Author
Roman Petráš
Bio: Roman Petráš is an academic researcher from Academy of Sciences of the Czech Republic. The author has contributed to research in topics: Hardening (metallurgy) & Slip (materials science). The author has an hindex of 8, co-authored 20 publications receiving 221 citations.
Papers
More filters
06 Oct 2014-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the internal dislocation structures of the material at room and at elevated temperature were studied using transmission electron microscopy and surface observations were used to identify the cyclic slip localization and to discuss fatigue softening/hardening behavior and the temperature dependence of the fatigue life.
Abstract: Austenitic heat resistant Sanicro 25 steel developed for high temperature applications in power generation industry has been subjected to strain controlled low cycle fatigue tests at ambient and at elevated temperature in a wide interval of strain amplitudes. Fatigue hardening/softening curves, cyclic stress–strain curves and fatigue life curves were evaluated at room temperature and at 700 °C. The internal dislocation structures of the material at room and at elevated temperature were studied using transmission electron microscopy. High resolution surface observations and FIB cuts revealed early damage at room temperature in the form of persistent slip bands and at elevated temperature as oxidized grain boundary cracks. Dislocation arrangement study and surface observations were used to identify the cyclic slip localization and to discuss the fatigue softening/hardening behavior and the temperature dependence of the fatigue life.
55 citations
TL;DR: In this paper, the profiles of persistent slip markings produced by uniaxial and baoxial cyclic straining in four different polycrystalline materials with f.c. structure were investigated using focused ion beam (FIB) cutting and TEM observation of oriented surface foils.
49 citations
05 Jan 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of grain boundary oxidation and surface oxide cracking on fatigue life was discussed, and the mechanisms responsible for fatigue crack initiation and growth were revealed using scanning electron microscopy combined with FIB cutting and EBSD imaging.
Abstract: Heat resistant austenitic Sanicro 25 steel was subjected to in-phase and out-of-phase thermomechanical fatigue (TMF) loading conditions with different amplitudes of mechanical strain in a wide interval of temperatures (250–700 °C). Cyclic hardening/softening curves, cyclic stress-strain curves and fatigue life curves were evaluated for both type of loadings. Scanning electron microscopy combined with FIB cutting and EBSD imaging in longitudinal sections containing cracks revealed the mechanisms responsible for fatigue crack initiation and growth. Fatigue cracks developed rapidly in oxidized grain boundaries during in-phase loading and intergranular crack growth resulted in short fatigue life. Multiple cracks in out-of-phase loading perpendicular to the stress axis have arisen only afterwards oxide layer was formed. The delayed initiation and transgranular growth led to longer fatigue life. The effect of grain boundary oxidation and surface oxide cracking on fatigue life was discussed.
44 citations
TL;DR: In this article, the effect of the dwell in the loading cycles on fatigue life is discussed in relation to the surface and internal damage evolution, and the crack paths and their relationship to the grain and twin boundaries were studied by means of electron back scatter diffraction.
25 citations
TL;DR: In this paper, the cyclic plastic response of the austenitic heat resistant steel Sanicro 25 has been studied during strain controlled low cycle fatigue tests performed at ambient and at elevated temperature.
24 citations
Cited by
More filters
TL;DR: In this article, defects as root cause of fatigue failure are discussed, such as defects due to local damage during manufacturing, service and maintenance such as dents, scratches and localized corrosion.
89 citations
TL;DR: In this article, the cyclic mechanical characters of 316L stainless steel at elevated temperature are extensively investigated by the experimental and cyclic constitutive models. And the authors proved that the proposed model is proved to effectively describe the complex evolution of not only cyclic stress amplitude but also hysteresis loops for the 316L steel.
69 citations
TL;DR: In this paper, the profiles of persistent slip markings produced by uniaxial and baoxial cyclic straining in four different polycrystalline materials with f.c. structure were investigated using focused ion beam (FIB) cutting and TEM observation of oriented surface foils.
49 citations
20 Jan 2020-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the mechanisms driving high cycle fatigue fracture of the as-built 12CrNi2 low alloy steel were investigated and a concurrent process-microstructure-property relationship was established through microstructural analysis.
Abstract: In this research, 12CrNi2 low alloy steel was successfully prepared by laser melting deposition (LMD). The mechanisms driving high cycle fatigue fracture of the as-built LMD 12CrNi2 low alloy steel were investigated and a concurrent process-microstructure-property relationship was established through microstructural analysis. The results showed that the crystal structures of the as-built LMD 12CrNi2 steel mainly consisted of the ferrite and a small amount of Cr23C6 carbides. No preferred texture was observed as a result of the complicated heat flux direction during fabrication. Based on the examination of the fracture surface, fatigue cracks of the as-built LMD 12CrNi2 steel initiated from subsurface defects for all the cases. Crack propagation zones showed a mixed mode of transgranular and intergranular fracture in a brittle manner, whereas the final fracture zones displayed dimples typical of ductile fracture. The kernel average misorientation (KAM) map indicated that the strain localization predominantly occurred at the grain boundaries and slightly appeared at the interior of the ferrite grains. Schmid factor distribution results implied that fatigue cracks originated from grains with {123} slip system due to the prior activation of {123} slip system.
47 citations
05 Jan 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of grain boundary oxidation and surface oxide cracking on fatigue life was discussed, and the mechanisms responsible for fatigue crack initiation and growth were revealed using scanning electron microscopy combined with FIB cutting and EBSD imaging.
Abstract: Heat resistant austenitic Sanicro 25 steel was subjected to in-phase and out-of-phase thermomechanical fatigue (TMF) loading conditions with different amplitudes of mechanical strain in a wide interval of temperatures (250–700 °C). Cyclic hardening/softening curves, cyclic stress-strain curves and fatigue life curves were evaluated for both type of loadings. Scanning electron microscopy combined with FIB cutting and EBSD imaging in longitudinal sections containing cracks revealed the mechanisms responsible for fatigue crack initiation and growth. Fatigue cracks developed rapidly in oxidized grain boundaries during in-phase loading and intergranular crack growth resulted in short fatigue life. Multiple cracks in out-of-phase loading perpendicular to the stress axis have arisen only afterwards oxide layer was formed. The delayed initiation and transgranular growth led to longer fatigue life. The effect of grain boundary oxidation and surface oxide cracking on fatigue life was discussed.
44 citations