Creep behavior of ODS materials: A study of dislocations/precipitates interactions

Creep experiments performed at 650 °C and 250 MPa on MA957 and CEA-developed 18%Cr ferritic Oxide Dispersion Strengthened (ODS) steels emphasize the particular creep behavior of ODS alloys. To understand the influence of oxide particles, we focused on the dislocation microstructure and their interaction mechanisms with precipitates. Microstructural characterization were performed using Transmission Electron Microscopy (TEM) on both un-deformed alloys and on 650 °C–250 MPa creep tested MA957 samples. No noticeable differences were observed, and dislocations seem to be anchored by precipitate particles. The dynamic behavior was studied by in situ TEM straining experiments at room temperature on MA957. Observation of dislocation motions indicates that interactions with particles, including pinning, control the flow stress at least at room temperature. At 650 °C, other mechanism is probably predominant.