# The Reflection Coefficient |r| as a Nondestructive Measure of the Coating Adhesion to a Steel Substrate

## TL;DR

This paper introduces a nondestructive method using the reflection coefficient |r| to measure how well coatings stick to steel substrates.

## Contribution

The study demonstrates that ultrasonic reflection coefficient |r| can estimate coating adhesion without damaging the material.

## Key findings

- Glass-beading surface preparation resulted in the best coating adhesion.
- Reflection coefficients between 0.61–0.83 corresponded to mechanical adhesion of 1.75–4.56 MPa.
- The method allows nondestructive evaluation of coating adhesion based on ultrasonic measurements.

## Abstract

The main property of a steel substrate is the adhesion of its coating, which determines the quality and durability of the adhesive joint. The main objective of the research presented in this article is to evaluate the adhesion of coatings to substrates based on ultrasonic measurements and the determined reflection coefficient |r|. An experiment was carried out on disc samples, not only for ultrasonic measurements but also for the evaluation of the mechanical adhesion of coatings to substrates using the pull-off test. Three different methods of surface preparation of the samples were used: glass beading, surface treatment with P400 sandpaper, and the laser beam treatment. Based on the results, it was found that the best adhesion was obtained for samples with surfaces prepared by the glass-beading process. Reflection coefficient values in the range of 0.61–0.83 corresponded to mechanical adhesion in the range of 1.75–4.56 MPa. The results of the tests provide an important reference for the nondestructive evaluation of coating adhesion to substrates and allow for the estimation of mechanical adhesion based on the values of the reflection coefficient |r|.