A CRITICAL REVIEW ON DIFFERENT TYPES OF WEAR OF MATERIALS

International Journal of Mechanical Engineering and Technology (IJMET) Volume 6, Issue 11, Nov 2015, pp. 77-83, Article ID: IJMET_06_11_009 Available online at http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=6&itype=11 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication A CRITICAL REVIEW ON DIFFERENT TYPES OF WEAR OF MATERIALS Dr. A. Devaraju Principal and Professor, Department of Mechanical Engineering, Adhi College of Engineering and Technology, Affiliated to Anna University, Kanchipuram-631 605, Tamilnadu, India ABSTRACT Many mechanical equipments are subjected to sliding contact in real time applications. Pumps, valves, belt drives, bearings, machinery guide ways, piston- cylinder arrangements etc. are the few important sliding components which are continuously subjected to sliding wear. Much mechanical equipment s failure occurred due to wear related problems. Therefore, understanding of different wear mechanism is important to design the mechanical components. In this paper, various wear mechanisms have been discussed with the help previous published research works and text books. Key words: Wear Mechanism, Wear Rate, Mechanical Components, Lubrication Cite this Article: Dr. A. Devaraju. A Critical Review on Different Types of Wear of Materials, International Journal of Mechanical Engineering and Technology, 6(11), 2015, pp. 77-83 http://www.iaeme.com/currentissue.asp?jtype=ijmet&vtype=6&itype=11 1. INTRODUCTION When two solid surfaces are in contact, there is damage to the surface and/or subsurface. Wear is the removal of solid metal from the one or both surface of which are in solid state contact. Wear is quantified by the term 'wear rate' which is defined as "the mass or volume or height loss of material removed per unit time or sliding distance". The wear is characterized by mild and severe wear. The outcome of mild wear, the worn surfaces is smooth and smaller in wear debris (typically 0.01µm to 1µm in particle size). In contrast, the severe wear results in larger wear debris size (20 µm to 200 µm) which can be seen in naked eye and roughened worn surface. The important wear mechanisms are adhesive wear, abrasive wear, delamination wear, erosive wear, fretting wear, fatigue wear and corrosive wear [1]. The wear behavior of materials is important in tribology like frictional force [2]. The wear surfaces can be protected http://www.iaeme.com/ijmet/index.asp 77 editor@iaeme.com

Dr. A. Devaraju mainly in two ways: (1) separation of surfaces by applying a lubricant, and (2) surface modification. 2. WEAR AND ITS MECHANISMS As per available literature and current researcher s knowledge concerned, seven important types of wear mechanisms exhibit for different metal pairs. These seven mechanisms are discussed as follows; 2.1. Adhesion Adhesive wear is due to transfer of material from one surface to another surface by shearing of solid welded junctions of asperities. It leaves pits, voids, cavities or valley on the surface [3]. This wear occurs because of the adhesive bond. At the contact points, the adhesive bond is stronger than the cohesive bond of the weaker material of the Pair. Normally, adhesion occurs when two similar chemical composition metals are in contact or contact surface are free from oxide layer (vacuum or an inert atmosphere).fig. 1.illustrates the adhesive wear mechanism of steel vs. indium Pair. Figure 1 A schematic diagram illustrating adhesive wear mechanism [4]. When a clean steel or brass rounded end rod is pressed on the block of soft and ductile metals such as lead and indium, strong adhesion will occur. When the rod is removed, a fragment of soft metal (indium) adheres to the rod. It shows that the adhesive strength of the contact junctions are stronger than the cohesive strength of indium. The small addition of alloying element in the bulk material can alter the adhesion between the solid surfaces. For example, the addition of sulfur in steel enhances its machinability. Further, during sliding process, the iron sulfide comes out of the surface and reduces friction as well as wear. Similarly, the cast iron produces better tribological property than iron based alloys. The reason is that the graphite becomes smeared out over the contact zone and provides a lubricating film [3]. In the case of dissimilar metals, when the mutually insoluble metals come in contact with each other, they would generally exhibit poor adhesion [2,5,6]. However, if the surfaces are atomically clean, the adhesion would be strong for this case also. Irrespective of solubility, the degree of softness also plays an important role in adhesion. The soft metals exhibit a large real area of contact which is responsible for high adhesion [7]. Although the use of lubricants at the contact surfaces reduces the surface energy, the condensate of liquid film or pre-existing film can significantly increase the adhesion [8,9]. 2.2. Abrasion Wear occurs due to hard particles or protuberances sliding along a soft solid surface. It results in ploughing, wedging and cutting phenomena. In ploughing (also called ridge formation) process, material is displaced at both the sides and forms a groove with or without removal of material. The fundamental abrasive wear mechanism is shown in Fig.2. There are two modes of abrasive wear: (1) Single body abrasive wear http://www.iaeme.com/ijmet/index.asp 78 editor@iaeme.com

A Critical Review on Different Types of Wear of Materials (Fig. 2(a)) in which abrasive marks will occur on one surface. The practical example for single body abrasive wear is grinding, cutting and machining. (2) Two body abrasive wear (Fig. 2(b)) in which abrasive marks will occur on both surfaces. In tribological systems, the debris becomes entrapped between the contact surfaces and makes grooves on one or both the contact surfaces. In some practical applications like polishing process, the abrasive particles are beneficial or desirable since it produces polished surfaces. The ridges formed during abrasion or ploughing process become flattened after some sliding distance and fractured due to repeated cyclic system [10, 11]. It also causes subsurface deformation and surface as well as subsurface crack nucleation. The hardness is an important property to control the abrasive wear. The experimental evidence reported that the wear rate of two body abrasions is inversely proportional to the hardness [12] and proportional to the normal load and abrasive particle size for many pure metals [13]. However, the complex behavior has been observed for alloys [14-16]. Wear resistance of annealed pure metals are also directly proportional to their hardness but more complex for alloys [12, 17, 18]. The reason for decrease of wear rate for longer sliding distance experiments has been reported as (a) result of blunting of abrasive surfaces and (b) clogging of the abrasive surface by wear debris [2]. Figure 2 A schematic diagram of abrasive wear mechanism (a) Single body abrasive (b) Two body abrasive [3] 2.3. Erosive wear Wear due to mechanical interaction between solid surface and fluid, or impinging liquid or solid particles is called erosive wear. When particles with some velocity are impacted on the surface of metal, the pits and large scale subsurface deformation occur on the metal surface. The best example is when the rain droplets with different velocities hit normal earth surface; it removes the surface and causes erosive wear. In http://www.iaeme.com/ijmet/index.asp 79 editor@iaeme.com

Dr. A. Devaraju plasma nitriding process, the sputtering is done to clean the specimens. In sputtering, the argon ion which is in the gaseous form strikes the specimen surface and removes the oxide layer. From the practical point of view, the erosive wear is important. However, in some experiments conducted with ceramic surfaces, the impingement of silicon carbide particles with high velocity causes localized surface melting [19]. There is a fundamental relationship between material loss and cohesive binding energy of the metal. It has been proved that the cohesively stronger metals exhibit lower erosive wear than cohesively weaker metals [20]. 2.4. Fretting wear Wear due to small amplitude of oscillatory or reciprocating movement between two surfaces is known as fretting wear. It is a two step mechanism. Initially, the adhesive wear occurs due to rubbing of two surfaces and then they become oxidized due to large quantity of energy stored in wear particles. 2.5. Fatigue/ Delamination wear Wear caused by fracture arising from surface fatigue due to cyclic loading is called Fatigue/ Delamination wear. It results in a series of pits or voids. It usually occurs in rolling or sliding contact bodies such as bearings, roads, etc. After repeated cyclic loading, a crack is observed on the subsurface or the surface. The subsurface cracks propagate, connect with other cracks, reach the surface and generate wear particles. Similarly, the surface cracks move downward into bulk, connect with other cracks and liberate a wear particle. The crack propagation is influenced by a number of factors. The relative humidity in the air is one of the important factors. It has been experimentally reported that the crack growth occurs rapidly in high moisture environment rather than in dry air [21]. 2.6. Corrosive/ Oxidative wear Corrosive wear occurs when sliding takes place in corrosive or oxidative environment. During dry sliding also, the oxygen from the normal environment or other gases present in the environment can react with the solid surface. The excessive presence of antiwear additives or other chemical agents also can bring corrosive wear. At elevated temperature, oxygen can interact with sliding surface and form oxides called oxidative wear. For example, oxidation of Inconel (nickel chromium alloys containing some iron) occurs at 100ºC resulting in the formation of nickel oxide (NiO) and chromium oxide (Cr 2 O 3 ). However, when the temperature is increased to 280ºC, the surface contains spinel of NiFe 2 O 4 near the surface and Cr 2 O 3 near the metal interface [22]. It results in the formation of weak, mechanically incompatible corrosive/oxide layer. 2.7. Deformation and Ploughing When hard rough surface slides over a soft metal surface, the frictional resistance is mainly developed by the asperities of hard surface ploughing through soft material [23]. The force required for plastic flow of softer material represents the friction coefficient. The ploughing of the surfaces by hard asperities and wear particles is found to be the most important mechanism in most sliding situations [24]. http://www.iaeme.com/ijmet/index.asp 80 editor@iaeme.com

A Critical Review on Different Types of Wear of Materials 3. LUBRICATION Lubrication is the process of introducing lubricants between contact surfaces to reduce the frictional force. The main property of the lubricant is that it should produce very lower shear strength and form a layer between the sliding surfaces [25]. In some lubricating systems, although the lubricant film may not completely separate the asperity contacts, it reduces the strength of the junctions formed. In other cases, the lubricant film completely separates the surfaces and no asperity junctions are formed at all. Regimes of lubrication are normally associated with dominant lubrication mechanism involved in the mechanical system. The three main methods of lubrication are: (1) hydrodynamic (or full film) lubrication, (2) boundary lubrication, and (3) mixed lubrication [26]. Figure3 Methods of lubrication (a) Hydrodynamic lubrication (b) Boundary lubrication and (c) Mixed lubrication In hydrodynamic lubrication (Fig. 3(a)), the adequate pressure of fluid is supplied between two contact surfaces which are in relative motion. The layers of fluid completely separate the contact surfaces and support the load. In boundary lubrication regime (Fig.3(b)), thin mono-layer of fluid film is formed between the frequent asperity contact that leads to high values of coefficient of friction and wear compared to hydrodynamic lubrication. Mixed film lubrication (Fig.3(c)) is the combination of http://www.iaeme.com/ijmet/index.asp 81 editor@iaeme.com

Dr. A. Devaraju full film lubrication and boundary lubrication. Boundary lubrication can be defined as the regime in which average film thickness is less than the composite roughness. 4. CONCLUSION The various types of wear mechanism and different lubrication process have been discussed in detail. This review concludes that wear cannot be completely eliminated between the sliding surfaces. However, it can be reduced (1) by applying lubricants between sliding surfaces, (2) hardening the contact surfaces by mechanical and chemical process and (3) designing the component material according to sliding contact conditions. Wear is occurred by combination of two or more wear mechanisms. Hence, understanding of wear mechanisms exhibited between sliding surfaces are important while designing the any mechanical component. REFERENCES [1] Halling, J. Principles of tribology, Macmillan Education Ltd., London, 1978. [2] Rabinowicz, E. Friction and Wear of Materials, Second edition, Wiley, New York, 1995. [3] Buckley, D. H. Surface effects in Adhesion, Friction, Wear and Lubrication, Elsevier Scientific Publishing Company, New York, USA, 1981. [4] Hucthings, I. M. Tribology: Friction and Wear of Engineering Materials, Edward Arnold, London, 1992. [5] Keller, D. V. Adhesion between solid metals, Wear, Vol.6, pp. 353-365, 1963. [6] Keller, D. V. Recent results in particle adhesion: UHV measurements, light modulated adhesion and the effect of adsorbates, J. Adhesion, pp. 83-86, 1972. [7] Bhushan, B. Principles and Applications of Tribology, A Wiley- Interscience Publication, John wiley& sons, Inc., New York, 1999. [8] Adamson, A.W. Physical chemistry of surfaces, 5th edition, Wiley, New York, 1990. [9] Israelachvili, J. N. Intermolecular and Surface Forces, 2nd edition, Acadamic, San Diego, 1992. [10] Stout, K. J., King, T. G. and Whitehouse, D. J. Analytical techniques in surface topography and their application to a running in experiment, Wear, Vol. 43, pp. 99-115, 1977. [11] Suh, N. P. Tribophysics, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1986. [12] Kruschov, M. M. Resistance of metals to wear by abrasion as related to hardness, in Proc. Conf. Lubrication and wear, Instn.Mech. Engrs.Lond., UK, pp. 655-659, 1957. [13] Misra, A. and Finnie, I. Some observations on two body abrasive wear, Wear, Vol. 68, pp. 41-56, 1981. [14] Mulhearn, T. O. and Samuels, L. E. In abrasion of metals: A model of the process, Wear, Vol. 5, pp. 478-498, 1962. [15] Goddard, J. and Wilman, M. A theory friction and wear during the abrasion of metals, Wear, Vol. 5, pp. 114-135, 1962. [16] Moore, M. A. and King, F. S. Abrasive wear of brittle solids, Wear, Vol. 60, pp. 123-140, 1980. [17] Kruschov, M. M. Principles of abrasive wear, Wear, Vol. 28, pp. 69-88, 1974. http://www.iaeme.com/ijmet/index.asp 82 editor@iaeme.com

A Critical Review on Different Types of Wear of Materials [18] Kruschov, M. M. and Babichev, M. A. Resistance to abrasive wear of structurally inhomogeneous materials, Friction and wear in machinery, ASME, New York, Vol. 12, pp. 5-23, 1958. [19] Yust, C. S. and Crouse, R. S. Melting at particle impact sites during erosion of ceramics, Wear, Vol. 51, pp. 335-343, 1978. [20] Vijh, A. K. Resistance of metals to erosion by solid particles in relation to the solid state cohesion of metals, Wear, Vol. 39, pp. 173-175, 1976. [21] Endo, K. and Goto, H. Effects of environment on fretting fatigue, Wear, Vol. 48, pp. 347-367, 1978. [22] McIntyre, N. S., Zetaruk, D. G. and Owen, D. XPS study of initial growth of oxide film on Inconel 600 alloy, Appl. Surf. Sci., Vol. 2, pp. 55-73, 1978. [23] Bowden, F. P. and Tabor, D. The Friction and Lubrication of Solids, Part-I, Clarendon Press, Oxford, 1950. [24] Kim, D. E. and Suh, N. P. On microscopic mechanisms of friction and wear, Wear, Vol. 149, pp. 199-208, 1991. [25] Ludema, K. C. Friction, wear, lubrication A text book in Tribology, CRC press, New York, 1996. [26] Stachowiak, G. W. and Batchelor, A. W. Engineering tribology, Butterworth Heinemann, 2001. [27] Santhosh Sivan. K, Chandrasekar Sundaram, Hari Krishnan. R and Anirudh Srinivasan. Fairing Flap Drag Reduction Mechanism (FFDRM), International Journal of Mechanical Engineering and Technology, 5(9), 2014, pp. 435 439. [28] Qayssar Saeed Masikh, Dr. Mohammad Tariq and Er. Prabhat Kumar Sinha. Analysis of A Thin and Thick Walled Pressure Vessel for Different Materials, International Journal of Mechanical Engineering and Technology, 5(10), 2014, pp. 9-19. http://www.iaeme.com/ijmet/index.asp 83 editor@iaeme.com