**2. Basics of metal corrosion**

Commonly, metal corrosion is defined as the deterioration of metals as a result of exposure to a corrosive environment, such as the atmosphere or even more aggressive corrosive media like seawater and chemical plants [3]. Definitely, our daily life is negatively affected by metal corrosion as automobiles, buildings, infrastructure, appliances, and energy distribution systems are all susceptible to corrosion because of metal pieces. Metals are rarely used in pure form (only in special applications), and they are generally used as alloys. There are many debates about which pure metal or alloy is the best, but what is clear is that alloys can provide unique properties. For instance, stainless steel, which is an alloy of iron, is more resistant to corrosion and has a slower corrosion rate than pure iron. In addition, it is an extremely tough and highly durable material with high impact resistance in comparison with pure iron [4]. But this does not necessarily mean that alloys do not corrode. Therefore, it can be said that corrosion in metals and even alloys is inevitable and measures must be taken to prevent it. Before pointing out the methods to prevent metal corrosion, it is beneficial to understand the causes and mechanisms of metal corrosion. Although corrosion is mainly a chemical phenomenon, mechanical factors, such as tensile or compressive forces and wear, can also aggravate it in many situations called mechanically assisted corrosion. For example, in offshore environments, waves, tides, and strong winds can cause mechanically assisted corrosions such as stress-corrosion cracking, fatigue corrosion, corrosion-erosion, and fretting-corrosion [5]. **Figure 1** depicts the most common types of mechanically assisted corrosion.

*Self-Healing Coatings DOI: http://dx.doi.org/10.5772/intechopen.109500*


#### **Figure 1.**

*The most probable types of mechanically assisted corrosion [5].*

Generally, Corrosion consists of a series of complex chemical reactions and may initiate by several different mechanisms that depend on the surrounding environment and involves simultaneous oxidation and reduction reactions. In fact, first, an aqueous adlayer forms on the metal surface followed by electrochemical and chemical reactions. Furthermore, corrosion products may participate in these reactions. The mechanism and rate of chemical reactions that lead to corrosion depending on the corrosive factors in the surrounding environment which cause various classifications

of corrosion. The most important factor contributing to metal corrosion can be classified as following [ 6 ]:


The most common types of metal corrosion can be listed as follows:
