##  [Intergranular Corrosion](/intergranular-corrosion-0) 

 Definition

Preferential chemical or electrochemical attack that progresses along the grain boundaries of a polycrystalline material because those boundaries differ in composition or microstructure from grain interiors.

 

 

 

 

 

 





## Principle

Principle

Grain boundaries can be sites of precipitate formation, solute segregation, second-phase depletion or altered electrochemical potential, producing continuous or discontinuous paths that are anodic (or more reactive) relative to grain interiors and so concentrate corrosion along boundaries.

 

 

 

 

 





## Demonstration

Demonstration

Illustrative scenario: austenitic stainless steel that has been heated through a sensitization range forms chromium carbides at boundaries, depleting chromium locally and permitting attack in aggressive solutions. Observable outcome: penetration following boundary network and loss of intergranular cohesion. Uncertainty: the precise boundary chemistry and environment required for attack can vary with alloy and thermal history.

 

 

 

 

## Misapplication

Misapplication

Calling any non-uniform corrosion 'intergranular' when attack is actually transgranular pitting or general surface attack; attributing a boundary-following appearance to mechanical cracking without chemical evidence.

 

 

 

 

 





## Consequence

Consequence

Loss of grain-to-grain cohesion, rapid through-thickness penetration or network attack that undermines load-bearing capability even when gross thickness loss is small; inspection metrics must target boundary penetration rather than average corrosion rate.

 

 

 

 

## Reversal

Reversal

Transgranular corrosion, where attack progresses through grains rather than along grain boundaries, typically when grain interiors are less noble or when precipitates are distributed uniformly.

 

 

 

 

 





## Boundary

Boundary

Applies to polycrystalline solids with distinct grain boundaries (metals, some ceramics); does not describe corrosion of amorphous materials, coatings that mask boundaries, or purely mechanical intergranular cracking without chemical attack.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Often conflated with 'grain-boundary corrosion' or with intergranular fracture; the tension is between a chemical/electrochemical mechanism (this term) and mechanical separation of boundaries (fracture).

 

 

 

 

 





## Synthesis

Synthesis

Intergranular corrosion is a chemically driven, boundary-focused degradation phenomenon: when microstructural features at grain boundaries create a local electrochemical advantage for dissolution, corrosion preferentially follows the boundary network and can rapidly compromise structural integrity despite modest overall material loss.