Friction and wear in different engine components have crucial effects on the engine performance, combustion efficiency, oil consumption and lifetime of the internal combustion (IC) engine. Under certain loads, speeds, and temperatures, the metallic components of the IC engine, especially the piston and valve system suffer from a higher friction. Thin film coating is one of the novel techniques to reduce the frictional forces and improve the mechanical properties of engine components. Due to some versatile tribological properties, increasing attention has been paid to the physical vapor deposition (PVD) technology in the recent decade to deposit thin film coating on engine components. This article presents a comprehensive literature review on thin film coatings for IC engine components deposited by PVD technique. Issues related to tribological properties (wear and coefficient of friction) and mechanical properties (hardness and roughness) are also highlighted. Scientific improvements are presented in the light of literature. It is revealed that PVD coating is significantly effective on wear resistance, scuffling resistance, surface roughness, and friction of the components in IC engine. Laboratory test and data from actual service so far suggest that the plasma-activated electron beam evaporation coating is perhaps one of the best choices for smooth surface finishing with improved mechanical and tribological properties. However, there are still some problems in its practical usage. This compressive review paper presents the major shortcomings of PVD coatings on IC engine components and the possible solutions if any. Finally, a number of issues have been reported which need to be encountered for further studies.

The adhesion between coating-substrate systems is an important factor in determining the performance and durability of coated engineering components. This paper reviews the microstructures and adhesion strength of titanium nitride (TiN) coating produced using two different processing methods: chemical vapor deposition and physical vapor deposition. Three methods to evaluate the adhesion strength of the coatings, namely the indentation test, laser spallation technique, and scratch test are presented and discussed in terms of their working principles, their advantages and disadvantages. The extrinsic and intrinsic factors influencing the adhesion strength of coating-substrate system, particularly for TiN coating, are also elaborated. The mechanisms and modes of coating failures in adhesion evaluation techniques are discussed with respect to the variation of coating-substrate system combination such as brittle, ductile, soft, and hard. Possible improvements on the adhesion strength of coating-substrate systems, focusing on the processing methods, compositions, and structures of coatings, are also reported.