Measuring adhesion of Cr2O3 and Al2O3 scales on Fe-based alloys

Adhesion of oxide scales on metals and alloys is one of the key parameters to better understand spallation phenomena. Three adhesion tests are described, from which interface fracture energy may be derived. In the inverted blister test, a circular crack is propagated due to water pressurizing at the scale-metal interface. In the three-point bending test, the interface is mechanically loaded using a rigid counterplate glued to the external surface of the scale. In the tensile test, the oxide scale is forced to spall, releasing the elastic energy stored. Examples of measurements are given, where it is shown that adhesion values depend on the test used, particularly on the mixed mode angle at the crack tip.