1. Wear
   
   1. Wear of Mechanical Systems
      
   2. Wear of nanoComposites
      
2. Friction and Lubrication
   
   1. Granular Lubrication and Wear
      
   2. Gas Surface Interactions
      
3. Biomaterials Tribology
   
   1. Wear of Total Knee Replacements
      
   2. Hydrogels
      

Gas Surface Interactions

iamond-like carbon (DLC) films are of tribological interest due to their low friction, low wear rate, high hardness, and chemical inertness. A class of diamond-like carbon coatings termed near frictionless carbon (NFC) developed at Argonne National Laboratory has been shown to sustain superlow coefficients of friction ( <0.003) and wear rates ( <3-10 mm3/Nm) in self-mated contacts. The tribological behavior of these films is sensitive to the environment, only realizing their low friction coefficient and wear rate in inert, dry, or vacuum environments. The NFC films used in this study have high hydrogen content. When gaseous water is added to the environment the friction coefficient in NFC self-mated contacts rises, suggesting a gas-surface interaction where water molecules disrupt the low friction of the NFC pair.

Velocity-dependent friction coefficients of these films in nitrogen atmospheres were measured by Heimberg et al. They hypothesized that the velocity dependence was due to a gas-surface interaction that had longer times to affect the film at slower sliding speeds. This hypothesis was further supported by experiments that varied exposure time under constant sliding speeds using periods of dwell at the reversal locations. These tests showed a clear dependence on exposure time as opposed to velocity.

 Environment/surface interaction models have been created by many research groups in an attempt to describe friction coefficient variations in tribological experiments.

Vapor Phase Lubrication

APOR PHASE LUBRICATION is a technique that uses chemical reactions to form solid-lubricants on the bearing surfaces even as these lubricants are being worn away. Due to the thermal limits of conventional liquid lubricants (~350C), the demand for high temperature lubrication alternatives, and the relative ease of vapor delivery systems, vapor phase lubrication is an extremely attractive continuous lubrication technique. Although a promising technology, vapor phase lubrication systems are not currently being used in industrial applications. This is primarily due to the difficulty of pre-dicting the necessary concentrations of vapor needed to provide adequate lubrication. There have been relatively few studies in which the capacity of the lubricant has been systematically evaluated.

There is currently a need for continued modeling and experimentation with vapor phase lubrication systems. Early models of the vapor phase lubrication process assumed a thin continuous film of solid lubricant that was either sufficiently maintained or non-existent. Experiments focused on the locating of transition conditions that caused the lubricating system to move from adequate lubrication (sufficiently maintained film) to inadequate lubrication (insufficient film maintenance). Current modeling efforts assume that the solid lubricant forms as islands and these islands prescribe a fractional coverage of lubricant on the surface. The experimental effort now focuses on finding steady state conditions where the resulting friction coefficient can be used to estimate the amount of fractional coverage of lubricant.

Candidate applications for vapor phase lubrication are metal working processes (isothermal forging, drop forging, hot rolling, and metal cutting), reciprocating engines (low heat rejection diesel engines), and turbine engines.

Oxford English Dictionary

Where observation is concerned, chance favors only the prepared mind.

Louis Pasteur