I have been trying to calculate the grain size of some polycrystalline CoCrNi alloy models. I created the polycrystalline structures in Atomsk, and then visualized them in OVITO. I know that Atomsk gives the volume of the grains in the polycrystalline structures. But I have observed that in a few published papers, the authors have represented the grain size of polycrystals in nanometers. How do I calculate the grain size (in nm) of a polycrystalline structure? Thanks in advance.
There is no universally correct answer to your question.
For grains that are more or less regularly shaped, you can approximate them as spheres and calculate the radius from the grain volume using the formula: V = 4/3 π r^3
For irregularly shaped grains, you can use OVITO’s Grain Segmentation modifier in combination with the Construct Surface Mesh modifier to extract the outer mesh of each grain. This mesh can then be further processed using a custom Python Script modifier to extract properties such as the major and minor axis lengths of the grains.