INVESTIGATION OF THE RELATIONSHIP BETWEEN LOCAL PLASTIC STRAIN ESTIMATED BY EBSD AND LOCAL NANOINDENTATION HARDNESS IN ALLOY 690

摘要

Plastic strain distribution in Alloy 690 has been of interest since laboratory experiments showed that cold deformation may trigger susceptibility to stress corrosion cracking. In operating plants, the plastic strains in Alloy 690 generally originate from manufacturing processes, e.g. grinding, tube straightening or welding. In recent years, the plastic strains from such operations have typically been mapped using electron backscatter diffraction. This method quantifies curvature of the crystal lattice, which has been shown to correlate with plastic strain on both the macroscopic and the mesoscopic levels, and has a high enough spatial resolution to potentially show the plastic strain distribution within individual grains. In this work, the correlation between local estimated plastic strains and nanoindentation hardness has been investigated. Local estimated plastic strains were able to predict the spatial distribution of local increases and decreases in hardness, but vastly overestimated the magnitude of variation. It is believed that the calibration curve used to estimate macroscopic plastic strain from macroscopic average misorientations overestimates local plastic strains where local misorientations are high, and underestimates the strains where the local misorientations are low. A calibration curve based on local strain measurements and local misorientations could possibly be a suitable alternative.