Propagation along grain boundaries is called what?

• A. Transgranular
• B. Ductile
• C. Cavitation
• D. Intergranular

Answer: (D)

Propagation along grain boundaries is called intergranular propagation. This describes cracks that travel along the interfaces between grains, rather than cutting through the crystal lattices of the grains themselves (which would be transgranular propagation). The term intergranular specifically refers to the boundary path, not the amount of plastic deformation or void formation. Ductile describes a fracture mode with significant plastic deformation before failure, not the crack’s path. Cavitation is the formation of voids and is not about the crack traveling along grain boundaries. Intergranular cracking often occurs because grain boundaries are higher-energy regions that can be weakened by impurities, precipitates, or corrosive attack, making cracks prefer the boundaries under certain conditions.