Quantitative characterization of cleavage and hydrogen-assisted quasi-cleavage fracture surfaces with the use of confocal laser scanning microscopy

© 2016 Elsevier B.V."True" cleavage (TC) and quasi-cleavage (QC) fracture surfaces of low-carbon steel specimens tested in liquid nitrogen and after hydrogen charging respectively were investigated by quantitative confocal laser scanning microscopy (CLSM) and conventional scanning electron microscopy (SEM) with electron-backscattered diffraction (EBSD). Topological and crystallographic features of the TC fracture surface are found in good agreement with the generally accepted cleavage mechanism: TC facets diameters correspond to those of grains; the crack path strictly follows the crystallographic orientation of grains and the most of the cleavage cracks are parallel to [100] planes. On the 2D SEM images, the QC facets appeared resembling the TC ones in terms of river line patterns, shapes and sizes. However, the substantial differences between the topography of these two kinds of fracture surfaces were revealed by 3D CLSM: the average misorientation angle between QC facets and the roughness of the QC fracture surface were much lower than those measured for TC. It is demonstrated that all these features are attributed to the specific fracture mechanism operating during hydrogen-assisted cracking

Quantitative characterization of cleavage and hydrogen-assisted quasi-cleavage fracture surfaces with the use of confocal laser scanning microscopy

© 2016 Elsevier B.V."True" cleavage (TC) and quasi-cleavage (QC) fracture surfaces of low-carbon steel specimens tested in liquid nitrogen and after hydrogen charging respectively were investigated by quantitative confocal laser scanning microscopy (CLSM) and conventional scanning electron microscopy (SEM) with electron-backscattered diffraction (EBSD). Topological and crystallographic features of the TC fracture surface are found in good agreement with the generally accepted cleavage mechanism: TC facets diameters correspond to those of grains; the crack path strictly follows the crystallographic orientation of grains and the most of the cleavage cracks are parallel to [100] planes. On the 2D SEM images, the QC facets appeared resembling the TC ones in terms of river line patterns, shapes and sizes. However, the substantial differences between the topography of these two kinds of fracture surfaces were revealed by 3D CLSM: the average misorientation angle between QC facets and the roughness of the QC fracture surface were much lower than those measured for TC. It is demonstrated that all these features are attributed to the specific fracture mechanism operating during hydrogen-assisted cracking

Quantitative characterization of cleavage and hydrogen-assisted quasi-cleavage fracture surfaces with the use of confocal laser scanning microscopy

© 2016 Elsevier B.V."True" cleavage (TC) and quasi-cleavage (QC) fracture surfaces of low-carbon steel specimens tested in liquid nitrogen and after hydrogen charging respectively were investigated by quantitative confocal laser scanning microscopy (CLSM) and conventional scanning electron microscopy (SEM) with electron-backscattered diffraction (EBSD). Topological and crystallographic features of the TC fracture surface are found in good agreement with the generally accepted cleavage mechanism: TC facets diameters correspond to those of grains; the crack path strictly follows the crystallographic orientation of grains and the most of the cleavage cracks are parallel to [100] planes. On the 2D SEM images, the QC facets appeared resembling the TC ones in terms of river line patterns, shapes and sizes. However, the substantial differences between the topography of these two kinds of fracture surfaces were revealed by 3D CLSM: the average misorientation angle between QC facets and the roughness of the QC fracture surface were much lower than those measured for TC. It is demonstrated that all these features are attributed to the specific fracture mechanism operating during hydrogen-assisted cracking

Quantitative characterization of cleavage and hydrogen-assisted quasi-cleavage fracture surfaces with the use of confocal laser scanning microscopy

© 2016 Elsevier B.V."True" cleavage (TC) and quasi-cleavage (QC) fracture surfaces of low-carbon steel specimens tested in liquid nitrogen and after hydrogen charging respectively were investigated by quantitative confocal laser scanning microscopy (CLSM) and conventional scanning electron microscopy (SEM) with electron-backscattered diffraction (EBSD). Topological and crystallographic features of the TC fracture surface are found in good agreement with the generally accepted cleavage mechanism: TC facets diameters correspond to those of grains; the crack path strictly follows the crystallographic orientation of grains and the most of the cleavage cracks are parallel to [100] planes. On the 2D SEM images, the QC facets appeared resembling the TC ones in terms of river line patterns, shapes and sizes. However, the substantial differences between the topography of these two kinds of fracture surfaces were revealed by 3D CLSM: the average misorientation angle between QC facets and the roughness of the QC fracture surface were much lower than those measured for TC. It is demonstrated that all these features are attributed to the specific fracture mechanism operating during hydrogen-assisted cracking

Assessing Fracture Surface Ductility by Confocal Laser Scanning Microscopy

Hitherto there is no generally accepted quantitative parameter which, on the one hand, would reliably characterize the ductility of the whole fracture surface, and, on the other hand, could be relatively quickly measured. This circumstance substantially affects the objectivity of the fractographic analysis which effectiveness is still strongly dependent on the experience and skills of an expert. Recent studies showed that the value of the normalized fracture surface area Rs can serve as the measure of the fracture surface ductility. This parameter can be evaluated by the quantitative confocal laser scanning microscopy (CLSM). In the present study we investigated the Rs value for the fracture surfaces of the low carbon steel specimens tested in the temperature range from 200 to -196 °C where the steel undergoes ductile-to-brittle transition accompanied by the alternation of the fracture mode from ductile to brittle. The temperature dependence of the Rs value is found to have a sigmoidal shape with the sharp drop in the range from 100 to -100 °C. It is demonstrated that the Rs is strongly correlated with the fracture surface appearance: the Rs decreases concurrently with increasing brittleness of the fracture surface

Assessing Fracture Surface Ductility by Confocal Laser Scanning Microscopy

Hitherto there is no generally accepted quantitative parameter which, on the one hand, would reliably characterize the ductility of the whole fracture surface, and, on the other hand, could be relatively quickly measured. This circumstance substantially affects the objectivity of the fractographic analysis which effectiveness is still strongly dependent on the experience and skills of an expert. Recent studies showed that the value of the normalized fracture surface area Rs can serve as the measure of the fracture surface ductility. This parameter can be evaluated by the quantitative confocal laser scanning microscopy (CLSM). In the present study we investigated the Rs value for the fracture surfaces of the low carbon steel specimens tested in the temperature range from 200 to -196 °C where the steel undergoes ductile-to-brittle transition accompanied by the alternation of the fracture mode from ductile to brittle. The temperature dependence of the Rs value is found to have a sigmoidal shape with the sharp drop in the range from 100 to -100 °C. It is demonstrated that the Rs is strongly correlated with the fracture surface appearance: the Rs decreases concurrently with increasing brittleness of the fracture surface.publishedVersion© 2018 The Author(s). Published by Elsevier B.V. CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0