Friction Coefficient In Air Research Articles

Iron ions induced self-assembly of graphene oxide lubricating coating with self-adapting low friction characteristics

Graphene oxide (GO) is a promising solid lubricant for moving mechanical systems to implement reliable and effective lubrication due to its easy modification and excellent tribological properties. However, obtaining highly dense GO coatings simultaneously with high hardness and extensibility is still a challenge for available self-assembly techniques, and these characteristics are beneficial to tribological properties. Inspired by the advanced abrasion resistance system of mussel byssus threads, a surprisingly simple and versatile metal ions (namely Fe2+ and Fe3+ ions) directed self-assembly strategy has been developed to rapidly fabricate GO coatings. GO as a solid lubricant is highly sensitive to the interface structure and test environment. Consequently, the influence of the valence state of iron ions on the macroscopic tribological properties of GO-based coatings in air, nitrogen gas and vacuum environments are comparatively investigated. The results show that the GO-Fe3+ coating with a highly compact characteristic and unique granular microarchitecture resulting in higher hardness and strain capacity displays a lower friction coefficient and remarkable wear resistance than the GO-Fe2+ coating. Additionally, because water molecules generate strong hydrogen bonding gradually disrupting the ordered layered structure, both GO-Fe2+ and GO-Fe3+ coatings exhibit a higher friction coefficient in air than in nitrogen gas and vacuum.

Expanding of conditions for use of solid lubricant coatings based on molybdenum diselenide due to their sulfur doping

Comparative studies of the tribological properties of MoSex /Mo and MoSexSy /Mo coatings in an environment of humid air and nitrogen at an increased contact load have been carried out. The coatings were obtained by pulsed laser deposition from a MoSe2 target, which ensured the formation of a nanocomposite structure consisting of an amorphous matrix and Mo nanoparticles. To dope the coatings with sulfur atoms, the MoSe2 target was ablated in H2S gas of varying pressure. It has been established that optimization of the reactive gas pressure is required to improve the tribological properties of the MoSex /Mo coatings. When sulfur atoms are introduced up to a concentration of 7...14 at. %, a significant increase in the wear resistance of the coatings was observed both during tribological tests in air and in nitrogen. In this case, a notice able effect was achieved in reducing the coefficient of friction. As a result of alloying with sulfur, the friction coefficient in air decreased to 0.035, and in nitrogen to 0.015. The results of the study of wear tracks and wear debris by micro-Raman spectroscopy are presented, which made it possible to reveal the features of tribo-induced processes in the created coatings.

Frictional properties of electron beam-deposited a-C:Si films

Most films are deposited by chemical vapor deposition, but further expansion of their applications demands their fabricability by physical vapor deposition. In this study, hydrogen-free Si-incorporated diamond-like carbon (a-C:Si) films, which exhibit a low friction coefficient in air, were fabricated by electron beam deposition, and their hardness and frictional properties were investigated. a-C and a-C:Si films with Si contents of 5 and 15 at.% were deposited at substrate temperatures of 200, 300, and 500 °C. The ID/IG ratios calculated from the Raman spectra of the films tended to increase with increasing Si content and higher substrate temperature. a-C:Si with low Si content exhibited a hardness of only 10–20 GPa, similar to that of a-C, while a-C:Si with high Si content exhibited a hardness above 25 GPa when deposited at a substrate temperature of 200 or 300 °C. The friction coefficient of a-C:Si with high Si content was as low as 0.07–0.09. In sum, a-C:Si film with high Si content deposited at low substrate temperature without ion bombardment showed high hardness and low friction.

Nvestigation of Tribological Properties and Optimal Coating Material Selection for AISI 4140 Using TOPSIS and Taguchi Method

Depositions of surface coating materials is one of the important approaches in improving friction and wear properties of the surface, there is a growing demand for low friction coatings like TiN, TiAlN & WCC that allow contacting surfaces to rub against with reduced friction and wear. Selection of different types of Nitriding process and coatings used on AISI 4140 steel to improve tribological properties by Multi Criteria Decision Making methods (MCDM) .The MCDM method used for selection namely TOPSIS (technique for order performance by similarity to ideal solution). Analytical hierarchy process (AHP) is used to find out weightage for the material criteria’s like young’s modulus(E), Hardness (H),H/E ,H 3 /E 2 and critical load for adhesion of coating for AISI 4140 steel. Each property is measured according appropriate standard. Selected AISI 4140 steel is optimized for tribological test settings using the grey relational analysis method. Taguchi method is implemented for experimental design which gives nine experimental runs based on orthogonal array. Coefficient of friction (COF) and wear is measured for nine different test on Pin on disc Tribometer. The optimal setting is selected and confirmation test is performed which gives clear indication of best material as well as optimum operating condition for AISI 4140 steel. Keywords— COF, Pin on Disc, Taguchi, TOPSIS, Wear. INTRODUCTION The machining industry is constantly seeking ways to enhance performance (metal removal rate) and reduce cost of the manufactured parts. One way to enhance the machining performance is to utilize high speed machining. One of the problems associated with high speed machining is the high tool wear, leading to reduction in tool life. When the normal load and the sliding speed increased, the friction coefficient in air increased from 0.65 to 0.72, whereas decreased from 0.58 to 0.36 in water and 0.20 to 0.08 in oil [1] . The wear resistant and thermally stable oxides formed by the tribo-chemical reactions of chromium and aluminum protected the AlCrN coating against wear admirably [3] . The results showed that the AlCrN coating exhibited higher hardness, but lower wear resistance as compared to the CrN coating. The AlCrN coating formed by CrN alloying with aluminum would show significantly improvement in high temperature oxidation resistance but not necessarily in wear resistance under the condition of ambient temperature [4] . The superiority of the AlTiN coating is confirmed by wear rates estimations [5] . Plasma nitriding has been carried-out to enhance surface related properties of steel components. The hardened case in these components comprise of a compound (white) layer on top followed by a diffusion zone underneath it. The increase in hardness and strength at the surface, yield improvement in fatigue life. However, increase in thickness of the compound layer beyond a certain critical reduces the fatigue life of the base material [7]. CrN coating gives better result against wear under dry and lubricated condition. AlCrN coating showed

The role of tribo-pairs in modifying the tribological behavior of the MoS2/Ti composite coating

Mechanical contact conditions and the shear strength of the interface are the two independent factors that control the friction behavior of the MoS2 coating. Although ZrO2 and GCr15 had similar mechanical contact conditions, they showed rather different friction behaviors. Therefore, the shear strength of the interface was prominent in determining the friction behavior of the MoS2/Ti composite coating, particularly in the initial stage of friction. The strong interfacial shear strength between GCr15, WC and MoS2/Ti resulted in the high friction coefficient in air and short wear life in vacuum. Furthermore, we found that the interfacial shear strength was affected by the Ti content in the MoS2/Ti coatings, and the adhesive behavior of Ti and GCr15 was responsible for the high friction coefficient and high wear rate. The shear strength between the two sliding materials was amplified with the increase in the vacuum degree. These results benefit us to tailor or select the MoS2-based composite coatings and the corresponding tribo-pairs for vacuum operating conditions.

Processing of Sliding Hybrid Composites with Aluminum Alloy Matrix Containing Solid Lubricants

This paper presents the information about manufacturing processes of hybrid composites with aluminum alloy matrix containing glassy carbon as a solid lubricant. Two methods have been described: the method based on mixing glassy carbon and ceramic particles with a liquid metal matrix; and the precursor method. In the precursor method, carbon is introduced into a composite with the application of liquid precursor and porous ceramic foams. It is then followed by precursor pyrolysis where, as the result, glassy carbon is obtained. Ceramic foams help liquid precursor penetrate the ceramic spheroid pores by forming a thin film of glassy carbon on their walls. Composites produced by the both methods feature good tribological properties. Sliding friction coefficient in air of the new obtained by mixing method composite against cast iron (μ = 0.08 − 0.17 at wearing in and 0.12 after wearing in by reciprocating sliding and 0.14 − 0.17 by rotating sliding) is much lower than in the case of composite containing only ceramic foam as a reinforcing phase (μ = 0.28 − 0.36 by reciprocating sliding and 0.28 − 0.40 by rotating).

Sliding Friction in Seawater Environment of Porous Carbon Materials made from Rice Hull

Rice hull, which is one of the agricultural wastes in Japan, is required to be reused from a viewpoint of recycling. The rice hull silica carbon (RHSC), made from rice hull is manufactured by mixing rice hull particles with a phenol resin, pressure forming, drying, and then carbonizing the mixture in the nitrogen gas environment at high temperatures. RHSC contains about 30 mass% of inorganic constituent and 70 mass% of organic constituent. The main inorganic constituent is silica (SiO2), which content is more than 95 mass%. Silica has excellent corrosion resistance and oxidation resistance. Thus, it can be expected improvement of water resistance. In this study, focusing on the sliding friction and the water resistance, which are a core competence, the sliding friction was evaluated through wear amount and dynamic friction coefficient in air and pure water and seawater. The results showed that the dynamic friction coefficient of RHSC in each environment was low excellent value from 0.11 to 0.15. The wear amount in the air was about 50 μm in the 130 km running. By contrast, the wear amount in both pure water and seawater was reduced to 37 μm and 2 μm respectively. Thus, the use of RHSC can be expected in pure water and seawater.

Chip morphology of normalized steel when machining in different atmospheres with ceramic composite tool

Dry cutting tests in air and nitrogen atmospheres with a ceramic cutting tool were carried out on normalized AISI 1045 steel. SEM and EDX techniques are employed to observe the chip morphology and tribological mechanisms are simultaneously discussed. The finite element model of chip formation was created to determine the effective stress and strain distributions in the chip and workpiece. Compared in nitrogen, the friction coefficient in air was reduced when the cutting speed is at 160 m/min and the feed rate is 0.1 mm/r. Experimental data and observation revealed the formation of a lubricating film at the tool–chip interface, which related to the difference chip morphology in air and nitrogen.

Friction and Wear Properties of Zr and TiC-Based Cermet Specimens in a Hydrogen Gas Atmosphere

In this study, Zr, Ti and TiC-based cermet specimens were prepared, and their friction and wear properties in various gas atmospheres were examined. The Zr specimens exhibited the lowest friction coefficients and the smallest volume change in the H2 gas atmosphere. This reason would have been due to the formation of the -type Zr hydride, which has a layered crystal structure. The Ti specimens exhibited similar friction and wear properties, although the TiC-based cermet specimens containing small amount of Mo, Ni and W exhibited the lowest friction coefficients in air, not in the H2 gas atmosphere. The low friction coefficients of the cermet specimens in air is likely to have been due to the formation of the low friction Mo oxides and W oxides.

Effect of cutting atmosphere on dry machining performance with Al2O3/ZrB2/ZrO2 ceramic tool

In this paper, Al2O3/ZrB2/ZrO2 ceramic cutting tool was produced by hot pressing. Dry cutting tests in air and nitrogen atmospheres were carried out on normalized AISI 1045 steel. The tool wear, cutting temperature, cutting force, and friction coefficient were measured. Compared in nitrogen, the friction coefficient in air was reduced when the cutting speed was higher than 160 m/min. Scanning electron microscopy and energy dispersive X-ray analysis techniques were employed to observe the worn surfaces of the ceramic tools, and the wear mechanisms were simultaneously discussed. Experimental data and observations revealed the formation of oxide film under air in dry machining, which related to the decrease of the friction coefficient and the improvement of cutting performance.

Friction and wear properties of duplex MAO/CrN coatings sliding against Si3N4 ceramic balls in air, water and oil

It is evident that the micro-arc oxidation (MAO) ceramic coatings often exhibit relatively high friction coefficients as sliding against many mating materials. To reduce the friction coefficient for the MAO coatings, the duplex MAO/CrN coatings were deposited on 2024Al alloy using combined micro-arc oxidation and reactive radio frequency magnetron sputtering. The microstructure and phase of the duplex coatings were observed and determined using scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The friction and wear behaviors of the duplex coatings sliding against Si3N4 balls in air, water and oil were investigated using a ball-on-disk tribometer. The wear rate of the duplex coating was determined by non-contact optical profilometer and the wear tracks on the duplex coatings were observed by SEM. The results showed the CrN coatings mainly consisted of Cr, CrN and Cr2N phases. The duplex coatings/Si3N4 tribopair exhibited the highest friction coefficient in air, while displayed the lowest friction coefficient in oil. When the normal load and the sliding speed increased, the friction coefficient in air increased from 0.65 to 0.72, whereas decreased from 0.58 to 0.36 in water and 0.20 to 0.08 in oil. The specific wear rates for the duplex coatings in air were higher than those in oil. In comparison to the MAO coatings, the duplex MAO/CrN coatings displayed excellent tribological properties under the same conditions.

Structure and properties of multi-component and multilayer TiCrBN/WSe x coatings deposited by sputtering of TiCrB and WSe 2 targets

Single-layer (SL), double-layer and multilayer (ML) TiCrBN/WSe x coatings were deposited by sputtering of TiCrB and WSe 2 targets in a gaseous mixture of argon and nitrogen. To enhance film adhesion, ion implantation was employed at the initial stage of deposition for 5 min. The structure and chemical composition of the coatings were studied by means of X-ray diffraction, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The coatings were characterized in terms of their adhesion, hardness, elastic modulus, elastic recovery, internal stress, corrosion resistance, friction and wear. All coatings showed a dense structure free of columnar grains. The ML TiCrBN/WSe x coating demonstrated a sequence of nanocrystalline TiCrBN and amorphous WSe x layers with various thicknesses. The SL TiCrBN/WSe x coating deposited at magnetron current of 2 A displayed completely amorphous structure. As the magnetron current was decreased to 1 A, the coating consisted of mixture of face centred cubic (Ti,Cr)(B,N), WSe 2, and amorphous a-phases. This multi-component TiCrBN/WSe x coating showed almost the same hardness of 30 GPa as the SL TiCrBN coating. The incorporation of WSe x into TiCrBN coating was shown to decrease the friction coefficient in air from 0.5 to 0.2–0.25 with only little influence on the wear resistance and electrochemical behavior. In the case of SL TiCrBN/WSe x coatings, the friction curves were typically flat with a very short running-in stage which did not exceed 50 m, whereas in the case of ML TiCrBN/WSe x coating, the fluctuations and spikes of friction coefficient were observed. It has been confirmed by Raman spectroscopy that the existence of WSe 2 phase in sliding contact during the tribological test provides low friction. To evaluate thermal stability, the SL TiCrBN/WSe x coating deposited at magnetron current of 1 A was annealed in vacuum at 550 °C for 1 hour. The superior tribological performance of the SL TiCrBN/WSe x coating after annealing can be explained by the presence of two constituents, of which one is a hard and oxidation resistant (Ti,Cr)(B,N) phase with a grain size of a few nanometers and the other is a mixture of WSe 2 + a-WSe x solid lubricant grains and/or inter-granular phases.

Friction characteristic of micro-arc oxidative Al 2O 3 coatings sliding against Si 3N 4 balls in various environments

The alumina ceramic coatings were prepared on 2024Al alloy by micro-arc oxidation (MAO) technique. The phase structure of the MAO Al 2O 3 coating was determined using X-ray diffraction. The thickness and micro-hardness of the MAO Al 2O 3 coatings was measured using eddy current thickness equipment and micro-hardness tester. The friction property of MAO Al 2O 3 coatings sliding against Si 3N 4 ceramic balls were investigated in air, water and oil by a ball-on-disk tribo-meter, and the worn surfaces of the MAO Al 2O 3 coatings were observed using scanning electron microscope (SEM). The results showed that the MAO Al 2O 3 coatings mainly contained α-Al 2O 3 and γ-Al 2O 3 phase. The micro-hardness of the polished MAO coatings was HV1740 ± 87. With an increase in normal load and sliding speed, the friction coefficient in air increased from 0.74 to 0.87, while decreased from 0.72 to 0.57 in water and 0.24 to 0.11 in oil. This indicates that the fluid lubrication could improve the friction behavior of the MAO Al 2O 3 coatings. The worn surfaces' observation indicated that the wear mechanism of the MAO Al 2O 3 coatings changed from abrasive wear in air to mix wear in water, and became microploughing wear in oil.

Solid Lubrication with Carbon Onions at High Temperature in Vacuum

ABSTRACTSolid lubricant properties of carbon onions prepared from diamond nanoparticles through a heat treatment at 1700°C have been examined at high temperatures up to 300°C in air and vacuum. Sliding friction between a silicon disk on which carbon onions were dispersed and a stainless steel ball was measured by means of ball-on-disk type friction testing. Friction coefficients in vacuum decreased with temperatures and became stable above 100°C for longer service lives. On the contrary to this, friction coefficients in air increased with temperatures despite Raman spectroscopic analysis showed that the structure of carbon onions were stable in dry air up to 300°C.

Pulsed laser deposition of antifriction thin-film MoSe x coatings at the different vacuum conditions

MoSe x coatings were obtained by pulsed laser deposition in vacuum at the pressure of background Ar gas up to 10 Pa. The deposition temperature was 200 °С. The films were studied by means of X-ray diffraction, scanning and transmission electron spectroscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy of helium ions. The tribological properties of thin-film coatings were investigated by pin-on-disk testing in air with 50% relative humidity. In addition, wear tracks were studied by micro-Raman spectroscopy. Chemical composition, structure, and tribological properties of the coatings were found to be sensitive to the presence of the inert gas. Thus, increasing the gas pressure from 10 − 4 to 10 Pa changes the chemical composition, so that the ratio of the atomic concentrations of Se and Mo ( x = Se/Mo) increases from 1.5 to 2.4 in the principal deposition zone. The changing of the structure concerns the accumulation of distortions in the lattice of MoSe x nano-crystals as increasing the distance between the basal planes and intensive formation of nano-sized inclusions of the amorphous phase and Mo nano-crystals in the volume of the coatings. At the optimal gas pressure (∼ 2 Pa), the composition of the coating was close to the stoichiometric one, and the layer adjacent to the substrate consisted of MoSe x nano-crystals with the basal planes parallel to the substrate surface or oriented at small angles to the surface. The thickness of the oriented layer in such coatings was greater than the thickness of the similar layer in the coatings deposited in vacuum (10 − 4 Pa). The tribological properties of MoSe x coatings deposited on substrates of stainless steel type 95 × 18 (18 at.% Cr) depend on the gas pressure. The friction coefficient in air decreases from 0.08 for deposition at the background pressure of 10 − 4 Pa to 0.04 for deposition at the optimal pressure. This change in the deposition conditions has only a marginal effect on the coating durability. Means to increase the durability are also considered.

Fretting wear studies on uncoated, plasma nitrided and laser nitrided biomedical titanium alloys

Fretting wear resistance of uncoated and surface modified biomedical titanium alloys (Ti–6Al–7Nb) in air and Ringer fluid has been investigated in the present work. Laser nitrided specimen has shown superior performance with minimum surface damage and wear rate (<0.1 × 10 −6 mm 3/Nm) despite high friction coefficient in air (0.6) compared to uncoated and plasma nitrided (>12 × 10 −6 mm 3/Nm) specimens. This is due to presence of TiN dendrites (60–80%) in the laser nitrided layer. Plasma nitrided surface is relatively softer and hence wear rates and surface damage are comparable with uncoated alloys. Friction coefficient is high for uncoated (0.8) and plasma nitrided alloys (0.6) in air as well as Ringer fluid. Fretting induced electrochemical dissolution is responsible for higher wear rates in uncoated and plasma nitrided specimens. The fretting damage resistance is primarily governed by relative hardness and modified layer thickness of the mating components.

Super low friction of DLC applied to engine cam follower lubricated with ester-containing oil

This paper presents a material combination that reduces the friction coefficient markedly to a superlow friction regime (below 0.01) under boundary lubrication. A state approaching superlubricity was obtained by sliding hardened steel pins on a hydrogen-free diamond-like carbon (DLC) film (ta-C) lubricated with a poly-alpha-olefin (PAO) oil containing 1 mass% of an ester additive. This ta-C/steel material combination showed a superlow friction coefficient of 0.006 at a sliding speed of 0.1 m/s. A hydrogencontaining DLC coating/steel combination also showed a lower friction coefficient in air than a steel/steel combination, 0.1 vs. 0.8, but no large reduction was observed when the sliding surfaces were lubricated with ordinary 5W-30 engine oil and the PAO oil containing an ester additive. The friction coefficient of the hydrogen containing DLC/steel combination lubricated with the PAO containing an ester additive was above 0.05. On the other hand, the superlow friction performance demonstrates that the rolling contact friction level of needle roller bearings can be obtained in sliding contact under a boundary lubrication condition. It is planned to apply this advanced DLC coating technology to valve lifters lubricated with a newly formulated engine oil in actual mass-produced gasoline engines. A larger friction reduction of more than 45% is expected to be obtained at an engine speed of 2000 rpm.

Friction Measurement Between Polyester Fibres Using the Fibre Probe SPM

An SPM has been used to measure frictional interactions between two crossed fibres for the first time. The preparation of the surfaces is briefly described, but the crucial element is that the fibre attached to the AFM cantilever is glued parallel to the long axis. The fibres consist of polyester and frictional forces were measured both in air and solutions of cationic surfactant C14TAB. The friction coefficients reduce markedly with increasing concentration of surfactant which is ascribed to the formation of a boundary lubricating film between the surfaces. On removal of the solution, the subsequent friction coefficient in air was reduced by more than a factor of two compared to its value before immersion.

Friction and wear behavior of BCN coatings sliding against ceramic and steel balls in various environments

Ion beam assisted deposition (IBAD) techniques have been performed to synthesize ternary compound films composed of boron, carbon and nitrogen atoms (BC x N y ). BCN coatings were deposited on Si wafers and Si 3N 4 disks by evaporating B 4C target, with simultaneous N ion bombardment. The composition and chemical bonding were analyzed by XPS and the nanohardness was measured by Nano Indenter. The friction and wear property of the BCN coatings against Al 2O 3, SiC, Si 3N 4 and SUS440C balls was investigated in air, N 2 gas and water, respectively. The worn surfaces on the BCN coatings and the balls were observed by optical microscope. The results showed that, the atomic ratio in the BCN coatings was 49 at.% B, 42 at.% C and 9 at.% N and there were several bonding states such as B–N, B–C and C–N with B–C–N hybridization in the BCN coatings. The nanohardness of the BCN coatings was 33 GPa. As the BCN coatings slid against ceramic balls, the friction coefficients in air were largest, while those in water were smallest among three kinds of environment. But as the BCN coating slid against the SUS440C ball, the friction coefficients in N 2 gas were slightly higher than those in air, whereas the friction coefficients in water also exhibited the lowest values. Among four kinds of tribo-pairs, the BCN/Al 2O 3 tribo-pair showed the largest friction coefficient of 1.13 in air, but the BCN/Si 3N 4 tribo-pair exhibited the smallest friction coefficient of 0.64 in N 2 gas and 0.03 in water. The specific wear rates of the BCN coatings were largest in N 2 gas, while lowest in water in all cases. The observation of worn surfaces on the BCN coatings and balls showed that the many roll-like materials were produced during sliding tests in air and N 2 gas, while the smooth surfaces were formed in water. The experimental results indicated that the interface reaction between the BCN coatings and water or oxygen had many influences on the friction and wear property of the BCN coatings.

Effects of Environment on Friction and Wear of Al-Si Alloy Impregnated Graphite Composite

Pin-on-disk-type wear experiments for an Al-Si alloy impregnated graphite composite (pin) in contact with a bearing steel (disk) were conducted at 100N normal load (100 Newtons) in air, argon, and deionized water to investigate the effects of environment on the tribological characteristics of the composite. The friction and wear behavior and the pin-lifting phenomenon due to wear particle ingress into the contact surfaces were continuously measured during the experiments. At low relative humidity (RH) levels, the friction coefficients in air and argon are high (0.32 to 0.39) and decrease with increasing RH to values around 0.2. The friction coefficients in air have reached a minimum of 0.15 to 0.17 between 50 and 70% RH and increased slightly at 80% RH. The friction coefficients in argon are constant at about 0.2 between 10 and 80% RH. Because of the lubricating action of a water film, the friction coefficient in deionized water is slightly lower (0.1 to 0.17) than that in air. The mean wear rate of 10−4 to 8 × 10−4 mm 3 /mm (specific wear rate; w s = 10 −6 to 8 × 10− 6 mm 2 /N) is very high in a severe wear regime at RH levels lower than 10% in air, decreases with increasing RH to a minimum in the middle RH range (30 to 60%), and increases slightly at RH levels higher than 70%. Although the mean contact pressure is very high (31.8 MPa), mild wear with the rates of 10−8 to 10−7 mm 3 /mm (w s = 10−10 to 10−9 mm 2 /N) occurs in the middle RH range. The same change in wear with RH as that in air is found in argon but the wear rate in argon is slightly lower than the wear rate in air. The height of the pin-lifting, having a wear reduction effect, is greater in argon than in air over almost the whole RH range. The wear rate in deionized water is nearly equal to the rate at 70% RH in air and argon. Presented at the STLE/ASME Tribology Conference in Ponte Vedra Beach, Florida October 26-29, 2003 Review led by Somuri Prasad