Bimodal grain size distribution of nanostructured ferritic ODS Fe-Cr alloys

Oxide dispersion strengthened Fe-Cr alloys produced by mechanical alloying and spark plasma sintering were found to form different heterogeneous hardness distribution and microstructures depending on the milling parameters. Microstructure investigations by means of electron diffraction techniques and atom probe tomography revealed the presence of large particle-free zones in one material, which is, together with the inhomogeneous deformation at short milling times, considered the main reason for the formation of a heterogeneous microstructure. The inhomogeneous temperature distribution in the sample volume during the sintering process is also expected to contribute to the formation of a heterogeneous grain size distribution in the final material.