Unexpected friction behaviours due to capillary and adhesion effects

Area of Science:

• Materials Science
• Tribology
• Surface Chemistry

Background:

• Friction and wear of silicon carbide (SiC) are critical in various engineering applications.
• Understanding the influence of environmental factors like water on SiC tribology is essential for predicting material performance.
• Existing research on SiC friction often focuses on dry conditions, leaving the effects of liquid lubrication less explored.

Purpose of the Study:

• To investigate the complex tribological behavior of SiC-SiC interfaces when water is introduced.
• To elucidate the mechanisms behind the observed changes in friction coefficient and force under varying load conditions with water present.
• To analyze the role of capillary forces and adhesion in the multi-stage friction response.

Main Methods:

• Experimental tribometry was employed using SiC-SiC sliding pairs.
• Controlled introduction of water into the tribological interface was performed.
• Friction force and coefficient were measured under incrementally increasing normal load.
• Microscopic analysis was considered to understand interface changes (implied).

Main Results:

• Pouring water onto the SiC-SiC interface significantly increased the friction coefficient compared to dry friction.
• An initial load increase led to a substantial, abnormal decrease in friction force.
• Further increasing the load to a critical value resulted in a sharp increase in friction force.
• These stages were correlated with capillary bridge formation, water ingress, and subsequent adhesion.

Conclusions:

• Water significantly modifies the tribological response of SiC-SiC interfaces, leading to a multi-stage friction behavior.
• Capillary forces play a crucial role in the initial friction increase and subsequent changes.
• Adhesion generated by water squeezing out is a key factor in the final friction increase, highlighting the importance of lubrication conditions.