Degradation of a Metal-Polymer Interface Observed by Element-Specific Focused Ion Beam-Scanning Electron Microscopy

Area of Science:

• Materials Science
• Surface Science
• Tribology

Background:

• Metal-polymer interfaces are critical in applications like tire reinforcement.
• Understanding interface degradation is key to improving material durability.
• Brass-rubber interfaces are commonly used in steel cord tires.

Purpose of the Study:

• To investigate the three-dimensional degradation mechanisms of a brass-rubber interface.
• To analyze the chemical and structural changes occurring at the interface during aging.
• To correlate interface changes with the degradation of mechanical properties.

Main Methods:

• Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) for 3D imaging.
• Energy-Dispersive X-ray Spectroscopy (EDS) for elemental analysis.
• Electron Diffraction and Electron Energy Loss Spectroscopy (EELS) for structural and chemical state analysis.

Main Results:

• FIB-SEM revealed a 3D structure of the adhesive layer (brass, Cu₂S, ZnO/ZnS).
• Wet-heat aging caused Cu₂S diffusion into the rubber, exposing bare steel.
• Cu₂S crystals transformed into CuS, altering copper valence and weakening adhesion.

Conclusions:

• The degradation of the metal-polymer interface is driven by diffusion and phase transformation of the adhesive layer.
• Loss of the adhesive layer integrity directly leads to the deterioration of mechanical properties.
• Understanding these degradation pathways is crucial for designing more durable metal-polymer composites.