The Influence of Substrates on the Evaluation of Mechanical Properties of CrB Thin Films

Abstract

In this study, the influence of substrate effect on the evaluation of mechanical properties of thin films was investigated by making nanoindentation tests on the CrB thin films on the different substrates. These results show that the critical contact depth/thickness ratio (D/t ratio) for determine the true hardness of the thin films is 0.06, which is smaller than the suggested value of 0.1 by ASTM and UK National Physical Laboratory. In the case hard film on the hard substrate, the tested hardness value decreases with increasing D/t ratio above 0.06 due to the pile-up of film materials next to the indenter. In the case of hard film on the soft substrate, the tested hardness value decreases with increasing D/t ratio above 0.06 because deformation zero extends to the interface and the substrate due to the low hardness value of the substrate. Although the Young's modulus values of the films keep constant below the critical contact depth/thickness ratio (D/t ratio) of 0.06 in this study, they show a great difference with different film substrate systems. These results show the rule that CrB film on the substrate, which has a high Young's modulus, shows high Young's modulus and no clear trend with hardness of substrate is apparent.