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Register a new userIn situ studies of evolution of microstructure with temperature in heavily deformed Ti-modified austenitic stainless steel by X-ray Diffraction technique
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Added by
Gayathri N Banerjee
Publication date
2010
fields
Physics
and research's language is
English
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The mechanism of the evolution of the deformed microstructure at the earliest stage of annealing where the existence of the lowest length scale substructure paves the way to the formation of the so-called subgrains, has been studied for the first time. The study has been performed at high temperature on heavily deformed Ti-modified austenitic stainless steel using X-ray diffraction technique. Significant changes were observed in the values of the domain size, both with time and temperature. Two different types of mechanism have been proposed to be involved during the microstructural evolution at the earliest stages of annealing. The nature of the growth of domains with time at different temperatures has been modelled using these mechanisms. High-resolution transmission electron microscopy has been used to view the microstructure of the deformed and annealed sample and the results have been corroborated successfully with those found from the X-ray diffraction techniques.
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The diffraction peaks of Zircaloy-2 and Zr-2.5%Nb alloys at various deformations are found to be asymmetric in nature. In order to characterize the microstructure from these asymmetric peaks of these deformed alloys, X-Ray Diffraction Line Profile Analysis like Williamson-Hall technique, Variance method based on second and fourth order restricted moments and Stephens model based on anisotropic strain distribution have been adopted. The domain size and dislocation density have been evaluated as a function of deformation for both these alloys. These techniques are useful where the dislocation structure is highly inhomogeneous inside the matrix causing asymmetry in the line profile, particularly for deformed polycrystalline materials.
Irradiation Assisted Stress Corrosion Cracking (IASCC) is a material degradation phenomenon affecting austenitic stainless steels used in nuclear Pressurized Water Reactors (PWR), leading to the initiation and propagation of intergranular cracks. Such phenomenon belongs to the broader class of InterGranular Stress Corrosion Cracking (IGSCC). A micromechanical analysis of IGSCC of an irradiated austenitic stainless steel is performed in this study to assess local cracking conditions. A 304L proton irradiated sample tested in PWR environment and showing intergranular cracking is investigated. Serial sectioning, Electron BackScatter Diffraction (EBSD) and a two-step misalignment procedure are performed to reconstruct the 3D microstructure over an extended volume, to assess statistically cracking criteria. A methodology is also developed to compute Grain Boundary (GB) normal orientations based on the EBSD measurements. The statistical analysis shows that cracking occurs preferentially for GB normals aligned with the mechanical loading axis, but also for low values of the Luster-Morris slip transmission parameter. Micromechanical simulations based on the reconstructed 3D microstructure, FFT-based solver and crystal plasticity constitutive equations modified to account for slip transmission at grain boundaries are finally performed. These simulations rationalize the correlation obtained experimentally into a single stress-based criterion. The actual strengths and weaknesses of such micromechanical approach are discussed.
Zirconium based alloys have been irradiated with 11 and 15 MeV proton and 116 MeV oxygen ions at different doses. The changes in the microstructure have been studied for the ion irradiated alloys as a function of dose using X-Ray Diffraction Line Profile Analysis (XRDLPA) based on the whole powder pattern fitting technique. It was observed that the microstructural parameters like domain size, microstrain within the domain, dislocation density did not change significantly with the increase in dose for proton irradiated samples. A clear change was noticed in these microstructural parameters as a function of dose for oxygen irradiated samples. There was a drastic decrease in domain size at a dose of 1x10^17 O5+/m2 but these values reached a plateau with increasing dose. The values of microstrain and dislocation density increased significantly with the dose of irradiation.
Two sets of amorphous carbon materials prepared at different routes are irradiated with swift (145 MeV) heavy ion (Ne6+). The structural parameters like the size of ordered grains along c and a axis i.e. Lc & La, the average spacing of the crystallographic planes (002) i.e. d002 and the fraction of the amorphous phase of the unirradiated and the irradiated samples are estimated by X-ray diffraction technique. The fraction of the amorphous phase is generally found to increase with the irradiation dose for both sets of the samples. The estimated and values are found to be almost unaffected by irradiation. The estimated values of corroborate with the increase of disorder in both sets of the samples with the increasing dose of irradiation. Keywords: X-ray Diffraction, Amorphous Carbon, Irradiation
Different techniques of the X-ray Diffraction Line Profile Analysis (XRDLPA) have been used to assess the microstructure of the irradiated Zr-1.0%Nb-1.0%Sn-0.1%Fe alloy. The domain size, microstrain, density of dislocation and the stacking fault probabilities of the irradiated alloy have been estimated as a function of dose by the Williamson-Hall Technique, Modified Rietveld Analysis and the Double Voigt Method. A clear signature in the increase in the density of dislocation with the dose of irradiated was revealed. The analysis also estimated the average density of dislocation in the major slip planes after irradiation. For the first time, we have established the changes in the electron density distribution due to irradiation by X-ray diffraction technique. We could estimate the average displacement of the atoms and the lattice strain caused due to irradiation from the changes in the electron density distribution as observed in the contour plots.
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