Coatings play a crucial role in engine valve train components, reducing friction and wear to enhance engine efficiency and longevity. Common coatings in internal combustion engines include Diamond-Like Carbon (DLC) and Hard coatings, all of which improve tribological performance. These coatings are vital for valve trains, which face high stress and temperature variations. Deposition techniques like Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), and Plasma-Assisted Chemical Vapor Deposition (PACVD) influence coating performance. DLC coatings, often metalloid-doped, are noted for their low friction and high hardness. Hard coatings excel in wear resistance and friction reduction. This review brings together experimental findings on tribological coatings for engine valve train components, focusing on materials, deposition methods, testing conditions, and performance metrics. It highlights the best coatings for reducing wear and friction, ultimately enhancing the performance of internal combustion engines. Among the coatings evaluated, Chromium Nitride with Tungsten Carbide/Carbon (CrN + WC/C) stood out. This coating significantly reduced friction torque at low to moderate rotational speeds (with reductions of 20%–30% at 800 rpm and 1400 rpm) and maintained this reduction at high speeds (30% reduction at 2000 rpm). Additionally, under high load conditions, the CrN + WC/C coating achieved a remarkable 75% reduction in mean friction torque (reducing it from 4 to 1 Nm at both 800 and 2000 rpm). These tests were conducted using SAE 10W-30 oil at 80°C. The consistent performance of CrN + WC/C across varied conditions makes it the superior choice. CrN + WC/C coatings optimize the efficiency and longevity of valve train components by reducing friction, wear, and maintenance needs, significantly enhancing engine system reliability.
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