Contact Pressure Dependent Mechanisms of Ultralow Wear PTFE Composites
Contact Pressure Dependent Mechanisms of Ultralow Wear PTFE Composites
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DOI：
10.1016/j.wear.2023.204715
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发表时间：
2023-03
期刊：
影响因子：
5
通讯作者：
Kylie E. Van Meter;A. Pitenis;Kathryn L. Harris;W. Sawyer;B. Krick
中科院分区：
文献类型：
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作者：
Kylie E. Van Meter;A. Pitenis;Kathryn L. Harris;W. Sawyer;B. Krick
PTFE磨损最显著的降低之一是通过将PTFE与1- 5wt%的氧化铝颗粒复合实现的;据报道，这产生了磨损率K <$10 − 7 mm 3/Nm。与这种磨损减少相关的机制是多方面的，包括1）防止PTFE磨损表面的裂纹扩展和分层，2）促进摩擦化学，以及最近的3）摩擦诱导填料破碎成纳米级碎片以稳定和增强摩擦膜。然而，为了保持实验的可比性，文献中的许多研究都集中在狭窄的接触压力范围内。在这些实验中，我们探索了接触压力对不同PTFE和氧化铝复合材料摩擦学行为的影响，据报道，其中一种复合材料实现了超低磨损（10 × 10− 7 mm 3/Nm），另一种复合材料与未填充PTFE（10 × 10− 4 mm 3/Nm）相比，磨损仅轻微减少（10 × 10− 5 mm 3/Nm）。我们发现，随着接触压力的降低，以前被报道为高磨损的PTFE-氧化铝复合材料可以实现超低磨损率。之前报道的PTFE-氧化铝复合材料在低至高接触压力范围内实现了超低磨损，较高的压力极限对应于磨损的增加。PTFE-氧化铝复合材料的摩擦行为被发现是高度依赖于接触压力，随着压力的增加导致摩擦系数降低（在0.62-8.5 MPa范围内为0.5-0.17）。当接触压力在测试过程中逐渐变化时，这种影响变得更加明显，分别由于增加或减少压力而导致摩擦系数减少或增加高达70%。聚合物磨损表面的红外光谱表明，在测试的全范围接触压力下，甚至在极端条件下，都形成了富含羧酸盐和金属氧化物的摩擦膜。这种在滑动界面处形成的摩擦膜不仅有助于这些材料的超低磨损，而且在观察到的摩擦行为中起作用。由此，我们对氧化铝填料的作用、功能和局限性有了新的认识。
One of the most dramatic reductions in the wear of PTFE has been achieved by compositing PTFE with as little as 1–5 wt% of alumina particles; this has been reported to produce wear ratesK∼10−7mm3/Nm. The mechanisms associated with this reduction in wear are multifaceted, including 1) preventing crack propagation and delamination of the PTFE wear surface, 2) promoting tribochemistry and more recently 3) tribologically-induced breaking of the filler into nanoscale fragments to stabilize and reinforce tribofilms. However, in an effort to keep experiments comparable, many of the studies throughout the literature have focused on a narrow contact pressure range. In these experiments, we explored the effects of contact pressure on the tribological behavior of different PTFE and alumina composites, one of which is reported to achieve ultra-low wear (∼10−7mm3/Nm) and another that is reported to only have mild reductions in wear (∼1 × 10−5mm3/Nm) compared to unfilled PTFE (∼4 × 10−4mm3/Nm). We found that with decreased contact pressures, the PTFE-alumina composite that was previously reported as high wear could achieve ultralow wear rates. The PTFE-alumina composite previously reported to achieve ultralow wear achieved ultralow wear at a range of low to high contact pressures, with a higher pressure limit corresponding to increases in wear. The friction behavior of PTFE-alumina composites was found to be highly dependent on contact pressure, with increasing pressures resulting in decreasing friction coefficients (∼0.5–0.17 over a 0.62–8.5 MPa range). This effect became more pronounced when the contact pressure was incrementally varied during testing resulting in up to a 70% decrease or increase in friction coefficient due to increasing or decreasing the pressure, respectively. IR spectra of the polymer wear surface showed that tribofilms rich in carboxylates and metal oxides form at the full range of contact pressures tested, even at the extremes. This formation of tribofilms at the sliding interface not only contributes to the ultralow wear of these materials, but plays a role in the friction behavior observed. From this, we gained new insight into the role, functionality and limitations of the alumina fillers.