A form of severe adhesive wear in which two sliding metal surfaces under high contact pressure and insufficient lubrication form local adhesive bonds that tear out material and transfer it between surfaces, producing surface roughness, raised lobes, and loss of dimensional fit.

Principle

When asperity contact under high normal stress and inadequate lubricant film leads to metallic adhesion stronger than the shear strength of the adjacent bulk material, relative sliding causes localized tearing and transfer rather than smooth frictional motion.

Demonstration

Illustrative scenario: Two mating stainless-steel fastener threads assembled without proper lubricant experience repeated tightening. Local asperities weld under contact pressure during relative motion; subsequent turns tear out raised material that transfers to mating threads, producing raised ridges and increasing required torque until removal becomes difficult.

Misapplication

Mistaking galling for general abrasive wear: abrasive wear attributes material removal to hard third‑body particles grinding surfaces, whereas galling is removal by adhesive bonding and tearing between the contacting metals under boundary conditions.

Consequence

Progressive surface roughening, increased torque or friction, impaired assembly/disassembly, loss of thread fit or sealing, and ultimately functional failure of the joint or component if not prevented or repaired.

Reversal

If a continuous hydrodynamic or full-film lubricant regime is established, or if surface chemistry/coatings prevent metallic adhesion, the adhesive bonding mechanism fails to develop and galling is suppressed; at very high temperatures other mechanisms (e.g., diffusion or oxidation) may dominate surface damage instead of galling.

Boundary

Clearly within: direct metal-to-metal sliding of similar ductile alloys under boundary lubrication producing adhesive transfer. Boundary case: partial lubrication with intermittent metal contact where both adhesive and abrasive mechanisms operate. Clearly outside: wear dominated solely by abrasive third bodies or fatigue‑initiated pitting without adhesive transfer.

Semantic Tension

Surface hardness and hardness mismatch reduce tendency to adhere but increase brittleness and wear susceptibility; designers must trade material pairing, hardness, and lubrication for assembly fit and durability.

Synthesis

Galling is the adhesive end‑member of sliding failure modes: it arises when metallic adhesion under boundary conditions outpaces shear resistance, so prevention requires controlling contact chemistry, lubrication regime, and material pairing rather than relying solely on increased load capacity.