A fracture mode in polycrystalline materials in which crack propagation preferentially follows grain boundaries, producing characteristic faceted or flat fracture surfaces and reflecting weakened boundary cohesion.

Principle

When grain boundaries are embrittled by segregation, precipitate films, depletion of strengthening solutes, environmental attack or mechanical damage, the fracture path follows boundaries because interfacial cohesive strength is lower than that of grain interiors.

Demonstration

Illustrative scenario: a ductile metal exposed to impurity segregation at boundaries or to intergranular corrosion exhibits a fracture surface composed of interlocking facets that correspond to grain outlines; macroscopic behavior is low-energy separation rather than necking. Uncertainty: mixed-mode fractures that include both inter- and transgranular features can complicate attribution.

Misapplication

Interpreting brittle-looking planar features as intergranular fracture when they result from cleavage or transgranular fatigue; assuming that any boundary-following crack must be chemically caused rather than mechanically or thermally induced.

Consequence

Evidence of intergranular fracture indicates loss of boundary toughness or chemical attack at boundaries, directing remediation toward eliminating segregation, altering heat treatment, reducing corrosive exposure or modifying grain boundary chemistry.

Reversal

Transgranular fracture, where cracks cut through grains and fracture surfaces show cleavage or dimpled rupture across grain interiors, contrasts with the boundary-following morphology.

Boundary

Pertains to polycrystalline solids with distinct grain boundaries; does not include fracture of amorphous solids, nor necessarily indicate the underlying mechanism (environmental vs mechanical) without additional analysis.

Semantic Tension

Closely related to intergranular corrosion and hydrogen embrittlement: the tension is between describing the morphological path of a crack (this term) and inferring the causative chemical or mechanical process.

Synthesis

Intergranular fracture names the morphological route of crack growth along grain boundaries; it signals that boundary cohesion or chemistry has been compromised and that corrective action must target boundary-strengthening or the environmental/mechanical factors that weakened those interfaces.