Tribological performance and thermal stability of different coated piston rings under simulated fired top dead centre conditions in internal combustion engines

This study compares the tribological performance, thermal stability, and damage evolution of piston rings with chromium–aluminium oxide ceramic (C1), chromium–microdiamond (C2), and chromium nitride (C3) coatings on cast iron (S1), cast steel (S2), and stainless steel (S3) substrates under simulated fired top dead centre conditions. A TE77 linear tribometer and original engine components were used with quasi-continuous lubrication (TS1) and discontinuous lubrication (TS2) to determine seizure limits, temperature responses, friction, and damage progression. C3/S3 achieved the highest mean seizure limit under TS1 (16.7 MPa), whereas C2/S2 performed best under TS2 (21.5 MPa). Near-surface measurements indicated system-dependent near-surface temperature responses: S1 systems exhibited higher piston-ring temperatures and lower contact-near liner temperatures than S2 systems, together with slightly lower coefficients of friction. Thermal cycling and controlled-stop tests showed earlier crack formation for C1, delayed cracking for C2, and no visible cracking for C3/S3 under the tested conditions. By expanding the previously investigated single reference system to five industrial coating–substrate combinations and introducing a discontinuous lubrication scenario, this study provides new comparative evidence of system-dependent seizure resistance, thermal response, and damage evolution.