Surface Topography Influences Scratch Resistance

Table of Contents

Introduction
Materials and Methods
Scratch Deformation
Surface Topography

Introduction

Many surfaces which have special functions or are patterned must be scratch or mar-resistant, as a key parameter in their performance, product life, and reliability. What is more, the presence or lack of scratch resistance may severely affect the appearance of the exterior, including its look and feel, two major factors in deciding whether a product favorably impresses a customer. The following experiment shows how a nanoindenter may be used to test the scratch resistance and surface deformation of a glass/silicon surface with a pattern on it. The experiment reveals the effects of surface topography on its resistance to scratching by solid particles.

Materials and Methods

An iNano Nanoindenter from Nanomechanics, Inc. was used for the scratch testing, after fitting it with a diamond Berkovich tip. The tested material was a patterned glass surface mounted to a wafer of silicon. The pattern was spaced to 10 µm and contained square holes. The iNano produced scratches over a length of 200 µm under a constant load of 20 mN, at about 20 µm/s to pass over as many holes as possible in the glass surface.

Figure 1. Test equipment and methodology: (a) Nanomechanics, Inc. iNano Nanoindenter; (b) geometric representation of a Berkovich indenter tip; (c) Patterned 10 µm wavelength glass/silicon surface.

Scratch Deformation

The 20 mN scratch damaged the area of application producing slight depressions in the pattern of squares in a single line. The trough represents smooth plastic deformation while the surface material was not removed by the scratch. However, one side of each square was consistently more damaged than the other over the whole length of the scratch, in this case the right side. This was because the glass on the right side came into sudden contact with the hard Berkovich tip and was disrupted, while the tip went on and climbed out of the hole without as much destruction. The point is that the mechanical properties of the sample were not as important in scratch resistance as the surface topography was.

Figure 2. Optical micrograph of damage to glass/silicon AFM grid during 20 mN scratch.

Surface Topography

The initial profile of the tested surface is compared to the profile during the 20 mN scratch, both being mapped against scratch position. Both profiles are similar. The initial profile has first a downward inclination and then flattens out, with vertical spikes which represent the passage from higher to lower regions of the glass/silicon AFM grid. The during scratch profile shows the same patterns, but with some differences in peak shape, probably because of higher areas of contact when more force is brought to bear on the surface.

Figure 3. Initial surface profile (a) and scratch profile during the 20 mN constant load scratch (b) on a glass/silicon AFM grid.

 

This information has been sourced, reviewed and adapted from materials provided by Nanomechanics, Inc.

For more information on this source, please visit Nanomechanics, Inc.

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