In- situ testing is a new and progressive method of material analysis, which can offer new information about behavior of individual phases and structural components in metals. Local mechanical properties or strain distribution can be directly obtained for fine multiphase microstructures. The second application of in-situ stages lies in observation of phase transformations that occur either during heating, cooling or straining of metals. EBSD analysis can be also performed during in-situ testing if the stage allows tilting of the sample toward EBSD detector. Preparation of samples for in-situ testing is of the utmost importance for successful analysis. This work concentrated on sample preparation techniques used for flat samples of 42SiCr steel. Preliminary in-situ cold deformation tests of this steel with EBSD acquisition and observation of microstructure development were also carried out.
In-situ tensile testing of a 27CrNiMoV alloy which is used for steam turbine rotors was carried out using scanning electron microscope (SEM). Deformation and crack formation and propagation were examined with this test. Small (45 × 10 × 1.5 mm, with gauge length of 20 mm), flat samples based on dog-bone shape were prepared from the steel. The material in its initial state contained high number of defects in form of microcracks. A comparison of behaviour at tensile tests of samples without visible defect and with crack in the gauge section was performed. Apparently, the presence of defect in the initial state showed direct influence on properties like lower tensile strength. The sample, its necking and propagated crack is displayed at different stages of the tensile load. In-situ testing reveals differences in the sample deformation. The defect-free sample is affected in its whole body and regular necking can be observed, whereas the presence of the crack in the defect samples concentrates stress to a smaller area and also changed the shape of the stress-strain curve.
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