Strain heterogeneity and the production of coarse grains in mechanically alloyed iron-based PM2000 alloy

Mechanically alloyed iron-based ODS alloys have the potential for application in heat exchangers for biomass processing, with gas operating temperatures and pressures of approximately 1100°C and 15–30 bar. The yttria dispersion in such alloys improves the high-temperature creep and stress rupture life. The elevated temperature strength is enhanced by the development of a coarse-grained microstructure during recrystallisation. Factors controlling the evolution of this desirable microstructure are explored in this work, focusing specifically on PM2000, which is a yttria dispersion strengthened, mechanically alloyed material. The microstructure following mechanical alloying and consolidation is fine and uniform, making it difficult to nucleate recrystallisation. Therefore, the introduction of a strain heterogeneity in the microstructure is found to promote the nucleation of recrystallisation. In contrast, uniform deformation reduces the chances of nucleation and hence leads to the development of a coarser microstrutructure.