Influence of the indenter tip defect in classical indentation: Application to the hardness determination of DLC thin films

Abstract

For an accurate determination of the materials hardness, instrumented indentation test is undoubtedly the most adequate technique compared to the classical one. However, numerous laboratories or industries have no access to such instrumented device. Consequently, they have no other alternative methods that the use of classical indentation test. However, this technique can lead to wrong interpretation because it does not allow considering the indenter tip defect.In this paper, we suggest to introduce the indenter tip defect into the classical hardness calculation. The proposed methodology is validated on a diamond like-carbon thin film deposited onto a tungsten carbide. Firstly, the truncated indenter tip defect length is estimated from the indentation size effect observed for the substrates which is attributed to the influence of the indenter tip defect. As a result, the tip defect is found to have the same value independently of the tested samples. Afterwards, the tip defect length is introduced into the composite hardness computation and the model of Jönsson and Hogmark is applied to predict film hardness. As a main result, the film hardness is found equal to 37.3GPa independently of the film thickness and in a good accordance with literature data regarding the diamond hybridization sp3/sp2 ratio.