基于转移膜二维连续性和相对吸附强度的新型聚合物减磨模型研究

Polymers are used as self-lubricating materials in applications where the use of traditional lubricants is undesirable or precluded. Neat polymers often lack sufficient lubricity or wear resistance for bearing applications, so fillers are used to reinforce the polymer and improve its performance in sliding conditions. In the last two decades, the use of nanofillers has been explored to provide reinforcement without the abrasive effects of the more traditional fillers. For the most successful of these tribological nanocomposites, thin uniform films of polymer are found to be strongly adhered to the hard bearing steel countersurfaces. The improvements in tribological properties for these nanocomposites are widely attributed to the quality of these so-called transfer films. The proposed transfer film attributes responsible for the wear reductions include: (1) film thickness, (2) film area fraction at the surface, (3) film uniformity and continuity, (4) tenacity of transfer film, (5) counterface-film adhesion strength. However, few of these attributes has been studied quantitatively and it remains unclear which is most closely related to tribological performance. This proposal aims to elucidate how these attributes affect wear performance by 1) developing quantitative metrics for transfer film properties and 2) correlating these properties to wear properties using a wide range of high performance polymer nanocomposite systems. Transfer film’s thickness, area fraction, continuity, adhesion strength and wear resistance will be characterized quantitatively as a function of the sliding distance. The result will elucidate the correlations between various transfer film attributes and the system’s wear resistance. An adhesive wear model proposed by the applicant based on transfer film’s quality will also be analyzed and examined. More broadly, study will offer important insights in designing new tribological coatings that can survive long time service without delamination failure.

纯聚合物作为一种固体自润滑材料通常缺乏足够的润滑性或者耐磨性，各种填料因而被用来改善聚合物的摩擦磨损性能。过去20年间，纳米填料被发现可以有效改善聚合物的摩擦学性能，而且不会像微米填料那样高度磨损金属配合面。超高性能聚合物纳米复合材料在与高硬度的轴承钢进行摩擦时，一层薄且均匀的聚合物会转移到金属配合面上。研究表明复合材料摩擦学性能的提升与这层聚合物转移膜的性能提高密切相关，具体假设集中在考察（1）转移膜厚度，（2）转移膜覆盖率，（3）转移膜均匀性和连续性，（4）转移膜自身耐磨性和（5）转移膜与金属基底的吸附性对减磨的影响。然而，国内外研究中仍然缺少对转移膜性能的量化表征，也就缺少对相关耐磨机理的有效支持。本课题旨在通过 1）定义一套新的转移膜量化表征参数，并 2）针对一批高性能聚合物纳米复合材料转移膜，考察复合材料磨损率与转移膜性能的量化关系，进一步阐明本领域中的相关科学问题。

超低磨损聚合物固体自润滑材料对于航空航天、食品加工等领域关键摩擦副的长寿命、免维护设计具有较高的潜在应用价值，本项目聚焦影响体系摩擦磨损最大的因素界面转移膜，选取了一种超高耐磨PTFE基纳米复合材料，重点研究了：（1）转移膜二维分布形貌的量化表征及其与摩擦磨损的关联；（2）转移膜自身耐磨性对体系磨损性能的影响；（3）转移膜-基底界面的动态演变和（4）金属表面织构、粗糙度对转移膜和体系磨损的影响。研究结果首次对转移膜的二维连续性和均匀性进行了量化表征，并证明了其与聚合物及金属磨损的密切关联。其中，转移膜覆盖率被发现与金属基底的磨损存在极强的线性关系（R2=0.92）。此外，研究还发现金属表面的粗糙度峰谷对于转移膜形成和抑制磨损具有相互竞争的作用。通过正交实验法寻找到一种可以降低测试体系磨损体积90%的金属表面织构，有望用于新一代耐磨涂层设计。最后，通过将聚合物与激光蚀刻的金属表面沟槽样品对磨，发现金属表面沟槽的间距与深度对于聚合物固体自润滑材料的磨损均具有自我竞争式的、高度耦合的作用，其原因主要是干摩擦过程中聚合物对金属表面粗糙度方向性的改变。本项目发现了一种高效减磨的金属表面织构，进一步阐明了转移膜这一界面屏障对于聚合物固体自润滑材料磨损的影响以及与金属表面形貌的关系，首次揭示了转移膜-基底界面的动态演变过程，对于相关领域的进一步发展提供了良好基础。

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