Terahertz Nondestructive Evaluation for Adhesion Properties of Self-Lubricating Sliding Bearing Coatings

The adhesion between self-lubricating coatings and substrates is a crucial indicator for assessing self-lubricating sliding bearing production quality. Poor adhesion exacerbates coating wear. Hence, evaluating the adhesion properties of the self-lubricating coating is essential to ensure the healthy service of bearings in critical applications. However, conventional destructive testing methods for adhesion properties are difficult to consider both of global and local evaluation of self-lubricating coatings, and have challenges in comprehensively analyzing the inhomogeneous adhesion distribution of self-lubricating coating interfaces. In this study, we explore a terahertz nondestructive testing method for evaluating the adhesion properties of self-lubricating bearing coatings. By investigating the propagation of terahertz waves in coating structures, we find that the terahertz reflection can respond to adhesion interface conditions, and mapping the reflection coefficient distribution enables comprehensive visualization of the adhesion interface conditions nondestructively. Furthermore, the adhesion work-derived coefficient based on the scratch test is used to reflect the condition of the adhesion interface. The comparison results demonstrate a strong positive correlation between terahertz reflection coefficients at the adhesion interface and adhesion work-derived coefficients, which indicates that the reflection loss of terahertz waves at the adhesion interface with good adhesion is minor. The proposed method for coating adhesion properties is validated regarding the applicability, which offers a novel evaluation approach for adhesion properties of self-lubricating coatings.