Tribological Properties Study of Solid Lubrication with TiO₂ Powder Particles

Area of Science:

• Materials Science
• Tribology
• Solid Lubrication

Background:

• Titanium dioxide (TiO ₂ ) exhibits solid lubricant properties, similar to tungsten disulfide (WS ₂ ) and molybdenum disulfide (MoS ₂ ), reducing friction and wear.
• Compacted TiO ₂ powder forms pellets, which have been investigated for their tribological behavior in various contact configurations.
• The concept of a 'third body' in lubrication, referring to intermediate materials like transferred particles, is crucial for understanding lubrication mechanisms.

Purpose of the Study:

• To investigate the tribological behavior and lubrication characteristics of titanium dioxide (TiO ₂ ) as a solid lubricant, particularly in an oil-free context.
• To evaluate the self-repairing and self-replenishing capabilities of TiO ₂ -based solid lubricant coatings.
• To develop and validate a theoretical model (Control Volume Fractional Coverage - CVFC) for predicting the performance of TiO ₂ in sliding contacts.

Main Methods:

• Tribological experiments were conducted using a tribometer with simultaneous pellet/disk and slider pad/disk contacts.
• TiO ₂ powder was compacted into pellets, and its lubrication characteristics were studied by intentionally transferring particles onto a disk surface.
• A theoretical Control Volume Fractional Coverage (CVFC) model was employed to estimate wear rates and friction coefficients based on material properties, operational parameters, and fractional coverage.

Main Results:

• Titanium dioxide (TiO ₂ ) pellets demonstrated effective oil-free lubrication, exhibiting self-repairing and self-replenishing behavior.
• The CVFC model successfully estimated pellet wear rates and slider pad friction coefficients, correlating well with experimental data.
• Fractional coverage, a parameter in the CVFC model, proved useful in quantifying the amount of third-body material on the disk asperities.

Conclusions:

• Titanium dioxide (TiO ₂ ) is a viable and effective oil-free solid lubricant with self-sustaining lubrication properties.
• The developed CVFC model accurately describes the tribological behavior of sliding contacts involving TiO ₂ , both qualitatively and quantitatively.
• Experimental and theoretical results align, confirming the model's predictive capability for TiO ₂ -based lubrication systems.