Influence of Femtosecond Laser Surface Nanotexturing on the Friction Behavior of Silicon Sliding Against PTFE.

Alves-Lopes Alves-Lopes,Vilar Vilar,Almeida Almeida,Oliveira Oliveira

doi:10.3390/nano9091237

Alves-Lopes Alves-Lopes, Vilar Vilar + Show 2 more

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https://doi.org/10.3390/nano9091237

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Abstract

The aim of the present work was to investigate the influence of laser-induced periodic surface structures (LIPSS) produced by femtosecond laser on the friction behavior of silicon sliding on polytetrafluoroethylene (PTFE) in unlubricated conditions. Tribological tests were performed on polished and textured samples in air using a ball-on-flat nanotribometer, in order to evaluate the friction coefficient of polished and textured silicon samples, parallel and perpendicularly to the LIPSS orientation. In the polished specimens, the friction coefficient decreases with testing time at 5 mN, while it increases slightly at 25 mN. It also decreases with increasing applied load. For the textured specimens, the friction coefficient tends to decrease with testing time in both sliding directions studied. In the parallel sliding direction, the friction coefficient decreases with increasing load, attaining values similar to those measured for the polished specimen, while it is independent of the applied load in the perpendicular sliding direction, exhibiting values lower than in the two other cases. These results can be explained by variations in the main contributions to friction and in the wear mechanisms. The influence of the temperature increase at the interface and the consequent changes in the crystalline phases of PTFE are also considered.

Highlights

Laser surface texturing is one of the most versatile methods for controlling the tribological properties of materials, since it allows creating a variety of surface textures at the micro and nanoscales in a wide range of materials, with excellent control of the surface features shape and size and negligible degradation of the bulk material [1]
When surfaces are irradiated with femtosecond laser pulses at fluences slightly above the material ablation threshold, parallel surface undulations known as laser-induced periodic surface structures (LIPSS) are formed on the surface of a wide variety of materials [6,7,8,9]
We studied the influence of surface textures produced by femtosecond laser on the friction behavior of single crystalline silicon sliding on PTFE, under unlubricated conditions

Summary

Introduction

Laser surface texturing is one of the most versatile methods for controlling the tribological properties of materials, since it allows creating a variety of surface textures at the micro and nanoscales in a wide range of materials, with excellent control of the surface features shape and size and negligible degradation of the bulk material [1]. The formation of LSFL is due to a periodic modulation of the absorbed radiation intensity that arises as a consequence of the interference between the incident laser beam and electromagnetic waves propagating parallel to the surface [13,14]. This modulation of the laser absorbed energy generates a periodic variation of the material surface temperature and, of the transformations that occur in the material, leading to the imprinting of the surface topography by differential ablation [15]. LIPSS affect surface properties such as wettability [16], light reflectivity and transmittance [17,18,19], cell behavior and osseointegration capability of implant materials [16,20], bacteria adhesion and biofilm formation [21], as well as the materials tribological behavior, in particular its friction coefficient [6,22,23,24,25,26,27,28]

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