Nanostructuring of an additively manufactured CoCrFeNi multi-principal element alloy using severe plastic deformation

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Statističke analogije između potresa, mikropotresa u metalima i lavina u 1D Burridge-Knopoff modelu

Universalities and intriguing analogies in the statistics of avalanches are revealed for three physical systems defined on largely different length and energy scales. Earthquakes induced by tectonic scale dynamics, micro-scale level quakes observed from slipping crystallographic planes in metals and a one-dimensional, room-scale spring-block type Burridge-Knopoff model is studied from similar statistical viewpoints. The validity of the Gutenberg-Richter law for the probability density of the energies dissipated in the avalanches is proven for all three systems. By analysing data for three different seismic zones and performing acoustic detection for different Zn samples under deformation, universality for the involved scaling exponent is revealed. With proper parameter choices the 1D Burridge-Knopoff model is able to reproduce the same scaling law. The recurrence times of earthquakes and micro-quakes with magnitudes above a given threshold present again similar distributions and striking quantitative similarities. However, the 1D Burridge-Knopoff model cannot account for the correlations observed in such statistics.Univerzalnosti i intrigantne analogije u statistici lavina otkrivene su za tri fizička sustava definirana na uvelike različitim duljinama i energijskim skalama. Potresi uzrokovani dinamikom na tektonskoj skali, mikro-potresi koji nastaju na klizećim kristalografskim ravnina u metalima i jednodimenzionalni Burridge-Knopoffov model opruga i blokova na skali sobe proučeni su sa sličnih statističkih stajališta. Valjanost Gutenberg-Richterove relacije za gustoću vjerojatnosti energija disipirane u lavinama dokazana je za sva tri sustava. Analizom podataka za tri različita seizmički aktivna područja i detekcijom akustičkih valova za različite uzorke Zn pod deformacijom, otkrivena je univerzalnost za uključeni eksponent skaliranja. S pravilnim izborom parametara 1D Burridge-Knopoffov model može reproducirati isti zakon skaliranja. Vremena ponavljanja potresa i mikropotresa s magnitudama iznad zadanog praga opet predstavljaju slične distribucije i zapanjujuće kvantitativne sličnosti. Međutim, 1D Burridge-Knopoffov model ne može objasniti korelacije opažene u takvim statistikama

Interpretation of certain features of the interface stress vs. electrode potential curves of gold with the help of dual dynamic voltammetry

It is a widespread opinion that the electrochemical behavior of gold in aqueous media has been thoroughly studied, and the interface stress changes of gold can be explained by monolayer oxide formation/removal and adsorption phenomena. However, in spite of the voluminous literature on this subject, an understanding of these systems and processes is far from complete. The combination of in-situ interface stress measurements and dual dynamic voltammetry brings new insights into the complexity of such systems. One remarkable result is that in the oxide reduction region of gold in sulfuric acid solutions a sudden change in the slope of the interface stress vs. electrode potential curve recorded during the negative-going scan of the cyclic voltammogram can be observed. By applying the dual dynamic voltammetric method to a gold/gold rotating ring-disk electrode (RRDE) it could be shown that the sharp change in the slope of the surface stress vs. potential curve recorded in the oxide reduction region of gold in sulfuric acid solutions is accompanied by the formation of soluble, electrochemically reducible gold species which can be detected at the ring electrode. © The Electrochemical Society

A Sequence of Phase Transformations and Phases in NiCoFeCrGa High Entropy Alloy

The present investigation is directed to phase transitions in the equimolar NiCoFeCrGa high entropy alloy, which is a mixture of face-centered cubic (FCC) and body-centered cubic (BCC) crystalline phases. The microstructure of the samples was investigated by using scanning electron microscopy (SEM), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), transmission electron microscopy-based energy-dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS), as well as X-ray diffraction (XRD) measurements. Based on the phases observed in different temperature ranges, a sequence of the phase transitions can be established, showing that in a realistic process, when freely cooling the sample with the furnace from high to room temperature, a microstructure having spinodal-like decomposition can also be expected. The elemental mapping and magnetic behaviors of this decomposed structure are also studied

The metastable states of some amorphous Fe-B alloys

The interdependence of the electronic and thermal properties and their effect on the stability of some Fe86.5-xTMxB13.5 (TM is transition metal, 0 less-than-or-equal-to x less-than-or-equal-to 5) alloys is investigated. Differential thermoanalysis and soft X-ray fluorescent spectroscopy were used to measure the thermodynamic phase changes and the partial electronic density of states, respectively. A general role of the electronic effects on the thermal stability is suggested from the trend of the measured data. It is concluded that the thermal stability is effectively controlled by the actual electronic structure of the alloy

The metastable states of some amorphous Fe-B alloys

The interdependence of the electronic and thermal properties and their effect on the stability of some Fe86.5-xTMxB13.5 (TM is transition metal, 0 less-than-or-equal-to x less-than-or-equal-to 5) alloys is investigated. Differential thermoanalysis and soft X-ray fluorescent spectroscopy were used to measure the thermodynamic phase changes and the partial electronic density of states, respectively. A general role of the electronic effects on the thermal stability is suggested from the trend of the measured data. It is concluded that the thermal stability is effectively controlled by the actual electronic structure of the alloy

Statistical properties of fractal type dislocation cell structures

International audienceThe dislocation microstructure developing during plastic deformation strongly influences the stress-strain properties of crystalline materials. Resent theoretical investigations based on the 2D continuum theory of straight parallel edge dislocations were able to predict a periodic dislocation microstructure. The results obtained, however, can only be considered as a very first step toward the understanding of the origin of dislocation patterning. One of the most challenging problems is the modeling of the formation of the fractal like dislocation microstructure. So, it is crucial to determine the statistical properties of such a structure developing at ideal multiple slip orientation. In the paper, by x-ray line profile analysis and the method of high resolution electron backscatter diffraction (HR-EBSD) a complex experimental characterization of dislocation microstructure developing in uniaxially compressed Cu single crystals is presented. With these methods, the maps of the internal stress, the Nye tensor, and the geometrically necessary dislocation (GND) density were determined at different load levels. It is found from the fractal analysis of the GND maps that the fractal dimension of the cell structure is decreasing with increasing average spatial dislocation density fluctuation. Moreover, it is shown that the evolution of different types of dislocations can be successfully monitored with the HR-EBSD-based technique