INFLUENCE OF Y2O3 PARTICLES AND DEFORMATION ON RECRYSTALLISATION OF ODS STEELS MA956 AND MA957

Abstract

Commercialised mechanically alloyed yttria dispersion strengthened alloys exhibit unusual recrystallisation behaviour i.e. instead of recrystallising in an equiaxed grain structure they recrystallise in a manner which closely resembles that obtained by directional solidification, with the elongated columnar grains aligned along a particular sample axis. In spite of their large stored energy content, they tend to recrystallise at temperatures close to melting. The recrystallised microstructure is often very coarse and highly anisotropic, characterised by columnar grains. In the present paper influence of dispersed particles and deformation on recrystallisation behaviour of oxide dispersion strengthened MA956 and MA957 are investigated. It was found that degree of deformation prior to recrystallisation and manufacturing process, which tends to align the dispersoid particles along the principal fabrication direction, encourages recrystallisation to be directional.