Abstract

PTFE composite wear rates are known to vary by 1000 × depending on the size and strength of their nanofiller aggregates. While these effects have been attributed to variations in subsurface reinforcement, debris regulation, transfer films, and filler abrasivity, the chain of causation has proven difficult to test. This study aimed to clarify these causal relationships by eliminating confounding transfer film effects on wear reduction. We conducted indexed reciprocation experiments and tracked the interfacial development for PTFE filled with 5 wt% nano-alumina aggregates of varying strength (weak, strong, or a fully dense control). Weak aggregates were broken down most by processing, created the fewest abrasions, and produced the largest wear debris (~ 10 μm). Strong aggregates were largely retained following processing, produced the densest abrasions, and radically reduced debris size (< 100 nm). Despite these key interfacial differences, the composites produced comparable wear rates (2–7 × 10^–5 mm³/Nm). The results provide the first direct evidence of the following: (1) even weak nanoparticle aggregates can be extremely abrasive; (2) ultralow wear rates (10^–7 mm³/Nm) require transfer film stability; (3) the wear-reducing effects of unstable transfer films and loose debris are negligible; and (4) fillers directly reduce debris size even without a protective transfer film. The results suggest that successful fillers reduce debris size directly, that small debris nucleates a stable transfer, that stable transfer films reduce transfer wear rates, and that interfacial stability provides the time for needed for tribochemical reinforcement.

Graphical Abstract

中文翻译：

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暴露的聚合物摩擦学：消除转移膜效应以澄清PTFE的超低磨损

摘要

已知PTFE复合材料的磨损率相差1000倍，具体取决于其纳米填料聚集体的大小和强度。尽管这些影响归因于地下增强，碎屑调节，转移膜和填料磨蚀性的变化，但因果关系链已被证明难以测试。这项研究旨在通过消除混杂的转移膜对减少磨损的影响来澄清这些因果关系。我们进行了指数往复实验，并跟踪了填充有5 wt％强度不同的纳米氧化铝聚集体（弱，强或完全致密对照）的PTFE的界面发展。弱集料在加工过程中被分解得最多，产生的磨损最少，产生的磨损碎屑最大（〜10μm）。加工后，大部分的强骨料得以保留，产生最密集的擦伤，并从根本上减少了碎屑的大小（<100 nm）。尽管存在这些关键的界面差异，但复合材料的磨损率却相当（2–7×10^–5 mm ³ / Nm）。结果提供了以下的第一个直接证据：（1）即使是较弱的纳米颗粒聚集体也可能具有极强的研磨性；（2）超低磨损率（10 ^–7 mm ³ / Nm）需要转移膜的稳定性；（3）不稳定的转移膜和松散的碎屑的减少磨损作用可忽略不计；（4）即使没有保护性转移膜，填料也可以直接减少碎屑的大小。结果表明，成功的填料可直接减少碎屑的大小，小的碎屑会形成稳定的转移，稳定的转移膜会降低转移的磨损率，界面稳定性为摩擦化学增强提供了时间。

图形概要