Microstructure evolution in a GOES thin strip

This paper focuses on the evolution of the microstructure in a grain-oriented electrical steel (GOES) thin strip after casting. After solidification, the microstructure consisted of delta-ferrite. A small fraction of austenite was formed during the cooling of the thin strip in the two-phase region (gamma+delta). Fine Cr2CuS4 particles precipitated in the ferrite and along the delta/gamma interfaces. Laths of primary Widmanstätten austenite (WA) nucleated directly on the high-angle delta-ferrite grain boundaries. The formation of WA laths in both adjacent ferritic grains resulted in a zig-zag shape of delta-ferrite grain boundaries due to their local rotation during austenite nucleation. Based on the EBSD results, a mechanism of the formation of the zig-zag grain boundaries has been proposed. Besides the Widmanstätten morphology, austenite also formed as films along the delta ferrite grain boundaries. Sulfide precipitation along the delta/gamma interfaces made it possible to prove that austenite decomposition upon a drop in temperature was initiated by the formation of epitaxial ferrite. Further cooling brought the decay of austenite to either pearlite or a mixture of plate martensite and some retained austenite.Web of Science131art. no. 5

Acoustic emission signal characterisation of failure mechanisms in CFRP composites using dual-sensor approach and spectral clustering technique

The characterisation of failure mechanisms in carbon fibre-reinforced polymer (CFRP) materials using the acoustic emission (AE) technique has been the topic of a number of publications. However, it is often challenging to obtain comprehensive and reliable information about individual failure mechanisms. This situation was the impetus for elaborating a comprehensive overview that covers all failure mechanisms within the framework of CFRP materials. Thus, we performed tensile and compact tension tests on specimens with various stacking sequences to induce specific failure modes and mechanisms. The AE activity was monitored using two different wideband AE sensors and further analysed using a hybrid AE hit detection process. The datasets received from both sensors were separately subjected to clustering analysis using the spectral clustering technique, which incorporated an unsupervised k-means clustering algorithm. The failure mechanism analysis also included a proposed filtering process based on the power distribution across the considered frequency range, with which it was possible to distinguish between the fibre pull-out and fibre breakage mechanisms. This functionality was particularly useful in cases where it was evident that the above-mentioned damage mechanisms exhibited very similar parametric characteristics. The results of the clustering analysis were compared to those of the scanning electron microscopy analysis, which confirmed the conclusions of the AE data analysis.Web of Science151art. no. 4

Phase transformation after heat treatment of Cr-Ni stainless steel powder for 3D printing

Today, Ni-Cr steel is used for advanced applications in the high-temperature and electrical industries, medical equipment, food industry, agriculture and is applied in food and beverage packaging and kitchenware, automotive or mesh. A study of input steel powder from various stages of the recycling process intended for 3D printing was conducted. In addition to the precise evaluation of the morphology, particle size and composition of the powders used for laser 3D printing, special testing and evaluation of the heat-treated powders were carried out. Heat treatment up to 950 degrees C in an air atmosphere revealed the properties of powders that can appear during laser sintering. The powders in the oxidizing atmosphere change the phase composition and the original FeNiCr stainless steel changes to a two-phase system of Fe3Ni and Cr2O3, as evaluated by X-ray diffraction analysis. Observation of the morphology showed the separation of the oxidic phase in the sense of a brittle shell. The inner part of the powder particle is a porous compact core. The particle size is generally reduced due to the peeling of the oxide shell. This effect can be critical to 3D printing processing, causing defects on the printed parts, as well as reducing the usability of the precursor powder and can also change the properties of the printed part.Web of Science1515art. no. 534

Using of the EBSD method in structural analysis of modern metallic materials

Tato disertační práce byla vypracována v rámci vědecko - výzkumného projektu Regionální materiálově technologické výzkumné centrum na Vysoké škole báňské – Technické univerzitě Ostrava. Velká pozornost byla věnována rozvoji metodiky moderních technik strukturní a fázové analýzy, především metody difrakce zpětně odražených elektronů (EBSD) v řádkovacím elektronovém mikroskopu. Experimentální práce byly zaměřeny na dvě skupiny progresivních technických materiálů: • ultrajemnozrnný CP-Ti-1 materiál po zpracování v ECAP matrici navržené a zkonstruované v Oddělení přípravy materiálů, které je součástí projektu RMTVC. Metoda EBSD byla použita k charakterizaci strukturních parametrů experimentálního materiálu ve výchozím stavu a po 4 a 6 průchodech ECAP matricí. Studium vývoje substruktury v průběhu ECAP zpracování bylo doplněno TEM analýzou tenkých kovových fólií. • transformátorovou ocel s přísadou mědi, která je významnou součástí výrobního programu společnosti ArcelorMittal Ostrava a.s. Hlavním cílem bylo studium strukturních charakteristik plechů po různých etapách průmyslového výrobního procesu. Výsledky byly součástí řešení projektu FR–TI3–053 s názvem Zlepšení magnetických a užitných vlastností pásů z orientovaných transformátorových ocelí. Velká pozornost byla věnována analýze mikrotextury pomocí techniky EBSD a studiu vlivu přísady mědi v oceli na precipitaci inhibičních fází v průběhu výroby transformátorových plechů. Experimentální výsledky studia struktury byly porovnány s výsledky simulace termodynamicky rovnovážného stavu, které byly získány za použití software Thermocalc. Výsledky detailní strukturní analýzy těchto progresivních materiálů byly interpretovány v návaznosti na parametry aplikovaného technologického zpracování a dosažené mechanické a fyzikální vlastnosti.This dissertation thesis was prepared within the research project of the Regional Materials Science and Technology Center at the VSB – Technical University of Ostrava. Great attention was paid to the development of the methodology of modern methods of structural and phase analysis, in particular the method of electron backscattered diffraction (EBSD) in scanning electron microscope. The experimental part of this thesis was focused on two classes of progressive technical materials: • ultrafine-grained CP-Ti-1 after processing in ECAP die designed and constructed in the Department of Preparation of Materials, which is part of the project RMSTC. The EBSD method was used to characterize the structural parameters of the experimental material in the as-received state and after processing by 4 and 6 ECAP passes. The study of the evolution of the substructure during ECAP processing was supplemented by TEM analysis of thin metal foils. • grain oriented electrical steel (GOES) with an addition of copper, which is a significant part of the production program of ArcelorMittal Ostrava a.s. The main objective was to study the microstructural characteristics of the GOES sheets after the various production steps of AlN + Cu industrial route. The results were part of the solution of the FR–TI3–053 project with the name “Improvement of the Magnetic and the Useful Properties of the Sheets of Grain Oriented Electrical Steel”. Great attention was paid to analysis of microtexture using the EBSD technique and the study of influence of copper addition on precipitation processes of the inhibition phases during the production of GOES. Experimental results of the study of microstructure were compared with the results of simulation of a thermodynamically equilibrium state, obtained using the software Thermocalc. The results of the detailed structural analysis of these advanced materials have been interpreted in relation to the parameters of applied technological processing and the mechanical and physical properties achieved.636 - Katedra materiálového inženýrstvívyhově

Mikrostrukturní a mikrotexturní charakteristiky transformátorové oceli

Prezenční653- Katedra materiálového inženýrství a recyklaceNeuveden

Microstructure Evolution in a GOES Thin Strip

This paper focuses on the evolution of the microstructure in a grain-oriented electrical steel (GOES) thin strip after casting. After solidification, the microstructure consisted of delta-ferrite. A small fraction of austenite was formed during the cooling of the thin strip in the two-phase region (gamma+delta). Fine Cr2CuS4 particles precipitated in the ferrite and along the delta/gamma interfaces. Laths of primary Widmanstätten austenite (WA) nucleated directly on the high-angle delta-ferrite grain boundaries. The formation of WA laths in both adjacent ferritic grains resulted in a zig-zag shape of delta-ferrite grain boundaries due to their local rotation during austenite nucleation. Based on the EBSD results, a mechanism of the formation of the zig-zag grain boundaries has been proposed. Besides the Widmanstätten morphology, austenite also formed as films along the delta-ferrite grain boundaries. Sulfide precipitation along the delta/gamma interfaces made it possible to prove that austenite decomposition upon a drop in temperature was initiated by the formation of epitaxial ferrite. Further cooling brought the decay of austenite to either pearlite or a mixture of plate martensite and some retained austenite

Hot deformation behaviour and microstructure evolution of TiAl-based alloy reinforced with carbide particles

The hot deformation behaviour and microstructure evolution of TiAl-based alloy with nominal composition TT 43Al-8Nb-3.6C-0.7Mo (at.%) reinforced with carbide particles were studied. The compression tests were carried out in the temperature range from 900 to 1000 degrees C and strain rates from 0.0001 to 0.01 s(-1) up to a true strain of 0.5. The microstructure of the compression specimens was characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). The work hardening stage of the flow curves results from an increment of the dislocation density and deformation twins. The work softening of the composite results from the dynamic recovery (DRV), dynamic recrystallization (DRX) and fragmentation of some coarse Ti2AlC particles. The size of recrystallised grains increases with decreasing Zener-Hollomon parameter. The non-uniform distribution of local strains in the deformed specimens and deformation temperature affect the orientation and fragmentation of coarse Ti2AlC particles. A constitutive model predicting hot deformation behaviour of the studied alloy is proposed and its validity is evaluated and discussed.Web of Science127art. no. 10696

Microstructure Evolution in a GOES Thin Strip

This paper focuses on the evolution of the microstructure in a grain-oriented electrical steel (GOES) thin strip after casting. After solidification, the microstructure consisted of delta-ferrite. A small fraction of austenite was formed during the cooling of the thin strip in the two-phase region (gamma+delta). Fine Cr2CuS4 particles precipitated in the ferrite and along the delta/gamma interfaces. Laths of primary Widmanstätten austenite (WA) nucleated directly on the high-angle delta-ferrite grain boundaries. The formation of WA laths in both adjacent ferritic grains resulted in a zig-zag shape of delta-ferrite grain boundaries due to their local rotation during austenite nucleation. Based on the EBSD results, a mechanism of the formation of the zig-zag grain boundaries has been proposed. Besides the Widmanstätten morphology, austenite also formed as films along the delta-ferrite grain boundaries. Sulfide precipitation along the delta/gamma interfaces made it possible to prove that austenite decomposition upon a drop in temperature was initiated by the formation of epitaxial ferrite. Further cooling brought the decay of austenite to either pearlite or a mixture of plate martensite and some retained austenite

The effect of long-term ageing at 475 degrees C on microstructure and properties of a precipitation hardening martensitic stainless steel

The effect of long-term ageing (1000, 2000, and 3000 h) at 475 degrees C on mechanical properties, microstructure, and substructure of CUSTOM 465 (R) maraging stainless steel was studied. The additional precipitation of nanometric particles of eta-Ni3Ti phase in partly recovered lath martensite and decomposition of the BCC solid solution accompanied by the formation of nanometric Cr-rich alpha'particles were identified. The fraction of reverted austenite in the final microstructure gradually increased with time of ageing at 475 degrees C. Ageing resulted in a gradual slight decline (up to 10%) in yield strength, ultimate tensile strength, and hardness. On the other hand, for all ageing, dwells ductility and impact energy values remained almost unchanged. The reason for this phenomenon lies in the gradual increase in the fraction of reverted austenite during long-term ageing at 475 degrees C and at the same time in the sluggish kinetics of microstructural changes in lath martensite. No susceptibility to 475 degrees C embrittlement was proved.Web of Science1210art. no. 164