equiaxed

Equiaxed refers to a polycrystalline material whose grains have approximately equal dimensions in all directions. This contrasts with elongated, plate-like, or columnar grains that grow preferentially along a particular direction, often aligned with heat flow during solidification or deformation.

Equiaxed grains commonly form when nucleation during solidification is abundant and grain growth is unconstrained in all directions, such as under low thermal gradients or with grain-refining inoculants. In cast metals, inoculation with grain refiners (for example, TiB2-containing master alloys in aluminum or similar refiner additions in steels) promotes microstructural fragmentation into many small, roughly equiaxed grains. In wrought alloys, annealing and recrystallization after deformation also produce equiaxed, relatively uniform grains.

The equiaxed geometry tends to produce more isotropic mechanical properties, reducing directional variation in strength and toughness. Grain refinement, which yields smaller equiaxed grains, generally increases yield strength according to the grain size effect and can improve toughness and formability.

Observation is by optical or electron microscopy after proper polishing and etching; grain size and shape are quantified by intercept methods or planimetric analysis. The term applies across metals and ceramics and is a key indicator of processing history and expected anisotropy in properties.