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 applicati on in heat exchangers for biomass processing, with gas operating temperatur es and pressures of approximately 1100 degreesC and 15-30 bar. The yttria. dispersion in such alloys improves the high-temperature creep and stress ru pture life. The elevated temperature strength is enhanced by the developmen t of a coarse-grained microstructure during recrystallisation. Factors cont rolling the evolution of this desirable microstructure are explored in this work, focusing specifically on PM2000, which is a yttria dispersion streng thened, mechanically alloyed material. The microstructure following mechani cal alloying and consolidation is fine and uniform, making it difficult to nucleate recrystallisation. Therefore, the introduction of a strain heterog eneity in the microstructure is found to promote the nucleation of recrysta llisation. In contrast, uniform deformation reduces the chances of nucleati on and hence leads to the development of a coarser microstrutructure. (C) 2 001 Elsevier Science B.V. All rights reserved.