Synthesis and characterization of Fe-15 wt.% ZrO2 nanocomposite powders by mechanical milling

• A model Fe-15 wt.% ZrO2 composite powder was ball milled for various durations.
• 100 h milling was optimum from microstructural and microchemical considerations.
• Nanocrystalline Fe and ZrO2 dispersoids were uniformly distributed after 100 h.
• ZrO2 does not amorphise even after 100 h, unlike yttria.
• ZrO2 is established as a potential alternate dispersoid for ODS steels.

Fe-15 wt.% ZrO2 nanocomposite powder was synthesized via mechanical milling with an aim to study the morphology of the powder particles and refinement of the oxide and Fe crystallites during milling. Detailed microstructural and microchemical investigations were carried out in order to optimize the milling condition and to highlight the advantages for the choice of ZrO2. A homogeneous mixture was confirmed by X-ray mapping and ZrO2 dispersoids were observed to retain crystallinity even after 100 h of milling. It was also observed that both Fe and ZrO2 crystallites refine to very fine nanocrystalline (nc) sizes after such milling. The result has 2-fold significance: (a) Yttria, which is a standard dispersoid in oxide dispersion strengthened (ODS) steels, usually amorphised under similar conditions, which is detrimental to its structural stability and (b) nanocrystallites of Fe have useful magnetic properties. Modified Williamson–Hall technique (mod. W–H) was employed to measure the size and dislocation density of the matrix ferrite phase. Nanoindentation technique was used to evaluate the nanohardness of the milled powder as a function of milling duration.

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