Solids Under Extreme Shear: Friction-Mediated Subsurface Structural Transformations.

Area of Science:

• Materials Science
• Mechanical Engineering
• Tribology

Background:

• Tribological contacts, crucial in systems from nanoelectromechanical systems to engines, dissipate significant energy as friction and wear.
• Subsurface material deformation under sliding leads to the formation of layered microstructures with reduced grain sizes.

Purpose of the Study:

• To elucidate the fundamental mechanisms governing subsurface microstructure formation in dry frictional contacts.
• To understand the role of stress fields and crystallographic orientation in microstructure evolution.

Main Methods:

• Systematic model experiments were conducted on dry frictional contacts.
• Discrete dislocation dynamics simulations were employed to model microstructure formation.
• Analysis of subsurface dislocation structures and stress fields under moving spherical contacts.

Main Results:

• Simulations demonstrated the transformation of pre-existing dislocations into prismatic dislocation structures under tribological loading.
• The stress field beneath a moving spherical contact and crystallographic orientation were identified as critical factors.
• Experimental evidence showed localized dislocation structures at depths of 100-150 nm after the first loading pass, linked to inhomogeneous stress fields.

Conclusions:

• The study clarifies the mechanisms of subsurface microstructure formation, driven by dislocation dynamics and stress fields.
• These findings are essential for guiding material selection and alloy design for enhanced tribological performance.
• Tailoring materials based on these principles can lead to improved efficiency and longevity in tribological applications.