Irradiation creep and microstructural changes in an advanced ODS ferritic steel during helium implantation under stress

An advanced oxide dispersion strengthened (ODS) ferritic steel with very fine oxide particles has been homogeneously implanted with helium under uniaxial tensile stresses from 20 to 250MPa to a maximum dose of about 0.38dpa (1650appm-He) with displacement damage rates of 4.4×10−6 dpa/s at temperatures of 573 and 773K. The samples were in the form of miniaturized dog-bones, where during the helium implantation the straining and the electrical resistance were monitored simultaneously. Creep compliances were measured to be 4.0×10−6 and 11×10−6 dpa−1MPa−1 at 573 and 773K, respectively. The resistivity of ODS steel samples decreased with dose, indicating segregation and/or precipitation. Evolution of microstructure during helium implantation was studied in detail by TEM. The effects of ODS particle size on irradiation creep and microstructural changes was investigated by comparing the results from the present advanced ODS (K1) to a commercial ODS ferritic steels (PM2000) with much bigger oxide particles.