The Effect of Cryogenic Mechanical Alloying and Milling Duration on Powder Particles’ Microstructure of an Oxide Dispersion Strengthened FeCrMnNiCo High-Entropy Alloy

Oxide dispersion strengthened materials are commonly used for high-temperature applications. Among other possibilities, these oxides are mostly introduced by mechanical alloying comprising cold welding and fracturing of powders by high-impact loads during milling. However, despite their outstanding high-temperature performance, these materials are still not established because of their laborious and thus expensive processing. Therefore, to improve mechanical alloying’s efficiency, the effect of lower milling temperatures is investigated on an oxide-dispersion strengthened high-entropy-alloy in the proposed study. To this end, prealloyed FeCrMnNiCo powders were milled together with yttria at cryogenic and room temperature by using a novel attritor cryomill. Powders milled at both temperatures were subsequently compared regarding their macroscopic morphology, amount and size distribution of detectable yttria as well as defect structure by means of high-resolution scanning electron microscopy and X-ray diffraction, respectively. Investigations showed a significant decrease of powder particle size and an insignificant influence on their aspect-ratio at cryogenic conditions. Furthermore, the phase fraction of detectable yttria got reduced by cryomilling, indicating increased dissolution or at least refinement. Additionally, a higher full width at half maximum accompanied by increased stacking fault probability of the fcc FeCrMnNiCo matrix gained by X-ray diffraction measurements suggests an improved milling efficiency during cryomilling intensified by higher defect density as well as strength of FeCrMnNiCo powders.