Microstructure Influence on the Dry Sliding Wear Behavior of Cr2O3–nTiO2 APS Coatings

Cr2O3-based ceramic coatings are widely used in wear-critical applications; however, their tribological performance under dry sliding conditions can be limited by brittleness and frictional instability. In heavy-duty vehicles, the king pin–bushing contact operates under severe dry sliding conditions, motivating the investigation of composite Cr2O3–nTiO2 coatings as a potential surface engineering solution. In this study, Cr2O3–TiO2 coatings containing 0, 10, 20, 30, and 40 wt% TiO2 were deposited by atmospheric plasma spraying (APS) from mechanically mixed powders. Phase composition was analyzed by X-ray diffraction using an X’Pert PRO MRD diffractometer, while microstructure and elemental distribution were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) on a FEG Quattro C microscope. Mechanical properties were evaluated by Vickers microhardness, instrumented indentation and scratch testing, while dry sliding wear behavior was assessed by pin-on-disc tests performed on a CETR UMT-2 tribometer against a bronze counterbody, with continuous monitoring of the coefficient of friction (COF). The results show that plasma spraying produces lamellar composite coatings with intrinsic porosity and locally modified phase composition. Cr2O3-rich coatings exhibit higher hardness (1198 HV2 compared with 877 HV2 for Cr2O3–40TiO2 corresponding to an increase of approximately 36%) and improved resistance to indentation, reflected by lower penetration depths and higher elastic modulus values (134 GPa for S0 compared with 77 GPa for S2). These coatings also exhibit a more stable friction response and reduced material transfer from the bronze counterbody, as confirmed by the lower mass loss of the pins (0.0295 g for S0 compared with 0.0473 g for S4, corresponding to a reduction of about 38%). Increasing TiO2 content leads to changes in friction stability and wear behavior associated with microstructural heterogeneity. These findings indicate that the sliding wear performance of Cr2O3–nTiO2 coatings is governed by elastic–plastic stability under localized contact loading and support their applicability for dry sliding king pin–bushing systems in heavy-duty vehicles.