デジタル画像相関法と高分解能電子線後方散乱回折法の併用による微視・局所的な応力–ひずみ曲線情報のマッピング

Microscopic stress–strain curves were obtained by applying stress measurements using the HR–EBSD method and strain measurements using the DIC method to the same field of view in SEM in–situ tensile tests. From the analysis of these microscopic stress–strain curves, yield stress map and work hardening rate map were successfully produced. The relationship between these mechanical property value maps and the microstructure is investigated. The yield stress maps confirm the tendency of the local yield stress to show different values for different grains, but the Schmid factor alone cannot explain the magnitude of the yield stress. When adjacent grains with significantly different Schmid factors deformed cooperatively, the yield stress is found to increase as a result of stress partitioning. Localized regions of extreme work hardening rates were observed in the work hardening rate maps. These regions were located close to grain boundaries with low mA values where slip transfer was difficult and an interruption of the slip bands was observed. In addition, the rate of increase of GND density with strain was large in these regions. From these results, it can be understood that the extreme work hardening rates are due to increased back stresses caused by the accumulation of dislocations on low mA grain boundaries.