Local fatigue characterisation of ARB processed copper sheets by dynamic micropillar compression

Local fatigue experiments on microscale samples offer the opportunity to isolate microstructural contributions to the mechanical deformation behavior. In contrast to macroscopic fatigue testing, it is therefore possible to independently characterize the effect of individual defects, as for example grain boundaries. In this study accumulative roll bonding (ARB) architectured copper sheets with a bimodal microstructure were analyzed (Figure 1). Micropillars were fabricated by FIB milling inside individual layers of the material. Due to the bimodal microstructure, they exhibit two extremely different grain sizes, which results in a change of the respective fatigue properties. Additionally micropillars were fabricated at the interface in order to study the interfacial contribution to the fatigue behavior. The investigations were performed by a novel approach that combines dynamic nanoindentation and micropillar compression [1]. With this technique the high cycle fatigue range is easily accessible for microscale samples. Observation of the underlying deformation processes was performed by recording SEM micrographs of the deformed samples. FIB cross-sectioning of the deformed samples was used to investigate the deformed microstructure in the bulk of the specimens. Please click Additional Files below to see the full abstract

Mechanical testing of twinned copper and copper alloy micropillars

Nanotwinned metals are a promising class of modern materials combining a very high strength and ductility with excellent electrical properties. Their remarkable strength is connected to the high effectiveness of twin boundaries as obstacles to dislocation motion. In order to further characterize these interactions, micropillars containing single coherent twin boundaries with different orientations were compressed with a flat punch and subsequently investigated in the scanning electron microscope. The crystal orientations for compression were selected to activate different slip modes. The aim is to probe the different barrier effects that can act on gliding dislocations. The investigations concentrated on copper and α-brass. The latter is a low stacking-fault energy alloy exhibiting a high density of recrystallization twins. Coherent twin boundaries were selected from an EBSD orientation mapping of the sample and oriented by means of a custom sample holder. FIB-milling at these interfaces yielded micropillar samples containing a single twin boundary. Single crystal reference samples were obtained from the bulk of the grain located on both sides of the twin boundary. The microcompression tests enabled the quantification of the influence of the twin boundary barrier on the strength of each sample. The tests evidenced a strong dependency of the strength of the sample on crystal orientation and stacking-fault energy. The activated glide systems were subsequently identified from slip trace analysis and STEM mapping of lamellas obtained by FIB lift-out from the bulk of the tested micropillars. Please click Additional Files below to see the full abstract

Mechanical testing of copper and copper alloy micropillars containing a single twin boundary

Nanotwinned metals are a promising class of modern materials combining a very high strength with a high ductility and excellent electrical properties. This remarkable strength is believed to be connected to the good efficiency of twin boundaries as obstacles to dislocation motion. The present study aims at identifying and characterizing the possible interaction modes between dislocations and coherent twin boundaries. This is achieved by compressing micropillars containing a single twin boundary of a controlled orientation. The influence of the stacking fault energy on the intrinsic strength of the twin boundary is also investigated by varying the investigated material. In detail, the micropillars are fabricated from recrystallized polycrystalline samples of copper and α-brass, which is a low stacking-fault energy alloy exhibiting a high density of recrystallization twins. Coherent twin boundaries are selected from an EBSD orientation mapping of the sample and oriented by means of a custom 3D-printed sample holder. FIB-milling at these interfaces yields micropillar specimens containing a single twin boundary. Single crystalline reference samples are obtained from the bulk of the grains located on both sides of the twin boundary. The microcompression tests allow quantifying the influence of the twin boundary barrier on the strength of the sample as a function of the stacking fault energy of the material. The activated glide systems are subsequently identified from slip trace analysis and STEM mapping of lamellas obtained by lift-off from the bulk of the tested micropillars. This allows identifying the different deformation modes, which will be discussed in the presentation

Structural reorientation and compaction of porous MoS2 coatings during wear testing

Industrial upscaling frequently results in a different coating microstructure than the laboratory prototypes presented in the literature. Here, we investigate the wear behavior of physical vapor deposited (PVD) MoS2 coatings: A dense, nanocrystalline MoS2 coating, and a porous, prismatic-textured MoS2 coating. Transmission electron microscopy (TEM) investigations before and after wear testing evidence a crystallographic reorientation towards a basal texture in both samples. A basal texture is usually desirable due to its low-friction properties. This favorable reorientation is associated to a tribological compaction of the porous specimens. Following running-in, sliding under high contact pressure ultimately leads to a wear rate as small as for an ideal chemical vapor deposited (CVD) grown bulk MoS2 single crystal reference. This suggests that the imperfections of industrial grade MoS2 coatings can be remediated by a suitable pretreatment

A Privacy-aware Data Access System for Automotive Applications

The introduction of Information technology (IT) in modern vehicles enables a plethora of new applications ranging from value added services up to autonomous driving vehicles. However, this also introduces new threats with regard to IT security and privacy. In this paper, we discuss the new privacy issues and propose a privacy-aware data access system for automotive applications. Our system informs the user over all privacy aspects and enables him to control third-party access to his personal data. We developed an easily usable human machine interface (HMI) and an underlying policy system to control data flows which is compliant to the European General Data Protection Regulation (GDPR). Our system can be easily integrated in future automotive architectures

Population estimation in urban areas based on "mixed/cross" stereo models

In the project X3D4Pop we investigate if "mixed" satellite image pairs acquired on two different dates can be used to calculate meaningful building heights in urban areas. Based on These results, the dependency of urban population estimation models on the availability and quality of 3D data is tested. Study areas are Port-au-Prince and Salzburg. The 3D-models are validated against LiDAR-derived elevation models, population numbers are compared with rastered population data from Statistik Austria. The project explores first steps towards an urban population estimation Service by remote sensing, for the humanitarian community