Background

Surface topography strongly modifies adhesion of hard-material contacts, yet roughness of real surfaces typically exists over many length scales, and it is not clear which of these scales has the strongest effect. Objective: This investigation aims to determine which scales of topography have the strongest effect on macroscopic adhesion.

Methods

Adhesion measurements were performed on technology-relevant diamond coatings of varying roughness using spherical ruby probes that are large enough (0.5-mm-diameter) to sample all length scales of topography. For each material, more than 2000 measurements of pull-off force were performed in order to investigate the magnitude and statistical distribution of adhesion. Using sphere-contact models, the roughness-dependent effective values of work of adhesion were measured, ranging from 0.08 to 7.15 mJ/m² across the four surfaces. The data was more accurately fit using numerical analysis, where an interaction potential was integrated over the AFM-measured topography of all contacting surfaces.

Results

These calculations revealed that consideration of nanometer-scale plasticity in the materials was crucial for a good quantitative fit of the measurements, and the presence of such plasticity was confirmed with AFM measurements of the probe after testing. This analysis enabled the extraction of geometry-independent material parameters; the intrinsic work of adhesion between ruby and diamond was determined to be 46.3 mJ/m². The range of adhesion was 5.6 nm, which is longer than is typically assumed for atomic interactions, but is in agreement with other recent investigations. Finally, the numerical analysis was repeated for the same surfaces but this time with different length-scales of roughness included or filtered out.

Conclusions

The results demonstrate a critical band of length-scales—between 43 nm and 1.8 µm in lateral size—that has the strongest effect on the total adhesive force for these hard, rough contacts.

中文翻译：

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硬质材料附着力：哪些粗糙度重要？

背景

表面形貌强烈地改变了硬材料接触的附着力，但真实表面的粗糙度通常存在于许多长度尺度上，目前尚不清楚这些尺度中哪一个具有最强的影响。目的：本研究旨在确定哪些地形尺度对宏观粘附的影响最强。

方法

使用足够大（0.5 毫米直径）的球形红宝石探针对不同粗糙度的技术相关金刚石涂层进行附着力测量，以对所有长度尺度的地形进行采样。对于每种材料，进行了 2000 多次拉拔力测量，以研究粘附的大小和统计分布。使用球接触模型，粗糙度依赖性有效测定粘附功的值，范围从0.08至7.15毫焦/米²在四个表面。使用数值分析更准确地拟合数据，其中相互作用势被整合到所有接触表面的 AFM 测量的地形上。

结果

这些计算表明，考虑材料中的纳米级塑性对于测量的良好定量拟合至关重要，并且在测试后通过探针的 AFM 测量证实了这种塑性的存在。这种分析能够提取与几何形状无关的材料参数；红宝石和钻石之间的固有粘附功被确定为 46.3 mJ/m ²。粘附范围为 5.6 nm，比通常假设的原子相互作用长，但与最近的其他研究一致。最后，对相同的表面重复进行数值分析，但这次包含或过滤掉了不同的粗糙度长度尺度。

结论

结果表明，长度尺度的临界带（横向尺寸在 43 nm 和 1.8 µm 之间）对这些坚硬、粗糙的触点的总粘合力具有最强的影响。