Dislocation loops and bubbles in oxide dispersion strengthened ferritic steel after helium implantation under stress

The oxide dispersion strengthened (ODS) ferritic steel PM2000, was homogeneously implanted with α-particles under uniaxial tensile stresses ranging from 20 to 250 MPa, causing irradiation creep. The irradiation temperatures were 573, 673, and 773 K, respectively. Maximum helium concentrations of 3000 appm were attained, causing a concurrent displacement dose of approximately 0.75 dpa (damage rate about 5 x 10-6 dpa s-1). Microstructural changes were studied in detail by transmission electron microscopy (TEM). Two sets of dislocation loops were identified, both interstitial in nature, with Burgers vectors b = <1 0 0> and b = 1/2<1 1 1>, and habit planes of (1 0 0) and (1 1 1), respectively. No influence of stress applied during the irradiation creep tests on loop formation and growth could be detected. TEM investigation also showed the formation of bubbles attached to loops already during implantation at 573 K, the formation of bubble-loop complexes at 673 K, and Y2O3 particles changing their shape by the attachment of bubbles at 773 K