Analysis of the running-in of thermal spray coatings by time-dependent stribeck maps

Abstract

As thermal spray coated cylinder surfaces eliminate the need for cast iron sleeves or hypereutectic AlSi alloys, these coatings are becoming the main cylinder liner technology. Moreover, it has been found that these coatings also lead to low friction and wear. The reason for improved tribological performance is believed to result from a nanocrystalline layer that forms in the sliding contact. In this paper, we use on-line wear measurement to study the dynamics of the running-in process. A pin-on-disk tribometer coupled to a radionuclide wear measurement (RNT) system was used to investigate the friction and wear behavior of wire arc spray (LDS) coatings sliding against chromium coatings under lubricated conditions. After the friction experiments, X-ray photo electron spectroscopy (XPS) and Focused Ion Beam analysis (FIB) was used to characterize the worn surfaces. By introducing a time-dependent Stribeck plot, we analyzed running-in under constant and transient sliding c onditions and observed a strong reduction of friction in the boundary lubrication regime. Wear rates of the LDS disks as well as of the chromium plated pins are ultra-low. XPS revealed carbon diffusion at room temperature in wear tracks of disks that showed a very low coefficient of friction (CoF) of 0.01, whereas this carbon diffusion could not be detected in the wear track of a disk without running-in, i.e. a final CoF of 0.12. As this is the most significant difference found between differently run-in systems, the described carbon diffusion might be relevant for the observed friction behaviour. Running-in behaviour can only be discussed in terms of friction, as, even with RNT, no significant wear could be measured. The comparison of running-in under transient and constant conditions showed only minor differences in the final friction behavior

Lubricated friction behaviour of thermal spray steel coated cylinder bores studied using a long-stroke reciprocating tribometer

“…The EHL regime could be replicated under laboratory conditions using high-speed tribometers. An examination of the laboratory-scale tribological tests in the open literature indicates that tests at sliding speeds >1.0 m/s could be achieved using the tribometers operating under unidirectional sliding contact configurations (Linsler et al , 2017; Biberger and Füßer, 2017). However, they may not address the effects of instantaneous speed variations on the COF.…”

Atomistic Insights Into Lubricated Tungsten/Diamond Sliding Contacts

“…Indeed, diamond particles are added to tribological coatings sliding against steel in order to reduce friction and improve wear resistance (Wang et al, 2005;Venkateswarlu et al, 2009;Kim et al, 2011;Yin et al, 2017). For instance, piston rings used in diesel engines showing superior tribological performance employ galvanic chromium coatings that are filled with microscale diamond particles (Kennedy et al, 2014;Linsler et al, 2017). Therefore, since piston rings slide against metallic cylinder liners, the fundamental tribological mechanisms governing friction and wear in lubricated metal/diamond contacts are not only of academic (Mehan and Hayden, 1981) but also of industrial interest (Esser et al, 2004).…”