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Abstract: The ultrafine scale microstructure of three MA/ODS ferritic alloys (12YWT, 14YWT and MA957) have been characterized by atom probe tomography in the as-received condition and after isothermal heat treatments at temperatures of up to 24h at 1300°C (∼85% T m). Atom probe tomography revealed the presence of a high number density of 2–4nm diameter titanium-, yttrium- and oxygen-enriched particles. These ultrafine particles were found to be extremely resistant to coarsening during isothermal aging at 1300°C. Solute segregation of the alloying elements to dislocations and grain boundaries was also observed. [Copyright &y& Elsevier]

Abstract: The stress relaxation behavior of 14YWT and ODS-Eurofer97 was examined within the framework of an internal-variable theory of inelastic deformation. Stress versus strain rate curves obtained by stress relaxation tests for 14YWT were described well by the equations for grain-matrix deformation while those of ODS-Eurofer97 were fitted with the combined curves of grain matrix deformation and grain boundary sliding. The sudden drop of total elongation of 14YWT was discussed in light of fracture surface observations. Grain boundary decohesion at 900°C was identified. [Copyright &y& Elsevier]

The development of porosity at 1000°C in an oxide dispersion-strengthened ferritic alloy containing nanoscale (∼2–4nm) oxide particles is investigated. A comparison with an alloy fabricated by internal oxidation instead of mechanical alloying demonstrates that the porosity formation is associated with mechanical alloying of the alloy powder with Y2O3 in argon. The pores grow in spite of a submicron grain size suggesting that the grain boundaries are not effective paths for removing entrapped gas from the pores. [Copyright &y& Elsevier]

Texture and microstructure of tubes and plates fabricated from a nanostructured ferritic alloy (14YWT), produced either by spray forming followed by hydrostatic extrusion (Process I) or hot extrusion and cross-rolling a plate followed by hydrostatic tube extrusion (Process II) have been characterized in terms of their effects on texture and grain boundary character. Hydrostatic extrusion results in a combination of plane strain and shear deformations which generate low intensity α- and γ-fiber components of {001}<110> and {111}<110> together with a weak ζ-fiber component of {011}<211> and {011}<011>. In contrast, multi-step plane strain deformation by hot extrusion and cross-rolling of the plate leads to a strong texture component of {001}<110> together with a weaker {111}<112> component. Although the total strains are similar, shear dominated deformation leads to much lower texture indexes compared to plane strain deformations. Further, the texture intensity decreases after hydrostatic extrusion of the alloy plate formed by plane strain deformation, due to a lower number of activated slip systems during shear dominated deformation. Notably, hot extruded and cross-rolled plate subjected to plane strain deformation to ~50% engineering strain creates only a modest population of low angle grain boundaries, compared to the much larger population observed following the combination of plane strain and shear deformation of ~44% engineering strain resulting from subsequent hydrostatic extrusion. [ABSTRACT FROM AUTHOR]