Characterization of Oxide Nanoparticles in Al-Free and Al-Containing Oxide Dispersion Strengthened Ferritic Steels

Abstract

Oxide nanoparticles in oxide dispersion strengthened (ODS) ferritic steels with and without Al have been characterized by transmission electron microscopy. It is confirmed that most of the complex oxide particles consist of Y2TiO5 for 18Cr-ODS steel and YAlO3 or YAl5O12 for 18Cr5Al-ODS steel, respectivley. The addition of 5% Al in 18Cr-ODS steel leads to the formation of larger oxide particles and the reduction in their number density. For 18Cr-ODS steel, 87% of the oxide particles are coherent. The misfit strain of the coherent particles and a few semi-coherent particles is about 0.034 and 0.056, respectively. For 18Cr5Al-ODS steel, 75% of the oxide particles are semi-coherent, of which the misfit strain is 0.091 and 0.125, respectively. These results suggest that for the Al-containing ODS steel the Al addition accelerates the formation of semi-coherent oxide particles and its larger coherent and semi-coherent particles result in the larger misfit strain between the oxide particle and alloy matrix, indicating that the coherence of oxide nanoparticles in ODS steels is size-dependent.

Oxide nanoparticles in an Al-alloyed oxide dispersion strengthened steel: crystallographic structure and interface with ferrite matrix

“…But there are at least four different yttrium aluminum oxides known in the Y-Al-O system [20], namely Y4Al2O9 (yttrium-aluminum-monoclinic, YAM), YAlO3 (yttrium-aluminumhexagonal, YAH), YAlO3 (yttrium-aluminum-perovskite, YAP) and Y3Al5O12 (yttriumaluminum-garnet, YAG). These possible variants complicate the identification of the oxide nanoparticles in Al-alloyed ODS ferrtic steels and their relationships with the ferrite matrix [16,17,[21][22][23][24][25][26]. Using EELS technique, Kimenkov et al [16] found that the oxide dispersoids in a Fe-20Cr-5Al ODS steel are mainly composed of YAG and YAP.…”