Tribology and 3D Metrology for Stainless Steel Analysis

Table of Contents

Introduction
Importance of Tribology Inspection for Quality Control
Measurement Objective
Pin-On-Disk Test Method
Profilometry Measurement Principle
Pin-On-Disk Test Results
Profilometry Measurement Results
Conclusion

Introduction

A key field of study covering almost all industries is Tribology. Tribology is the science and engineering of interacting surfaces in relative motion and includes the study of lubrication, friction and wear. Any application in motion and contact with another application and/or the same is faced with the consequence of wear. Wear costs money for replacements and results in downtime of machinery equipment. The existing challenge for engineers is to source and/or design materials that are the most wear resistant to prolong the life of the application or part, thereby reducing the frequency of replacement. The study of Tribology is most commonly applied in machinery and automotive design; however, it also extends into virtually all other facets of modern technology, including medical, electronics, cosmetics, etc.

Importance of Tribology Inspection for Quality Control

Tribology is vital to the development of modern and advanced economical applications, which are in constant battle with the forces of wear and friction. The purpose of Tribology research is eventually the elimination and minimization of losses resulting from friction and wear at all levels of technology, which involves the rubbing of surfaces. Tribology research is crucial to greater application performance, production efficiency, controlled replacement breakdowns, and chiefly to the cost savings to support industrial growth.

Measurement Objective

To study a material’s wear, the process must be simulated in a controlled manner to evaluate the effect on different samples under identical test conditions. A Nanovea Pin-On-Disk Tribometer will be used to achieve this precision measurement. In the following test example, a block of stainless steel and the static sample is subjected to wear. The static sample, which will be in contact with this surface, will be a stainless steel ball with a 6 mm diameter. Measurements will be made with and without lubrication. With such a type of test, wear can be simulated with the material and geometry of the contact point, the control of sliding speed, the load applied, and the test’s duration. In addition, built-in optics, 3D non-contact profilometry, precisely acquires pre and post surface measurement, including quantified surface wear loss among others.

Tribology

Pin-On-Disk Test Method

The sample, mounted on a rotating stage and a ball or pin, comes in contact with the surface of the sample, with a known force, to produce the wear. Generally, the pin-on-disk test is used as a comparative test in which controlled wear is carried out on the samples to study. The volume lost allows for the calculation of the wear rate of the material. The wear rate can be used as a quantitative comparative value for wear resistance since identical action is performed on all the samples.

Pin-On-Disk Test Method

Profilometry Measurement Principle

The technique of axial chromatism uses a white light source, where light passes through an objective lens with a high degree of chromatic aberration. The refractive index of the objective lens will differ relative to the wavelength of the light. Essentially, each separate wavelength of the incident white light will again focus at a different distance from the lens (different height). A single monochromatic point will be focalized to form the image when the measured sample is within the range of possible heights. Owing to the system’s confocal configuration, only the focused wavelength will pass through the spatial filter with high efficiency, thus causing all other wavelengths to be out of focus.

Profilometry Measurement Principle

Using a diffraction grating, the spectral analysis is conducted. This method deviates each wavelength at a different position, intercepting a line of CCD, which consecutively pinpoints the maximum intensity position and allows direct correspondence to the Z height position.

Pin-On-Disk Test Results

The following parameters are used for the pin-on-disk test:

Force applied 20.0 N
Speed of rotation 200.0 RPM
Radius of wear track 3.00 mm
Duration of test 3.0 minutes
Total disk rotations 602.0
Distance traveled 11.35 m
Lubrication (Super Lube) Synthetic Lightweight Oil

The recorded coefficient of friction between the pin and the sample over the course of the test is shown in the following graph:

No lubrication | Coefficient of friction during test for stainless steel with

No lubrication | Coefficient of friction during test for stainless steel with

With lubrication | Coefficient of friction during test for stainless steel

With lubrication | Coefficient of friction during test for stainless steel

Using this test data, an average coefficient of friction for the SS with no lubricant of 0.780 was calculated by the software and the SS with lubrication resulted in a coefficient of friction of 0.146. Only the coefficient of friction data is required in some applications. The friction reading scan slope or step up when a coating is worn though and a substrate with higher friction is uncovered, or when a particular type of energetic failure happens (collapsing, crumbling, etc.). Usually, the objective of the test will be to observe the number of cycles required to attain this failure. In this example, the friction data is sufficient to calculate wear resistance. When the objective of the test is to measure friction between materials, the friction data is also sometimes used on its own.

Profilometry Measurement Results

To determine the roughness of the surface area, a profile of the stainless steel was noted before taking measurements of the wear tracks.

Top view of surface area for stainless steel

Top view of surface area for stainless steel

3D view of surface area for stainless steel

3D view of surface area for stainless steel

Roughness Parameters

ST501328
Sa 0.121 µm Arithmetical Mean Height
Sq 0.152 µm Root Mean Square Height
Sp 0.645 µm Maximum Peak Height
Sv 0.536 µm Maximum Pit Height
Sz 1.182 µm Maximum Height
Ssk -0.01576 Skewness
Sku 3.038 Kurtosis

No lubrication| False color surface height representation of Stainless Steel

No lubrication| False color surface height representation of Stainless Steel

With lubrication | False color surface height representation of Stainless Steel

With lubrication | False color surface height representation of Stainless Steel

No lubrication | 2D cross-sectional profile of wear track for Stainless Steel

No lubrication | 2D cross-sectional profile of wear track for Stainless Steel

With lubrication | 2D cross-sectional profile of wear track for Stainless Steel

With lubrication | 2D cross-sectional profile of wear track for Stainless Steel

The maximum depth of the wear track is 1.781 µm and the area of the red-shaded region is 407.5 µm2 which is inferred from the profile represented in Figure 8 (SS with no lubricant). These values can be measured from the complete wear track area for more precise results. From the wear track, a wear rate of 3.387X10-5 mm3/Nm is measured. The maximum depth of the wear track is 1.557 µm and the area of the red-shaded region is 320.9 µm2 for the profile depicted in Figure 9 (SS with lubricant). These values can be measured from the complete wear track area for more precise results. A wear rate of 2.667X10-5 mm3 is measured from the wear track.

No lubrication | 3D view of wear track for Stainless Steel with

No lubrication | 3D view of wear track for Stainless Steel with

With lubrication | 3D view of wear track for Stainless Steel

With lubrication | 3D view of wear track for Stainless Steel

Conclusion

The precise calculation of wear rate to a chosen material is shown using the Nanovea Tribometer with optical integration. The Tribometer allowed for wear calculations to be carried out through a pin-on-disk method in a controlled and repeatable manner, which will allow testing and comparison of numerous samples under the same conditions. The integrated optics measured the topography of the sample surface to accurately calculate the volume of wear loss and roughness. The parameters of the test can be adjusted and modules can be added to better simulate specific wear applications.

Different materials and geometries can be used as static samples: different size balls, pins, or other custom sizes and shapes. The Tribometer can perform wear in a linear or circular motion. The test can be performed under lubrication or at elevated temperatures. The applied load can go to a maximum of 60 N, and rotation speeds up to 500 rpm (custom instruments with higher speeds and loads also possible). It can be concluded that the Nanovea Tribometer with optical integration is an ideal instrument with unparalleled choices for evaluating and conducting Tribology studies in research or industrial environments.

Nanovea.

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

For more information on this source, please visit Nanovea.

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