Metallurgy pitting corrosion

The complex interactions between these factors may cause major differences on how pitting corrosion will initiate and develop in real situations. Copper, for example, a relatively simple material in terms of its metallurgy, can suffer three well-documented types of pitting corrosion depending on specific conditions in the water it carries ... 

Metallurgy, the science of producing useful metallic materials, almost always requires some kind of compromise. In the case of stainless steel, inclusions of MnS make the steel easier to machine into useful parts, but such inclusions are also the source of pit corrosion. Recently a group of British researchers analyzed stainless steel using a high-energy beam of ions that blasted atoms loose from the steel surface. Studies of the resultant atom vapor revealed the source of the problem. It turns out that when the stainless steel is cooling, the... 

Coupon tests involved a number of metallurgies and were done to evaluate precipitator-plate alloys. Test stainless steel plates failed, not only because of pitting but also because stress-corrosion cracks developed. 

The metallurgical characteristics of the aluminum oxide layer also depend on its physical metallurgy, such as defects and metallurgical structure included in the oxide layer. For instance, when intermetallic compound particles as secondary phases are exposed on the surface, a discontinuous oxide film with various defects is often produced at the metal-particle interface. This discontinuous oxide film is weakly or non-protective chemically and physically. Because corrosion is a chemical and electrochemical reaction on the surface, corrosion behavior is readily influenced by surface morphology. The aluminum surface is usually adsorbed or contaminated by water, gases and many kinds of micron-sized substances. Microscopic heterogeneous structures such as vacancies, steps, kinks, and dislocations, and macroscopic heterogeneous structures such as scratches, pits and other superficial blemishes influence the corrosion behavior of aluminum and its alloys to different extents. 

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