Micro- and Nanowear of Self-Mated Steel Generated and Studied With an AFM at the Single Asperity Level

Manuel Reichelt,Brunero Cappella

doi:10.3389/fmech.2021.722434

Manuel Reichelt, Brunero Cappella

Open Access

https://doi.org/10.3389/fmech.2021.722434

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Abstract

Single asperity nanowear phenomena are fundamental for understanding basic tribological mechanisms. Yet, they are studied mostly through theoretical and simulation works. Few experiments were conducted in the past decades, usually with materials which are commonly used in micro- and nanotechnology, but not for macroscopic components with relevance in tribology. In the present work, we show for the first time tribotests performed with self-mated 100Cr6 steel, a very widespread material at the macroscale, taking advantage of an AFM, employed as a tribometer for the tribotests as well as for the inspection of wear of both tribopartners. Emphasis is put on the morphology of the scars, on wear particles, and on wear of the “colloidal” particles glued on the AFM cantilever. Measurements demonstrate the possibility of characterizing single asperity events leading to very small wear (scars with isolated, down to 1-nm-deep scratches). We highlight several phenomena, for example, transfer of wear particles and their negative contribution to wear volume, which are elementary key constituents of tribological processes. Such phenomena, probably occurring also at the macroscale, can be detected, identified, and characterized with high spatial and time resolution only at the nanoscale, thus giving insight into conditions and causes of their emergence.

Highlights

Friction and wear in macroscopic tribotests are the result of numerous single contact events at the micro- or nanoscale
Common tribometers cannot be employed for the study of nanowear, and the use of an atomic force microscope (AFM) as a tribometer is indispensable
Four random-shaped wear particles were glued to tipless cantilevers and tribotests were performed by scanning them in contact with a steel disc under the variation of test parameters, notably of the normal force and number of cycles

Summary

Introduction

Friction and wear in macroscopic tribotests are the result of numerous single contact events at the micro- or nanoscale. Several theoretical studies and simulations have been conducted to gain insight into the number of those contacts (Zugelj and Kalin, 2018), their properties (e.g., pressure, duration, and mechanical and chemical properties), and their contribution to friction and wear. To investigate such nanoscale phenomena experimentally, a stark downscaling of the specimens and measuring tools toward single asperity contact and corresponding forces is necessary. Common tribometers cannot be employed for the study of nanowear, and the use of an atomic force microscope (AFM) as a tribometer is indispensable. Tribotests at the nanoscale were usually performed with silicon or similar materials used as standards in microtechnique but rather irrelevant at the macroscale

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