|
|
High Temperature Deformation Mechanisms
Heczko, Milan ; Gröger,, Roman (oponent) ; Spätig, Philipp (oponent) ; Kruml, Tomáš (vedoucí práce)
Two advanced highly-alloyed austenitic steels based on the Fe-Ni-Cr matrix were studied in conditions of low cycle fatigue both at room and elevated temperature. Extensive set of experimental and characterization tools was used for the investigation of inter-related effects of alloys composition, microstructure, deformation mechanisms and overall material response under load. Key mechanisms and factors determining mechanical properties and performance in the service were analysed and discussed in the relation to the materials design. • Standard fatigue experiments were performed at room temperature and at 700°C. Cyclic hardening/softening curves, cyclic deformation stress-strain curves, Coffin-Manson and Wöhler fatigue life curves were determined. • Various characterization techniques of electron microscopy were used to study changes of the microstructural state of the alloys due to the cyclic loading at room and elevated temperatures. • Fatigue behaviour, strength and cyclic plastic response of studied materials were explained in relation to the microstructure and microstructural aspects of deformation mechanisms both at room and elevated temperatures. • It was found that Sanicro 25 exhibits the highest high temperature strength of all alloys from the same class. Its extraordinary properties are related to the two nanoparticle populations, Cu-rich coherent precipitates and dispersoid-like MX nanoparticles, which play fundamental role in the determination of strength and overall cyclic response. As a result of pinning effects and associated obstacles, dislocation motion in this alloy is significantly retarded preventing formation of substructures with lower stored internal energy. With recovery heavily suppressed, forest dislocation strengthening supported by precipitation and solid solution hardening, leads to the remarkable increase of cyclic strength at elevated temperatures.
|
|
|
High Temperature Deformation Mechanisms
Heczko, Milan ; Gröger,, Roman (oponent) ; Spätig, Philipp (oponent) ; Kruml, Tomáš (vedoucí práce)
Two advanced highly-alloyed austenitic steels based on the Fe-Ni-Cr matrix were studied in conditions of low cycle fatigue both at room and elevated temperature. Extensive set of experimental and characterization tools was used for the investigation of inter-related effects of alloys composition, microstructure, deformation mechanisms and overall material response under load. Key mechanisms and factors determining mechanical properties and performance in the service were analysed and discussed in the relation to the materials design. • Standard fatigue experiments were performed at room temperature and at 700°C. Cyclic hardening/softening curves, cyclic deformation stress-strain curves, Coffin-Manson and Wöhler fatigue life curves were determined. • Various characterization techniques of electron microscopy were used to study changes of the microstructural state of the alloys due to the cyclic loading at room and elevated temperatures. • Fatigue behaviour, strength and cyclic plastic response of studied materials were explained in relation to the microstructure and microstructural aspects of deformation mechanisms both at room and elevated temperatures. • It was found that Sanicro 25 exhibits the highest high temperature strength of all alloys from the same class. Its extraordinary properties are related to the two nanoparticle populations, Cu-rich coherent precipitates and dispersoid-like MX nanoparticles, which play fundamental role in the determination of strength and overall cyclic response. As a result of pinning effects and associated obstacles, dislocation motion in this alloy is significantly retarded preventing formation of substructures with lower stored internal energy. With recovery heavily suppressed, forest dislocation strengthening supported by precipitation and solid solution hardening, leads to the remarkable increase of cyclic strength at elevated temperatures.
|
host ::
RSS.