2. C. Lutynski, G. Simansky, and A.J. McEvily, Fretting Fatigue of Ti-6Al-4V Alloy, Materials Evaluation Under Fretting Conditions, STP 780, ASTM, 1982, p 150-164 3. R.G. Bayer, Mechanical Wear Prediction and Prevention, Marcel Dekker, 1994 4. R.G. Bayer, Wear Analysis for Engineers, HNB Publishing, New York, 2002 5. R. M. Voitik, Realizing Bench Test Solutions to Field Tribology Problems by Utilizing Tribological Aspect Numbers, Tribology: Wear Test Selection for Design and Application, STP 1199, A W. Ruff and R.G. Bayer, Ed, ASTM, 1993 6. P.J. Blau, Ed, Friction, Lubrication, and Wear Technology, Vol 18, ASM Handbook, ASM International. 1992 7. P.J. Blau, Friction and Wear Transitions of Materials, Noyes Publications, Park Ridge, NJ, 1989 8. S.C. Lim and M. F. Ashby, Acta Metall., Vol 35(No. 1), 1987, p 1-24 9. R.G. Bayer, Mechanical Wear Prediction and Prevention, Marcel Dekker, 1994, Section C2 10. A W. Ruff and R.G. Bayer, Ed, Tribology: Wear Test Selection for Design and Application, STP 1199 ASTM. 1993 11. M. Anderson and F.E. Schmidt, Jr, Wear and Lubricant Testing, Chapter 25, ASTM Manual on Fuels, Lubricants, and Standards: Application and Interpretation, ASTM, 2002 Abrasive wear Failures Jeffrey A. Hawk and Rick D. Wilson, Albany Research Center; Daniel R. Danks, Danks Tribological Services; Matthew T. Kiser, Caterpillar Inc. Abrasive wear mechanisms Of all the areas where abrasive wear is a problem, probably the most severe environment is in the excavation earth moving, mining, and minerals processing industries, where component deterioration occurs in a wide variety of equipment, such as bulldozer blades, excavator teeth, rock drill bits, crushers, slushers, ball mills and rod mills, chutes, slurry pumps, and cyclones. However, abrasive wear is not limited to these activities Abrasion presents problems in many wear environments at one point or another, even though it may not be the primary wear mechanism to begin with. In any tribosyste m where dust and wear debris are not, or cannot be controlled and/or excluded, abrasive wear is eventually a major problem. The wear of parts, the cost of repair and replacement of these parts, and the associated downtime related to these activities result in significant costs The individual factors that influence abrasive wear behavior are shown in Table 2 for both the abrasive and wear material, the majority of factors that affect abrasive wear behavior are related to their respective mechanical properties. Also of importance is the mechanical aspect of the abrasive/wear material interaction Chemical processes, however, are also important, that is, corrosion or oxidation, because they directly influence the rate of wear of a material in the environment of interest Table 2 Factors influencing abrasive wear behavior Abrasive properties Particle size Thefileisdownloadedfromwww.bzfxw.com
2. C. Lutynski, G. Simansky, and A.J. McEvily, Fretting Fatigue of Ti-6Al-4V Alloy, Materials Evaluation Under Fretting Conditions, STP 780, ASTM, 1982, p 150–164 3. R.G. Bayer, Mechanical Wear Prediction and Prevention, Marcel Dekker, 1994 4. R.G. Bayer, Wear Analysis for Engineers, HNB Publishing, New York, 2002 5. R.M. Voitik, Realizing Bench Test Solutions to Field Tribology Problems by Utilizing Tribological Aspect Numbers, Tribology: Wear Test Selection for Design and Application, STP 1199, A.W. Ruff and R.G. Bayer, Ed., ASTM, 1993 6. P.J. Blau, Ed., Friction, Lubrication, and Wear Technology, Vol 18, ASM Handbook, ASM International, 1992 7. P.J. Blau, Friction and Wear Transitions of Materials, Noyes Publications, Park Ridge, NJ, 1989 8. S.C. Lim and M.F. Ashby, Acta Metall., Vol 35 (No. 1), 1987, p 1–24 9. R.G. Bayer, Mechanical Wear Prediction and Prevention, Marcel Dekker, 1994, Section C2 10. A.W. Ruff and R.G. Bayer, Ed., Tribology: Wear Test Selection for Design and Application, STP 1199, ASTM, 1993 11. M. Anderson and F.E. Schmidt, Jr., Wear and Lubricant Testing, Chapter 25, ASTM Manual on Fuels, Lubricants, and Standards: Application and Interpretation, ASTM, 2002 Abrasive Wear Failures Jeffrey A. Hawk and Rick D. Wilson, Albany Research Center; Daniel R. Danks, Danks Tribological Services; Matthew T. Kiser, Caterpillar Inc. Abrasive Wear Mechanisms Of all the areas where abrasive wear is a problem, probably the most severe environment is in the excavation, earth moving, mining, and minerals processing industries, where component deterioration occurs in a wide variety of equipment, such as bulldozer blades, excavator teeth, rock drill bits, crushers, slushers, ball mills and rod mills, chutes, slurry pumps, and cyclones. However, abrasive wear is not limited to these activities. Abrasion presents problems in many wear environments at one point or another, even though it may not be the primary wear mechanism to begin with. In any tribosystem where dust and wear debris are not, or cannot be, controlled and/or excluded, abrasive wear is eventually a major problem. The wear of parts, the cost of repair and replacement of these parts, and the associated downtime related to these activities result in significant costs to many industries. The individual factors that influence abrasive wear behavior are shown in Table 2. For both the abrasive and wear material, the majority of factors that affect abrasive wear behavior are related to their respective mechanical properties. Also of importance is the mechanical aspect of the abrasive/wear material interaction. Chemical processes, however, are also important, that is, corrosion or oxidation, because they directly influence the rate of wear of a material in the environment of interest. Table 2 Factors influencing abrasive wear behavior Abrasive properties Particle size The file is downloaded from www.bzfxw.com
Particle shape Yield strength fracture properties Concentratie Contact conditions Force/impact level Impact/impingement angle Sliding/rolling Temperature Wetd pH Wear material propertiesHardness Elastic modulus uctility Work-hardening characteristics Fracture toughness Microstructure Corrosion resistance The influence of the parameters listed in Table 2 can be explained by their effect on the mechanism by which material is removed from a worn surface. The simplest model of abrasive wear is one in which rigidly supported hard particles indent and are forced across the surface of the wear material. Depending on the properties of the abrasive and wear materials, one of several wear mechanisms( Fig. 4)may occur(Ref 7, 10) Plowing occurs when material is displaced to the side, away from the wear particles, resulting in the formation of grooves that do not involve direct material removal. The displaced material forms ridges adjacent to grooves, which may be removed by subsequent passage of abrasive particles Cutting occurs when material is separated from the surface in the form of primary debris, or microchips, with little or no material displaced to the sides of the grooves. This mechanism closely resembles conventional machinin Fragmentation occurs when material is separated from a surface by a cutting process and the indenting abrasive causes localized fracture of the wear material. These cracks then freely propagate locally around the wear groove, resulting in additional material removal by spalling
Particle shape Hardness Yield strength Fracture properties Concentration Contact conditions Force/impact level Velocity Impact/impingement angle Sliding/rolling Temperature Wet/dry pH Wear material properties Hardness Yield strength Elastic modulus Ductility Toughness Work-hardening characteristics Fracture toughness Microstructure Corrosion resistance The influence of the parameters listed in Table 2 can be explained by their effect on the mechanism by which material is removed from a worn surface. The simplest model of abrasive wear is one in which rigidly supported hard particles indent and are forced across the surface of the wear material. Depending on the properties of the abrasive and wear materials, one of several wear mechanisms (Fig. 4) may occur (Ref 7, 10): · Plowing occurs when material is displaced to the side, away from the wear particles, resulting in the formation of grooves that do not involve direct material removal. The displaced material forms ridges adjacent to grooves, which may be removed by subsequent passage of abrasive particles. · Cutting occurs when material is separated from the surface in the form of primary debris, or microchips, with little or no material displaced to the sides of the grooves. This mechanism closely resembles conventional machining. · Fragmentation occurs when material is separated from a surface by a cutting process and the indenting abrasive causes localized fracture of the wear material. These cracks then freely propagate locally around the wear groove, resulting in additional material removal by spalling
Microplowing icrocutti Microcracking Fig. 4 Microscopic mechanisms of material removal between abrasive particles and the surface of materials. Source: Ref 6 The plowing and cutting mechanisms involve predominately plastic deformation of the wear material, while the third mechanism also involves fracture. Thus, the dominant mechanisms that occur for a particular operating condition are influenced to a great extent by the plastic deformation and fracture behavior of the wear material Materials that exhibit high fracture resistance and ductility with relatively low yield strength are more likely to be abraded by plowing. Conversely, materials with high yield strength and with low ductility and fracture resistance abrade through fragmentation(Ref 7, 10, 11) Thefileisdownloadedfromwww.bzfxw.com
Fig. 4 Microscopic mechanisms of material removal between abrasive particles and the surface of materials. Source: Ref 6 The plowing and cutting mechanisms involve predominately plastic deformation of the wear material, while the third mechanism also involves fracture. Thus, the dominant mechanisms that occur for a particular operating condition are influenced to a great extent by the plastic deformation and fracture behavior of the wear material. Materials that exhibit high fracture resistance and ductility with relatively low yield strength are more likely to be abraded by plowing. Conversely, materials with high yield strength and with low ductility and fracture resistance abrade through fragmentation (Ref 7, 10, 11). The file is downloaded from www.bzfxw.com
Additional wear mechanisms can operate in materials that exhibit a duplex microstructure or that are made up of two or more component phases(e.g, a composite-type material, such as a high-chromium white iron, or a composite drill bit, such as diamond or tungsten carbide inserts in a steel matrix), the individual components of which vary in their mechanical properties. Under some abrasive wear conditions, removal of the softer phase (usually the matrix) can occur by one or more of the previously mentioned mechanisms. This process then leaves the harder phase unsupported, in which case it may either become detached from the wear surface by a pull-out mechanism or be more susceptible to wear by fragmentation. In addition, the presence of an interface between the various components of the composite may promote cracking and fragmentation of the harder phase, particularly under impact-abrasion conditions The rate of material removal (or its wear rate) for any of the previously mentioned processes is influenced by the extent of indentation of the wear material surface by the abrasive particle. This depth of indentation, for a given load, is a function of the hardness of the wear material and the shape of the abrasive particle. Angular particles indent the wear surface to a greater extent than rounded particles, leading to higher wear rates. In addition, angular particles are more efficient in cutting and machining(Ref 11) The hardness of the wear material, or more particularly, the hardness of the worn surface, is an important parameter in determining the resistance of a material to abrasion. An increase in the surface hardness of the wear material reduces the depth of penetration by the abrasive particle, leading to lower wear rates. However, an increase in the hardness of a material is also accompanied by an attendant reduction in its ductility, resulting in a change in the abrasion mechanism, for example, from predominately plowing and/or cutting to fragmentation(Ref 12) For mechanisms involving predominately plastic deformation, that is, plowing and cutting, the wear rate can be expressed through the following parameters(Ref 7, 9 ): the probability of wear debris formation, the proportion of plowing and cutting processes, the abrasive particle shape and size, the applied stress, and the hardness of the wear surface For brittle materials(e.g, ceramics), a transition from a purely cutting mechanism to one that also involves fragmentation occurs when the nature of contact changes from elastic-plastic indentation to Hertzian fracture (Ref 11). The conditions under which this transition occurs are dependent on the size and shape of the abrasive particles, the applied stress, and the hardness of the wear surface. In addition, the fracture resistance of the wear aterial, as measured by the fracture toughness, is also important. Decreasing the hardness of the wear material. and increasing the fracture toughness increases the critical abrasive size at which the transition to fragmentation occurs. Thus, reducing the hardness of brittle materials, or alternatively, increasing their fracture toughness leads to lower wear rates(Ref 7, 10 Abrasive wear mechanisms involving plastic deformation, cutting, and fragmentation occur predominantly in materials with relatively high elastic modulus, that is, metals, ceramics, and rigid polymers. As the elastic modulus decreases, the nature of the abrasive/ wear material contact changes, with localized elastic deformation becoming more significant. The probability of wear occurring by plastic deformation mechanisms decreases, ch that for elastomers, cutting mechanisms can occur only with contact against sharp abrasive particles. For contact against blunt abrasive particles, the two main wear mechanisms are tensile tearing and fatigue For the abrasive wear of polymeric materials, the following material parameters are important(Ref 10): elastic modulus and resilience, friction coefficient, tensile strength and tear resistance, elongation at break, and hardness. The wear behavior of elastomers is particularly sensitive to abrasive impingement angle, because this influences the dominant modes of deformation and hence, the wear mechanisms. At low impingement angles, tensile tearing occurs, and the tear resistance of the material is important. At impingement angles close to 90, the behavior of the elastomer is essentially elastic, and resilience is a major factor in determining wear resistance. For abrasive wear conditions in which significant energy levels are dissipated in the abrasive/wear material contact, elastomeric linings are usually designed such that impingement angles are as close to 90as possible Contact Pressure. In general, higher contact pressures between the abrasive particle and the wear surface in abrasive wear situations cause higher rates. As the force applied to an abrasive particle increases, the contact pressure between the abrasive and component wear surface also increases. As the contact pressure nears and exceeds the yield strength of the wear surface in the contact zone the depth of abrasive penetration increases. For a given length of relative motion between the abrasive and the wear surface, deeper penetration generally removes more material or causes damage to a larger volume of material. The contact pressure/wear rate relationship has been discussed in more detail by several authors(Ref 13, 14, 15, 16, 17, 18, 19)
Additional wear mechanisms can operate in materials that exhibit a duplex microstructure or that are made up of two or more component phases (e.g., a composite-type material, such as a high-chromium white iron, or a composite drill bit, such as diamond or tungsten carbide inserts in a steel matrix), the individual components of which vary in their mechanical properties. Under some abrasive wear conditions, removal of the softer phase (usually the matrix) can occur by one or more of the previously mentioned mechanisms. This process then leaves the harder phase unsupported, in which case it may either become detached from the wear surface by a pull-out mechanism or be more susceptible to wear by fragmentation. In addition, the presence of an interface between the various components of the composite may promote cracking and fragmentation of the harder phase, particularly under impact-abrasion conditions. The rate of material removal (or its wear rate) for any of the previously mentioned processes is influenced by the extent of indentation of the wear material surface by the abrasive particle. This depth of indentation, for a given load, is a function of the hardness of the wear material and the shape of the abrasive particle. Angular particles indent the wear surface to a greater extent than rounded particles, leading to higher wear rates. In addition, angular particles are more efficient in cutting and machining (Ref 11). The hardness of the wear material, or more particularly, the hardness of the worn surface, is an important parameter in determining the resistance of a material to abrasion. An increase in the surface hardness of the wear material reduces the depth of penetration by the abrasive particle, leading to lower wear rates. However, an increase in the hardness of a material is also accompanied by an attendant reduction in its ductility, resulting in a change in the abrasion mechanism, for example, from predominately plowing and/or cutting to fragmentation (Ref 12). For mechanisms involving predominately plastic deformation, that is, plowing and cutting, the wear rate can be expressed through the following parameters (Ref 7, 9): the probability of wear debris formation, the proportion of plowing and cutting processes, the abrasive particle shape and size, the applied stress, and the hardness of the wear surface. For brittle materials (e.g., ceramics), a transition from a purely cutting mechanism to one that also involves fragmentation occurs when the nature of contact changes from elastic-plastic indentation to Hertzian fracture (Ref 11). The conditions under which this transition occurs are dependent on the size and shape of the abrasive particles, the applied stress, and the hardness of the wear surface. In addition, the fracture resistance of the wear material, as measured by the fracture toughness, is also important. Decreasing the hardness of the wear material, and increasing the fracture toughness, increases the critical abrasive size at which the transition to fragmentation occurs. Thus, reducing the hardness of brittle materials, or alternatively, increasing their fracture toughness, leads to lower wear rates (Ref 7, 10). Abrasive wear mechanisms involving plastic deformation, cutting, and fragmentation occur predominantly in materials with relatively high elastic modulus, that is, metals, ceramics, and rigid polymers. As the elastic modulus decreases, the nature of the abrasive/wear material contact changes, with localized elastic deformation becoming more significant. The probability of wear occurring by plastic deformation mechanisms decreases, such that for elastomers, cutting mechanisms can occur only with contact against sharp abrasive particles. For contact against blunt abrasive particles, the two main wear mechanisms are tensile tearing and fatigue. For the abrasive wear of polymeric materials, the following material parameters are important (Ref 10): elastic modulus and resilience, friction coefficient, tensile strength and tear resistance, elongation at break, and hardness. The wear behavior of elastomers is particularly sensitive to abrasive impingement angle, because this influences the dominant modes of deformation and hence, the wear mechanisms. At low impingement angles, tensile tearing occurs, and the tear resistance of the material is important. At impingement angles close to 90°, the behavior of the elastomer is essentially elastic, and resilience is a major factor in determining wear resistance. For abrasive wear conditions in which significant energy levels are dissipated in the abrasive/wear material contact, elastomeric linings are usually designed such that impingement angles are as close to 90° as possible. Contact Pressure. In general, higher contact pressures between the abrasive particle and the wear surface in abrasive wear situations cause higher wear rates. As the force applied to an abrasive particle increases, the contact pressure between the abrasive and component wear surface also increases. As the contact pressure nears and exceeds the yield strength of the wear surface in the contact zone, the depth of abrasive penetration increases. For a given length of relative motion between the abrasive and the wear surface, deeper penetration generally removes more material or causes damage to a larger volume of material. The contact pressure/wear rate relationship has been discussed in more detail by several authors (Ref 13, 14, 15, 16, 17, 18, 19)
One of the more general(and generally accepted) wear equations was developed by Archard in 1953(Ref 20) P where W is volume of worn(removed or disturbed)material, K is a constant related to probability of surface contact and debris formation, s is sliding distance, P is applied load, and pm is flow pressure(related to hardness)of wearing surface The constant K is usually treated as a material property and is determined empirically. Typical values for various materials have been established through extensive wear testing(Ref 20). Sliding distance is one part of the volume aspect of affected material. Applied load combined with the flow pressure/hardness provide a measure of the depth of penetration of abrasive particles and supply the second volume dimension Abrasive Characteristics. Abrasive particle size has a significant effect on material wear, with the greatest effect being for nonmetals(i.e, ceramics and polymers)(Ref 21). In nonmetals, the effect of particle size is associated with changes in the predominant mechanism of material removal. Ceramics undergo a transition to fragmentation above a critical abrasive particle size, whereas elastomers undergo a transition from elastic behavior to either tearing or fatigue In metals, the effect of abrasive particle size is minimal for particle sizes >100 um. Below this particle size, the wear rate decreases rapidly with decreasing particle size(Ref 11). This particle size effect is usually attributed to the nature of the abrasive/wear material contact, with decreasing size favoring elastic rather than plastic contact Abrasive hardness, or the ratio of hardness(Vickers) of the wear material to the hardness(vickers) of the abrasive(H/Ha), is a critical parameter in abrasive wear. It is well known that the abrasive wear rate decreases as the hardness of the worn surface approaches that of the abrasive(Ref 10, 14, 15, 16, 19). When the hardness of the worn material exceeds that of the abrasive, the wear rate decreases rapidly. Figure 5 shows this particular effect for metals and ceramics 10 102 102 10 Hardness of worn surface/hardness of abrasive Fig 5 Effect of abrasive hardness on wear behavior of metals and ceramics Source: Ref 7 Thefileisdownloadedfromwww.bzfxw.com
One of the more general (and generally accepted) wear equations was developed by Archard in 1953 (Ref 20): m P W ks P æ ö = ç ÷ è ø where W is volume of worn (removed or disturbed) material, K is a constant related to probability of surface contact and debris formation, s is sliding distance, P is applied load, and pm is flow pressure (related to hardness) of wearing surface. The constant K is usually treated as a material property and is determined empirically. Typical values for various materials have been established through extensive wear testing (Ref 20). Sliding distance is one part of the volume aspect of affected material. Applied load combined with the flow pressure/hardness provide a measure of the depth of penetration of abrasive particles and supply the second volume dimension. Abrasive Characteristics. Abrasive particle size has a significant effect on material wear, with the greatest effect being for nonmetals (i.e., ceramics and polymers) (Ref 21). In nonmetals, the effect of particle size is associated with changes in the predominant mechanism of material removal. Ceramics undergo a transition to fragmentation above a critical abrasive particle size, whereas elastomers undergo a transition from elastic behavior to either tearing or fatigue. In metals, the effect of abrasive particle size is minimal for particle sizes >100 μm. Below this particle size, the wear rate decreases rapidly with decreasing particle size (Ref 11). This particle size effect is usually attributed to the nature of the abrasive/wear material contact, with decreasing size favoring elastic rather than plastic contact. Abrasive hardness, or the ratio of hardness (Vickers) of the wear material to the hardness (Vickers) of the abrasive (H/Ha), is a critical parameter in abrasive wear. It is well known that the abrasive wear rate decreases as the hardness of the worn surface approaches that of the abrasive (Ref 10, 14, 15, 16, 19). When the hardness of the worn material exceeds that of the abrasive, the wear rate decreases rapidly. Figure 5 shows this particular effect for metals and ceramics. Fig. 5 Effect of abrasive hardness on wear behavior of metals and ceramics. Source: Ref 7 The file is downloaded from www.bzfxw.com