Evaluation of the adhesion strength using digital microscope and international standards

The most frequently used method for scratch test in the international standards is progressive loading scratch test mode. Although the mentioned standards to measure practical adhesion of nano and micro thin films require optical microscope with magnifications between 100× and 500×, not only the optical microscopes, but even the international standards are not usually and largely used to study new biocompatible thin films. The authors designed a method and a custom-written program for the measurement and evaluation of scratches using digital microscope and digital microscope image analysis, which is based on the requirements of international standards for the determination of critical normal forces and capabilities of existing scratch testers. The proposed procedure and software were tested on the samples of TiN, Au, Pt and Pd biocompatible nano-thin layers. Delamination or loss of adhesion was observed in all cases, and two types of critical normal forces were determined. It was found that the calculated critical normal forces are largely similar in the three operations of the measurement of a sample. Thus, evaluation using critical scratch loads measured by three test operations seems to be sufficient. The new software and procedures allow us to evaluate the practical adhesions of a wide range of substrate and thin film materials, and gave us credible results.