Mapping Residual Plastic Strain in Materials Using Electron Backscatter Diffraction
Residual strains that accrue from stresses imposed on materials during manufacturing, installation, and service often enhance the susceptibility to degenerative effects such as corrosion, cracking, and fatigue. Mapping strains in Alloy 600, a Ni-base non-age hardenable alloy, Steam Generator (SG) tubing used in boiler systems of CANadian Deuterium Uranium (CANDU) reactors is of particular interest to the nuclear industry. Interactions between residual strains from roller-expansion of the tubing during installation with prevailing environmental conditions during reactor operation (e.g., water chemistry and temperature) contribute to initiation and propagation of stress corrosion cracks (SCC), which can influence boiler reliability and service-life (Danko, 1996). Therefore, having a means of accurately characterizing the magnitude and spatial distribution of plastic deformation in relation to material defects including cracks, pits, and dents, is essential for identifying components at high risk of failure. Hardness measurements have traditionally been used to identify regions of high strain in SG tubes. However, obtaining a sufficient number of such measurements to infer details regarding the spatial distribution of complex strain fields is tedious and often impractical. Moreover, in so far as hardness indentations locally alter the strain distribution, these methods can be considered destructive.
KeywordsPlastic Zone Stress Corrosion Crack Angular Deviation Misorientation Distribution Face Centered Cubic
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