Investigating thermally activated deformation mechanisms by high temperature nanoindentation – A Study on W-Re alloys

Since the advent of indentation at elevated temperatures the technique of high-temperature nanoindentation has been further developed, currently enabling testing temperatures above 1000 °C. Due to small sample sizes and a variety of different testing techniques this method provides the opportunity for alloy development at a new level regarding composition variety or efficiency. In this study the thermally activated deformation mechanisms in binary W-Re alloys will be investigated by using a high-end in-situ nanoindenter. For that purpose, three different materials were tested, namely commercially pure W, W5Re and W10Re, all of them in both, coarse grained and ultra-fine grained condition. Nanoindentation experiments were conducted from ambient temperatures up to 800 °C, thereby overcoming the critical temperature TC of tungsten at around 450 °C. With temperature increments of 100 °C a large range of the normalized temperature with respect to TC is covered, allowing general conclusions regarding the appearing deformation mechanisms in bcc metals. Additionally to constant indentation strain rate tests, strain rate jump tests were utilized to determine the mechanical properties and to evaluate the impact of temperature and microstructure on rate-dependent parameters. A strong influence of the alloying level with Re as well as the grain size on both, the thermal and athermal contribution to the flow stress, is observed. The origin and effects, such as solid solution softening for W5Re at temperatures far below TC, will be discussed in detail. Furthermore, the dominating deformation mechanisms in dependence of temperature and grain size are determined. In the coarse grained materials a change in deformation processes from kink-pair mechanism to dislocation-dislocation interaction at higher temperatures can be observed, while in ultra-fine grained materials grain boundary/dislocation interactions are responsible for the maintained time-dependent mechanical behavior

Implementation of a Wiki-based Information and Communication System for Academia Europaea

In recent years, online collaboration tools such as wikis have experienced a tremendous expansion. Their success and popularity is due to their simple and efficient content creation facilities. Moreover, the formatting syntax is basically easy to learn allowing users to easily create and edit web content and thus share knowledge with each other.Despite these advantages, the content creation process is still obscure if authors belong to a computer inexperienced user group. In this paper we present our experiences, challenges, and problems with a specific application of a wiki-based system called the Academia Europaea Information and Communication System. Furthermore, key solutions for bypassing user interaction barriers are discussed throughout this paper

Microstructure Evolution of a New Precipitation-Strengthened Fe–Al–Ni–Ti Alloy down to Atomic Scale

Ferritic materials consisting of a disordered matrix and a significant volume fraction of ordered intermetallic precipitates have recently gained attention due to their favorable properties regarding high-temperature applicability. Alloys strengthened by Heusler-type precipitates turned out to show promising properties at elevated temperatures, e.g., creep resistance. The present work aims at developing a fundamental understanding of the microstructure of an alloy with a nominal composition of 60Fe–20Al–10Ni–10Ti (in at. %). In order to determine the microstructural evolution, prevailing phases and corresponding phase transformation temperatures are investigated. Differential thermal analysis, high-temperature X-ray diffraction, and special heat treatments were performed. The final microstructures are characterized by means of scanning and transmission electron microscopy along with hardness measurements. Atom probe tomography conducted on alloys of selected heat-treated conditions allows for evaluating the chemical composition and spatial arrangement of the constituent phases. All investigated sample conditions showed microstructures consisting of two phases with crystal structures A2 and L21. The L21 precipitates grew within a continuous A2 matrix. Due to a rather small lattice mismatch, matrix–precipitate interfaces are either coherent or semicoherent depending on the cooling condition after heat treatment

Exploring the mechanical character of molybdenum grain boundaries via nanoindentation and three-point-bending

The interactions of interfaces with dislocations have been extensively studied in the past. Still, there is a lack of high throughput methods, which can potentially be used for systematic studies to cover a wide range of grain boundary types. Nanoindentation offers the opportunity to combine a high spatial resolution with high effectiveness, thus enabling to obtain comprehensive mechanical data in the vicinity of grain boundaries. The present study on coarse-grained molybdenum will show results of mechanical property mapping near grain boundaries. Here, for the first time also the indenter tip rotation angle with respect to the loading axis as well as the grain orientation are considered. Results will show that neglecting these parameters can bias interpretations of the interface/dislocation interactions, as the localized deformation paths around the indentation are thereby significantly changed. Systematic experiments on commercially pure, recrystallized molybdenum have been performed to investigate the dependence of the hardness increase near grain boundaries with respect to the boundary misorientation angle. As a complementary method, three-point-bending is applied on mm-sized specimens until individual grain boundaries delaminate, which in turn will be identified and cross-checked with findings of the nanoindentation tests. Doping molybdenum with elements like carbon and/or boron is known to suppress intercrystalline failure. For this reason, the presented grain boundary characterization methods will be applied to extract mechanical changes caused by these doping elements

Bioenergy production and sustainable development: Science base for policymaking remains limited

The possibility of using bioenergy as a climate change mitigation measure has sparked a discussion of whether and how bioenergy production contributes to sustainable development. We undertook a systematic review of the scientific literature to illuminate this relationship and found a limited scientific basis for policymaking. Our results indicate that knowledge on the sustainable development impacts of bioenergy production is concentrated in a few well‐studied countries, focuses on environmental and economic impacts, and mostly relates to dedicated agricultural biomass plantations. The scope and methodological approaches in studies differ widely and only a small share of the studies sufficiently reports on context and/or baseline conditions, which makes it difficult to get a general understanding of the attribution of impacts. Nevertheless, we identified regional patterns of positive or negative impacts for all categories – environmental, economic, institutional, social and technological. In general, economic and technological impacts were more frequently reported as positive, while social and environmental impacts were more frequently reported as negative (with the exception of impacts on direct substitution of GHG emission from fossil fuel). More focused and transparent research is needed to validate these patterns and develop a strong science underpinning for establishing policies and governance agreements that prevent/mitigate negative and promote positive impacts from bioenergy production

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements