Fracture Behavior of Brittle Coating Layer on Metal Substrate

Abstract

The compressive fracture and spalling of multiply-cracked brittle coating layer on metal substrate under tensile stress was studied for the anodic-oxidized aluminum wire with the Al2O3 coating layer and galvannealed IF steel plate with the intermetallic compound coating layer consisting of ζ, δ1 and Γ1 and Γ phases. The thin Al2O3 coating layer on Al wire was fractured by buckling in the circumferential direction by the compressive hoop stress, but thick layer was debonded by the tensile radial stress at interface. The thickness of the coating layer at the transition from the compressive fracture to interfacial debonding was around 30 µm. In the galvannealed steel plate sample, the (ζ+δ1) phases were fractured by buckling in the width direction, resulting spalling of the (ζ+δ1) phases in the first stage, and the remained (δ1+Γ1+ Γ) phases or (Γ1+Γ) phase was again fractured by buckling, followed by the spalling of the remained phase.