**4.5 Corrosive and oxidation wear**

Metal surface is normally covered with a layer of oxide, which could restrict metal-to-metal interaction, and therefore evading the development of adhesion and reducing the tendency of adhesive wear. In this connection, oxide is a favorable factor in reducing wear rate of metallic materials. However, whether such beneficial effect can be realized or not, is intensely reliant on the material properties and on contact conditions. When the hardness of the metal underlying an oxide layer is low, or when the contact load is relatively higher, the metal beneath the oxide layer will deform plastically, and asperities in the rigid surface will penetrate through the thin oxide layer, leading to the normal metal-to-metal contact. In such case, wear by abrasion or adhesion will occur depending on the mechanical properties and chemical properties of the contacting metals. The beneficial effect of oxide is minimal and wear rate is generally high. On the other hand, when the underlying metal is hard enough to support the oxide film, such as on a surface engineered hard surface, a process known as oxidation wear (**Figure 16**) will occur.

It needs to be mentioned that during sliding, the increased surface temperature promoted by frictional heating, and the less activation energy of oxide formation caused by plastic deformation, can increase the oxidation rate. Thus, rapid oxidation can be achieved, and the oxide layer can grow thicker during sliding than that

**291**

in the chamber.

*Wear: A Serious Problem in Industry*

by some orders of magnitude.

**6. Types of surface coating**

**6.1 Physical vapor deposition (PVD) coating**

materials selection should be considered carefully.

**6.2 Chemical vapor deposition (CVD) coating**

**6.3 Micro-arc oxidation (MAO) coating**

*DOI: http://dx.doi.org/10.5772/intechopen.94211*

under static conditions. This ensures the fresh metal is rapidly covered with a new layer of oxide after the original oxide film was worn away. Oxidation wear will not happen in vacuum or in inert atmosphere, since re-oxidation is not possible. Oxidation is a minor form of wear. When the predominant wear mechanism is changed from abrasive or adhesive to oxidation wear, degree of wear can be reduced

As wear is a surface or near surface phenomenon it has long been realized that the wear resistance of a component can be improved by providing a surface of different composition from the bulk material. After a brief introductory chapter wear phenomena and the properties required from a coating are addressed. Coating processes provide protection to a specific part or area of a structure exposed to harsh and corrosive environments in different fields ranging from aerospace and the automotive industry to tiny biomedical devices and implants inside the human body.

PVD process is well-known for offering corrosion, wear resistance, and thin protective films on the surface of the materials that are exposed to corrosive media, and its applications range from decorative objects to industrial parts. The benefit of this technique is that the mechanical, corrosion, and esthetic properties of the coating layers could be adjusted on demand. Generally, PVD is a method that occurs in a high vacuum, and the solid/liquid materials transfer to a vapor phase followed by a metal vapor condensation, which creates a solid and thick film. The common types of PVD methods are sputtering and evaporation. Since the coating layers created by PVD are thin in nature, there is always a need for multilayered coatings while the

Another type of vapor deposition is called CVD. This process undergoes a high vacuum and is widely used in the semiconductors industry providing a solid, high quality, and a high resistance coating layer on any substrate. CVD can be used for mechanical parts in continuous interaction, which need protection for corrosion and wear. In this method, the substrate, known as a wafer, would be exposed to a set of volatile material precursors where a chemical reaction creates a deposition layer on the surface of the material. However, some by products of these chemical reactions, which are removed by continuous airflow of the vacuum pump, can stay

MAO method is known as a flexible method of coating concerning the composition of coatings. In general, MAO utilizes a high voltage difference between anode and cathode to generate micro-arcs as plasma channels. When these arcs hit the substrate, they melt a portion of the surface, depending on the intensity of the microarcs. Simultaneously, plasma networks discharge their pressure, which supports the

**5. Use of surface coating for the protection from wear**

**Figure 16.** *Corrosive wear mechanism.*

*Wear: A Serious Problem in Industry DOI: http://dx.doi.org/10.5772/intechopen.94211*

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

Fretting wear arises as a result of the following order of events:

shaves the asperities and produces wear debris that stores.

cracks can be produced in one or both surfaces.

surface, a process known as oxidation wear (**Figure 16**) will occur.

**4.5 Corrosive and oxidation wear**

surfaces.

• The normal load causes asperities to stick and the tangential oscillatory motion

• The surviving (harder) asperities eventually act on the smooth surfaces causing them to undergo plastic deformation, create voids, propagate cracks and shear off sheets of particles which also gather in depressed areas of the

• Once the particles have accumulated sufficiently to span the gap among the surfaces, abrasion wear follows and the wear zone extents laterally.

• As adhesion, delamination, and abrasion wear lasts, wear debris can no longer be contained in the primary zone and it outflows into surrounding valleys.

• Because the maximum stress is at the center, the geometry becomes curved, micropits form and these coalesce into larger and deeper pits. Finally, depending on the displacement of the tangential motion, worm tracks or even big

Metal surface is normally covered with a layer of oxide, which could restrict metal-to-metal interaction, and therefore evading the development of adhesion and reducing the tendency of adhesive wear. In this connection, oxide is a favorable factor in reducing wear rate of metallic materials. However, whether such beneficial effect can be realized or not, is intensely reliant on the material properties and on contact conditions. When the hardness of the metal underlying an oxide layer is low, or when the contact load is relatively higher, the metal beneath the oxide layer will deform plastically, and asperities in the rigid surface will penetrate through the thin oxide layer, leading to the normal metal-to-metal contact. In such case, wear by abrasion or adhesion will occur depending on the mechanical properties and chemical properties of the contacting metals. The beneficial effect of oxide is minimal and wear rate is generally high. On the other hand, when the underlying metal is hard enough to support the oxide film, such as on a surface engineered hard

It needs to be mentioned that during sliding, the increased surface temperature promoted by frictional heating, and the less activation energy of oxide formation caused by plastic deformation, can increase the oxidation rate. Thus, rapid oxidation can be achieved, and the oxide layer can grow thicker during sliding than that

**290**

**Figure 16.**

*Corrosive wear mechanism.*

under static conditions. This ensures the fresh metal is rapidly covered with a new layer of oxide after the original oxide film was worn away. Oxidation wear will not happen in vacuum or in inert atmosphere, since re-oxidation is not possible. Oxidation is a minor form of wear. When the predominant wear mechanism is changed from abrasive or adhesive to oxidation wear, degree of wear can be reduced by some orders of magnitude.
