24th International Colloquium Tribology - January 2024 147 Identification of the Dominant Wear Mechanism in Dry Contacts by Numerical Modeling F. Koehn Research Institute for Innovative surfaces FINO, Aalen University, Beethovenstr. 1, D-73430 Aalen, Germany Investigating the wear behavior of sliding contacts is of paramount importance in numerous industrial applications. A promising approach is focusing on the two-dimensional cross section profile of the wear scar, particularly emphasizing the resulting geometric shape. For this purpose, two mathematical limit cases for wear mechanisms are developed. A third-body-driven process, in which a two-dimensional load occurs constantly during the wear process. Here it is assumed that a homogeneous removal takes place over the contact area due to abrasion particles. In the second process the stress is not homogenous. Here it is assumed that due to particle displacement from the frictional contact, stress occurs excessively at the outer edge. In each case, a characteristic cross-sectional area is created by multichannel analysis, considered that the contact area changes during the wear process. The investigated friction pairings are characterized by both sub-processes. The width and area of the cross-sectional geometry of the generated wear scar are determined in order to identify the respective fractions of the wear mechanisms of a friction pairing that occur. These data are then used to normalize the mathematical models. In this way, they can be offset against each other and the proportion of the processes occurring can be determined. The application of this method allows the comparison of wear scars of different specimens and testing parameters. By using this method, it is possible to quickly and reliably determine which of the investigated wear mechanisms is predominant. Therefore, important conclusions about the role and behavior of wear particles in the investigated friction contact can be drawn from the results. The contact pairs studied comprise flat ceramic wear resistant coatings (Tungsten Carbide Cobalt coatings manufactured by High Power Impulse Magnetron Sputtering (HiPIMS)) with varying surface roughnesses and spherical counterbodies (CB) made of steel (100Cr6). By comprehensively analyzing the geometric features of the wear scar, valuable insights can be gained into the underlying wear mechanisms and the tribological behavior of the sliding interface. Moreover, this investigation aims to examine the influence of the presence or absence of wear particles within the contact. The experimental method involves conducting controlled sliding tests while monitoring the resulting wear scars with optical and interferometric measurements. Subsequently, a precise two-dimensional cross-sectional profiling technique is employed to obtain detailed geometric information from the wear scar. The obtained data is then analyzed and correlated with the operating conditions and the presence of wear particles. The findings from this study have significant implications for understanding the wear processes and enhancing the performance of dry sliding contacts operating under high loads. The analysis of the geometric cross-sectional shape of the wear scar provides crucial information about the effectiveness of the wear-resistant coatings and the presence of wear debris in the contact. Such knowledge can contribute to the development of improved wear protection strategies and the optimization of materials and surface treatments. 1. Introduction Surfaces in direct contact with a friction partner are subjected to significant stresses, particularly in the absence of lubrication. Wear processes, including mechanical, chemical, and thermal actions, occur under varying ambient conditions [1] . Upon initial wear, the formation of particles occurs, either expelled or trapped between the friction partners, significantly influencing the wear behavior [2] . Applying hard coatings, like nitrides (e.g., TiN, TiAlN, MoN) [3] and carbides (e.g., WC) [4] , is a standard wear reduction method. Microstructuring surfaces to trap particles in cavities also minimizes abrasion [5,6] . Wear of component surfaces is pivotal economically, environmentally, and functionally. Understanding wear processes aids in generating models for optimizing surface properties and lifespan. Manual wear analysis predominates, but computer model approaches also exist, necessitating large databases. This work presents an experimental method for qualitative assessment of wear-resistant coating lifespans with minimal data. Diverse industrial methods manufacture hard coatings, each influencing surface wear behavior differently and providing a wide range of coating thicknesses [7] . The maximum wear depth in a tribological contact effectively describes the coatings wear resistance lifespan, with failure occurring when the wear depth equals the coating thickness. Adapting coatings to external conditions and CBs is crucial, as is the role of surface topography and microstructures in reducing friction and wear by capturing and removing abrasive particles from the tribological contact. This study investigates the cross-sectional geometry of wear scars in hard coatings after tribological stress, aiming to quantify wear mechanisms without lubrication. Understanding the wear process facilitates adapting coatings to external loads, extending their lifespans. 2. Experimental Details Thin WC(Co) films are deposited on high-speed steel substrates (1.3343) with different surface roughnesses via magnetron sputtering using a 5-6 at. % cobalt binder. The smooth or textured surfaces are deposited on high-speed steel substrates. Friction and wear analysis is conducted using a SRV3 tribometer under dry conditions with spherical 100Cr6 steel CBs. The wear track’s topography is examined with Zygo ZeGage. Wear track shapes, including Uor W-shapes, are identified, affecting the coating’s lifespan. 148 24th International Colloquium Tribology - January 2024 Identification of the Dominant Wear Mechanism in Dry Contacts by Numerical Modeling 3. Methods The surface topography, obtained through white-light interferometry, allows the extraction of a wear track’s cross-section. Figure 1 illustrates two instances: a wear track on a rough (top) and a smooth (bottom) surface. The extracted profiles serve as the initial data for further analysis. Figure 1: Profiles of wear scars with different geometric shapes. The tribotesting is performed perpendicular to the surface structure. The cross-sectional profile extracts in the x-axis over a range of 834-µm and 1024 data points. The respective height is depicted in the y-axis. The model is created from the measured data as follows. Isolation: The wear scar is automatically isolated from the non-loaded sample by an algorithm. Data extraction: Area, width and maximum depth of the wear scar are determined. Model creation: CB abrasion alters the contact geometry, causing continuous changes. The CB’s surface experiences planar abrasion, leading to a continual shift in the contact area with more cycles. V CB represents the missing volume, signifying the removed spherical cap from the CB, with ‘r’ as the spheres radius and ‘a’ as the caps radius. Using a Taylor series we can simplify this to to describe the contact area with 2*a. Subsequently, limit cases of the wear mechanisms are created for each cycle by means of multichannel analysis. In one case, constant, laminar wear over 2*a is assumed (U-shape). In the other limit case, only a boundary load is assumed (W-shape). The constant change of a results in different geometries (Figure 2). Quantification: The models are proportionally calculated with each other, and the resulting geometries are compared in the integral with the isolated wear track. The ratio whose integral shows the greatest correlation with the measured area provides information about the proportions of the respective wear mechanisms. Figure 2: Top left: unedited Profile, top right: isolated profile, bottom: W-shaped and U-shape models with the same width an area. 4. Results and Conclusions It was possible to develop a tool that can perform an analysis of the underlying wear mechanisms in particle-delivering, unlubricated friction contacts by means of a small amount of data. The finding of a percentage ratio and the minimum in height, allows conclusions to be drawn about the influence of a wear mechanism on the lifetime. In the case of the specimens studied, it can be obtained that the W-ratio is three times higher for smooth specimens than for unstructured specimens. A possible explanation for this is that emerging particles are prevented from moving outward by the microstructure. References [1] K. Kato in Wear - Materials, Mechanisms and Practice (Hrsg.: G. W. Stachowiak), Wiley, 2005, S. 9-20. [2] M. Godet, Wear 1984, 100, 437. [3] R. Gopi, I. Saravanan, A. Devaraju in Lecture Notes in Mechanical Engineering (Hrsg.: I. A. Palani, P. Sathiya, D. Palanisamy), Springer Nature Singapore, Singapore, 2022, S. 803-811. [4] N. Singh, A. Mehta, H. Vasudev, P. S. Samra, Int J Interact Des Manuf 2023, 31, 598. [5] C. Gachot, A. Rosenkranz, S. M. Hsu, H. L. Costa, Wear 2017, 372-373, 21. [6] T. Sube, M. Kommer, M. Fenker, B. Hader, J. Albrecht, Tribology International 2017, 106, 41. [7] F. Köhn, M. Sedlmajer, J. Albrecht, M. Merkel, Coatings 2021, 11, 1240.