Initial stage: particle flattening and shape change
During the initial stage of the grinding process, the particles of the feed material get flattened as well as their shape is changed because of the impact force of the grinding media. This is the stage when most particles of large size are converted into smaller pieces.
Intermediate stage: significant changes compared to the initial stage
The particles are subjected to considerable changes as the grinding process progresses; this is in contrast to the initial stage. The particles get more spherical and uniform in shape, and the rate of size reduction is slower. This stage is brought about by impact and attrition forces, resulting in a finer particle size.
Final stage: particle size reduction and homogeneous microstructure
In the final stage of the grinding process, the particles are reduced to their ultimate size, and a homogenous microstructure is obtained. The particles are now very fine and uniform, with a narrow size distribution. This stage is predominantly made up of attrition forces because the particles are too small to be effectively broken down by impact itself.
Completion stage: extremely deformed metastable structure
The particles have suffered a lot of deformation and have reached a metastable state at the end of the process. This stage is referred to as a high-strain and lattice defects stage in the particles, and it can be associated with enhanced reactivity and unique properties. The last stage is often required in applications such as mechanical alloying where the aim is to obtain unique microstructures and properties of the material.