Thomas Mehner

Effect of additive and current mode on surface morphology of palladium films from a non-aqueous deep eutectic solution (DES)

Electrodeposition of palladium from a non-aqueous electrolyte solution [choline chloride/urea/palladium(II)chloride] has been carried out by direct and pulse current electroplating. In this study, the influence of an organic additive (nicotinic acid amide), current mode (direct current or pulse current deposition) and hydrodynamic on the surface morphology of electroplated palladium films was investigated. In order to determine the surface morphology and thickness of the electrodeposited palladium layers, a scanning electron microscope and an energy dispersive X-ray fluorescence spectroscope were used. In addition, the cell voltage during the different electrodeposition experiments was recorded and analysed. The experimental results showed that the surface morphology of the palladium deposits could be remarkably affected either by addition of the additive or by applying pulse current. Pulse plating and the selected inhibitor mutually interfere with each other, causing changes in the microstructure of the palladium deposits (e.g. smoothening or forming of micro-cracks). It was possible to optimise the palladium deposit quality by applying pulse current or by addition of the appropriate inhibitor.

Microstructural evolution in the bonding zones of co-extruded aluminium/titanium

In the present study, the interfacial microstructure of dissimilar Al/Ti joints formed by a co-extrusion process has been investigated. The material combinations used for the experiments were commercially pure aluminium and titanium, respectively, in the alloys EN AW-6082 and TiAl6V4. X-ray diffraction, energy-dispersive X-ray spectroscopy, electron microscopy and electron backscatter diffraction revealed titanium aluminide formation in the interface, the development of deformation bands in the sleeve material, and the occurrence of grain size refinement and twinning in the core material. The results are discussed with respect to the concept of a hard core–soft sleeve co-extrusion comprising plastic deformation to promote solid-state diffusion. The study shows the phase distribution and the microstructural evolution in the bonding zone with the aim to improve the quality of the bonding by adequately adjusting the process parameters.

Influence of Titanium on Microstructure, Phase Formation and Wear Behaviour of AlCoCrFeNiTi x High-Entropy Alloy.

The novel alloying concept of high-entropy alloys (HEAs) has been the focus of many recent investigations revealing an interesting combination of properties. Alloying with aluminium and titanium showed strong influence on microstructure and phase composition. However, detailed investigations on the influence of titanium are lacking. In this study, the influence of titanium in the alloy system AlCoCrFeNiTix was studied in a wide range (molar ratios x = 0.0; 0.2; 0.5; 0.8; 1.0; 1.5). Detailed studies investigating the microstructure, chemical composition, phase composition, solidification behaviour, and wear behaviour were carried out. Alloying with titanium showed strong influence on the resulting microstructure and lead to an increase of microstructural heterogeneity. Phase analyses revealed the formation of one body-centred cubic (bcc) phase for the alloy without titanium, whereas alloying with titanium caused the formation of two different bcc phases as main phases. Additional phases were detected for alloys with increased titanium content. For x ≥ 0.5, a minor phase with face-centred cubic (fcc) structure was formed. Further addition of titanium led to the formation of complex phases. Investigation of wear behaviour revealed a superior wear resistance of the alloy AlCoCrFeNiTi0.5 as compared to a bearing steel sample.

Experimental and numerical investigation on cold flat rolling processes of DC04 sheets with special focus on residual stresses

The process of cold flat rolling is a widespread industrial technique to manufacture semi-finished products, e.g., for the automotive or homewares industry. Basic knowledge of the process regarding dimensioning and adjustment of defined characteristics is already state of the art. However, a detailed consideration and analysis with respect to local inhomogeneous residual stresses in several process steps mostly remains disregarded. A broad understanding of the process due to the distribution of residual stresses in the workpiece and the direction of the stress tensors allows for a definition of the characteristics of the workpiece even before the actual manufacturing process. For that purpose, it is necessary to perform numerical investigations by means of the finite element analysis (FEA) of cold flat rolling processes. Within this contribution, several approaches for the calibration of the FEA with the real flat rolling process will be addressed and discussed. To ensure that the numerical consideration provides realistic results, this calibration is indispensable. General parameters such as geometry, height reduction, rolling temperature, process time, and the rolling speed are considered as well as a photogrammetric survey, and calculated residual stresses with results of X-ray diffraction (XRD) will be compared. In the course of the experiments, a good agreement between the stress results of the FEA and the XRD was found in the center of the specimen. In combination with the allocation of the stress orientations, the agreement close to the edges is also fine. Some issues that cause differences between the FEA and the experiment are dis-cussed.

EDS/EBSD studies and HR‐EBSD pattern analysis on pre‐Inca ceramic fragments recovered during San José de Moro Archaeology Program

Pre-Inca civilizations like the coastal cultures Moche and Nazca (Early Intermediate) and the inland culture Wari (Middle Horizon) were agrarian societies which supported indigenous elites of impressive wealth, power, and organization. With the expansion of the Wari Empire, the polychrome style and technique of Nazca propagated to the other cultures [1, 2]. High status burials, most of the Late Moche Fine Line ceramics and a large corpus of ceramics with Wari-derived decoration have been recovered in San Jose de Moro since 1991 [1]. The degree of transfer of procedures in this highly interactive scenario is of special interest: is there a limitation to decoration or is it adopted by the local potters also regarding the formulation of the ceramic bodies? In this context the relative amount, size and type of incorporated non-plastic inclusions as temper are important. Two kinds of ceramic artefacts from Peru were compared: fragments of a baker in Wari Vinaque style (Wari, Ayacucho, Peru [3]) and a canteen in Mochica Policromo style (San Jose de Moro, Jequetepeque valley, Peru [1]). Bulk composition and elemental distribution were analyzed by combined scanning electron microscopy and energy-dispersive X-ray spectroscopy on cross-sections (Fig. 1). Analyzing appropriate regions of interest in the element maps evidenced composition differences of the fired clay and the mineral inclusions (Fig. 1, 2). On principle, electron backscatter diffraction is appropriate for mineral phase analysis of the artifacts, but apart from quartz the crystallographic identification by automatic indexing commonly fails due to the micro granular aspect and the porosity of the body, weak diffraction patterns and varying composition of the feldspars. Image analysis of the Kikuchi pattern quality maps (Fig. 1) reveals the fractions of silty crystalline inclusions and of micro-pores in the clayey matrix. However, the clear crystallographic identification of non-plastic inclusions was possible by setting the electron beam at distinct crystals of interest, averaging accumulated patterns and comparing the resulting analysis with dynamical pattern simulation thereby identifying mostly quartz, ilmenite, magnetite, albite, epidote and kaersutite (Fig. 3), sanidine and apatite. Thus additional indications for the use as well as the provenience of the raw clays, the formulation of the ceramic material and the firing conditions can be provided. Keywords: pre-Inca ceramics; composition of paste; mineral phases of non-plastic inclusions

Phosphorus Distribution in Electrodeposited Ni-P-Diamond Composites Influencing Structure and Mechanical Properties

The properties of Ni-P composite coatings are related to the microstructure evolution by co-deposition of phosphorus, particle incorporation and subsequent annealing. This study focuses primarily on the effect of phosphorus content in the electrolyte on the incorporation of sub-micron diamond particles in order to understand the complex influence of Ni/Ni3P crystallization and particle embedment on Martens hardness.