Unusual thermal stability of nano-structured ferritic alloys

Bimodal Grain Size Distribution of Nanostructured Ferritic ODS Fe–Cr Alloys

“…When the primary recrystallization is complete, abnormal grain growth, in which single grains grow fast at the expense of smaller ones, can occur. A fine dispersion of highly stable oxide particles can inhibit such grain growth up to high temperatures . In the following paragraph, the role of milling and sintering effects on the microstructure formation will be discussed.…”

“…Even the reported possible spatial resolution of down to 20 nm it would be hard to detect nanograins, which are expected to have a size below 100 nm . This shortcoming can be overcome by the application of Transmission Kikuchi Diffraction (TKD) which has a spatial resolution of about 2–10 nm, depending on the material . In the measurement with an applied voltage of 30 kV, a step size of 11 nm was achieved, resulting in a minimum detectable grain size of 22 nm.…”

“…In ODS materials particles act as obstacles for grain boundary and dislocation migration. For that reason the activation energy for recrystallization in ODS materials is usually significantly higher than in non‐ODS steels . In general, the ratio of driving force (dominated by initial deformation and dislocation density) and the particle pinning force governed by the number density and size of particles, is essential for the recrystallization of an ODS material .…”

“…For that reason the activation energy for recrystallization in ODS materials is usually significantly higher than in non-ODS steels. [19][20][21] In general, the ratio of driving force (dominated by initial deformation and dislocation density) and the particle pinning force governed by the number density and size of particles, is essential for the recrystallization of an ODS material. 21 Although basic recrystallization mechanisms are well studied, there are still effects in the microstructure evolution of particle-strengthened alloys, which are not fully understood yet.…”

Thermal stability of consolidated metallic nanomaterials

“…In particular, new grades of ferrite and ferrite ± martensite steels are produced by powder technique (high-energy milling of the starting components and consolidation under nanostructure-preserving conditions). 5,45 The presence of oxide inclusions in the iron ± chromium steels such as Y 2 Ti 2 O 7 and Y 2 TiO 5 of 2 ± 4 nm size, which are thermally stable and possess good adhesion to the matrix, is a prerequisite to thermal stability of the nanostructure of these steels and, hence, to the retention of their mechanical characteristics on exposure to radiation. These steels the radiation stability of which is determined by the presence of multiple grain boundaries, which absorb radiation defects, are the materials used for fuel element cans of fast-neutron reactors of new generation; thus, the available experimental data are encouraging.…”