Review on Adhesion Strength between Coatings and Substrates : Influencing Factors, Adhesion Mechanisms, and Evaluation Methods

Adhesion strength between coatings and substrates is a fundamental property. It determines the reliability, durability, and performance of coated materials in engineering applications. Coating technologies are widely used in semiconductors, displays, automotive, energy, and biomedical industries. However, there is still no universally accepted method to evaluate adhesion strength. This review examines the key factors that influence adhesion, such as surface energy, contact angle, interfacial chemistry, and microstructure. It also classifies adhesion mechanisms into mechanical interlocking, interdiffusion, and compound layer formation. Evaluation methods are critically compared. Adhesive-based tests, such as lap shear, pull-off, and tensile adhesion, are standardized by ASTM and ISO. They provide quantitative values but are limited by the strength of the adhesive itself. In contrast, adhesive-free methods, including scratch, indentation, and peel tests, can directly reveal interfacial failure modes, but their outcomes are markedly influenced by test parameters and specimen preparation. Consequently, no single method can comprehensively characterize adhesion strength. Therefore, a complementary approach using multiple methods is recommended. Reliable evaluation also requires careful specimen preparation, strict compliance with standards, and the use of auxiliary diagnostics such as acoustic emission and microscopy. This review provides researchers and engineers with a clear framework for standardized and reliable evaluation of adhesion strength between coatings and substrates.