Friction, Lubrication, and Wear Technology (1997) Part 4 pps

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Jakus, Erosion and Strength Degradation in Alumina, Wear, Vol 111, 1986, p 335-346 78. J.E. Ritter, Erosion Damage in Structural Ceramics, Mater. Sci. Eng., Vol 71, 1985, p 195 79. J.E. Ritter, P. Strzepa, K. Jakus, L. Rosenfiel d, and K.J. Buckman, Erosion Damage in Glass and Alumina, J. Am. Ceram. Soc., Vol 67, 1984, p 769 80. K. Breder, J.E. Ritter, and K. Jakus, Strength Degradation in Polycrystalline Alumina Due to Sharp- Particle Impact Damage, J. Am. Ceram. Soc., Vol 71, 1988, p 1154 81. S. Srinivasan, "Erosion of Partially Stabilized Zirconia," M.S. thesis, North Carolina State University, 1987 82. M.E. Gulden, Solid-Particle Erosion of High-Technology Ceramics (Si 3 N 4 , Glass-Bonded Al 2 O 3 , and MgF 2 ), in Erosion: Prevention and Useful Applications, STP 664, ASTM, 1979, p 101-122 83. M.E. Gulden, Solid Particle Erosion of Si 3 N 4 Materials, Wear, Vol 69, 1981, p 115-129 84. J.L. Routbort, C Y. Chu, J.M. Roberts, J.P. Singh, W. Wu, and K.C. 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Kosel, A Comparison of Carbide Fracture During Fixed Depth and Fixed Load Scratch Tests, Proceedings of International Conference on Wear of Materials, American Society of Mechanical Engineers, 1985, p 59-66 90. T. Kulik, T.H. Kosel, and Y. Xu, Effect of Depth of Cut on Second- Phase Particle Fracture in Abrasion of Two-Phase Alloys, Proceedings of International Conference on Wear of Materials, American Society of Mechanical Engineers, 1989, p 23-34 91. T.H. Kosel and S.S. Aptekar, Effect of Hard Second- Phase Particles on the Erosion Resistance of Model Alloys, Paper 113, Corrosion '86, National Association of Corrosion Engineers, 1986 92. T. Ahmed, "Enhanced Removal at Edges or Brittle Materials During Solid Particle Erosion," M.S. thesis, University of Notre Dame, 1987 93. T.H. Kosel, "Erosion in Dual- Phase Microstructures," Final Report to U.S. Dept. of Energy, ORNL/Sub/83-43336C/01, Dec 1987 94. A.J. Ninham and A.V. Levy, The Erosion of Carbide-Metal Composites, Proceedings of International Conference on Wear of Materials, American Society of Mechanical Engineers, 1987, p 825-831 95. R. Brown and J.D. Ayers, Solid Particle Erosion of Al 6061 with a Laser Melted and TiC Particle Injected Surface Layer, Proceedings of International Conference on Wear of Materials, American Society of Mechanical Engineers, 1983, p 325-332 96. S.S. Aptekar and T.H. Kosel, Erosion of White Cast Irons and Stellite, Proceedings of International Conference on Wear of Materials, American Society of Mechanical Engineers, 1985, p 677-686 97. B.R. Rossing and M.A. Rocazella, Slurry Erosion of Silicon Carbide Particulate Reinforced Alumina Composites, Proceedings of Corrosion-Erosion-Wear of Materials at Elevated Temperatures, National Association of Corrosion Engineers, 1990, p 39-1 to 39-21 98. T. Kulik and T.H. 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Vedula, Ed., TMS- AIME, 1989, p 315-333 Cavitation Erosion Carolyn M. Hansson, Queen's University, Canada; Inge L.H. Hansson, Alcan International Ltd., Canada Introduction CAVITATION is defined as the repeated nucleation, growth, and violent collapse of cavities, or bubbles, in a liquid. The term has been used in this context by the fluid mechanics and physics communities for centuries. It should not be confused with the metallurgical use of the term, which describes the growth of voids within a solid material, usually as a result of creep. When a liquid is subjected to sufficiently high tensile stresses, vapor-filled voids, or cavities, are formed at weak regions within the liquid and usually grow under tensile conditions. In practice, all liquids contain gaseous, liquid, and solid impurities, which act as nucleation sites for the cavities. When the liquid that contains cavities is subsequently subjected to compressive stresses, that is, to higher hydrostatic pressures, these cavities will collapse. This collapse is directly responsible for the erosion process. In practice, cavitation can occur in any liquid in which the pressure fluctuates either because of flow patterns or vibrations in the system. If, in a particular location in a liquid flow system, the local pressure falls below the vapor pressure of the liquid, then cavities may be nucleated, grow to a stable size, and be transported down-stream with the flow. When they reach a higher-pressure region, they become unstable and collapse, usually violently. This form of cavitation commonly occurs in hydrofoils, pipelines, hydraulic pumps, and valves. The pressures produced by the collapse may cause localized deformation and/or removal of material (erosion) from the surface of any solid in the vicinity of the cavities. Similarly, when a stationary liquid is subjected to vibrational pressure fluctuations, the fluctuations may be sufficient to nucleate, grow, and collapse cavities, again resulting in erosion of any solid in the vicinity of the cavity cluster. Such cavities can produce the type of erosion that is typically observed on the coolant side of a diesel engine cylinder liner. The collapse velocity, v, of a cavity is a function of the hydrostatic pressure, P, under which the cavity collapses, the volume, V, of the initial cavity, and the density, , of the liquid (Ref 1): (Eq 1) Cavity radii for flow cavitation are typically from 0.25 to 1.0 mm ( 0.01 to 0.04 in.), and for vibratory cavitation, 50 m ( 2 mils). P is of the order of a few atmospheres. For a cavity of 1 mm (0.04 in.) radius collapsing at 0.1 MPa (1 atm) overpressure in water, the cavity collapse velocity typically ranges from 100 to 150 m/s (330 to 490 ft/s). Furthermore, the collapse time, t, of the cavity is related to the initial radius, R 0 , of the cavity, the liquid density, , and the hydrostatic pressure at collapse, P, as follows (Ref 1): (Eq 2) For the above case, the time is 100 ns. The effects of surface tension and viscosity on the collapse of a cavity are relatively insignificant. However, the compressibility of the liquid, vapor, and any trapped gases has a profound effect on the final stages of the collapse and will cushion the erosive effect of the single cavities (Ref 2). It is important to note that the driving force for the cavity collapse is the difference between the hydrostatic pressure and the vapor pressure of the liquid. A more detailed description of cavity dynamics and the parameters influencing the cavitation process is given by Mørch (Ref 3). The mechanism by which cavitation causes erosion is briefly described below. When a cavity collapses within the body of the liquid, away from any solid boundary, it does so symmetrically and emits a shock wave into the surrounding liquid. On the other hand, those cavities that are either in contact with or very close to a solid surface will collapse asymmetrically, forming a microjet of liquid directed toward the solid, as shown in Fig. 1 (Ref 4). Fig. 1 Asymmetrical collapse of cavity. (a) In contact with solid surface. (b) Adjacent to solid surface. Source: Ref 4 The shock wave from spherical collapse and the jet impact from asymmetrical collapse have earlier been regarded as the most likely causes of erosion. However, each has features that do not permit a ready explanation of the observed erosion phenomena (Ref 5, 6). For example, the shock wave attenuates too rapidly, and the microjet diameters are typically too small to account for the degree and extent of the overall erosion damage. The discrepancies are now attributed (Ref 6, 7) to the fact that single cavities do not act independently but instead collapse in concert. The collapse of the cavity cluster enhances the effects of the cavities adjacent to, or in contact with, the solid. In all practical situations involving cavitation, large numbers of cavities are generated at the same time and constitute what can be described as cavity clusters (Ref 2). When these clusters are subjected to an increased external hydrostatic pressure, they collapse in a concerted manner, stating with the cavities at the outer perimeter of the cluster and proceeding inward toward the central cavities (Ref 8). In this sequence, much of the energy generated by the collapse of the outer cavities is transferred to the cavities in the inner part of the cluster through an increased local hydrostatic pressure at the individual collapse. This results in a significant increase in the intensity of collapse of the central cavities (Ref 9). This concerted collapse mechanism has been demonstrated for flow cavitation as well as for vibratory cavitation (Ref 8, 10). Because of the localized nature of the cavitation process, the energy dissipation has a significant temperature increase associated with the collapse. Local temperatures up to 5000 K have been reported (Ref 11). Cavitation Erosion Cavitation erosion is the mechanical degradation of materials caused by cavitation in liquids. The mechanical loading of a solid surface that is due to a cavitating liquid is caused by asymmetrical collapse of cavities either at or near the surface. These asymmetrical collapses result in liquid microjets that are directed toward the solid surface. The mechanical loads are very localized and, because of the concerted collapse of the cavity cluster, can be extremely severe, resulting in deformation of the surface. The repeated loading eventually leads to removal of material from the surface, that is, erosion. The erosive effect of a cavity cluster is dependent on a number of factors, including hydrostatic pressure, cavity cluster size, distance of the individual cavities from the solid surface, cavity size distribution, and the temperature and density of the liquid. The total inherent energy of the cavity cluster is transferred to the solid material and must be either absorbed or dissipated by the solid or reflected as shock waves in the liquid. The solid material will absorb the impact energy as elastic deformation, plastic deformation, or fracture; the latter two processes lead to erosion of the material. The more elastic or plastic deformation energy that the material can absorb, the greater will be the cavitation erosion resistance of the material. Erosion is generally regarded as mass loss from the surface and, for most materials under most forms of cavitation, is preceded by an incubation period, during which the material will deform either elastically or plastically (Ref 5). However, it should be noted that for some applications, a roughening of the surface by plastic deformation without actual loss of mass can render the part unusable for that application. Thus, cavitation damage without mass loss can be regarded as "erosion" for those applications. At the other extreme, material losses of >10 mm/year (0.4 in./year) from tough construction materials are observed in such applications as hydraulic turbines (Ref 12). After the initiation of material loss from the surface, the rate of erosion as a function of continued exposure to cavitation is usually nonlinear (Ref 5). The observed time dependencies of the erosion rates are similar to those described in the article "Liquid Impingement Erosion" in this Volume. Materials Factors Localized Nature of Material Deformation and Removal. As described above, the loading that a material experiences during exposure to a cavitating liquid is localized, dynamic, and, at least initially, compressive in nature. However, the localized nature of the loading and the fact that it occurs at a free surface means that the deformation is not under the constraints normally imposed under bulk compressive or shock stressing. Therefore, the material is free to deform, both on a local and an extended level, in a manner that is unlike that of any other, more common, form of stressing. Because the material is not deformed as a whole, the deformation of one grain or one phase within a grain is not influenced by the behavior of the surrounding grains of phases, as it would be under bulk deformation conditions. Thus, the theoretical and empirical "rules" that have been developed to describe and explain the various strengthening mechanisms in different materials do not always apply to the resistance of the material to cavitation erosion. Added to this localized loading factor is the dynamic, shocklike nature of the loading. It is not surprising, therefore, that no universal correlation with quasistatic mechanical properties has been observed. Consequently, the approach to materials selection and/or materials development for cavitation erosion resistance cannot be based on general experience in the selection and/or development of materials for resistance to bulk deformation and has, therefore, been almost exclusively empirical. Until very recently, structural components have been predominantly fabricated of metallic alloys. A search of the literature has revealed very little information concerning cavitation erosion of either bulk ceramics of polymers. The only data concerning cavitation erosion of nonmetallic structures in practice has been of concrete (Ref 13), which, as a structural member of dams and sluices, is often exposed to cavitating liquids. Consequently, the discussion of the materials aspects of cavitation erosion will concentrate on metallic alloys and on the coatings and surface treatments that have been employed to minimize the erosion rates. There is little discussion of the very limited data on laboratory studies of nonmetallic bulk materials. Erosion of Metals and Alloys. The deformation and failure mechanisms of both metals and alloys are markedly influenced by strain-rate sensitivity (and, therefore, the crystal structure) and the ability to absorb the energy of the shock loading without macroscopic deformation (which is related to the stacking fault energy). In multiphase alloys, the volume fraction, size, and dispersion of a second phase generally have a different and usually less significant influence on erosion rates than they do on the quasistatic mechanical properties. Face-centered metals and alloys are isotropic and are the least sensitive to strain rate of the three common metallic structures. Consequently, their response to cavitation is similar to their quasistatic mechanical behavior in that they are highly ductile and fail by a void growth and coalescence mechanism (Ref 7) or by a ductile rupture (Ref 14) mechanism. Very early damage in the face-centered cubic (fcc) metals and single-phase fcc alloys consists of isolated depressions (Ref 15), Fig. 2, which can be attributed to the jet impact of individual cavities collapsing close to the surface. Also during this early stage, the grain boundaries become delineated, coarse slip bands develop across the width of the grains, and the grains become increasingly undulated. Eventually, the undulations develop into craters and material is lost by necking of the rims of the craters. Fig. 2 Scanning electron micrographs of polyc rystalline aluminum exposed to vibratory cavitation at varying lengths of time. (a) 12 s. (b) 24 s. (c) 40 s. (d) 60 s. (e) 75 s. (f) 90 s. Source: Ref 7 Body-centered cubic (bcc) metals and alloys are usually also isotropic, but their deformation is highly strain-rate sensitive. Their response to an applied stress is always a competition between flow and fracture. As the temperature decreases or the strain rate increases, flow becomes more difficult, and there is an increased tendency to brittle fracture. When pure iron is subjected to vibratory cavitation, it exhibits both brittle and ductile failure mechanisms. The brittle failure mode is illustrated in Fig. 3. [...]... Engineers, 19 64 40 P Veerabhadra Rao, Correlating Models and Prediction of Erosion Resistance to Cavitation and Drop Impact, J Test Eval., 1976, p 3- 14 41 H Wiegand and R Shulmeister, Investigations with a Vibratory Apparatus on the Influence of Frequency, Amplitude, Pressure, and Temperature on Material Destruction by Cavitation, Motortechnische Zeitschrift, Vol 29 (No 2), 1968, p 41 -50 42 S Pedersen,... equations for maximum erosion rate and for incubation period are given in Ref 39 and 41 , based on an interlaboratory test program sponsored by ASTM Technical Committee G-2 on Wear and Erosion These are: log Re = 4. 8 log V - log NER - 16.65 + 0.67 log d + 0.57 J - 0.22 K log N0 = -4. 9 log V + log NOR + 16 .40 -0 .40 J where Re and N0 are the rationalized erosion rate and incubation period, respectively,... bulk properties and in repairing and regenerating eroded surfaces References 1 Lord Rayleigh, Philos Mag., Vol 34, 1917, p 94- 98 2 L van Wijngaarden, 11th International Congress of Applied Mechanics (Munich), 19 64 3 K.A Mørch, Dynamics of Cavitation Bubbles and Cavitating Liquids, Erosion, C.M Preece, Ed., Academic Press, 1979, p 309-355 4 M.S Plesset and R.B Chapman, J Fluid Mech., Vol 47 , 1971, p 283-290... Erosion of Aluminum in Water Flow, J Phys., Vol D11, 1978, p 147 -1 54 16 E.H.R Wade and C.M Preece, Cavitation Erosion of Iron and Steel, Metall Trans., Vol 9A, 1978, p 12991310 17 S Vaidya and C.M Preece, Cavitation-Induced Multiple Slip, Twinning, and Fracture Modes in Zinc, Scr Metall., Vol 11, 1977, p 1 143 -1 146 18 S Vaidya, S Mahajon, and C.M Preece, The Role of Twinning in the Cavitation Erosion... (Ref 44 ) Since liquid impingement and cavitation erosion is due to repeated stress pulses and thus related to fatigue, some authors have tried unsuccessfully to correlate resistance with endurance limit or finite fatigue life Recently, however, Richman and McNaughton (Ref 47 ) demonstrated good correlation with cyclic deformation properties for a number of alloys and pure metals Several authors (Ref 48 ,... Academic Press, 1979, p 249 6 C.M Preece and I.L.H Hansson, A Metallurgical Approach to Cavitation Erosion, Advances in the Mechanics and Physics of Surfaces, R.M Latanision and R.J Courtel, Ed., Harwood Academic Publishers, 1981, p 191-253 7 B Vyas and C.M Preece, Cavitation-Induced Deformation of Aluminum, Erosion, Wear and Interfaces with Corrosion, ASTM, 1973 8 I.L.H Hansson and K.A Mørch, Comparison... Ed., Treatise on Materials Science and Technology, Vol 16, Erosion, Academic Press, 1979 3 W.F Adler, The Mechanics of Liquid Impact, Treatise on Materials Science and Technology, Vol 16, Erosion, C.M Preece, Ed., Academic Press, 1979, p 127-183 4 J.H Brunton and M.C Rochester, Erosion of Solid Surfaces by the Impact of Liquid Drops, Treatise on Materials Science and Technology, Vol 16, Erosion, C.M... conjoint (synergistic) action between corrosive and erosive processes, such that the resulting material loss rates are greater than the sum of the individual processes taken by themselves Corrosive actions in the presence of solid particles, slurries, and sliding wear are covered in detail in the articles "Solid Particle Erosion," "Slurry Erosion," and "Corrosive Wear" in this Volume For purely fluid systems,... 30 to 60% of the maximum rate and continues indefinitely Rao and Buckley (Ref 54) have also tried to unify the time dependence from many test data Some other comprehensive prediction methods and theories should be mentioned Springer (Ref 48 ) presents semianalytically based relationships, but they overestimate incubation periods and underestimate erosion rates by about 4 orders of magnitude; this was... silica-silica Materials for optical and infrared domes Recommended Not recommended Glasses and ceramics: Sapphire Spinel Calcium aluminosilicate Calcium borosilicate Magnesium fluoride Clear fused silica Chalcogenides: Germanium Zinc sulfide Gallium arsenide Zinc selenide Source: Ref 25 References 1 "Standard Terminoloy Relating to Wear and Erosion," G40, Annual Book of ASTM Standards, ASTM 2 C.M Preece, . 291-309 47 . K. Wellinger and H. Uetz, Gleit-Spül and Strahlverschleiss Prüfung, Wear, Vol 1, 1957-58, p 225-231 48 . K. Anand, S.K. Hovis, H. Conrad, and R.O. Scattergood, Flux Effects in Solid Particles. 1989, p 143 -153 35. J.W. Edington and I.G. Wright, Study of Particle Erosion Damage in Haynes Stellite 6B, I: Scanning Electron Microscopy of Eroded Surfaces, Wear, Vol 48 , 1978, p 131- 144 36 1991, p 123-127 45 . R.C.D. Richardson, The Wear of Metals by Relatively Soft Abrasives, Wear, Vol 11, 1968, p 245 -275 46 . R.C.D. Richardson, The Wear of Metals by Hard Abrasives, Wear, Vol 10,