Showing papers on "Tribology published in 1996"

A Model for Mechanical Seals with Regular Microsurface Structure

Abstract: A mathematical model is developed to allow performance prediction of all-liquid noncontacting mechanical seals with regular microsurface structure in the form of hemispherical pores. Seal performance such as the equilibrium face separation, friction torque and leakage across the seal are calculated and presented for a range of sealed pressure, pore size and pore ratio of ring surface area. An optimum pore size is found that depends on the other variables and corresponds to maximum axial stiffness and minimum friction torque. Also, a critical pore size is found above which seal failure is possible. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in Kisslmmee, Florida, October 8–11, 1995

Friction Wear Lubrication: A Textbook in Tribology

Abstract: Chapter 1. The State of Knowledge in Tribology Available Literature in Tribology Conferences on Friction, Lubrication, and Wear Held in the U.S. The Several Disciplines in the Field of Tribology The Consequences of Friction and Wear The Scope of Tribology References Chapter 2. Strength and Deformation Properties of Solids Tensile Testing (Elastic) Failure Criteria Plastic Failure (Yield Criteria) Transformation of Stress Axes and Mohr Circles Material Properties and Mohr Circles von Mises versus Mohr (Tresca) Yield Criteria Visco-Elasticity, Creep, and Stress Relaxation Damping Loss, Anelasticity, and Irreversibility Hardness Residual Stress Fatigue Fracture Toughness Applications to Tribology References Chapter 3. Adhesion and Cohesion Properties of Solids: Adsorption to Solids Atomic (Cohesive) Bonding Systems Adhesion Atomic Arrangements: Lattice Systems Dislocations, Plastic Flow, and Cleavage Adhesion Energy Adsorption and Oxidation Adsorbed Gas Films Chapter 4. Solid Surfaces Technological Surface Making Residual Stresses in Processed Surfaces Roughness of Surfaces Final Conclusions on Surface Layers References Chapter 5. Contact of Nonconforming Surfaces and Temperature Rise on Sliding Surfaces Contact Mechanics of Normal Loading Recovery Upon Unloading Adhesive Contact of Locally Contacting Bodies Area of Contact Electrical and Thermal Resistance Surface Temperature in Sliding Contact Comparison of Equations 5 through 9 Temperature Measurement References Chapter 6. Friction Classification of Frictional Contacts Early Phenomenological Observations Early Theories Development of the Adhesion Theory of Friction Limitations of the Adhesion Theory of Friction Adhesion in Friction and Wear and How it Functions Adhesion of Atoms Elastic, Plastic, and Visco-Elastic Effects in Friction Friction Influenced by Attractive Forces Between Bodies Friction Controlled by Surface Melting and Other Thin Films Rolling Resistance or Rolling Friction Friction of Compliant Materials and Structures, and of Pneumatic Tires Influence of Some Variables on General Frictional Behavior Static and Kinetic Friction Tables of Coefficient Friction Vibrations and Friction Testing Analysis of Strip Chart Data How to Use Test Data References Chapter 7. Lubrication by Inert Fluids, Greases, and Solids Fundamental Contact Condition and Solution Practical Solution Shaft Lubrication Hydrodynamics Tire Traction on Wet Roads Squeeze Film Lubrication with Grease Lubrication with Solids References Chapter 8. Wear Terminology in Wear History of Thought on Wear Main Features in the Wear of Metals, Polymers, and Ceramics Practical Design References Chapter 9. Lubricated Sliding - Chemical and Physical Effects Friction in Marginal Lubrication Wear in Marginal Lubrication Boundary Lubrication The Mechanical Aspects of Scuffing

Nanoscience: Friction and Rheology on the Nanometer Scale

Abstract: Part 1 Instrumental aspects: deflection sensors force sensors and probing tips implementation into different environments calibration procedures force vs. distance curves elasticity and adhesion measurements determination of friction coefficients 2-d histogram technique. Part 2 Theoretical concepts: forces, elasticity and adhesion viscosity Amontons laws adhesion model atomic-scale stick-slip. Part 3 Tribological experiments on the nanometer-scale: contrast mechanisms of friction force microscopy lubrication studies by friction force microscopy nanometer-scale modifications wear mechanisms conclusions and outlook.

Characterization of wear protective AlSiO coatings formed on Al-based alloys by micro-arc discharge treatment

Abstract: The wear life of components manufactured from Al-based alloys can be drastically increased by the application of ceramic coatings. However, coatings deposited by conventional methods such as vacuum deposition or plasma spray have either insufficient adhesion to Al-based materials or the deposition process causes the component to overheat. A recently developed micro-arc discharge oxidizing (MDO) technique allows for the formation 100–200 μm thick AlSiO coating on the surface of Al alloys. A composite Al2O3SiO2 coating is formed at room temperature as a result of a reactive process between Al in the alloy itself and O and Si supplied by an electrolyte. AlSiO coatings were investigated with XPS, Vickers and nanoindentation hardness tests, ball-on-disk, and block-on-ring friction and wear tests. Coatings were found to consist of at least two phases: a hard Al2O3 phase and a softer aluminasilicate phase. A maximum hardness of 17 GPa was found for coatings with highest content of Al2O3 phase. The tribological properties of AlSiO coatings with different composition are discussed. The lowest friction coefficient was found for the Al0.26Si0.08O0.66 coating and was measured around 0.15–0.25 depending on the test environment. The application of this coating decreased the wear rate of components fabricated from an Al-based alloy by several orders of magnitude and permitted operation of coated friction pairs at 1 GPa contact load.

Engineering issues and wear performance of metal on metal hip implants.

Abstract: A major concern in total hip arthroplasty is the generation of polyethylene wear particles at the articulating surfaces and resulting macrophage mediated periimplant osteolysis. There is renewed interest in metal on metal bearings as a solution to this problem in view of their potential for greatly improved wear performance. Using a commercially available hip simulator, the wear performance of metal on metal femoral head and acetabular cup combinations was evaluated and various parameters affecting metal on metal implant wear were identified. Nine implants custom manufactured from 2 medical grades of CoCrMo alloy (ASTM F1537-95 and F75-92) were tested within bovine serum as the lubricant to 3 million cycles (equivalent to approximately 3 years of service in vivo). The progressive wear of the components was determined by gravimetric methods at approximately every 300,000 cycles. The wear rates were characterized by an initial period of accelerated wear after which a lower steady state wear rate was observed for subsequent cycles. The presence of calcium phosphate films on the component surfaces, the microstructure of the lower carbon, wrought alloy, and increased effective radii (decreased diametral clearances) were identified as factors that may be favorable to improved wear performance. The extent of the effect on wear of each parameter, however, cannot be discerned at this point and necessitates a study in which parametric changes are more tightly controlled. The present study suggests that the use of metal on metal articulating surfaces may mitigate the problem of osteolysis by offering improved wear performance.

Contact Mechanics of Rough Surfaces in Tribology: Single Asperity Contact

Abstract: Contact modeling of two rough surfaces under normal approach and with relative motion is carried out to predict the real area of contact which affects friction and wear of an interface. The contact of two macroscopically flat bodies with microroughness is reduced to the contact at multiple asperities of arbitrary shapes. Most of deformation at the asperity contact can be either elastic or elastic-plastic. In this paper, a comprehensive review of modeling of a single asperity contact or an indentation problem is presented. Contact analyses for a spherical asperity/indenter on homogeneous and layered, elastic and elastic-plastic solids with and without tangential loading are presented. The analyses reviewed in this paper fall into two groups: (a) analytical solutions, primarily for elastic solids and (b) finite element solutions, primarily for elastic-plastic problems and layered solids. Implications of these analyses in friction and wear are discussed.

Boundary Film Formation by Viscosity Index Improvers

Abstract: Ultrathin film interferometry has been used to measure the film-forming properties of a range of viscosity index improver (VII) solutions in rolling, concentrated contacts. It has been shown that some VIIs form boundary lubricating films of thickness 10 to 30 nm in contacts. These films result from the presence of highly concentrated and thus very viscous layers of polymer solution formed on the two rubbing solid surfaces by polymer adsorption. These boundary films are formed only by some types of VII and can persist up to temperatures in excess of 120°C. The possible implications of this type of boundary lubrication are discussed. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in Kissimmee, Florida, October 8–11, 1995

Wear performance and mechanism of electroless NiP coating

Abstract: An electroless NiP coating has been deposited onto an AISI 1020 plain carbon steel by using an acid bath based on NiCl 2 , as source of nickel cations. The tribological behavior under dry non-lubricated conditions has been evaluated by employing the pin-on-disc test, where the pin was made of AISI 52100 steel. The effects of the heat treatment carried out at 400 and 260°C for 1 and 25 h, respectively on the hardness, friction and wear behavior of the coatings were investigated and compared against the properties of the unplated and as-deposited samples. Both optical and electron microscopic techniques were used to study the wear surface. It was shown that the wear resistance was greatly increased with both heat treatments, the treatment performed at 400°C being a little more effective, although no influence was observed on the frictional coefficient.

Effect of tribofilm formation on the tribological performance of hydrogenated carbon coatings

Abstract: Amorphous hydrogenated carbon (a-C:H) films were deposited by the r.f. plasma technique on stainless steel substrates. Pin-on-disc experiments were carried out over a wide range of normal loads (5–40 N) and sliding velocities (0.1–3.0 m s−1) in order to study the friction and wear performance of the coating against steel and alumina. The friction coefficient of a-C:H films against both steel and alumina pins decreased with increasing load and sliding velocity. On the pin wear surface, tribolayer formation was detected. The wear of the alumina pins increased with increasing load and sliding velocity when they contacted the coating. However, the thick tribolayer formed on the wear surface of the steel pin protected it from excessive wear when high loads and sliding velocities were applied. The wear surfaces were analysed by secondary ion mass spectroscopy and Auger electron spectroscopy. The analyses revealed that the thick tribolayer formed on the pin wear surface mainly consisted of the oxides of the pin material. However, evidence of carbon was found in the sliding deposit formed in front of the contact area of the pin and also in some cases on the pin wear surface. Carbon played an important role in the low friction behaviour although the amount of carbon was low. It is assumed that a thin tribolayer with low shear strength, consisting of carbon species, is formed on the disc wear surface. The coating wear increased when the normal load was increased. Some transfer of pin material was observed on the coating wear surface.

High-temperature wear and deformation processes in metal matrix composites

Abstract: Dry-sliding wear behaviors of a particulate-reinforced aluminum matrix composite 6061 Al-20 pet A12O3 and an unreinforced 6061 Al alloy were investigated in the temperature range 25 °C to 500 °C against a SAE 52100 bearing steel counterface. Experiments were carried out at a constant sliding speed of 0.2 m·s- at different test loads. The deformation behavior of the materials was studied by performing uniaxial compression tests in the same temperature range as the wear tests. Both alloys showed a mild-to-severe wear transition above a certain test temperature. In the mild wear regime, the wear rate and the coefficient of friction of the unreinforced 6061 Al decreased slightly with temperature, but the temperature had almost no effect on the wear rate and the coefficient of friction of the 6061 Al-20 pet Al2O3 in the same regime. Particulate reinforcement led to an increase in the transition temperature and a 50 to 70 pet improvement in the wear resistance in the severe wear regime. This was attributed to the formation of tribological layers consisting of comminuted A12O3 particles at the contact surface. High-temperature compression tests showed that the flow strength of 6061 Al-20 pet A12O3 and 6061 Al decreased monotonically with temperature and both alloys exhibited a work-softening behavior at temperatures higher than the inflection point on the flow stressvs temperature curves. The logarithmic maximum stressvs reciprocal temperature relationship was not linear, indicating that the deformation processes were too complicated to be characterized by a single activation energy over the whole temperature range. For the range of 250 °C to 450 °C, the activation energy for deformation was estimated to be 311 kJ·mol-1; for both the matrix alloy and the composite. Severe wear proceeded by thermally activated deformation processes involving dynamic recrystallization along a subsurface strain gradient. A power-Arrhenius type relationship was found to describe well the observed dependence of severe wear rates on the applied load and temperature. This relationship was used to calculate an apparent activation energy for wear of 87 kJ·mol-1 for the particulate-reinforced composite and 33 kJ·mol-1 for the matrix alloy. The wear regimes at elevated temperatures are represented in a deformation mechanism map and the relationship between high-strain deformation processes and severe wear are discussed.

Mechanics and chemistry of solids in sliding contact

Abstract: Wear behavior of coated surfaces has been studied extensively over the past 20 years. Although the behavior can be discussed in terms of classical models, it is described more completely using third-body concepts. These concepts consider the processes that take place at a moving interface : deformation and particle detachment, third-body formation and kinematics, and particle ejection. Tribological and analytical studies of several practical surface treatments, including TiN hard coatings and MoS2 lubricant coatings, will be presented to illustrate the influence of third bodies on friction and wear behavior. More fundamental aspects of solid lubrication have also been studied in an ultrahigh vacuum chamber using gases to lubricate well-characterized surfaces. These studies indicate how third bodies form, how they influence friction and wear, and why some surface treatments are better than others. They also point to the need for better understanding of (1) the physical protection afforded by surface films, (2) tribochemical processes, and (3) chemical and mechanical properties of third bodies.

Effects of Cu Powder, BaSO4 and Cashew Dust on the Wear and Friction Characteristics of Automotive Brake Pads

Abstract: Brake pads used in automotive disk brakes are generally made of many components such as phenolic resin, aramid fiber, Cu powder, BaSO4, and cashew dust. Using a slider-on-disk-type wear tester, the friction and wear characteristics of the pad against the disk made of cast iron at high disk temperature (above 80°C) were studied with varying the content of the components. In particular, the relation between the sudden decrease in friction (fade) and the wear rate were closely studied. The experimental, result of the wear test was also analyzed, systematically by the multiple regression method and the effects of the components were clarified quantitatively. Presented at the 50th Annual Meeting in Chicago, Illinois May 14–19, 1995

Titanium diboride particle-reinforced aluminium with high wear resistance

Abstract: A TiB2 particle (61 vol%, 4 μm mean size) reinforced aluminium fabricated by liquid-aluminium infiltration was subjected to unlubricated rolling wear and was found from the weight loss to be 1.5 times more wear resistant than 17-4 ph stainless steel, twice as wear resistant as 1020 steel, 7.5 times more wear resistant than 2024 aluminium, and 12.8 times more wear resistant than the aluminium matrix. This wear resistance is attributed to the lack of particle pull-out and the ability of the TiB2 particles to protect the softer underlying matrix from abrasion. This composite was approximately three times more wear resistant than AlN particle (50 vol%)-reinforced aluminium. The greater wear resistance of Al/TiB2 compared to Al/AlN is due to the slow wear of the TiB2 particles and the AlN particle pull-out. A slight decline in tensile strength and no effect on the modulus was observed in Al/TiB2 after heating at 300 or 600°C for 240 h. This high-temperature stability is attributed to the lack of reactivity between TiB2 and the aluminium matrix.

Tribological Performance of Diamond and Diamondlike Carbon Films at Elevated Temperatures

Abstract: In this study, the authors investigated the tribological performance of diamond and diamondlike carbon (DLC) films as a function of temperature. Both films were deposited on silicon carbide (SiC) by microwave plasma chemical vapor deposition and ion-beam deposition processes. Tribological tests were performed on a reciprocating wear machine in open air (20 to 30% relative humidity) and under a 10 N load using SiC pins. For the test conditions explored, the steady-state friction coefficients of test pairs without a diamond or DLC film were 0.7 to 0.9 and the average wear rates of pins were 10−5 to 10−7 mm3/N·m, depending on ambient temperature. DLC films reduced the steady-slate friction coefficients of the test pairs by factors of three to five and the wear rates of pins by two to three orders of magnitude. Low friction coefficients were also obtained with the diamond films, but wear rates of the counterface pins were high due to the very abrasive nature of these films. The wear of SiC disks coated with e...

Micro/nanoscale studies of boundary layers of liquid lubricants for magnetic disks

Abstract: The atomic force/friction force microscope is used to study the micro/nanotribiological properties of perfluoropolyether lubricants. Single‐crystal silicon wafers were lubricated with nonpolar (Fomblin Z‐15) and polar (Fomblin Z‐DOL and Demnum S‐100) lubricants. The nanowear tests show that the nonpolar (Z‐15) lubricant depleted from the wear track within few cycles whereas polar (Z‐DOL) lubricant exhibits excellent nanowear resistance with no degradation. The polar lubricant results in a lower value of microfriction as compared to the nonpolar lubricant and unlubricated silicon sample. The effect of thickness of polar lubricant is studied for the thermally bonded Z‐DOL lubricant before and after wash. Unwashed polar lubricant film with unbonded fraction exhibited better resistance to wear than that of washed lubricant film. Thicker films are also more durable. Wear experiments with magnetic disks show that lubricant film on a supersmooth disk is more effective in reduction of friction and wear than a smooth disk. Coefficients of friction on micro‐ and macroscales are compared. Variation in lubricant film thickness results in variation in the coefficient of friction. Thus, friction force microscopy can be used to measure lubricant uniformity with spatial resolution on the order of tens of nanometers. Finally, adhesive experiments show that bonded film behaves as a soft polymeric solid.