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Fracture behaviour of high-chromium 9% and 14% Cr-Mo and Cr-W steels
Hadraba, Hynek ; Stratil, Luděk ; Kazimierzak, B. ; Fournier, B. ; Dlouhý, Ivo
The paper describes the influence of the microstructure (coming from the chemical composition and extrusion shape) of 9 and 14%Cr- W(Mo)-Ti-Y2O3 ODS steels prepared by mechanical alloying and subsequent hot-extrusion on their impact properties. The chemical composition and corresponding microstructure plays a major role on the impact properties. 9Cr-2W ferritic-martensitic steel present lower upper shelf energy (USE) about 7 J and a lower ductile to brittle transition temperature (DBTT) about -30°C compared to 14Cr-1W ferritic steel one. The transition energy curves of low-activation ferritic 14Cr-1W ODS steel was shifted by about 50°C toward lower temperatures and USE by about 4 J towards higher energies. The extrusion shape also plays a role on the impact properties. The texture caused by the forming process strongly influenced the impact behaviour of the steels. The extensive splitting of the fracture surfaces of plate shaped steel comparing with steels extruded as bar was found.
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Fracture behaviour of ceramic laminates with strong linked layers
Chlup, Zdeněk ; Slabáková, Lenka ; Drdlík, D. ; Hadraba, Hynek ; Dlouhý, Ivo
Multi-component ceramics materials having layered structure possess potential to be more convenient than monolithic ones. Depending on design a number of laminated structures can be distinguished. The most common division is by behaviour of layer interface i.e. with strong or weak interfaces. In this contribution the fracture behaviour of the laminates with strong interface allowing creation of residual stresses within layers will be described. Presence of residual stresses can enhance fracture properties. The alumina and zirconia were the components and electrophoretic deposition was used to prepare the laminate. Fracture behaviour was investigated using three point bending test of SEVNB specimens. Fracture surfaces were reconstructed and crack propagation changes were determined. Influence of residual stresses on fracture behaviour was found and described.
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Prediction of Fracture Toughness Transition from Tensile Test Parameters Applying Artificial Neural Networks
Dlouhý, Ivo ; Hadraba, Hynek ; Chlup, Zdeněk ; Kozák, Vladislav ; Šmida, T.
Reference temperature localizing the fracture toughness temperature diagram on temperature axis was predicted based on tensile test data. Regularization artificial neural network (ANN) was adjusted to solve the interrelation of these properties. For analyses, 29 data sets from low-alloy steels were applied. The fracture toughness transition dependence was quantified by means of master curve concept enabling to represent it using one parameter - reference temperature. Different strength and deformation characteristics from standard tensile specimens and notched specimens, instrumented ball indentation test etc. have been applied. A very promising correlation of predicted and experimentally determined values of reference temperature was found.
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Microstructure and impact response of high-chromium ODS steels
Hadraba, Hynek ; Fournier, B. ; Stratil, Luděk ; Dlouhý, Ivo
A new class of ODS steels alloyed by Cr and W is developed as a high temperature structural material for prospective power sources, the fission reactors of IV generation and the fusion reactors. The aim of the work was to investigate the influence of microstructure on the fracture properties of ODS (9-18)Cr-W-Ti-Y2O3 steels. It was found that the increasing in the Cr and W content brought to the steels strength at elevated temperatures and increased upper shelf energy level and shifted transition region towards lower temperatures. The increase in the yttria content led to the decreasing the upper shelf energy and shifted the TDBTT towards higher temperatures. The impact energy of rolled ODS sheet depended strongly on the fracture plane orientation regarding to the rolling direction. The splitting edges profile changed according to the sample orientation and thus the energy portion consumed for the shearing was changed.
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Influence of surface hardening on fracture behaviour of steels
Dlouhý, Ivo ; Chlup, Zdeněk ; Hadraba, Hynek
The paper is focused on the phenomena associated with fracture in surface layer produced by three different procedures. Standard cementing, nitriding and surface hardening were applied onto surfaces of six low alloy structural steels. For fracture behaviour evaluation Charpy type specimen with U notch were applied the surface of the notch radius was hardened too. The samples were loaded by means of an instrumented impact pendulum. The evaluation and classification of different fracture behaviour modes have been based on evaluation of load – flexure traces supported by fractographic analysis. Knowledge obtained were summarised into general schematics of failure modes. As the most detrimental for the fracture resistance the surface cementing was found. The surface hardening showed the minimal negative effect on crack initiation and relatively small fracture resistance decrease.
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The properties of Eurofer´97 steel for developed fusion and fission reactors
Stratil, Luděk ; Hadraba, Hynek ; Dlouhý, Ivo
Ferritic martensitic steel show limited swelling and susceptibility to helium effects and can be made from low activation composition. These properties made them the reference steel for the development of breeding blankets in fusion power plants and also for components of fission power plants. Eurofer´97 is presently being characterized in the EU in order to obtain design data for blanket modules to be tested in International Thermonuclear Experimental Reactor (ITER). In this contribution metallurgical (microstructural and mechanical) properties and thermal thermal treatment for such applications are briefly introduced.
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Lomové chování oceli EUROFER´97 po tepelném stárnutí
Hadraba, Hynek ; Dlouhý, Ivo
Eurofer´97 steel is candidate structural material for in-vessel components of proposed fusion reactors. The use of the steel is limited up to a temperature about 550 °C. On the other hand the efficiency enhancement of the fusion reactors to the level suitable for energy production is predetermined by an increase of temperature in reactor. The long term exposition of the steel at high temperatures leads to microstructural changes. The aim of the work was to investigate the influence of short and long term thermal ageing on fracture properties of Eurofer´97 steel. Short term thermal ageing of the steel was simulated by step-cooling treatment and long term thermal ageing was simulated by isothermal annealing treatment at 550 °C/5000 h. No evident changes in impact properties have been registered comparing the properties of the steel in as-received state and in state after step-cooling. Outstanding embrittlement of the thermally aged steel was observed after long term isothermal ageing.
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Lomové chování RAFM oceli Eurofer´97 po tepelném stárnutí
Hadraba, Hynek ; Dlouhý, Ivo
Eurofer´97 steel is candidate structural material for in-vessel components of proposed fusion reactors. The use of the steel is limited up to a temperature about 550 °C. The aim of the work was to investigate the influence of short and long term thermal ageing on fracture properties of Eurofer´97 steel. Short term thermal ageing of the steel was simulated by step-cooling treatment and long term thermal ageing was simulated by isothermal annealing. No evident changes in impact properties have been registered comparing the properties of the steel in as-received state and in state after step-cooling. Outstanding embrittlement of the thermally aged steel was observed after long term isothermal ageing. Risk of grain boundary weakening by phosphorus segregation is very low while the carbide coarsening could led to outstanding embrittlement of the Eurofer´97 steel.
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Lomová houževnatost a mechanismy porušování intermetalika na bázi TiAl
Dlouhý, Ivo ; Chlup, Zdeněk ; Hadraba, Hynek ; Kozák, Vladislav
The paper is focused on the analysis of the role of microstructure in fracture performance of TiAl intermetalics at room and elevated temperatures. Tensile properties, flexural strength and fracture toughness have been evaluated for Ti-40Al-2Cr-2Nb-1B and Ti-46Al-0,7Cr-0,1Si-7Nb-0,2Ni alloys. Positive Nb effect on fracture resistance was found; fracture toughness of the high Nb alloy was increased at contemporary increase of tensile and flexural strength. Fracture surfaces were evaluated using scanning electron microscopy showing the key role of mechanical twinning in deformation of both alloys. As a governing mechanism of the crack initiation a microcrack nucleation at boundaries between -TiAl grains was confirmed. Based on findings obtained key aspects of the effect of separate microstructural components have been discussed. Summary of toughening effects acting in this group of intermetalics has been provided.
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