eJournals International Colloquium Tribology 23/1

International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231

The Identification of an Adequate Stressing Level to Find the Proper Running-In Conditions of a Lubricated DLC-Metal-System

125
2022
Joachim Faller
Matthias Scherge
ict2310409
23rd International Colloquium Tribology - January 2022 409 The Identification of an Adequate Stressing Level to Find the Proper Running-In Conditions of a Lubricated DLC-Metal-System Joachim Faller Fraunhofer IWM MikroTribologie Centrum, Karlsruhe, Germany Corresponding author: joachim.faller@iwm.fraunhofer.de Matthias Scherge Fraunhofer IWM MikroTribologie Centrum, Karlsruhe, Germany 1. Introduction Until today there is no straightforward method to achieve a proper running-in of a tribological system (except for trial-and-error) [1,2]. This contribution therefor presents an analysis of a lubricated DLC-metal-system. Initial experiments served to identify the critical stressing levels, this means critical normal forces and/ or sliding velocities that trigger significant responses of the friction and wear signal. These stressing levels are called key levels and were used to construct a dedicated running-in procedure. 2. Methods Experiments were conducted on a pin-on-disk using a flat pin made from iron-plated aluminum and a DLC coated steel disk. The wear behavior was determined with a radionuclide wear measuring unit using a radioactively marked pin. The lubricant (fully formulated engine oil) was applied continuously to the disk. The experimental conditions are stated in table 1. Table 1: Experimental conditions parameter set point unit oil temperature 80 °C velocities 0.5-4.2 m/ s applied load 500/ 700/ 900/ 980 N nominal pressure 26/ 38/ 48/ 52 MPa level duration 4 h 3. Results and Discussion Starting with an initial parameter field covering the velocity-pressure-plane (see figure 1) leads to an overall linear wear behaviour and significant decrease in COF during the single stress levels. The identified key levels were combined to a new parameter field (figure 2) starting with high pressure and low velocity in order to achieve a high-power stressing of the tribological system. With this procedure, the significantly higher initial wear rates (150 nm/ h) were reduced to around 5 nm/ h after running-in along with a decrease in COF to 0.02. Figure 1: Initial parameter field with COF (green), wear (black) and linearized wear rate (yellow) High-power stressing leads to a degressive wear behavior. High wear rates at the beginning are linked to a topographical running-in, while the slow decrease in COF with small wear rates is caused by tribo-chemical running-in. The latter is closely related to third body formation. In order to achieve a successful running-in, high initial stress proves to be advantageous. Figure 2: Derived parameter field with COF (green), wear (black) and linearized wear rate (yellow) 410 23rd International Colloquium Tribology - January 2022 The Identification of an Adequate Stressing Level to Find the Proper Running-In Conditions of a Lubricated DLC-Metal-System References [1] Dowson, D.; Taylor, C.; Godet,M.; Berthe, D. (Eds.) The Running-in Process in Tribology; Butterworth- Heinemann: Oxford, UK, 1982; p. iv. [2] Blau, P.J. Running-in: Art or engineering? J. Mater. Eng. 1991, 13, 47-53.