| Résumé : |
Corrosion that proceeds laterally from the sites of initiation along planes parallel to the surface, generally at grain boundaries, forming corrosion products that force metal way from the body of the material, giving it a layered appearance, is known as exfoliation or layer or lamellar corrosion. Any alloy that has been extruded or otherwise worked heavily, resulting in a microscopic structure of elongated, flattened grains, is particularly prone to this type of deterioration. As deterioration occurs along the grain boundaries the resulting corrosion by products exert pressure between the adjacent grains resulting in a lifting or leafing effect. This type of deterioration often initiates at the end grains of the metal that are exposed at machined edges, holes, or grooves and can progress through an entire section.
The damage of metal or alloy by atomic hydrogen involves the ingress of hydrogen into a component, an event that can seriously reduce the ductility and load-bearing capacity, cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Hydrogen damage occurs in a number of forms but the common features are an applied tensile stress and hydrogen dissolved in the metal. Hydrogen in metals can produce several kind of internai defects like blisters, shatter fractures, flakes, fish eyes and porosity etc. |
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Forms of corrosion : exfoliation corrosion and hydrogen damage - Part 11 in PAINTINDIA, Vol. LXIV, N° 3 (03/2014)
