Abnormal grain growth

In ceramic materials, this phenomenon can result in the formation of elongated prismatic, acicular (needle-like) grains in a densified matrix.

This microstructure has the potential to improve fracture toughness by impeding the propagation of cracks.

Coupled with spontaneous activation, this makes abnormal grain growth a largely erratic process.

While the activation of grain boundaries (leading to rotation and growth) can occur at temperatures well below the temperatures required for partial melting of the grain boundaries, the effect is emphasized when melting occurs.

In the sintering of ceramic materials, abnormal grain growth is often viewed as an undesirable phenomenon because rapidly growing grains may lower the hardness of the bulk material through Hall-Petch-type effects.

Abnormal or discontinuous grain growth leads to a heterogeneous microstructure where a limited number of grains grow much faster than the rest.
Abnormal grain growth observed in Rutile TiO 2 , induced by the presence of a zircon secondary phase. [ 3 ]