Application Note | High-Temperature Tribology
Arc Reciprocating Wear at High Temperature
Reciprocating Wear Up to 950 °C with the Contact Fully Enclosed in the Oven
Research & Experimental Testing
Duanjie Li
Visual Design & Editorial
Andrew Shore
Introduction
Wear is a process of removing material on a surface as a result of mechanical action of the opposite surface [1]. It is influenced by a variety of factors, such as temperature, speed, load, reciprocating and many others. Temperature plays a critical role on the extent of wear damage to materials. Wear at high temperature has a complex nature, involving different wear mechanisms such as adhesive wear, abrasive wear, surface fatigue and oxidation wear [2].
Importance of Analyzing Arc Reciprocating Wear at High Temperature
ASTM G133 [3] is a widely used standard setup for testing the reciprocating sliding wear behaviors of materials. Due to the back and forth movement of the sample involved during reciprocating wear testing, it is challenging to design an oven that fully encloses the sample and reaches a high and homogenous temperature. Our previous study has shown that the material tested using reciprocating and rotational setups can exhibit significantly different wear behaviors. Therefore, in order to study the reciprocating wear behaviors of materials at elevated temperatures, we developed the arc wear test setup. It rotates the sample stage for pin-on-disc test and continuously oscillates it clockwise and counterclockwise, creating an arc reciprocating sliding motion for the sample. The contact of the wear process can be totally enclosed in a large oven which ensures uniform and stable temperature up to 950 °C surrounding the sample and the counter material.
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Measurement Objective
The wear mechanism of a stainless steel SS304 plate sample is measured in a controlled and monitored manner using the arc reciprocating wear test setup at room temperature and 800 °C for comparison. In this study, we would like to showcase the capacity of the NANOVEA Tribometer in measuring the reciprocating wear of materials at high temperatures.
NANOVEA T2000 High Load
Pneumatic Tribometer
Test Procedure
The tribological behavior, e.g. coefficient of friction, COF, and wear resistance of the stainless steel SS304 sample was evaluated by the NANOVEA Tribometer using the arc reciprocating wear test setup. The wear tests were carried out at room temperature (RT) and 800 °C in an oven for comparison. The arc test setup allows measuring reciprocating wear at elevated temperature in an oven up to 950 °C. The contact of the wear process is totally enclosed in the large oven. The thermocouple is set up to directly touch the back of the ball inside the ball holder to achieve the best accuracy of the temperature reading. A SiN ball tip (6 mm dia., Grade 100) was applied against the tested samples. The test parameters are summarized in Table 1. Wear track profiles were evaluated by the NANOVEA Optical Profilometer, and the wear track morphology was examined using optical microscope.
| Test parameter | Value |
|---|---|
| Normal force | 10 N |
| Speed | 250 mm/s |
| Number of strokes | 10000 |
| Temperature | Room temperature or 800 °C |
| Counter material | SiN ball, 6 mm diameter, grade 100 |
Table 1: Test parameters of the wear measurement.
Results and Discussion
The COFs recorded in situ are shown in Fig. 2. The arc reciprocating wear motion consists of continuous back and forth movements, resulting in COF of positive and negative values. The sample tested at RT exhibits a low COF below 0.2 during the first minute run-in period, followed by an abrupt increase to high values above 0.5 in the rest of the wear test. In comparison, the sample tested at 800 °C shows a high COF at the beginning, which progressively decreases throughout the wear test.
The 3D wear track profiles of the SS304 sample after the arc reciprocating tests were measured using the NANOVEA non-contact optical profilometer as shown in Fig. 3, and the 2D cross section wear tracks are compared in Fig. 4. The wear volume calculated using the NANOVEA analysis software is comparable at 0.030 and 0.032 mm³ for the arc reciprocating wear tests at RT and 800 °C, respectively. However, it is interesting to observe that after the same number of strokes at different temperatures, the wear track of the SS304 sample shows very different morphology.
The wear tracks of the SS304 sample after the wear tests at RT and 800 °C were examined and compared under optical microscope as displayed in Fig. 5. The sample tested at RT exhibits a wear track with parallel grooves. During the run-in period, small work hardened wear debris were progressively generated due to the wear on the SS304 surface by the SiN ball. As the wear track surface got worn out and roughened, more directional scars on the SS304 surface were created by the abrasion of the hard debris trapped between the sliding surfaces.
In comparison, the wear track created at 800 °C shows a different morphology. When the SS304 sample was exposed to a high temperature environment at 800 °C, oxide film formed on the surface and generated a harder layer. Due to the low hardness of the metal underlying the oxide layer, the high concentrated shear stress at the contact point plastically deformed the metal underneath and damaged the oxide layer during the wear process. Such a process led to exfoliation of the oxide flakes and formation of the peculiar morphology of the wear track as shown in Fig. 5 b&d.
Two distinct wear mechanisms were observed in this wear study carried out at RT and at 800 °C, demonstrating the importance of analyzing the wear behavior of the materials using the test conditions in the realistic application environment. It illustrates that wear mechanism can change drastically when the tribosystem is exposed to different temperatures. The versatility of the NANOVEA Tribometer allows measuring the rotative and linear reciprocating wears in one single system under various conditions, including high temperature, lubrication, tribocorrosion and others, making it an ideal tool for research/testing labs dealing with a variety of materials applied in different tribological conditions.
Conclusion
In this study, we carried out a comprehensive analysis on the high temperature wear behavior of a SS304 sample using the arc reciprocating wear setup. The self-tuned high quality motor of the NANOVEA Tribometer possesses a 20bit internal speed and a 16bit external position (>0.006°) encoder, ensuring users to measure the arc reciprocating wear in an accurate and repeatable manner. With comparable wear rates, the SS304 exhibits significantly different wear mechanism measured at room temperature and 800 °C. This demonstrates the importance of investigating the wear mechanism at the temperature used in the realistic application. The arc wear test setup enables measuring reciprocating wear at elevated temperatures in an oven up to 950 °C.
The NANOVEA Tribometer offers precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes. It provides optional high temperature wear, lubrication and tribocorrosion modules available in one pre-integrated system. Such versatility allows users to better simulate the real application environment and improve fundamental understanding of the wear mechanism and tribological characteristics of various materials.
References
Rabinowicz, E. (1995). Friction and Wear of Materials. New York, John Wiley and Sons.
Jones, M. H., and D. Scott, Eds. (1983). Industrial Tribology: the practical aspects of friction, lubrication, and wear. New York, Elsevier Scientific Publishing Company.
ASTM G133 - 05(2010). Standard Test Method for Linearly Reciprocating Ball-on-Flat Sliding Wear.
Frequently Asked Questions About High-Temperature Reciprocating Wear
Why is reciprocating wear hard to test at high temperature?
In a linear reciprocating test (ASTM G133) the sample moves back and forth, which makes it hard to build an oven that fully encloses it at a high, uniform temperature.
What is arc reciprocating wear?
The pin-on-disk sample stage is oscillated clockwise and counterclockwise, creating an arc-shaped reciprocating sliding motion while the whole contact stays inside a large oven at stable temperatures up to 950 °C.
How was the stainless steel tested?
SS304 was worn against a 6 mm SiN ball at 10 N and 250 mm/s for 10000 strokes, at room temperature and at 800 °C, with a thermocouple touching the back of the ball.
Did temperature change the wear volume?
Not much: 0.030 mm³ at room temperature and 0.032 mm³ at 800 °C. The wear mechanism, however, was very different.
What wear mechanisms were observed?
At room temperature, work-hardened debris abraded parallel grooves into the track. At 800 °C an oxide film formed; the softer metal beneath deformed plastically and the oxide exfoliated in flakes.
How did friction differ?
At room temperature the COF stayed below 0.2 for the first minute, then jumped above 0.5. At 800 °C it started high and decreased progressively through the test.
