Volume 18 - Friction, Lubrication, and Wear Technology Part 10 ppsx

used with the SEM, because this instrument is applied primarily to the study of surface features of bulk specimens. In general, as will be discussed later, an accelerating voltage is selected that best suits the application at hand. Transmission electron microscopes are available in three different accelerating voltage ranges. The most commonly used instruments operate at a maximum of 120 kV, but allow the selection of voltages as low as 20 kV. With so-called intermediate-voltage microscopes, the maximum voltage is typically 200 to 400 kV. High-voltage instruments are capable of operating at 10 6 V and higher. In general, a higher accelerating voltage permits penetration of thicker specimens and provides improved resolution. However, the gain in going from the intermediate-voltage range to the high-voltage range is relatively small for all but the most specialized applications and is achieved at a very substantial increase in cost. Intermediate-voltage instruments allow routine observation of the atomic structure of all classes of crystalline materials. This, together with increased penetration, improved EELS capabilities, and the fact that specially constructed laboratory facilities (necessary for high- voltage instruments) are not required, has led to an increase in the popularity of intermediate-voltage instruments. In the SEM, the specimen is normally located below the final lens in the illumination system. For improved resolution, however, some instruments provide a second position within the final lens. The electron beam is focussed to a small spot and scanned serially over the specimen to form a rectangular raster. Secondary electrons (or one of the other sources in Fig. 2) are collected to provide a signal that is amplified and used to modulate the intensity of the electron beam in a CRT, The CRT beam is scanned in synchronism with the electron beam incident on the specimen, resulting in an observable image. The magnification of the image is determined by the ratio of the distance scanned on the specimen to the corresponding distance displayed on the CRT, the latter generally being kept constant. Thus, when the scanned area on the specimen is small, the magnification is high, and when the scanned area is large, the magnification is low. Resolution in the SEM is determined to a first approximation by the diameter of the beam incident on the specimen. In practice, the diameter of the beam is controlled by the type of filament, the excitation of the condenser lenses, the final aperture size, and the position of the specimen with respect to the final lens. The latter distance is referred to as the working distance. A critical factor limiting the useful probe size is the available beam current. Increasing the excitation of the condenser lenses or reducing the size of the final aperture results in a small electron probe diameter; however, the probe current is also reduced. This in turn reduces the strength of the signal available for amplification, so that the usable minimum probe size is limited by the capacity of the signal amplifier, that is, the signal-to-noise ratio of the amplifier. With a heated tungsten filament, the probe diameter is limited to about 5 nm; with LaB 6 and field emission sources, diameters of about 3 nm and 1 nm, respectively, are achievable. In actual operation, the nature of the specimen and the signal source (secondary electrons, x-rays, and so on) usually play a limiting role in determining resolution. If the features of interest result in only a small difference in the signal, then an increased probe current and correspondingly larger probe size are required, thereby reducing resolution. The TEM in its conventional mode of operation differs significantly from the SEM. The specimen is illuminated by a relatively broad, nearly parallel, stationary beam of electrons. Transmitted and diffracted electrons that have lost little or no energy and that do not deviate too far from the optical axis are focused by the objective lens. Subsequent lenses provide additional magnification and allow observation of either the image or a diffraction pattern. The image and diffraction pattern can be viewed directly on a fluorescent screen, photographed, or displayed by means of a TV system. As an additional enhancement, TEMs have also been adapted for operation in a scanning mode, similar to the SEM. For this purpose, the illuminating beam is focused to a small probe. Detectors are included to sense transmitted and diffracted electrons, as well as secondary and backscattered electrons as in the SEM. A transmission electron microscope designed to function either in the conventional stationary illumination mode or in the scanning mode is commonly referred to as a scanning transmission electron microscope (STEM). The acronym CTEM is often used to refer to a conventional transmission electron microscope without STEM capability, or simply to operation in the conventional mode. Transmission electron microscopes are available that have been designed and optimized to operate only in the scanning mode; such instruments are usually referred to as "dedicated" STEMs. Finally, a TEM equipped with x-ray detectors, and perhaps with electron energy loss spectrometers as well, is frequently referred to as an analytical electron microscope, or AEM. Originally, SEM and TEM instruments were essentially analog in operation. X-ray analysis systems designed as separate attachments to SEMs and later to TEMs incorporated digital technology. As development has progressed, these systems have become capable not only of processing x-ray data but also of controlling the position of the beam on the specimen. Thus, composition maps can be acquired and stored in computer memory. With suitable programming, the stored data can be used, for example, to provide information on the proportion of each compositionally different phase in the sample or to count particles having a particular composition. In essence, the x-ray analysis system has also become an image analysis system. Accommodating other signals in the system, such as secondary and backscattered electron signals, is a fairly easy step. Thus, image analysis can be done directly with these signals, eliminating the need for indirect analysis of photographs and separate image analysis equipment. Recent TEM and SEM instrument designs rely heavily on digital technology and computer control, incorporating keyboards and computer CRT screens. The operator interacts with a software program rather than directly manipulating an array of knobs, buttons, and switches. The image can be digitized and sent directly to computer memory or stored in a nonvolatile memory medium, such as a hard disk. As a result, image analysis and x-ray analysis capabilities are directly incorporated in the instrument. Finally, it should be mentioned that the SEM is not merely a passive instrument for examining wear-related specimens; it may also incorporate a wear testing device for in situ observation of wear processes. A number of important results have been obtained in this way (Ref 28, 29, 30, 31, 32, 33). Specimen Preparation Scanning Electron Microscopy An important advantage of the SEM is that a specimen can be examined with little need for special preparation beyond that required for the optical microscope. This does not imply that the condition and nature of the specimen do not have a significant bearing on the quality of the image and the information obtained. Indeed, revealing the desired information may require considerable effort with respect to sectioning, polishing, and etching. For a specimen to be suitable for examination, it must be free of volatile matter that might interfere with the attainment of an operational vacuum level or result in the contamination of apertures and other components, thus degrading the performance of the instrument. A contaminant film that hides the surface features of interest is certainly unacceptable. Even a thin deposit of oil may lead to the rapid appearance of a dark film over the area scanned by the electron beam. This is especially noticeable when focusing is carried out at a higher magnification, leaving a telltale dark square in the lower magnification field. Solvent cleaning or low-temperature vacuum bakeout for porous specimens may be required. The surface should also be free of extraneous dust particles, which may charge or otherwise detract from the image. Specimen cleaning is discussed in Ref 8 and 12. Before adopting a particular cleaning method, careful consideration should be given to the effect of the procedure on surface films and attached wear debris. Wear debris and triboreaction films almost always yield important information regarding wear processes. If necessary, loose films and debris may be removed for separate analysis, using methods discussed later, freeing the underlying surface for examination. A second requirement is that the specimen must have adequate electrical conductivity to allow electrons to flow to ground or to the specimen current amplifier connector without charging. For metal and some semiconducting specimens, the inherent conductivity is sufficient, and it is necessary only that the specimen make good electrical contact with the mounting device that attaches to the microscope stage. Specimens that are poor conductors or insulators must be coated with a conductive layer, usually a heavy metal such as gold or a gold-palladium alloy. Alternatively, if compositional or crystal structure studies are to be made, interference may be minimized by a carbon coating, assuming that carbon itself is not one of the constituents in the specimen of interest. The coating should not obscure the details of the microstructure and topography being examined. This becomes especially important in high- resolution studies, where care in the selection of coating material and coating method is of critical importance. Materials and methods for coating are discussed in several general references (Ref 8, 9, 10, 12). In addition to the direct observation of worn surfaces in the SEM, a replica of the surface may be prepared for examination. This approach is required when the component of interest is too large to be accommodated by the SEM or cannot be sectioned, or when it is not desirable or feasible to remove the component from its system. One method for preparing a replica is to employ the cellulose acetate tape used to prepare TEM replicas. A piece of the tape is moistened with acetone and pressed against the component surface. After a suitable drying time, the tape is stripped from the surface and coated for examination in the SEM. Rough surfaces may require use of a different replicating material (Ref 12, 20). It should be noted that the replica method is limited in its ability to provide an accurate representation of the surface. This is especially true in connection with cracks and holes, neither of which may be easily recognized using a replica. Also, a lip of folded-over material can often be identified by direct surface observation in the SEM, but usually not with a replica. Although much can be learned by direct examination of the worn surface, the subsurface is also an important source of information. Oxide layers, films, compacted debris, cracks, deformed layers, and transformed regions may be poorly revealed or not revealed at all when the outer worn surface is studied. Examination of the subsurface requires the preparation of a section through the specimen. It is common practice to prepare a cross section perpendicular to the surface. Moreover, because relative motion between the contacting bodies usually occurs along a specific direction on the surface, it is best to prepare two sections, one parallel and the other perpendicular to the direction of motion. In general, more information is obtained from the parallel section. The majority of material flow usually occurs in the direction of sliding, and the parallel section is best suited to reveal its pattern. If grain boundaries or other suitable microstructural features are present, it may be possible to measure the strain as a function of depth by the amount of bending or microstructural distortion (Ref 34, 35). Tensile cracks oriented with their plane roughly normal to the direction of sliding are also best observed in the parallel section. Preparation of cross sections requires considerable care and skill. Soft materials and specimens with fragile or poorly adherent films are probably the most difficult candidates. Figure 6 is an example of a section through the wear track on a copper surface. The specimen was electroplated with a layer of copper before sectioning parallel to the direction of sliding. The deformed region below the track is clearly visible. Dislocation cells and an annealing twin are displayed as a result of channeling contrast (discussed below). Fig. 6 Cross section through wear track on a copper surface parallel to sliding direction. T, annealing twin, and arrow indicate direction of motion with respect to counterface. Source: Ref 27 A taper section may also be prepared through the worn surface (Ref 36). This method makes it possible to obtain what is in effect a magnified view of linear and planar features on the surface, such as scratches and films, respectively. The length of the scratch or width of the film in the taper plane, together with the known taper angle, allows the scratch depth or film thickness to be determined. Note that scratches or ridges must not be parallel to the line of intersection of the taper plane and the surface and preferably should be perpendicular to that line. Furthermore, for an accurate determination, the feature of interest should be uniform in thickness or depth over the length of the taper plane. There are a number of methods for collecting and preparing debris specimens for examination in the SEM. When oil and other volatile materials are not present, loose debris remaining on the worn surface can be studied directly be placing the component in the SEM. If the component is too large or cannot be removed from its system, the debris must be removed by stripping it away with adhesive tape or by brushing it onto the tape. Double-sided adhesive tape facilities attachment to the specimen mount. Although conductive tape may be used, it is usually necessary to apply a coating for conductivity. The surface replica methods described above may also be used to remove debris for examination. When the debris is present in oil, a small amount may be placed in a suitable solvent, such as hexane. The oil can be eliminated by centrifuging and replacing the contaminated solvent with fresh solvent. Ultimately, a drop of debris-containing solvent is placed on a specimen mount for examination in the SEM. An alternative approach involves washing the solvent-oil-debris mixture through a porous membrane filter, which is then coated for examination in the SEM. Finally, it should also be mentioned that debris distributed on ferrography slides (see the article "Lubricant Analysis" in this Volume) can be examined in the SEM (Ref 37). Transmission Electron Microscopy In contrast to specimen preparation for the SEM, specimen preparation for TEM examination almost always involves considerable effort. Because specimen preparation plays such an important role, several volumes have been written that are devoted entirely to the subject (Ref 38, 39, 40, 41). The discussion that follows will first consider the preparation of specimens from bulk materials, including both thin sections and surface replicas. Methods used to prepare specimens from debris particles will then be reviewed. Specimens from Worn Surfaces. The main challenge in preparing TEM specimens from bulk materials is to obtain a section that contains a region approximately 100 m 2 or more in area with a thickness of 5 to 500 nm. Moreover, the surface of the thinned area should be smooth and free of contamination, and the internal structure should not be altered by the preparation process. For the study of defect structures, a thickness of approximately 200 nm is suitable, although thicker specimens may be acceptable for materials of low atomic number and thinner specimens would be favored for materials of high atomic number. Operation at high accelerating voltages will extend the maximum usable thickness. For high-resolution studies, the specimen should be no thicker than 40 nm; the optimum value depends on the material and the nature of the study to be performed. Because most preparation methods result in a wedge-shaped section, achieving the desired thickness is not that difficult; at some location within the wedge, a suitable thickness can usually be found. The only distinction between TEM specimen preparation methods for tribological studies and TEM specimen preparation methods in general concerns the strong emphasis placed by the former on surface and near-surface material. However, tribology is not the only field where interest is focused on the surface. The study of corrosion, of semiconductor devices, and of surface treatment processes, such as nitriding, ion implantation, and so on, have promoted the development of methods for preparing specimens from the surface region. A thin section may be taken parallel to the worn surface, or perhaps a sequence of several sections prepared in order to study the structure as a function of depth. If material immediately at the surface is to be studied, a soluble coating may be necessary to protect the surface during preparation. The parallel section approach to examining the immediate surface is feasible only if the worn surface is quite smooth. Otherwise, a cross section normal to the surface must be prepared. As discussed in connection with SEM specimen preparation, the orientation of the section may be chosen either parallel to a characteristic direction, such as the sliding direction, or perpendicular to that direction. An electrodeposited layer (for metal specimens) or a thick coating of cement (for example, epoxy) is usually applied to the surface for protection during sectioning and thinning. A technique commonly employed for semiconductor devices is to cement together a pair of specimens face to face (or a stack of several specimens, in the case of thin semiconductors) (Ref 42). Not only is protection provided, but having more than one specimen also improves the chances for success. A general scheme that is often followed in preparing TEM specimens from the bulk is illustrated in Fig. 7. It is assumed that the specimen is a cross section and that the worn surface has been protected by a thick coating layer (>1.5 mm). First, a thin section is cut, with care being taken that the section is thick enough that damage from the cutting process does not extend into the region of actual study. For hardened steels and ceramics, a thickness of 01.1 to 0.2 mm may be acceptable. For soft, annealed metals, 1 mm or larger may be required. A low-speed diamond saw or, for conductive materials, an electric discharge machine (EDM) is frequently used for cutting. Fig. 7 Schematic showing steps required to prepare TEM cross section specimen Then the thickness of the section must be reduced to about 0.1 mm. Conventional abrasive grinding, lapping, and polishing methods are usually employed (Ref 43). One or more disks 3 mm in diameter are cut from the thin section. Because this is a cross section, the line of intersection demarcating the worn surface is placed at the center of the disk. The disk may be cut with a hollow or tubular-shaped tool having an inside diameter of about 3 mm. One of several different cutting methods may be used, depending on the material for example, core drilling with a tool impregnated with diamond grit, abrasive slurry core drilling, ultrasonic abrasive impact machining, or EDM. The final step is to reduce the thickness of the center region of the disk until it becomes thin enough to be electron transparent. In practice, thinning is usually continued until perforation occurs. When successful, some of the area around the perforation will be thin enough for electron transmission. Thinning may be accomplished by electropolishing, chemical polishing, ion beam milling, possibly mechanical polishing, and combinations of these processes. Alternative methods and approaches for preparing specimens, as well as additional details, can be found in Ref 37, 38, 39, 40, 41, 42. Surface replicas have already been discussed in connection with the preparation of specimens for SEM study. As was mentioned, a technique that is often used involves pressing a thin section of cellulose acetate film moistened with acetone onto the surface. After a short time is allowed for drying, the film is stripped from the surface. For TEM study, the acetate replica is coated (shadowed) at oblique incidence with a heavy metal such as palladium-gold or chromium. The shadow produced by the heavy metal absorbs or scatters electrons, enabling the topography to be revealed by transmitted electrons. After shadowing, a uniform layer of carbon, 10 to 20 nm thick, is deposited in effect generating a carbon replica of the acetate film surface. Deposition of the shadowing metal and the carbon support film is usually done in vacuum evaporator. The shadowed and carbon-coated acetate film is cut into pieces 3 mm square. One of the squares may then be placed on a TEM support grid and the cellulose acetate film dissolved with acetone leaving the shadowed carbon replica, suitable for examination in the TEM. This describes only briefly one of many different methods (Ref 20, 37), for preparing replicas. The same cautionary note made with respect to accurate surface representation in reference to SEM replicas is also true for TEM replicas. Debris Specimens. Wear debris particles that are thin enough to be electron transparent can be studied directly in the TEM. In this case, preparation consists of collection, dispersion, and mounting the particles on a suitable support film. Specimen grids covered with a 10 to 20 nm thick film of carbon or silicon monoxide are often used for this purpose. If the particles are in the form of a dry powder, they can be brushed or blown such that some fall onto the support film. Alternatively, the particles may be dispersed in a volatile solvent and deposited as a small drop or sprayed onto the support film. Particles in-oil or grease can be extracted by solvent washing through an appropriate membrane filter or by repeated centrifuging in a solvent and decanting until the particles are free of contaminants, as discussed in connection with SEM specimen preparation. When a membrane filter is employed, it is treated like a replica; that is, the filter surface is coated with a layer of carbon to support the particles, and the filter material is dissolved away. When the wear debris particles are too thick to be electron transparent, they are usually embedded in mounting material (epoxy, for example) to form a composite, which is then sectioned and thinned like a bulk specimen (Ref 44), or they may be incorporated in a thick plating which is subsequently thinned. Additional information on particle specimen preparation can be found in texts dealing with particle analysis in general (Ref 45, for example). Imaging and Analysis in the SEM The most important signals that are employed for analysis in the SEM and the information that each provides are summarized in Table 1. Each signal requires an appropriate detector (except for specimen current, where the specimen itself is the detector) and an amplifier. In the case of x-rays for quantitative studies, a complete computer-based analysis system in necessary. Table 1 SEM signals Signal Information Special requirements Secondary electron Topography; some crystallography; some composition None Backscattered electron Composition; topography; crystallography; magnetic domains None Specimen current Similar to secondary and backscattered electrons None X-ray Composition Smooth surface for quantitative analysis Cathodoluminescent Composition Used for materials that exhibit cathodoluminescence Thermal wave Subsurface defects Smooth surface Secondary Electron Signal The main application of SEM is the investigation of surface topography, and the low-energy secondary electron signal ( 50 eV) is the primary source of this information. Secondary electron emission is strongly influenced by surface orientation and varies approximately as the secant of the angle of incidence of the electron beam. An element of surface that is inclined to the beam appears brighter than one that is normal to the electron beam. Enhanced brightness is seen at sharp edges, small particles, and fine-scale roughness because of the larger area from which secondary electrons can escape. With increased penetration at higher accelerating voltages, the area also increases, so that more detailed and sharper images of fine surface features are more often obtained at lower accelerating voltages ( 5 to 10 kV) than at higher voltages. The observed contrast is also influenced by the position of the secondary electron detector, which is usually located to one side and at about the same level as the specimen. More electrons are received by the detector from an element with its surface inclined toward the detector than from an element tilted away from the detector. The visual effect is to make the image appear as though the specimen were illuminated by a source located at the detector. Although secondary electrons are created throughout the interaction volume (Fig. 4), because of their low energies only secondary electrons originating close to the surface are able to escape and contribute to the image. The maximum escape depth ranges from about 1 to 10 nm for high- and low-density materials, respectively. Thus, the specimen surface immediately under the incident beam is the source of directly generated secondary electrons. If this were the only source of secondary electrons, the image resolution would be closely determined by the beam or spot size. However, secondary electrons are also generated by backscattered electrons as they leave the surface or strike the SEM polepiece and specimen chamber walls. Backscattered electrons have a large range and may exit the surface some distance from the location of the incident beam. This effectively increases the source size and decreases resolution. In general, the fraction of secondary electrons emitted is relatively insensitive to the atomic number, Z, although some compounds do have a significant effect on emission (Ref 8). However, the number of backscattered electrons generated is quite sensitive to Z (discussed below). Thus, secondary electron emission is indirectly, affected by Z through its influence on backscattered electron emission. For this season, phases with different average atomic numbers can be distinguished in secondary electron images. Similarly, the emission of secondary electrons is not directly sensitive to crystallographic orientation, but, because backscattered electron emission is influenced, differences in orientation produce contrast in secondary electron images. A notable example is the variation in contrast exhibited by different grains in the image of a carefully polished polycrystalline sample; these grains exhibit channelling contrast. This effect can be seen in Fig. 6, where an annealing twin is visible and dislocation cells with only slight differences in orientation can be distinguished. Moreover, grains in the electrodeposited layer of copper can be seen. Further examples of images obtained in the secondary electron imaging mode are shown in Fig. 8. The specimen is the worn sealing face of a diesel engine valve. The valve was titled at a large angle to the incident electron beam in order to display the lip of material that resulted from plastic flow. It is only because of the tremendous depth of field associated with the small angular aperture of the SEM objective lens, assisted by the dynamic focusing capability with which most SEM instruments are equipped, that such an image can be obtained. (Dynamic focus refers to the programmed change in focus as a function of raster position as the beam is scanned across the specimen.) In addition to the images in this article, secondary electron SEM images of worn surfaces can be found elsewhere in this Volume. Note especially those in the article "Surface Damage." Fig. 8 Secondary electron image of the sealing face of a diesel engine valve. (a) Low magnification. (b) Higher magnification of flowed lip. Note dark contrast at carbonaceous deposit. Other sources of contrast in addition to those discussed above are electric and magnetic fields. Both can strongly influence the number of secondary electrons collected. This permits the imaging of magnetic domains and is the basis for voltage contrast in semiconducting devices (Ref 9). Finally, the ability to carry out stereomicroscopy using secondary electron images can be of considerable value in the examination of surface topography. Stereopairs are produced by photographing the surface at two different angles of tilt, usually at a separation of 5° to 10°. A stereoviewer can be used to observe differences in height visually, or the difference in distance between corresponding pairs of points in the two images can be measured and the height difference obtained quantitatively by simple geometry utilizing the known tilt angle and magnification. Backscattered Electron Images Backscattered electrons are those electrons that leaves the specimen with energies greater than 50 eV (Fig. 3) and have a component of direction opposite to that of the incident beam. This includes inelastically scattered electrons and, at the high-energy limit, primary electrons that have undergone elastic scattering with almost no loss in energy. The majority of backscattered electrons have energies from 0.5 to 0.9 of the incident beam energy. As mentioned above, the efficiency with which backscattered electrons are generated is strongly dependent on the atomic number of the scattering atoms. This dependence is depicted schematically in Fig. 9, which shows that the scattering efficiency for light elements is less than that for heavy elements. The distribution of backscattered electrons is also a function of the beam orientation with respect to the specimen surface. Figures 10(a) and 10(b) illustrate the effect of surface orientation on distribution for normal and oblique incidence. Because of these dependencies, the backscattered electron signal carries both topographic and compositional information. Fig. 9 Backscattered electron yield dependence on atomic number Fig. 10 Angular distribution of backscattered electrons. (a) Incident beam normal to surface. (b) Incident beam inclined to surface The backscattered electron detector is often designed to detect electrons from several (usually four) separate locations around the specimen. The signals from each of these different quadrants may be individually selected, and added or subtracted. This feature allows the selective emphasis of atomic number contrast or topographic contrast. When the [...]... Bundschuh and K.-H Zum Gahr, Influence of Porosity on Friction and Sliding Wear of TZP-Zirconia, Wear of Materials 1991, K.C Ludema and R.G Bayer, Ed., American Society of Mechanical Engineers, 1991, p 319 5 L.K Ives, J.S Harris, and M.B Peterson, Evaluation of a New Wear Resistant Additive SbSbS4, Wear of Materials 1983, American Society of Mechanical Engineers, 1983, p 507 6 P.J Shuff and L.J Clarke,... Publishing, London, 1991, p 461 45 T Allen, Particle Size Measurement, 3rd ed., Chapman and Hall, 1981, p 196 46 A.W Ruff, Deformation Studies at Sliding Wear Tracks in Iron, Wear, Vol 40, 1976, p 59 47 K.F.J Heinrich, Electron Beam X-Ray Microanalysis, Van Nostrand Reinhold, 1981 48 L.K Ives, Abrasive Wear by Coal-Fueled Engine Particles, Proceedings Corrosion Erosion -Wear of Materials at Elevated Temperatures,... CRTs are available for visual observation and photography Alternatively, with a modern digital instrument, a computer screen replaces the visual CRT Bright- and dark-field detectors are basic equipment in the STEM system According to the principle of reciprocity (Ref 19) STEM bright-field and dark-field transmission images are similar to CTEM bright- and dark-field images, or at least can be made similar... Observations of Wear Processes in a Scanning Electron Microscope, Wear, Vol 110, 1986, p 419 32 K Hokkirigawa and K Kato, The Effect of Hardness on the Transition of the Abrasive Wear Mechanism of Steels, Wear, Vol 123, 1988, p 241 33 H Kitsunai, N Tsumaki, and K Kato, Transitions of Microscopic Wear Mechanism for Cr2O3 Ceramic Coatings During Repeated Sliding Observed in an SEM-Tribosystem, Wear of Materials... Devanathan and P Clayton, Rolling/Sliding Wear Behavior of Three Bainitic Steels, Wear of Materials-1991, K.C Ludema and R.G Bayer, Ed., American Society of Mechanical Engineers, 1991, p 91 3 I.L Singer, S Fayeulle, and P.D Ehni, Friction and Wear Behavior of TiN in Air: The Chemistry of Transfer Films and Debris Formation, Wear of Materials 1991, K.C Ludema and R.G Bayer, Ed., American Society of Mechanical... Electronics and Electron Physics, P.W Hawkes, Ed., Academic Press, London, 1984, p 16 1-2 88 25 T.F.J Quinn, The Application of Modern Physical Techniques to Tribology, Van Nostrand & Reinhold, 1971 26 T.F.J Quinn, Physical Analysis for Tribology, Cambridge University Press, 1991 27 A.W Ruff, L.K Ives, and W.A Glaeser, Characterization of Wear Surfaces and Wear Debris, Fundamentals of Friction and Wear, D.A... 1980, p 23 5-2 89 28 W.A Glaeser, Wear Experiments in the Scanning Electron Microscope, Wear, Vol 73, 1981, p 371 29 S.J Calabrese, F.F Ling, and S.F Murray, Dynamic Wear Tests in the SEM, ASLE Trans., Vol 26, 1983, p 455 30 W Holzhauer and F.F Ling, In-Situ SEM Study of Boundary Lubricated Contacts, ASME Trans., Vol 31, 1987, p 359 31 T Kayaba, K Hokkirigawa, and K Kato, Analysis of the Abrasive Wear Mechanism... off rapidly with increasing energy loss and becomes very small in the high-loss region In order to show the details of both the low- and high-loss regions in the same graph, as is customary, the high-loss region is displayed at an increased gain Fig 23 Schematic illustration of EELS spectrum In Fig 23, the first and largest peak in the low-loss region is the zero-loss peak This peak consists primarily... cases The nature and arrangement of dislocations resulting from tribological contact, thermal and stress-induced phase changes, the composition and microstructure of triboreaction films, and the properties of wear debris can all be characterized by means of TEM References 1 K.C Ludema and R.G Bayer, Ed., Wear of Materials 1991, American Society of Mechanical Engineers, 1991 2 R Devanathan and P Clayton,... of Lubricated Mild Wear With Zinc Dialkyl-dithiophosphate, Wear, Vol 107 , 1986, p 355 58 S.K Ganapathi and D.A Rigney, An HREM Study of the Nanocrystalline Material Produced by Sliding Wear Processes, Scr Metall Mater., Vol 24, 1990, p 1675 59 R.F Egerton, Electron Energy-Loss Spectroscopy in the Electron Microscope, Plenum Press, 1986 Scanning Tunneling Microscopy Yip-Wah Chung and T.S Sriram, Northwestern . Ref 8 and 12. Before adopting a particular cleaning method, careful consideration should be given to the effect of the procedure on surface films and attached wear debris. Wear debris and triboreaction. probe size is made small for higher-resolution studies, the limited bandwidth of the required high-impedance, high-gain, direct-current amplifier limits observation and recording to very slow scan. provides the means of revealing and characterizing lattice defects, such as dislocations and stacking faults, and for observing precipitates and other second-phase particles. To explain the origin