Metallurgy Phenomena

Corrosion

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen.

Corrosion on Heating Oil Tank. Source : https://www.bushman.cc/

Formation of an oxide of iron due to oxidation of the iron atoms in solid solution is a well-known example of electrochemical corrosion, commonly known as rusting. This type of damage typically produces oxide(s) and/or salt(s) of the original metal. Corrosion can also refer to other materials than metals, such as ceramics or polymers, although in this context, the term degradation is more common.
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Hydrogen Embrittlement

Hydrogen Embrittlement in carbon steel, zinc plated part. Source:https://www.atclabs.com/
When tensile stresses are applied to a hydrogen embrittled component it may fail prematurely.  Hydrogen embrittlement failures are frequently unexpected and sometimes catastrophic.  An externally applied load is not required as the tensile stresses may be due to residual stresses in the material.  The threshold stresses to cause cracking are commonly below the yield stress of the material. High strength steel, such as quenched and tempered steels or precipitation hardened steels are particularly susceptible to hydrogen embrittlement.   Hydrogen can be introduced into the material in service or during materials processing.

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Dislocation Phenomena

The Dislocation defect in crystals

In materials science, a dislocation is a crystallographic defect or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials. The theory was originally developed by Vito Volterra. Some types of dislocations can be visualized as being caused by the termination of a plane of atoms in the middle of a crystal. In such a case, the surrounding planes are not straight, but instead bend around the edge of the terminating plane so that the crystal structure is perfectly ordered on either side.

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