Recrystallisation of practical mechanically alloyed iron-base and nickel-base superalloys

Commercialised mechanically alloyed yttria dispersion strengthened alloys exhibit unusual recrystallisation behaviour. 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. Such a microstructure is often referred to as being ‘directionally recrystallised’. This and other features of these unique alloys are reviewed. It is found that many of the observed peculiarities can be attributed to the ultra-fine grained structure present prior to the recrystallisation heat-treatment. In some cases the manufacturing process tends to align the dispersoid particles along the principal fabrication direction. This in turn encourages recrystallisation to be directional.