Sintered Brake Pads Failure in High-Energy Dissipation Braking Tests: A Post-Mortem Mechanical and Microstructural...

Area of Science:

• Materials Science
• Tribology
• Mechanical Engineering

Background:

• Industrial sintering processes for metallic matrix pads aim to reduce copper content.
• Replacing copper with iron in these pads has performance limitations.
• High-energy rail braking tests push materials to their usage limits, revealing microstructural and mechanical property changes.

Purpose of the Study:

• To investigate the microstructural and mechanical property evolution of sintered metallic matrix pads under extreme braking conditions.
• To understand the material behavior and failure mechanisms in high-energy rail braking.

Main Methods:

• Sintered metallic matrix pads were subjected to high-energy braking tests.
• Compressive behavior was assessed using digital image correlation (DIC).
• Microstructure was analyzed using scanning electron microscopy (SEM).

Main Results:

• Worn pads exhibited three distinct layers with varying microstructures and compressive behaviors.
• An intermediate layer (2-15 mm depth) showed macroscopic and microscopic cracks.
• The top layer was hardened by copper resolidification, while carbon diffusion weakened iron-graphite interfaces.
• Submicronic particles and graphite particles contributed to the weak compressive behavior of the pads.

Conclusions:

• The limit of replacing copper with iron in metallic matrix pads has been identified.
• High-energy braking induces significant microstructural changes, including cracking and phase transformations.
• The presence of graphite and submicronic particles, along with weakened interfaces, critically impairs the compressive strength of the pads.