Showing papers by "Miroslav Karlík published in 2021"
TL;DR: In this paper, the authors developed a mathematical method for the fundamental understanding of the deformation mechanisms in metallic multilayers subjected to radiation damage, where the cumulative strain within a layer is described as the combination of two contributions coming from the interfacial region and the inner region of the layers.
20 citations
TL;DR: In this article, the authors showed that the blistering efficiency in He-H-ions co-implanted and annealed InP has been found to peak and vanish in a narrow range of ion fluence ratio (ΦH/ΦHe+/cm2).
9 citations
TL;DR: In this paper, the authors characterize the transformation processes in a superelastic nickel-titanium SMA wire subjected to a force-controlled tensile cycle and estimate the intrinsic dissipation heat associated with the nucleation and merging events.
Abstract: Shape memory alloys (SMAs) are phase transforming materials featuring strong thermomechanical couplings. Infrared thermography and heat source reconstruction (HSR) enable to track the calorific signature of deformation processes. The objective was to characterize the transformation processes in a superelastic nickel-titanium SMA wire subjected to a force-controlled superelastic tensile cycle. In-situ recorded thermographs were converted into spatiotemporal maps of heat sources using an in-house developed post-processing method based on the heat diffusion equation resolved numerically for unknown heat sources. Sequentially appearing patterns of localized transformation events of four types were identified and associated with martensite bands nucleations and their subsequent merging upon tensile loading. Analogically, the events associated with austenite bands nucleations and their subsequent merging were identified upon unloading. In addition, weak heat sources observed before and after the localized transformation events were associated with the homogeneous martensitic transformation. The intrinsic dissipation heat associated with the nucleation and merging events is estimated to be ~ 25% of the released/absorbed latent heat.
8 citations
TL;DR: In this article, a W-Cr solid solution is used as an intermediate step to produce ultrafine-grained composite alloys with rod-like microstructural features, and a significant increase in strength can be achieved without an increase in hardness using this top-down material design.
4 citations
TL;DR: In this article, fracture toughness and fatigue crack growth rates of free-standing thick W deposits produced in a protective atmosphere using radio frequency inductively-coupled plasma process were investigated and the results showed that the deposits had significantly lower stress-strain properties: the elastic modulus and tensile strength ranged from 30% to 50% of the reference bulk values.
Abstract: Fracture toughness and fatigue crack growth rates of free-standing thick W deposits produced in a protective atmosphere using radio frequency inductively-coupled plasma process were investigated. Stress-strain behavior of the deposits was studied using four-point bending and their fracture toughness was estimated from three-point bending following the ASTM E1820 standard. The fatigue crack growth rates were measured in symmetrical bending using a resonance approach. The results were compared with commercially available bulk tungsten prepared by powder metallurgy that served as a reference. The results showed that the deposits had significantly lower stress-strain properties: the elastic modulus and tensile strength ranged from 30% to 50% of the reference bulk values. The crack growth rate tests together with fractographic analysis suggested that a static failure by inter-granular decohesion predetermines the fatigue properties of the deposits and causes high slopes of the corresponding fatigue crack growth rate curves. Contrary to this, the reference sheet failed trans-granularly. The inter-granular failure mode of the deposits was caused by grain boundary embrittlement, a phenomenon probably related to oxides. The lowest obtained oxygen concentration in deposit was nearly by two orders of magnitude higher, than in reference sheet. The distribution of oxygen was studied by TEM and the amorphous and crystalline oxide phases were identified at splat interfaces. The presence of oxygen in the deposits produced by the inherently non-oxidizing RF technology calls for control of oxygen content in the feedstock powder. The performed characterization provided baseline data of mechanical and fatigue properties of RF plasma sprayed tungsten.
2 citations
TL;DR: In this article, the microstructure and mechanical properties of the so-called Cantor alloy composed of Co, Cr, Fe, Mn, and Ni in equiatomic ratios prepared by various techniques (casting, melt-spinning, spark plasma sintering) were examined.
Abstract: High entropy alloys (HEAs) are materials of great application potential and which have been extensively studied during the last two decades. As the number of possible element combinations is enormous, model materials representing certain groups of HEAs are used for the description of microstructure, properties, and deformation mechanisms. In this study, the microstructure and mechanical properties of the so-called Cantor alloy composed of Co, Cr, Fe, Mn, and Ni in equiatomic ratios prepared by various techniques (casting, melt-spinning, spark plasma sintering) were examined. The research focused on the indentation measurements, namely, the indentation size effect describing the evolution of the hardness with penetration depth. It was found that the standard Nix–Gao model can be used for this type of alloy at higher penetration depths and its parameters correlate well with microstructural observations. The Nix–Gao model deviates from the measured data at the submicrometer range and the applied modification affords additional information on the deformation mechanism.
1 citations
TL;DR: In this paper, the authors expressed their gratitude to the Czech Science Foundation and Engineering and Physical Sciences Research Council for funding received through the projects 14-32801P and EP/K005103/1, respectively.
Abstract: E.F. and T.P. wants to express their gratitude to the Czech Science Foundation and Engineering and Physical Sciences Research Council for funding received through the projects 14-32801P and EP/K005103/1, respectively. Furthermore, E.F. wants to give thanks to the program COMPETE - Programa Operacional Factores de Competitividade: POCI-01-0145-FEDER-030416- and by national funds through FCT – Fundacao para a Ciencia e a Tecnologia -, under the project UIDB/00285/2020, and to CENIM's X-ray laboratory for the support given on the analysis of XRD patterns. Finally, M.K. and T.P. would like to acknowledge the financial support of the European Regional Development Fund in the frame of the projects No. CZ.02.1.01/0.0/0.0/15-003/0000485 and CZ.02.1.01/0.0/0.0/16-019/0000778, respectively.