate combination of properties.

This study investigates the corrosion behavior of Cu-35Zn brass with 0 and 5 wt.% of tin in NaCl solution with a mass concentration of 3.5% containing 0, 400 and 1200 ppm of sulfide ions. For the purpose of assessing the corrosion behavior, open circuit potential, linear polarization resistance, electrochemical impedance spectroscopy and potentiodynamic polarization studies were employed. The results of the study show that on increasing the S 2− concentration, an increase in the corrosion rate of the samples was observed. Moreover, the addition of Sn to the alloy leads to an increase in the polarization resistance and electrochemical impedance of the alloy. The corrosion potential as well as the corrosion current density were calculated using the Tafel extrapolation method. Addition of S 2− shifts E corr towards more negative values and increases i corr . The surface of the samples was studied using light optical microscopy and pits were mainly observed in the grain boundaries of the Cu-35Zn sample.

The hardening of copper alloy by using powder metallurgy techniques and analysis of its effects on the strength of obtained material are discussed. Prealloyed Cu-0.5 wt.% Cr powder and mechanically alloyed Cu-0.5 wt.% Cr-3 wt.% Al 2 O 3 powder were consolidated by means of hot pressing. Optical microscopy, scanning electron microscopy and transmission electron microscopy were used for microstructure characterization of compacts. Hardness and electrical conductivity of both compacts were compared. High strengthening of the Cu–Cr compacts is achieved by aging as a consequence of the influence of precipitation particles rich in chromium. In the case of the Cu–Cr–Al 2 O 3 composite it is a consequence of precipitation of particles rich in chromium and the presence of Al 2 O 3 dispersoid nanoparticles.

Chromium–alumina composites are well known for their good mechanical properties in comparison to pure ceramics or metals. These composites are characterized by high hardness and high mechanical strength. The aim of the present work was to improve the properties of chromium–alumina composites even more and expand the range of their possible applications by addition of rhenium. To achieve this goal, chromium–alumina composites containing 2 and 5 vol.% of rhenium were produced via powder metallurgy. The microstructural characterization of the processed material was performed using light microscopy, scanning and transmission electron microscopy as well as X-ray diffraction analysis. Measurement of selected properties such as Young's modulus, bend strength and hardness revealed an advantageous influence of rhenium additions. The results are discussed in terms of the influence of rhenium volume content on the microstructure and on the physical and mechanical properties of the chromium–alumina composites. The solid solution is only partially formed. The properties strongly depend on the amount and distribution of both aluminium oxide and rhenium content.

The effects of the addition of Er 2 O 3 on the grain growth and sinterability of c-ZrO 2 were investigated using 8 mol.% yttria-stabilized cubic zirconia (c-ZrO 2 ) and various amounts of Er 2 O 3 . For these purposes, the content of 0–15 wt.% Er 2 O 3 and c-ZrO 2 powders were doped using a colloidal process. Undoped and Er 2 O 3 -doped c-ZrO 2 specimens were annealed for grain growth at different temperatures and holding times. An increase in annealing temperature and holding time caused grain growth in all specimens. Activation energy of the undoped c-ZrO 2 obtained was 358 kJ mol −1 and the activation energies of 1, 5, 10 and 15 wt.% Er 2 O 3 -doped specimens obtained were 388, 403, 432 and 476 kJ mol −1 , respectively. While excessive grain coarsening in the undoped c-ZrO 2 was observed, a lesser level of grain growth occurred in the Er 2 O 3 -doped specimens, due to the segregation of Er 2 O 3 at the grain boundaries and the restriction in the grain boundaries mobility of c-ZrO 2 .

Aluminium coatings applied using arc or flame spraying processes are frequently employed for protection of steel structures in maritime applications. Results of comparative testing of aluminium coatings produced by manual and robotized flame spraying on steel substrate are reported in the contribution. Particular attention during the investigation of coating properties has been given to the uniformity of coating thickness, adhesion and corrosion resistance. Analysis of the results yielded conclusions on the quality, adhesion and corrosion resistance of the aluminium coating when the coating is applied to the flat steel plate.