Effect of Loading-System Inertial Mass on Friction and Wear of TiAlN-Coated Steel under Unidirectional Sliding

Tribological behavior is determined not only by material properties and nominal testing parameters but also by the dynamic characteristics of the tribometer. Loading-system inertial mass may influence contact stability, surface evolution, friction, and wear even when nominal load and sliding conditions remain unchanged. This study investigates the effect of loading-system inertial mass on the wear behavior of TiAlN-coated steel. Dry ball-on-disc unidirectional sliding tests were conducted using TiAlN-coated steel discs against 3 mm diameter Si₃N₄ balls under a normal load of 7 N. Four loading-system inertial masses (0, 0.5, 2.5, and 4.5 kg) and four sliding radii (5.5, 7.0, 8.5, and 10 mm) were systematically distributed among four discs to improve reproducibility and minimize the influence of sliding radius. The linear sliding speed was maintained at 0.2 m/s. Each test lasted 2500 s, consisting of five 500-s steps, with a total sliding distance of 500 m. The coefficient of friction (COF) was continuously recorded. Wear volume was measured using a Bruker Contour GT-K0+ three-dimensional optical profilometer, while worn surfaces were analyzed by SEM/EDS and XRD. Loading-system inertial mass considerably affected both friction and wear. The 2.5 kg condition produced the lowest specific wear rate and COF, whereas the 0 kg condition resulted in the highest values. At 0 kg, extensive surface degradation involving fatigue wear, tribo-oxidation, material transfer from the counterbody, and abrasion resulted in severe coating destruction and exposure of the underlying steel substrate. In contrast, the 2.5 kg condition showed substantially less damage, with mild abrasion as the predominant wear mechanism and evidence of self-repair behavior. The results demonstrate that loading-system inertial mass significantly influences friction, wear, and surface degradation under comparable unidirectional sliding conditions, highlighting the importance of considering tribometer dynamics when interpreting laboratory wear-test results.