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Microstructural Investigation and Mechanical Testing of an Ultrafine-grained Austenitic Stainless Steel
Chlupová, Alice ; Man, Jiří ; Polák, Jaroslav ; Karjalainen, L. P.
Special thermomechanical treatment based on high degree deformation followed by reversion annealing was applied to 301LN austenitic stainless steel to achieve ultrafine-grained (UFG) structure with considerably enhanced mechanical properties. Two different conditions of the thermomechanical treatment were adopted and resulting microstructures with different grain sizes were characterised by optical and high resolution scanning electron microscopy (SEM-FEG). Hardness measurements and tensile tests were performed to characterize mechanical properties. To reveal structural changes induced during thermomechanical treatment and during tensile tests a magnetic induction method was additionally applied. Experimental study validated the ability of the above special treatment to produce austenitic stainless steel with grain size about 1.4 m which exhibits tensile strength about 1000MPa while ductility remains on level about 60 %. The results obtained for both thermomechanical conditions are compared and the relationship between microstructure refinement, phase content and mechanical properties is discussed.
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Proceedings of the 16th International colloquium Mechanical Fatigue of Materials
Polák, Jaroslav ; Kruml, Tomáš ; Man, Jiří
The XVI International Colloquium on Mechanical Fatigue of Metals was organized by the Institute of Physics of Materials, Academy of Sciences of the Czech Republic in Brno, in September 24-26, 2012. The Colloquium has been opened to participants from all countries interested in the subject of fatigue of metallic materials. The proceedings contains 39 abstracts of 35 oral and of 4 poster contributions by 122 authors from 18 countries to be presented during the Colloquium.
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Fatigue crack initiation — the role of point defects
Polák, Jaroslav ; Man, Jiří
The role of point defects in the formation of surface relief and in the initiation of a fatigue crack in crystalline materials is analyzed. The dislocation interactions in the bands of intensive cyclic slip are specified and relations describing the formation and annihilation of interstitial and vacancy type defects are derived. The formation, annihilation and migration of point defects is proposed to be responsible for the mass redistribution within PSB and between PSB and the matrix boundary. The redistribution of the matter results in local tensile and compressive stresses that are relaxed by continuous dislocation movement within PSB and lead to the formation of characteristic surface relief in the form of extrusions and intrusions.
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Initial stages of fatigue failure of polycrystalline materials
Man, Jiří ; Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav
Geometry of persistent slip markings (PSMs) formed during cyclic loading of polycrystalline stainless steels and superalloy was studied using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM-FEG). Internal dislocation structure was investigated using transmission electron microscopy (TEM). Persistent slip bands with dislocation structure corresponding to the cyclic strain localization were identified and correlated with PSMs observed on the specimen surface.
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Quantitative assessment of the surface relief in fatigue using AFM
Man, Jiří ; Obrtlík, Karel ; Polák, Jaroslav
Atomic force microscopy (AFM) was applied to study the early stages of fatigue damage in polycrystalline copper and stainless 316L steel. The analysis of the image formation using an AFM tip reveals the lateral distortion of the extrusions and intrusions in case of high extrusions and deep intrusions. The true extrusion height can be obtained in direct observation and the depth of intrusions using replica technique. The evolution of the shape and the height of extrusions allowed to judge the activity of the persistent slip bands (PSBs) during fatigue life.
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