*2.4.1 Introduction*

Generally, the term wear is defined as material removal or surface damage on the one or two surfaces while rolling, sliding or impact motion relative to one another. Particularly, the wear happens through surface interactions at asperities. While two objects/components in relative motion, the material can be displaced from the interacting surfaces. Consequently, the properties of the material may be changed at least or interface region. But, there is a possibility for less or no material losses. Then, the displaced material can be removed from the interacting surfaces and may cause the material transfer to the counterpart surface or may break as small wear debris. When material transfer from bulk to counterpart, the net mass or volume loss of the interacting surface is zero while the bulk material surface is worn. The wear loss leads the real material loss, and this may occur sometimes independently.

Generally, the wear is a system output and it is not a material property. In addition to that the working atmosphere affect the interface wear. In some cases, mistakenly assumed that the higher frictional force displays the increase in wear rate. For example, the polymers and solid lubricant interfaces showed with higher wear and lesser friction, whereas ceramic material showed the lower wear but moderate frictional force. In all the dynamic machine components such as cams, bearings and seals, the wear is almost undesirable one. Those components or machines need to be replaced after a small damage or material loss or if the surface showed with higher roughness. If the system is well defined in tribology, the material removal will be very slow and at the same time it must be continuous with steady process.

## *2.4.2 Classification of wear mechanism*

The wear occurs chemically or mechanically means and is normally induced through frictional heat. Mainly, the wear contains six principal quite distinct phenomena that have only one thing in common; the removal of material from the rubbing interface [24, 25]. The wear can be classified as follows: (1) abrasive; (2) adhesive; (3) fatigue; (4) impact by erosion; (5) corrosive; (6) electrical-arcinduced wear. The other commonly raised wear is fretting corrosion and fretting. However, the wear such as abrasive, adhesive and corrosive are the major combinations of wear. Based on the previously encountered issues, the abrasive and adhesives are the major wear mechanisms in the industry.

#### *2.4.2.1 Abrasive wear*

The abrasive wear happens while asperities of a rough and hard particles slides on the softer surface and remove the softer material and finally damages the surface through fracture or plastic deformation. Most of the ceramic and metallic materials with high toughness and hard particles result in the plastic stage of the soft material. Even the metal interfaces will deform plastically while applying higher loads. The abrasive wear can be occurred generally in two different situations as shown in **Figure 7**. In the beginning, the hard surface is the harder of two rubbing surfaces like two body abrasion. For example, in cutting, grinding and machining. In another case, the hard surface is the third body. Particularly, this must be small abrasive particle, identified in between the other two surfaces and this may be sufficiently harder. This may be able to scratch either one or both the sliding surfaces.

#### **Figure 7.**

*(a) Schematics of hard rough surface mounted with abrasive grits sliding on a softer surface and (b) free abrasive grits caught between the two surfaces.*

**195**

**Figure 8.**

*SEM picture of steel surface after abrasive wear with dry condition.*

*Friction, Lubrication, and Wear*

*2.4.2.2 Adhesive wear*

with loose particle formation.

other surface.

*DOI: http://dx.doi.org/10.5772/intechopen.93796*

In most of the cases, the adhesive is the begging mechanism of wear on the sliding surface and this wear debris get trapped into interfaces of mating surfaces, subsequently resulting the three-body abrasive wear [26]. Further, the scratching can be observed in many cases as a continuous groove which is parallel to the sliding direction. The worn-out surface of steel against hardened steel disc with dry condition is shown in **Figure 8**. From the scanning electron micrograph (SEM), the

Generally, the adhesive wear can be occurred while two solid body sliding on the flat surfaces with dry or lubrication. The bonding of metals is happening at the asperity contacts at the interface, and these contacts is sheared through sliding process, which may produce the plowing of material from softer surface to harder surface. With continuous sliding process, the transferred wear debris is stop on the transferred surface and the same debris may return to original surface or else this may be loose as wear debris particle. In some cases, the debris may have fractured through fatigue process with continuous loading and unloading process and causes

There is some mechanism was explained for the fragment detachment of a material. However, still the well identified mechanism for adhesion is shearing of the two solid bodies or the weakest surface from one of the two surface [27]. The schematic representing the two possible way of metal breaking through shearing process as shown in **Figure 9**. Normally, the interface adhesion strength is assumed to be lesser while compared with breaking strength of nearby regions; hence, the break through shearing arise at the interface regions (path 1) in many cases and there will be no material loss happen during these sliding process. In another case, with lesser fraction of contacts, break may happen in any one of the two solid bodies (path 2) and a minor piece of material (the blue dotted semi-circle) can be attached to the harder

The SEM picture (**Figure 10**) shows the steel worn out surface with adhesion wear. From the **Figure 10**, it can be seen clearly that the adhesive debris pullout from the softer surface. During the sliding process, the surface asperities severely suffer from fracture or plastic deformation. Further, the subsurface also underwent strain hardening and plastic deformation. The SEM micrograph of worn-out surface shows the severe pull out material with plastic deformation. In the picture, the yellow

continuous scratching is visible parallel to the sliding direction.

#### *Friction, Lubrication, and Wear DOI: http://dx.doi.org/10.5772/intechopen.93796*

In most of the cases, the adhesive is the begging mechanism of wear on the sliding surface and this wear debris get trapped into interfaces of mating surfaces, subsequently resulting the three-body abrasive wear [26]. Further, the scratching can be observed in many cases as a continuous groove which is parallel to the sliding direction. The worn-out surface of steel against hardened steel disc with dry condition is shown in **Figure 8**. From the scanning electron micrograph (SEM), the continuous scratching is visible parallel to the sliding direction.
