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The presence of wear debris in sliding contacts is often regarded as detrimental, since it can increase friction, induce abrasive wear, reduce actual lubricant film thickness and compromise lubrication systems. On the other hand, the presence of debris may be fundamental to the formation of a protective tribolayer, which can reduce friction and wear. This work investigates the effect of the presence of different iron oxides (F2O3 and Fe3O4) with different sizes on the unlubricated reciprocating sliding of tool steels. For that, sliding tests were carried out with and without the addition of iron oxides. The addition of Fe3O4 particles (larger and softer) resulted in friction (15%) and wear (95%) reduction. Two main factors seem to be responsible for friction and wear reduction when Fe3O4 particles were added into the contact. The first is the relative hardness of the debris in relation to the materials in contact. Since they are softer than the specimens and the counter bodies, they do not cause their severe abrasive wear, which is much more significant for the harder F2O3particles. The second is the relative size (RS) between the debris and the specimen surface topography. When RS is small, the debris get entrapped in the valleys of the specimen topography, thus not participating in the contact. On the other hand, for larger values of RS, the debris become active and therefore can participate in the formation of a protective tribolayer.

The literature is controversial in relation to the influence of wear debris on tribological behaviour. Some works have shown that the presence of debris is fundamental to the formation of a protective tribolayer, thus reducing friction, whereas others showed that the presence of wear debris could contribute to increase friction coefficient due to the energy spent dragging them into the contact. This work aims to study the influence of the presence of wear debris, simulated by Al 2 O 3 particles, on the tribological behaviour of an aluminium-steel pair under reciprocating sliding contact. Special emphasis is given to the particle size (0.05 µm, 0.1 µm, 1 µm and 10 µm). The particles were dispersed in distilled water (2 wt.%) as the source of debris. Reference tests were carried out solely in the presence of distilled water. The addition of alumina particles contributed to a significant reduction in friction coefficient, in particular for the largest particles (diameter ϕ =10 µm). When the larger particles were added, it was possible to observe the formation of a tribolayer on the sample surface leading to a gain of mass. In opposition, the wear rate of the counter body increased when large particles were added and the wear tracks showed strong evidence of abrasive wear. This suggests that hard and large wear debris, incorporated in the tribolayer formed on the samples, can act as hard protuberances, leading to abrasive wear of the counterbodies. When small particles were added, friction was still reduced when compared with the reference test, but the reduction of the friction coefficient was less significant. Small particles reduced the steel counter body wear rate and did not affect significantly the wear rate of the aluminium samples. It is proposed that small debris can get entrapped in the surface irregularities of the specimens and therefore participate less in the formation of the tribolayers.

Gray cast iron is widely used in diesel automotive engines due to its combination of low cost and good fusibility, but also to the presence of graphite flakes in their microstructure. Besides their role as mechanical dampers, graphite flakes can act as solid lubricant, reducing friction and wear of moving components. Surface texturing has been intensively investigated in recent years to improve lubrication and reduce friction and wear in tribological applications, but little attention has been given to surface texturing of gray cast irons. On the other hand, surface texturing adds costs, which can supplant the benefits achieved, in particular when high cost surface texturing techniques are employed. Maskless electrochemical texturing (MECT) is a promising technique, which combines simplicity, low cost and high speed. Recently, MECT was adapted to texture gray cast irons. This work investigates the tribological performance of gray cast iron textured by MECT using lubricated block-on-ring tests under two different rotational speeds and a constant normal load. The blocks consisted of textured cast iron and the rings of SAE 4620 steel. For comparative purposes, untextured polished gray cast iron blocks, as well as gray cast iron blocks subjected to electrochemical polishing (employing the same electrolyte used during MECT) were tested. The results showed a large reduction in friction (up to 2.5x) and wear (higher than 5x) when comparing the polished and the textured samples. Comparing the textured samples and the electropolished samples, this improvement in performance reduced, showing that the benefits were partly due to the texture pattern itself (arrays of pockets) and partly to the exposure of the graphite flakes during electrochemical dissolution of the metal matrix. As the wear progressed and the contact between the block and the ring became more conformal, the benefits obtained by MECT (and electro polishing) were reduced.

The synergistic effect between abrasion and corrosion has been widely investigated and debated, where according to some works this synergy accentuates wear, and for others attenuates it. Despite the considerable effort to understand the synergy between abrasion and corrosion, little progress has been made to understand this phenomenon for ferritic stainless steels. This paper analyses the micro abrasion-corrosion performance of ferritic stainless steel with different chemical compositions (11%wt Cr with and without Ti stabilization; 16%wt Cr with and without Nb stabilization) and, for comparative purposes, austenitic stainless steel (18%wt Cr − 8%wt Ni) and carbon steel (0.2%wt C). The specimens were tested for corrosion (turbulent and aerated environment), micro abrasion and micro abrasion-corrosion. For the corrosion tests, a 1 N H2SO4 solution was used, a 10%wt mixture of SiO2 in distilled water for the micro abrasion tests, and an abrasive-corrosive environment of 10%wt SiO2 in 1 N H2SO4 for the micro abrasion-corrosion tests. In the micro abrasive wear tests there was not a clear trend between the different materials tested, despite differences in their chemical composition, mechanical properties and microstructure. On the other hand, their performance was ruled by their chemical composition, in particular the Chromium content, under abrasion-corrosion conditions. This indicated the predominant role played by corrosion in abrasive-corrosive environments in this particular tribo-system. For all materials tested, micro abrasion wear coefficients were higher (4×) than those measured under abrasion-corrosion conditions. Friction coefficients could also be measured by a 3D load cell strategically positioned in the specially developed micro abrasion-corrosion device, showing a strong reduction (2×) in friction coefficient under abrasion-corrosion conditions when compared with solely abrasion conditions. This was attributed to the formation of a corrosion product, mainly constituted of iron sulphate (identified via FTIR), which has lubricant properties.

This work uses synchrotron radiation XANES and XPS measurements to investigate the structure of ZDDP tribofilms formed from lubricants contaminated with anhydrous and hydrated ethanol (5%wt). The tribofilms were formed at 40 °C from PAO8 lubricant containing only ZDDP additive onto carbon steel specimens using sliding tests, cylinder-on-flat configuration (line contact) under boundary lubrication. Ethanol increased friction as well as surface damage, detected by an increase in relative porous area. Angle-resolved measurements (15°, 45°, 90°) helped detecting differences along the thickness of the tribofilm. The amount of long-chain phosphates apparently reduced with ethanol, leading to reduced wear performance. The sulphides in the tribofilms were richer in Fe in the presence of ethanol, also indicative of more severe wear.

Topography control has been applied as strategy to improve the efficiency of lubricated systems by introducing specific textures to the surface. Surface texturing can significantly affect the lubrication regime, improving the system's efficiency and reducing wear of moving parts. The present work shows the effects of different topographies produced by electrochemical texturing on lubrication regime, and its effects on the wear resistance of the textured surfaces. The lubrication regime was described using the ratio of the lubricant film thickness by the rms roughness of the surfaces (λ parameter). The tests used a block-on-ring tribometer. Samples and rings were made of AISI 1045 steel and SAE 4620, respectively. Lubrication regimes ranged from mixed to boundary for normal loads of 216.9 N and 315 N, respectively. The effect of texture position (inlet and outlet) and relative orientation of the texture patterns were studied. The rotation speed was fixed in 1500 rpm. The lubricant temperature was monitored during the tests. In the case of boundary lubrication, partially textured surfaces and fully textured surfaces presented a reduction in the friction coefficient of 23% and of 9.4%, respectively, when compared to a reference smooth surface. The friction coefficient reduced 12.6% when texture was positioned in the inlet and 23% when positioned in the outlet, when compared to the smooth surface. Moreover, total texturing reduced the wear rate by 15.2%. Linear relationships between wear volume and λ parameter, as well as between friction coefficient and curvature radius were found, confirming a strong relationship between lubrication regime, wear rates and real contact area (given by the curvature radius of the wear tracks).

This work aims to contribute to the understanding of the topographic modification of the surface of the counter-body during micro-abrasion and its complex relationship with specimen wear. The topographic evolution of the surface of five different balls (O25.4 mm) was monitored: one ceramic (Si3N4), one metal (AISI 52100 steel), and three thermoplastic polymers (polypropylene, polyacetal and polyamide 6.6). AISI 304 austenitic stainless steel specimens were tested in a fixed-ball micro-abrasion test rig using a silica slurry (10%wt. in water), rotation speed of 150 rpm, and total test time of 90 min (in 15 min intervals). The topographic evolution of the ball topography was monitored by laser interferometry of the abrasive tracks at each measurement interval, always in the same region. The parameters Sq, Sz, Ssk, Sku, λq, Sdq and Str were computed. Significant wear and changes of the surface topography of the balls were observed along the tests. Harder balls underwent evident grooving, while the softer polymeric balls showed fibrillation characteristics, alignment of polymeric chains and transfer film. For the initial 15 min of test, before reaching a steady-state wear regime, the softer balls (polypropylene, polyamide 6.6 and polyacetal) showed, in general, an increase in Sq, λq and Sdq, possibly by the generation of a transfer film on the surface, which was not observed for the harder balls. After the steady-state regime was achieved, all balls reduced their values of Sq, λq and Sdq. Plots of Sku x Ssk identified non-Gaussian height distribution curves (mostly with high kurtosis and negative asymmetry) for all balls. Sq and Sdq presented a linear relationship with the wear coefficients of the specimens (k) dependent on the material of the ball, whereas an overall linear relationship between λq and k was observed independently of the ball material. Str was a good indicator of aligned grooving abrasion, but showed a linear relationship with k only for the steel ball.

Metal forming involves relative motion between a tool and a workpiece under very high contact pressures, thus possibly leading to severe tool wear, compromising the process stability and the quality of the final product. Despite being fundamental for forming, friction must be controlled to ensure stable forming conditions and reduced energy losses, often achieved by coating the tools. This work analyzed the tribological behaviour of commercial thin hard PVD coatings used in metalforming tools. Wear mechanisms were identified via scanning electron microscopy (SEM) and 3D topographic characterization before and after strip drawing tests, which were then correlated with friction coefficient measurements. Eight tool materials and three different coatings were tested: VN, CrN/TiN and TiAlN. The tools, characterized by SEM, optical interferometry and microhardness, were classified into four groups according to their manufacturing process: sintered, rolled, cast and recast. The VN coating was rougher, whereas CrN/TiN and TiAlN followed the substrate topography. The strip drawing tests showed that the VN and CrN/TiN coatings presented lower and more stable friction coefficient values, which was traced back to the formation of relatively smooth and partially oxidized transfer layers on the tool, leading to more favorable tribological conditions. The TiAlN coating presented higher and very unstable friction values, apparently due to protruding transfer layers, which increased friction and eventually led to galling. The best performance was attributed to the tools coated with CrN/TiN since the friction values were very stable along the tests. The tools coated with TiAlN presented the worst tribological performance, despite their initially smoother surfaces.

The present work used a new methodology proposed in previous work to analyse the tribological behaviour of coatings/surface modifications with potential to replace the carcinogenic hard chrome still applied in the rolls employed in cold rolling mills. For that, three surface modifications (chromium plating, electroless NiP coating, and plasma nitriding) were carried out on specimens that were previously either ground or surface textured by electrical discharge texturing. The specimens with electroless NiP coating presented the lowest friction coefficients, while plasma nitrided specimens showed the highest. A tribolayer rich in Nickel, Phosphorus, and Oxygen was found for the samples with electroless NiP coating on the surfaces of both the specimens and the counter-bodies, which was apparently responsible for providing low and stable friction coefficient values, as well as reduced wear rates.

Surface texturing to control friction and wear has been the focus of numerous studies in the last few decades. Despite this interest, understanding the underlying causes for surface texturing effects under different contact and lubrication conditions remains a subject of continuing controversy. Although there has been progress in the fabrication of precise surface textures and modeling of their influence in specific cases, many conflicting reports still exist concerning the effectiveness of surface texturing under certain contact conditions. This review therefore presents a critical assessment of the common understanding in this rapidly developing research field. First, the effects of surface textures under the operative lubrication regimes in the Stribeck curve, with a clear distinction between conformal- and non-conformal contacts, will be discussed. Finally, the strengths and weaknesses of various fabrication methods will be described, giving a summary of the fabrication methods with respect to their typical feature sizes, costs, and applicable materials. Special attention will be paid to the friction reducing mechanisms and their implications for the wear under different frictional regimes.

The production of pollution can be a significant industrial problem during cold rolling. Pollution is often attributed to the formation of wear debris during rolling, which mixes with the lubricant oil used to cover the rolled sheet. The cleanliness of the rolled sheet, its consequent aesthetics, and the downstream performance of the process are affected by the production of pollution. In the first stage of this study, the pollution formed during industrial cold rolling was collected and found to be composed of a mixture of small stainless steel debris and lubricant. Second, the study investigated the effect of rolling conditions on the generation of wear debris. Tests were carried out using laboratory cold rolling mills. The effects of the type of stainless steel (ferritic or austenitic), of the surface finish of the sheets before rolling, of the thickness reduction ratio, of previous annealing of the sheet, and of lubricant temperature on the wear of sheets due to rolling were investigated. Cold rolling resulted in weight reduction of the sheets due to the formation of wear debris. Weight loss for sheets finished by conventional acid pickling was greater than for sheets finished using shot blasting. A further reduction in the wear of the sheets due to rolling was observed when their surface roughness was decreased by polishing. An increase in the thickness reduction ratio lowered the elongation to fracture of the rolled sheets and increased their wear. Previous annealing of the sheets was then used to successfully reduce wear of the rolled sheets. An increase in the temperature of the oil used during rolling increased wear of the sheets due to rolling. Finally, industrial trials were carried out applying the rolling conditions that had resulted in lower weight loss for the sheets during the laboratory-scale tests. This significantly reduced the amount of pollution produced during industrial cold rolling of stainless steel, improving the final quality of the product.

Triboscopy was proposed over 20 years ago, but despite the powerful insight it brings to analyse friction and wear with temporal evolution of localised events, its use is still limited. In this paper, triboscopy has been further developed. A LVDT sensor measures the position of the counter-body inside the wear track in a reciprocating tribometer. A high frequency acquisition system allows 10 points to be acquired within the elastic contact width, calculated by Hertz equations. The necessary number of acquired points is computed as a function of reciprocating frequency and stroke length, which enables to represent inherent details of the phenomena involved without producing excessively large files. Triboscopic maps of the acquired data are generated, where colours quantify the Z variable under measurement, X is the position of the counter-body within the wear track and Y is the number of cycles. Four examples where the use of 3D colour maps has helped to visually phenomena that would be hard to detect otherwise are presented. First, sintered composites containing solid lubricant particles dispersed in a Fe–Si–C matrix were tested. Under dry sliding, triboscopic friction maps showed higher friction at the ends of the strokes, which was more significant for harder specimens. Evidence showed that this friction increase was due to the accumulation of wear debris at the ends of the wear tracks. Second, triboscopic images of reciprocating tests of DLC–CrN coatings clearly indicated the region of the wear tracks where spalling occurred. Third, bronze disks containing regularly distributed inserts composed of graphite particles dispersed in bronze presented triboscopic maps where friction decreased periodically following approximately the size and spacing of the graphite inserts. Fourth, starved lubrication tests of textured surfaces showed no effect of surface texturing on average friction, but triboscopic maps suggested a tendency for lower friction with texturing.

Microabrasion-corrosion tests were carried out to investigate how small changes in dilution affect abrasion-corrosion resistance of Ni–Cr PTA welded deposits onto carbon steel. For each specimen, corrosion tests, microabrasion tests and combined microabrasion-corrosion tests were conducted. Potentiodynamic corrosion tests under aerated conditions used three different electrolytes. Abrasion resistance was evaluated using a fixed-ball microabrasion test rig, for slurries of SiO2 in distilled water (20 wt%). Microabrasion-corrosion tests used SiO2 slurries for the same electrolytes used in the corrosion tests under potentiodynamic conditions. For the most aggressive electrolyte (NaCl + H2SO4 solution) it was possible to identify small variations in current density with dilution in the microabrasion-corrosion tests, whereas no significant differences were identified for the other electrochemical variables. However, as a general trend, all deposits presented high abrasion-corrosion resistance, evidencing that small variations in dilution do not compromise their performance for the conditions tested. As expected, the wear coefficients measured under microabrasion-corrosion conditions were higher than under pure microabrasion conditions. On the other hand, friction coefficients for microabrasion-corrosion were lower when compared with conventional microabrasion tests for all the slurries tested. This was apparently due to how the passive film affects particle entrainment during the tests.

In the 1980s, Brazil started a national program to use bio-fuels as one its main energy sources, in particular ethanol produced from sugar cane. Since then, the increase of production and efficiency in the crop fields has drastically reduced the period available for the annual maintenance of the industrial plants. One of the main reasons for the annual maintenance is premature wear of devices used to wash, cut and crush sugar cane. Samples of components of such devices were collected from different sugar plants and had their wear mechanisms characterized by SEM and laser interferometry. The predominant wear mechanisms were sliding and rolling of abrasive particles and corrosion. In order to reproduce these wear mechanisms, both a lapping-like tester using large soft abrasive particles and a free ball micro-abrasion tester using fine soft abrasive particles were used. A structural carbon steel (reference material) was compared with a low alloy steel and different stainless steels, using dry and wet versions of each tester. For tests where the rolling of abrasive particles predominated, all stainless steels presented superior performance, especially under wet conditions. On the other hand, for tests with predominance of particle sliding, the low alloy steel was superior under dry conditions, but under wet conditions, with a corrosive component, stainless steels performed better. The pilot use of these laboratorial results in three industrial plants, where abrasive and corrosive conditions coexist, showed their excellent correlation with field tests. The use of stainless steel increased wear life, corroborating the importance of the synergistic effect between corrosion and abrasion. With the successful results obtained with the pilot substitution of some parts that were conventionally manufactured using carbon steel by similar parts in stainless steel, which started in 2003, this substitution increased, so that since 2007 almost all parts in the initial stages of sugar cane processing in the main Brazilian industrial plants have been manufactured using P410D stainless steel.

The present work analyzed the wear behavior of surface modifications often used in cold rolling mill rolls. Different surface modifications were carried out on samples produced from a fragment of a rolling mill roll: i) shot blasting texturing using steel spheres (T); ii) chromium plating (C); iii) shot blasting texturing with subsequent hard chrome plating (TC); iv) and hard chrome plating with subsequent shot blasting texturing (CT). Before the surface modifications the samples were heat treated and ground on both faces. Sliding wear tests were performed using a reciprocating movement of a ball over flat configuration under a load of 9.8 N. Abrasive wear tests used a free ball microabrasion tester with SiO2 abrasive particles. Surface texturing increased Sq, Sdq and Spk and reduced Sbi of the uncoated samples, i.e., the surface became rougher, whereas hard chrome coating after texturing did not alter much the surface topography, although a slight decrease of Spk and a slight increase of Sbi of the samples were detected i.e., a slight smoothening of the textured surfaces occurred due to chromium plating. The results of the reciprocating tests showed, after running in, average friction coefficients of 0.38±0.01 for all the samples tested, evidencing no significant change in the coefficient of friction as a function of surface modification. Surface texturing increased the sliding wear of the counterbodies when compared with that obtained by the sample without modification (WM) by 70% for 1 h tests and by 35% for 10 h tests. When the surface was textured before chromium plating, the wear rate of the counterbody did not increase in relation to the C sample for the 1 h test, but was the highest for 10 h tests, with an increase of 200% in relation to the C sample. On the other hand, chromium plating increased the wear rate of the specimens, for conditions either with or without previous texturing. The addition of the hard chromium coating promoted the formation of a tribolayer on the counterbody consisting of chromium and oxygen. For the samples without hard chrome coating, the tribolayer consisted of iron and oxygen and it was located on the specimen surface. The results of microabrasion showed that, for the uncoated samples, surface texturing increased abrasion resistance (24%). The reduction was higher (67%) for the coated samples, but previous texturing of the coated samples increased abrasion (54%) when compared with the coated samples.

Engineered surfaces obtained by modification of surface topography have important industrial applications, many involving tribology. Nevertheless there is still lack of knowledge about fundamental aspects involved in the improvement of surface behaviour. Recent technological developments now permit us to texture surfaces in a flexible way and to assess the tribological efficiency of different microtopologies. Moreover, advances in surface analysis techniques provide methodologies that do not limit the investigation to microgeometry but allow the functional characterization of surfaces. This paper proposes functional surface parameters in order to capture the tribological efficiency of structured surfaces.

During abrasive wear, the prevailing wear mechanism has been shown to be connected to the movement of the active particles present at the wear interface. Two particle dynamics can occur: (i) rolling, which is evidenced by the presence of indentations on the worn surface, and (ii) sliding, which produces scratching and/or ploughing. The particle dynamics can vary with the imposed tribological conditions. In this work, single abrasive particle interactions are simulated using well-controlled indentation or scratch tests where an indentation represents the contact of a rolling abrasive particle without sliding, which can lead to deformation or cracking, and a groove represents the sliding of an abrasive particle, which can lead to ploughing, wedge formation, cutting or cracking. Two horizontal sliders (0.1 μm resolution) drive the sample while the indenter is controlled by a piezoelectric translator with a resolution of 5 nm. A 3D load cell controls and measures the load. A new parameter was introduced to evaluate wear mechanism transitions, which was called superimposition of interactions. In order to study the effect of superimposition, series of indentations and parallel scratches were created by varying the distance between mono-interactions and the size of the mono-interactions. The mass loss was determined using laser interferometry by measuring the volume of material above and below the initial surface. The results clearly showed transitions in the wear mechanisms when the degree of superimposition was varied for both the indentation and the scratch tests. Sequences of indentations produced on tool steel samples resulted in mass loss when the degree of superimposition of indentations was higher than 50%, whereas sequences of parallel scratches on tool steel samples resulted in mass loss for degrees of superimposition higher than 80%. Scratch tests on copper showed that the wear mechanism changed from ploughing and wedge formation at a low degree of superimposition to microcutting at a high degree of superimposition. Subsurface hardness increased slightly as a function of the superimposition degree, since surface work hardening was intensified for high degrees of superimposition. Also, the superimposition of the scratches reduced the support for subsequent scratches, increasing mass removal for higher degrees of superimposition.

A simple method is demonstrated for texturing metallic surfaces by electrochemical machining, termed ‘maskless electrochemical texturing’ (MECT). The method allows a single cathode tool, in which the texture is incorporated through a pattern of perforations, to be used for many texturing operations and avoids the need for masks to be applied to individual workpieces. It therefore has significant advantages over conventional methods of texturing by electrochemical machining. The method has been applied to low-carbon steel workpieces and features up to 50 μm in depth have been produced. Current efficiencies of more than 90% have been achieved, and the texturing time is short enough for application in an industrial context. The process has been characterised in terms of the effects of current pulse history and electrolyte flushing conditions on current efficiency, material removal rate and feature definition.

Strip-drawing tests with annealed stainless steel samples involving small strains were used to investigate the effect of surface texturing in tribological applications involving mixed lubrication and plastic deformation. Dies were prepared with surface patterns composed of circular pockets and parallel grooves, and comparison tests were performed with highly polished dies. The effects of surface texturing were detected by friction force measurements and examination of the deformed strip surfaces, under conditions of oil lubrication. Surface patterns consisting of circular pockets with very low area coverage did not improve the tribological performance. For grooves with larger area coverage (≈25%), significant effects were observed on the friction between the dies and the strip, which were reflected in the drawing force. The performance was strongly influenced by the relative orientation between the grooves and the drawing direction. For grooves perpendicular to the drawing direction, the friction was greatly reduced; the grooves were believed to act as lubricant reservoirs and to induce microplastohydrodynamic lubrication. On the other hand, when the grooves were oriented parallel to the drawing direction, the friction was much greater and the strip surface finish became poorer; these grooves were believed to allow the lubricant to escape from the contact.

Surface phenomena play a decisive role in the behaviour of engineering parts; their understanding and control are fundamental to the development of many advanced fields, such as: electronics, information technology, energy, optics, tribology, biology and biomimetics. Engineered surfaces rely on the control of surface characteristics to obtain a desired functional performance. This paper reports the advances in the state of the art considering the relationships between the properties of functional surfaces, their applications and the technologies to engineer surfaces.

Steam oxidation is an important industrial procedure for changing tribological properties, sealing porosity and improving aesthetics in sintered iron components. Manganese phosphate coatings are believed to have intrinsic lubricant properties and very low friction coefficients. In this work, after steam oxidation, sintered iron components were coated with manganese phosphate and their tribological behaviour was investigated. Components with two nominal film thicknesses were compared, either coated or uncoated with manganese phosphate. Their abrasion resistance was evaluated using micro abrasion wear tests. Reciprocating wear tests were used to study their sliding wear resistance. It was observed that phosphating of the oxidized samples resulted in an increase of the wear rate in both tests. Phosphating promoted a reduction of the oxide film thickness, probably due to the chemical conversion reaction with the oxide substrate. The reduction of wear resistance due to phosphating was associated with a reduction of oxide film thickness.

The influence of surface topography on lubricant film thickness has been investigated for the reciprocating sliding of patterned plane steel surfaces against cylindrical counterbodies under conditions of hydrodynamic lubrication. Patterns of circular depressions, grooves and chevrons were used, and the fractional area coverage, depth, width and sliding orientation relative to the texture were systematically varied. Textured samples with features much larger than the elastic contact width gave film thicknesses, which were smaller than those for non-textured samples. This effect was more significant for larger features. For patterns composed of circular pockets, maximum film thickness was achieved for an area coverage fraction f≈0.11. Chevron patterns pointing along the sliding direction gave higher film thicknesses than those pointing across. For an area coverage ratio of ca. 0.06, maximum film thickness was achieved for a feature depth to width ratio of about 0.07. Among the patterns investigated, chevrons were the most effective and grooves the least effective in increasing hydrodynamic film thickness.

Zirconia ceramics with different dopants, used to retain the tetragonal phase metastably, were evaluated to determine the effect of the difference in degree of transformability on the abrasive wear behavior. The abrasive wear tests, carried out on a multiple abrasive wear tester, showed that for two-body and three-body configurations the wear rate increases for higher normal loads and abrasive grain sizes. The specimen with low degree of transformability presented the worst behavior in every configuration owing to its low fracture toughness. For the three-body configuration, the specimen with intermediate degree of transformability presented the best behavior; this was associated with its higher hardness and flexural strength. For two-body abrasive tests, the change in wear severity conditions led to an inversion of wear behavior of the specimens with a high degree of transformability. The results obtained were associated with the microstructure generated, the physical and mechanical properties and the tetragonal to monoclinic transformation rates, since the stress induced transformation could be inhibited owing to the temperature developed in the contact between the zirconia sample and the abrasive material. Finally, the comparison between zirconia and white cast iron wear behavior under two different conditions revealed that the performance of zirconias was favorable only for low severity wear conditions and for intermediate and high degrees of transformability.