Coating adhesion evaluation by nanoscratching simulation using the molecular dynamics method

By using a molecular dynamics method, a computer simulation of a scratch test on bilayer thin films on a nanometer scale has been performed. In the present simulation, the substrate and thin-film material are TiN or SiO2 and Al or Cu, respectively. The indentor is assumed to be a perfect rigid body, and the Morse potential is utilized as the interaction between the indentor and a specimen atom. The extended Tersoff potential is assumed as the interaction between specimen atoms. Results indicate that the standard deviation of the friction constant becomes maximum when the scratching load is critical to spalling. The critical loads obtained by the present simulation and actual experiments do not match quantitatively. In contrast, the maximum standard deviation reproduces the spalling strength evaluated from actual experiments. On the basis of this finding, a new evaluation technique for adhesion strength using a nanoscratching test is proposed.