Influence of PTFE Filler Morphology on Friction and Wear

Filler morphology alters the stability of the friction coefficient, the wear rate of PTFE itself, and the risk of counterface wear through three mechanisms: load-bearing mode, interfacial shear behavior, and third-body (debris/transfer film) dynamics.  The advantages of different morphologies can only be fully realized by matching the counterface conditions

 1,Spherical Filler: Rolling friction has a low friction coefficient and reduces wear.

Typical Materials: Glass Beads, Spherical Oxides, Mineral Powders)

Mechanism Analysis: Provides uniform stress distribution and reduces asperity ploughing; however, detached hard spheres may induce severe three-body abrasive wear.

Friction & Wear Impact

Microscopically, spherical particles perform effective load-bearing functions, enhancing resistance to indentation and creep, and mitigating adhesive wear in certain conditions.

The effect on friction coefficient highly depends on particle size, concentration, interfacial bonding, and counterface status; they are not inherently low-friction.

Major Risks

If particles feature high hardness, large size, or poor matrix adhesion, detachment generates free abrasives, resulting in:

Elevated PTFE wear rate;

Severe counterface scratching/grooving;

Increased noise and friction fluctuation.

Conclusion

The compatibility of spherical fillers hinges on: particle size distribution (oversized tail), interfacial coupling treatment, and counterface hardness/roughness matching.

Lamellar Fillers (Rolling friction has a low friction coefficient and reduces wear.

Mechanism Analysis: Facilitates the formation of a continuous transfer film and a low-shear interface.

Friction & Wear Impact

2,Flake Filler

Flake Fillers:It is prone to form a transfer film, with extremely low friction and high wear resistance.

Typical shapes: Graphite, layered solid lubricants

Mechanism Analysis: Facilitates the formation of a continuous transfer film and a low-shear interface.

Friction & Wear Impact

• flake particles easily spread and orient along the shear direction, introducing a low-friction sliding layer at the interface, which reduces the friction coefficient and improves stability.
• When the transfer film is continuous and strongly adhered, the contact changes from "PTFE-to-metal/ceramic" to "film-to-film" or "film-to-PTFE", significantly lowering wear loss.

Common Risks

• Easy film formation ≠ Stable film formation: On overly smooth counterfaces with low surface energy (e.g., certain coated surfaces), the transfer film may repeatedly form and delaminate, causing large fluctuations in friction and wear.
• High loading of flake fillers may reduce bulk strength and elongation; under reciprocating motion, delaminated debris may occur, leading to unstable wear.

Conclusion: Ideal for applications prioritizing low friction, easy running-in, and stable film retention.

3, Fibrous filler

Typical Shape: Glass Fiber, Carbon Fiber, Whiskers

Core Mechanism: Dramatically improves load capacity and creep resistance, typically reducing PTFE wear; however, exposed fiber tips act as micro-cutters that plough the counterface.

Friction & Wear Impact

High aspect ratio fillers form a rigid skeleton structure, boosting stiffness, dimensional stability, and PV limit. Most low-wear PTFE compounds rely on fibrous reinforcement.

Under high load, elevated PV values, or strict dimensional tolerance requirements, fiber reinforcement significantly extends service life.

Counterface Damage Risk

Exposed or fractured fiber ends cause micro-ploughing on the counterface, especially severe when the counterface is soft, poorly finished, or improperly roughened.

Caution is required if zero counterface wear is mandatory (e.g., precision shafts/mirror finishes).

Anisotropy Effect (Critical Note)

Flow direction during molding/pressing induces fiber orientation, leading to directional differences in friction and wear performance. The same formula may yield drastically different results under varying processing conditions.

Summarize

Suitable for scenarios requiring strict wear resistance and anti-creep load capacity. Must be systematically validated with counterface hardness control, surface treatment, and optimized running-in procedures.