Vapor-Phase Lubrication in Combined Rolling and Sliding Contacts: Modeling and Experimentation

Abstract

The in situ vapor-phase lubrication of M50 steel, in combined rolling and sliding contacts at 540°C using nitrogen atmospheres containing acetylene, is achieved. Acetylene partial pressures of 0.05 atmospheres are capable of providing continuous lubrication to combined rolling and sliding contacts through pyrolytic carbon deposition. In these tests, friction coefficients as low as μ=0.01 are found for contacts at 2.0 m/s rolling speed, 10 cm/s sliding speed, 100 N load (1.3 GPa Hertzian contact pressure), and ambient temperature of 540°C, with even lower values observed at more modest sliding speeds. One example of a model for vapor phase lubrication of combined rolling and sliding contacts is developed which predicts the lubricant steady-state fractional coverage of the contact surfaces, and from this makes friction coefficient predictions using a linear rule-of-mixture. Friction coefficient responses to step changes in acetylene partial pressure, sliding speed, and disk wear-track diameter are measured. Increased partial pressure of acetylene and increased area available for deposition are observed to be beneficial, while increased sliding speed is detrimental to lubrication performance. Shapes and trends of steady-state friction coefficient versus acetylene partial pressure, sliding speed, and disk wear-track diameter are described and curve-fit by the model. In combined rolling and sliding this example model predicts large regions of operating conditions over which friction coefficient is independent of rolling speed, as well as regions of independence of vapor partial pressure. In the special case of pure sliding, a region of friction coefficient independence of a ratio of partial pressure to sliding speed and another region of independence of a ratio of partial pressure to the product of sliding speed and normal load are predicted.

Formation mechanisms of low-friction tribo-layers on arc-evaporated TiC1−xNx hard coatings

“…Similar to vapor-phase lubrication [25], such processes strongly depend on the partial gas pressure of the adsorbate (moisture), available areas for adsorption (active sites on the coating) as well as exposure time to the environment (passing frequency of the counterpart).…”

High-Temperature Vapor Phase Lubrication Using Carbonaceous Gases

“…In practice, the friction coefficient could vary smoothly between the two extremes. This finding of intermediate values in friction coefficient then led to the development of a series of fractional coverage models for vapor phase lubrication [7,8] and even a model for the removal of a fractional solid lubricant film [14]. During these modeling activities, a number of persistent questions emerged.…”

“…The authors' approach is essentially not destructive of the solid wear surface… Over the years, vapor phase lubrication with a number of different carbonaceous gases and tribological materials has been successfully demonstrated in the laboratory. The range of materials includes high performance ceramics (nitrides [3][4][5][6], carbides [2,3], metal-oxides [2,3]) and high-temperature metals and alloys (bearing steels [3,7,8], stainless steels [3], and nickel super alloys [1,3]). The range of gas chemistries include a wide variety of hydrocarbons (ethane, ethylene, acetylene, benzene, propane, and 1-propanol) [1,2,5,[9][10][11] as well as mixtures of carbon monoxide and hydrogen, and a simulated rich burn turbine engine exhaust gas [4,6].…”

A Nano- to Macroscale Tribological Study of PFTS and TCP Lubricants for Si MEMS Applications

“…The model parameters utilized the fraction of lubricant removed per stroke, frequency of oscillation, contact size, and surface diffusion coefficient of lubricant on a specific substrate to obtain a steady state concentration of lubricant at the center of contact. A similar ''windshield wiper'' model by Sawyer and Blanchet [23] involved lubricant replenishment from the vapor and does not take into account surface diffusion.…”

“…By heating TCP, the vapor pressure is raised enough to condense a lubricating layer on exposed surfaces. The low vapor pressure under ambient conditions and ability to condense a lubricant film on a surface without significant line-of-sight limitations makes TCP a candidate of interest for MEMS lubrication to increase performance over chemically bound monolayer films [22][23][24].…”