Composition Of Debris Research Articles

The tribochemical behaviour of TiN-coatings during fretting wear

To reveal the tribochemical reactions during fretting wear of TiN-coatings sliding against corundum, the microstructure and the chemical composition of debris have been investigated by analytical TEM. Novel observations on fretting wear debris are presented. These observations were possible thanks to a TEM-sample preparation procedure by ultramicrotomy. Based on friction force measurements, the tribological life of the TiN-corundum tribo-pair, was divided in five periods, namely: a running-period, a first transition, an intermediate steady state, a second transition, and a final steady state. Fretting experiments were stopped at different periods after which the debris were collected and characterised. The structure of fretting wear debris appeared to be dependent upon the moment of formation. The collected debris consisted of either amorphous or nanocrystalline rutile-like material. For comparison, fretting tests were also performed on pure titanium sliding against corundum. The debris originating from titanium consisted of nanocrystalline rutile. The observed difference in microstructure between the debris from TiN and pure titanium is mainly due to differences in the tribochemical reactions occurring during fretting wear. The evolution from amorphous to nanocrystalline debris on TiN, is proposed to be due to the combined effect of relative humidity, energy input, and continuous oxidation.

Geochemistry, Provenance and Environmental Conditions of Holocene Sediments of Upper Manso River Basin-Lake Mascardi, Argentina

The Upper Manso River drainage basin and Lake Mascardi (c., 41~ 72~ are located in Patagonian Andes, Argentina. The very steep Upper Manso River is 23 km long, has its headwaters at the Manso glacier (Mount Tronador, 3554 m a.s.1.) and discharges into Lake Mascardi (793 m a.s.1.). Turbid glacial melt water feeds the system, as well as rain and snowfall between May and July. The geology of the area includes phillitic, porphyric and granitic rocks, as well as Tertiary volcanic and sedimentary rocks. Varves, tephras, and glacial/ glacio-fluvial deposits are widely distributed throughout the basin. Rocks, suspended and river bed sediments, as well as lake bottom sediments, and material from sediment traps deployed in Lake Mascardi, were collected in the area of study. Samples from an AMS radiocarbon-dated sediment core obtained in Lake Mascardi at 30 m water depth were also included. Lake Mascardi sediments record variations in the transport of glacially-derived clay and silt to the basin, which reflects variations in Southern Hemisphere climatic characteristics for the last 15.0 kyr BP (Ariztegui et al., 1997). All the samples were analysed for 25 major and trace elements using instrumental neutron activation (INAA) in the RA-6 research reactor (S.C. de Bariloche, Rio Negro, Argentina). In this paper we analyse the chemical variability of glacio-fluvial sediments in a pristine area, also examining inorganic inputs in a lake core since Late Pleistocene. Glacial environments are characterized by low chemical weathering rates. However, the production of fine-grained, easily weathered material, may compensate this well-known fact and introduce an important variable in global weathering. In this particular case, a regenerated glacier at the uppermost reaches, introduces an important debris load into the river. The mineralogical composition of such debris, derived from basalts, shows a dominance of feldspars, pyroxenes and amphiboles. Feldspars are sensitive to weathering and their transformation to clays is indicative of the reached degree of alteration. In order to quantify such process, we have used the chemical index of alteration (CIA) and the chemical index of weathering (CIW). CIA values for presentday sediments suggest a clear dominance of plagioclase. A relatively uniform variation of CIW/CIA also indicates a constant mineralogical composition. The geochemistry of the Upper Manso river drainage basin is controlled by a weathering limited regime (Stallard and Edmond, 1983). Hence, detrital materials exhibit a close relationship with source rocks (Tronador Fm. Miocene basalts). This is clearly shown by R E E normalized patterns, Eu/Eu* values and the relative distribution of immobile elements. The main deviations from this trend were observed for high-mobility elements (U, Na, Sr) and those selectively adsorbed in clay-size materials (Cs, Rb). The available evidence also suggests an Nd enrichment in the finer size fractions. Although the textural differences are favoured by selective sorting, the immobile element distribution of source rocks is preserved in sediments of Upper Manso drainage basin. Due to the presence of plagioclase-bearing basalts in the drainage basin, the sediments offer excellent conditions for the study of the Eu behaviour during sedimentary processes. Following the Albarbde and Semhi's approach, the modelling of the Eu fractionation in relation with trivalent R E E suggests little reworking of sediments, with a total loss of soluble or weathered material of 36%. Material collected in sediment traps moored off the mouth of the Manso River has exhibited features

The basal ice layer of glaciers and ice sheets

In many glaciers and ice sheets there is a basal ice layer (BIL) in which the ice is conditioned primarily by processes operating at the bed. The BIL is chemically and physically distinctive, and is characterised by a component of basally derived sediment. The BIL is: a rheological control on ice-sheet dynamics; an indicator of subglacial conditions and processes; an agent of subglacial geologic processes; the source of a substantial proportion of glacial sediments; a limit to the downward extension of the climate record from deep ice cores. If debris characteristics of the BIL are preserved in glacial sediments, former glacier conditions can be inferred. Analysis of stable isotopes, gas and cation composition, ice crystallography, debris composition and structural glaciology has elucidated many mechanisms for BIL formation. Common elements can be identified from a range of locations. Key issues are entrainment of ice and debris from the bed, formation of new ice, metamorphism of existing ice in the BIL, and thickening of the BIL by deformation. A distinction can be made between basal ice formed by accretion of material from the bed (‘stratified facies’) and basal ice formed by metamorphic processes within the ice close to the bed (‘dispersed facies’).

Experimental investigation on migration of material during EDM of die steel (T215 Cr12)

This paper presents the Scanning Electron Microscopic (SEM) investigation on changes in chemical composition of resolidified layers of both the tools and the workpieces as well as debris. An investigation has also been made on variation of micro-hardness, depth of resolidified layer and heat affected zone (HAZ) with pulse current and electrode rotation. This change in chemical composition occurs due to migration of material from either of the electrodes during electro-discharge machining of high carbon high chromium die steel (hardened) with rotating copper-tungsten tool electrode. The machining characteristics of the material depend on the various machining parameters like discharge current, pulse duration, voltage, dielectric and electrode materials. The rotation of electrode during machining also contributes towards these. The experiments were conducted by varying discharge current and electrode rotation to study the effect of these parameters on alloying of tool and workpiece surfaces. An effort has also been made to compare these results with that of stationary electrode. The experiments were statistically designed and a mathematical model of the process has been developed. It is found that appreciable amount of elements has migrated from the tool electrode to workpiece and vice versa and got alloyed in the resolidified layer. The chemical composition of debris also changed due to the pick up of elements from both the electrodes.

Pest interactions and canopy gaps in ponderosa pine stands in the Black Hills, South Dakota, USA

Gap frequency and size, cause (predisposing factors, killing agents, and tree response), and coarse woody debris composition (snags and downed logs) were assessed in three stands differing in management history. Disturbance agents were usually coupled concurrently and sequentially. A qualitative model (relational diagram) developed to display these interactions and the activity distributed among different disturbance pathways suggests that management activity (1) diminishes pest-caused structural diversity in the forest ecosystem, (2) decreases functional diversity associated with interacting diseases, insects and other disturbance agents, and (3) alters the abundance and decomposition distribution of dead wood.

Comparison of stress-based and strain-based creep failure criteria for severe accident analysis

We conducted a parametic analysis of stress-based and strain-based creep failure criteria to determine if there is a significant difference between the two criteria for SA533B vessel steel under severe accident conditions. Parametric variables include debris composition, system pressure, and creep strain histories derived from different testing programs and mathematically fit, with and without tertiary creep. Results indicate significant differences between the two criteria. Stress gradient plays an important role in determining which criterion will predict failure first. Creep failure was not very sensitive to different creep strain histories, except near the transition temperature of the vessel steel (900 K to 1000 K). Statistical analyses of creep failure data of four independent sources indicate that these data may be pooled, with a spline point at 1000 K. We found the Manson-Haferd parameter to have better failure predictive capability than the Larson-Miller parameter for the data studied.

Microanalysis of debris formed during rotary EDM of titanium alloy (Ti 6A1 4V) and die steel (T 215 Cr12)

This paper presents the scanning electron microscopy investigation on formation of debris during rotary electrodischarge machining of titanium alloy and high carbon high chromium die steel. Microanalysis of chemical composition of debris, in the form of globules after resolidification of ejected material from the workpiece surface, has been carried out using qualitative energy-dispersive spectroscopy and electron probe microanalysis. Scanning electron micrographs indicate the various types of debris particles which are collected from the dielectric as well as the particles which remain attached on the workpiece surface. Many distinct types of spheroidal particles (globules) are witnessed and the mechanism of their formation has been discussed. The chemical composition of these particles differs considerably, from its parent material due to migration of material from the rotating tool electrode (copper-tungsten) and the dielectric fluid.

Composition and morphology of wear debris in failed uncemented total hip replacement

Interfacial membranes collected at revision from 11 failed uncemented Ti-alloy total hip replacements were examined. Particles in the membranes were characterised by electron microscopy, microchemical spectroscopy and particle size analysis. Most were polyethylene and had a mean size of 0.53 micron +/- 0.3. They were similar to the particles seen in the base resin used in the manufacture of the acetabular implants. Relatively few titanium particles were seen. Fragments of bone, stainless steel and silicate were found in small amounts. Most of the polyethylene particles were too small to be seen by light microscopy. Electron microscopy and spectroscopic techniques are required to provide an accurate description of this debris.

Palynofacies of Lignites and Associated Sediments in the Upper Paleocene Tuscahoma Sand of Southwestern Alabama and Eastern Mississippi

ABSTRACT The Tuscahoma Sand of the Wilcox Group is composed of fine-grained sand, laminated sandy clay, marl, and lignite. It forms a poorly exposed belt from southeastern Alabama extending north-westward into western Alabama and eastern Mississippi. It is assigned to the late Paleocene planktonic foraminiferal Morozovella velasocoensis interval zone. Lignites in the Tuscahoma Sand occur as parasequence deposits in the highstand systems tract of a type 2 depositional sequence near the top of the formation. Organic debris associated with these highstand systems tract deposits are dominated by land-derived plant tissues such as angiosperm and gymnosperm pollen, spores of ferns, lycopods, and fungi, plant cuticle, wood in various states of degradation, charcoal or inertinite, cysts of fresh-water algae, and resins. Marine influence in some samples is indicated by the rare occurrence of dinoflagellate cysts, microforaminiferal tests linings, and the presence of gray, amorphous organic matter. Three palynofacies are recognized within highstand systems tract deposits in the upper Tuscahoma Sand based on the occurrence of organic debris. They represent fresh-water swamp, brackish marsh, and marginal to shallow-water marine depositional environments. Lignites in the Tuscahoma Sand are dominated by an angiosperm pollen assemblage. Pollen similar to that produced by the Betulaceae and Myricaceae, modern arborescent angiosperms, is common in these assemblages, as are fern spores, spore of Sphagnum, woody tissue, and charcoal. Gymnosperm pollen is rare, and marine forms are absent. This assemblage reflects deposition under fresh-water swamp conditions. Carbonaceous clay samples vary in the composition of organic debris. However, many are characterized by the occurrence of herbaceous angiosperm pollen such as Carex, Arecipites, Calamuspollenites, and Liliacidities. Arborescent angiosperm pollen is also common, as are fern spores. Bisaccate conifer pollen is common, and dinoflagellate cysts are rare. Fungal elements are abundant, and woody tissue is commonly more degraded than in lignite samples. This assemblage represents deposition in coastal, brackish marsh environments. Organic debris in laminated clays, silts, and sands typically have angiosperm and gymnosperm pollen, dinoflagellate cysts, degraded terrestiral plant materal, and amorphous organic matter, and represent shallow marine and marginal marine deposits. End_of_Record - Last_Page 508-------

Ferrographic analysis of failure process in a full-scale journal bearing

The failure process of a full-scale journal bearing, caused by insufficient oil supply to the interface, was monitored and analyzed with ferrography and the spectrometric oil analysis procedure (SOAP). The temperature of the bearing metal and the journal deviation were also measured to monitor the behavior of the bearing. Wear debris was observed and analyzed in detail with a scanning electron microscope and a wavelength-dispersive X-ray analysis facility. It was found that ferrography and SOAP could promptly detect the failure symptoms. Ferrography could also detect the progressive failure, that is the progress of damage. With the progress of failure, the types, sizes and composition of wear debris changed significantly; a small amount of rubbing debris was generated from the journal at the normal state, much cutting and plate-like debris from the journal, some plate-like debris from the bearing at the early stage of failure, much polymer-like debris containing both the journal and bearing materials at the middle stage and much cutting, plate-like and oxide-like debris from both the journal and lining metal (steel) at the catastrophic stage. The wear mechanisms are discussed.

A study of fretting wear with particular reference to measurement of residual stresses by X-ray diffraction

The results presented in this paper demonstrate the role of the most important parameters that govern fretting wear. The effects of the fretting action are studied by “microweighing”, to assess the wear, and by X-ray diffraction for the debris composition composition and for residual stress measurements. The residual stresses introduced by the fretting action were compressive. They were highest in the direction perpendicular to that of fretting and shear stress was observed in the direction of fretting. All these stresses have their largest values on the surface and reach steady values very rapidly. For the tests covered in this study the amplitude of the motion was found to be the most important parameter.

Provenance mixing in an intraoceanic subduction zone: Tonga Trench-Louisville Ridge collision zone, southwest Pacific

Dredging on the lower slope of the Tonga forearc, at the intersection between the Louisville Ridge hotspot chain and the trench, yielded both Late Tertiary volcaniclastic sediments and Late Cretaceous slightly tuffaceous pelagic sediments. Petrography and phase chemistry of volcanic debris of Tertiary age samples indicates derivation from a low-K tholeiitic arc: volcanic glass has a low K 2O content and shows an Fe enrichment trend; plagioclase grains are high in An and low in Or components; pyroxene grains (calcic clinopyroxene, orthopyroxene and pigeonite) have low TiO 2 contents and show an Fe enrichment trend; alkali feldspar and biotite are absent. The composition of the Tertiary samples is similar to other Tonga forearc sediments and is consistent with their derivation from the adjacent magmatic arc. The character and composition of volcanogenic debris in Cretaceous age samples indicates derivation from an intraplate alkali igneous source: plagioclase compositions show an increasing Or component with increasing Ab; alkali feldspar is a rare additional component of these samples; calcic clinopyroxene has high TiO 2 contents and is titanaugite; amphibole is also rich in TiO 2 and is kaersutite; minor volcanic glass is rich in alkalis. Samples were dredged from the seaward slope of a small terrace on the lower trench slope. A planar reflector, located 2.6 km below the terrace is marked by an abrupt jump in seismic velocity and is interpreted as the top of an essentially undamaged Late Cretaceous guyot of the Louisville chain that was subducted at the Tonga trench about 0.5 Ma. This guyot is the likely source of the Late Cretaceous, intraplate igneous detritus collected at the dredge site. Some dredge samples yielded a mixed volcanic arc/intraplate provenance and/or Late Tertiary/Late Cretaceous ages. This probably represents the mixing of the Cretaceous seamount and Tertiary magmatic arc sources during post-collision slumping of the wedge of lower slope material as it re-establishes its critical taper.

Spatio-Temporal Patterns of Foraging Success for Fishes in an Illinois Stream

Stomach contents of 10 fish species were examined to evaluate several scales of spatio-temporal variation in foraging success within an Illinois stream. Most species fed primarily on aquatic or terrestrial invertebrates, but one species (Pimephales notatus) specialized on fine detritus. Fish ate a wide variety of invertebrate taxa, and diet overlap based on prey taxa was extensive among fish species and age classes. Foraging success, measured by number and size of prey eaten, varied among seasons, years, substrate composition and amounts of woody debris. However, no factor influenced foraging success of all species, and no two species responded identically to all factors. Fish generally fed most successfully in June, and least successfully in October. Some fish ate more or larger prey in a study area with gravel-cobble substrates than in a silt-sand area, and many ate more or larger prey in sites with woody debris than in sites from which debris was removed. In addition, aquatic invertebrates increased in abundance in silt-sand substrates when fish were excluded, but did not increase in gravel-cobble substrates, suggesting a greater potential for resource depression in the silt-sand area. Stream fishes apparently face continuous variation in food availability at several temporal and spatial scales. Because changes in availability are often unpredictable and influence each species differently, the competitive environment of stream fishes may be in a state of constant flux. Anthropogenic modifications of streams may create conditions that favor fishes such as certain cyprinids which have highly opportunistic feeding habits. INTRODUCTION Successful foraging is essential to reproduction of most animals; thus natural selection should favor individuals which are most efficient at obtaining food. Efficiency in foraging probably evolves in response to temporal and spatial variation in foraging success, which can result from inherent fluctuations in resource availability or from resource depression (sensu Charnov et al., 1976) due to coexploiters. Resource depression may, in turn, generate strong competitive interactions and lead to the evolution of food partitioning. Among vertebrates, selective advantages of rapid growth and efficient foraging are perhaps best known for fishes. For example, rapid growth of fish to a relatively large size may be adaptive through increased gamete production (Bagenal, 1978) or immunity from predation (Werner et al., 1983a) or success in dominance disputes. Thus, spatio-temporal patterns of' fish foraging success may reveal information that is useful in understanding their population dynamics. Aquatic or terrestrial invertebrates are the primary food resource of most fishes in small streams of the midwestern United States, whereas detritus, algae and other fish are less commonly consumed (Pflieger, 1975; Smith, 1979; Trautman, 1981). Although diets of most fish species are dominated by only one or two of these food resources, opportunistic feeding is widespread, and seasonal shifts in diet composition are common (Starrett, 1950; Whitaker, 1977). Furthermore, foraging rates often exhibit strong seasonal patterns (Mathur, 1977; Allan, 1981; Angermeier, 1982), which are probably induced by cycles of insect emergence and recruitment (Hynes, 1961; Resh, 1977). In addition to temporal variation, fish foraging patterns should also reflect spatial dynamics of invertebrate availability. For example, production and abundance of stream inverte'Present address: Virginia Cooperative Fishery Research Unit, Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061.

Specimen material reversal in pin-on-disc tribotesting

Results from pin-on-disc wear tests in which specimen and counterface materials were interchanged are presented in this paper. In one set of tests, pins of material A were slid against discs of material B; then, in another set of tests, pins of material B were slid against discs of material A. There are many factors to consider in such experiments, including the fact that the pin experiences a greater sliding distance and presumaly higher near-surface temperatures. However, test results from such specimen material reversals are useful in studying the roles of thermal, mechanical and chemical processes in sliding wear and also in assessing the validity of tribotesting against a “standard” counterface material.The results reported include data on volume change (obtained from weight change measurements), on wear track profiles, on subsurface zone morphology and composition and on debris composition. As expected, these data indicate that significantly different results will be obtained for a given pin-on-disc test for pin material A against disc material B compared with pin B against disc A.

Genesis of marginal moraines in the Caucasus

Composition and fabric of different moraines in the glaciated areas of Central Caucasus were studied to elucidate sedimentary environments and geomorphological processes. Methods used included particle‐size distribution, pebble and mineral counts, shape analysis of pebbles, and till fabric analysis. Samples were taken from superglacial and basal debris, marginal moraine ridges and till horizons, and quantitative parameters were established for different glacial environments and till accumulation processes. Considerable differences in composition and fabric of superglacial and basal debris were caused by their specific transport conditions. Most marginal moraines consist of material similar to basal debris and only the topmost parts of some ridges have a noticeable incorporation of superglacial debris. These results point to considerable erosion of mountain valleys by temperate glaciers. Previous geomorphological investigations have emphasized the importance of superglacial debris in the formation of marginal moraines by alpine glaciers, but this viewpoint is not supported by the studies performed.

Microorganisms and Detritus in the Water Column of a Subtidal Reef of Natal

The parameters measured in this study were light and dark-bottle uptake of NaHI4CO3, the chlorophyll content of seawater, direct counts of bacteria, microbial uptake of 14C glucose and a labelled algal extract, organic carbon in the seawater and the composition of debris washed onto the reef. The phytoplankton consisted largely of nannoplankton and primary production was low with an annual mean of P = 12.82 mg C n1r3h-', while the mean chlorophyll a content of 2.13 mg m-3 was equivalent to a dry biomass of 170.1 mg m-3 Microbial heterotrophic activity was relatively high with an annual mean glucose assimilation of V,,, = 0.612 @g l-'h-' and a total bacterial count of 2.02 X 106 ml-', equivalent to a dry biomass of 20.3 rng m-3. The largest proportion of this activity, measured by differential filtration and using antibiotic inhibitors, is performed by free bacteria as opposed to the smaller proportion conducted by bacteria attached to particles, or by microflagellates. Uptake of the labelled algal extract (V,,, 13.2-72.6 mg C m-3h-') indicates that microbial heterotrophic activity exceeds phytoplankton production. Carbon analyses gave an annual mean of 18.3 g m-3 total organic carbon, of which 20 % was particulate, the rest being dissolved organic carbon. Analysis of debris revealed that it consisted almost exclusively of seaweed, except when rivers were in flood, providing a large influx of terrestrial plant debris. These findings are compared with other published results, and their ecological significance is discussed in relation to the remainder of the environment. It is concluded that primary production by phytoplankton is not as important in supporting the biomass of filter feeders on the reef as is heterotrophic activity associated with organic detritus.

Comments on “The value of symmetrical configurations”

Results from pin-on-disc wear tests in which specimen and counterface materials were interchanged are presented in this paper. In one set of tests, pins of material A were slid against discs of material B; then, in another set of tests, pins of material B were slid against discs of material A. There are many factors to consider in such experiments, including the fact that the pin experiences a greater sliding distance and presumaly higher near-surface temperatures. However, test results from such specimen material reversals are useful in studying the roles of thermal, mechanical and chemical processes in sliding wear and also in assessing the validity of tribotesting against a “standard” counterface material.The results reported include data on volume change (obtained from weight change measurements), on wear track profiles, on subsurface zone morphology and composition and on debris composition. As expected, these data indicate that significantly different results will be obtained for a given pin-on-disc test for pin material A against disc material B compared with pin B against disc A.

Hereditary retinal dystrophy in the rat: Lipid composition of debris

In order to ascertain the molecular environment of rhodopsin in the rhodopsin-rich outerlayer debris of the retina of dark-reared mutant albino rats (BA) lipids and fatty acids were measured in fractions of the debris isolated by gently shaking the retina. In comparison to the outer segments (ROS) of dark-maintained adult normal rats (ROS-D) and of young mutants (ROS-M) the debris at the age of 100 days was depleted in phospholipids (PL) per rhodopsin (Rh) ∗ ∗ Abbreviations: PE, phosphatidylethanolamine; PC, phosphatidylcholine; PS, phosphatidylserine; PI, phosphatidylinositol; Sph, Sphingomyelin; RH, rhodopsin; Pe, pigment epithelium. on a molar basis. Maximal and minimal estimates for the PL Rh ratio of debris were 35 and 25, compared to 64 and 92 for ROS-D and ROS-M, respectively. Using Rh and docosahexaenoic acid (22:6) as markers for the outer segment origin of the debris, two estimates were derived: in comparison to ROS-D, 70% of debris PL could derive from outer segment membranes, but 90% in comparison to ROS-M. The major phospholipid of non-outer-segment origin appeared to be sphingomyelin; a pigment epithelial origin of this debris fraction is suggested. The PL/protein weight ratio of debris was 0·4. Cholesterol per rhodopsin was five times higher in debris than in ROS-D. The rate of disappearance of the debris after the age of 100 days was quantitatively the same for the histologically measured volume of the debris, rhodopsin, phospholipids and cholesterol (“bulk disappearance”).

Biochemical Studies on the Composition of Gingival Debris from Children with Black Extrinsic Tooth Stain

Gingival debris were collected from two groups of children, one group having black extrinsic tooth stain, and the other being a control group with no apparent coloured staining of the teeth. The material from the former group had a significantly higher content of calcium and phosphate than the latter but no significant difference in either carbohydrate or protein could be shown. The calcium and phosphate content of the debris from the black-staining group was significantly lower than that of samples of dental calculus. The increased calcium and phosphate content of the gingival debris from individuals with extrinsic black tooth stain is thought to largely account for the reduced incidence of caries.

Studies of the Unlubricated Wear of a Commercial Cobalt-Base Alloy at Temperatures up to about 400 C

Pins of a commercial cobalt-base alloy (Stellite 31) have been worn against disks of the same material at room temperature and at various externally-induced ambient temperatures between about 100 C and 400 C, under continuous and reciprocating sliding conditions without lubrication. An unexpected maximum in the wear rate versus ambient temperature curve occurred at about 200 C for specimens which had previously been exposed to ambient temperatures less than the temperature of any given experiment. For entirely new specimens, however, this maximum could not be detected, although there was a pronounced decrease in the wear rate at around 200 C. Friction coefficients, pin temperatures, surface topographies, and the compositions of the wear debris were determined for these experiments, and significant changes were also found to occur at disk temperatures around 200 C. The changes in wear, friction, temperature, wear debris composition, and surface topography around 200 C are discussed in terms of the onset of...