How Does Grain Refinement Change Metals? Achieving Both Strength and Ductility in a FeCoNi Alloy

Metals are usually either strong or ductile, but rarely both at the same time.
This study shows that a FeCoNi medium-entropy alloy can overcome this trade-off.

The researchers focused on how the size of crystal grains affects mechanical behavior.
Grain sizes were carefully controlled over a wide range, from about 0.7 μm to 145 μm.

The alloy was tested in tension at room temperature and at cryogenic temperature (−196 °C).
At low temperature, the material became both stronger and more stretchable.

At room temperature, deformation mainly occurs by dislocation slip.
At cryogenic temperature, deformation twinning is additionally activated inside the crystals.

This change in deformation mechanism allows the metal to deform more stably.
The results provide useful guidelines for designing metals for cold and extreme environments.

Journal: Scripta Materialia (2023)
DOI: 10.1016/j.scriptamat.2023.115392