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International audience; 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 37.3 GPa independently of the film thickness and in a good accordance with literature data regarding the diamond hybridization sp3/sp2 ratio.

The present study has been conducted in the objective of obtaining chromium carbide layers using a conversion treatment involving three main steps: 1) carburizing treatment in order to increase the amount of carbon atoms at the steel surface, 2) deposition of a pure chromium thin layer using electrolytic method and finally, 3) annealing treatment used for carbon diffusion and carbide formation until complete transformation of chromium layer. Depending on the treatment temperature, partial or complete conversion is obtained as a result of the diffusion process. The role of the annealing temperature on transformation rates of chromium into chromium carbide films was investigated. It is shown that for 1 h of treatment the layer is totally transformed at 1100 °C. Hardness and adhesion of layers produced were found to increase whatever the annealing treatment even for partial transformation at the lower annealing temperatures.

International audience; Diamond thin films are used to increase significantly the life time and to improve the performance of cutting tools. However, one the most important limitations to their industrial development in the case of severe mechanical conditions is their limited adhesion to the substrate. To improve the adhesion strength of the deposited diamond film on its substrate, several approaches have been suggested in literature with a relative success. For WC-Co substrates, one interesting approach consists in the neutralization of the cobalt element at the surface of the substrate by the use of a chemical agent. This methodology leads to a roughening of the surface that increases the contact area between the film and the substrate as well as the mechanical anchoring at the interface. The objective of the present paper is to study the conditions of substrate preparation as well as the conditions of deposition on the microstructure and hardness of the produced films. Diamond thin films of thickness ~ 1.5 μm were deposited on substrates made of Tungsten carbide-Cobalt submitted to different heating temperatures. The coated systems were characterized by means of physical and mechanical tests. Observations by Raman spectroscopy and scanning electron microscopy analysis confirm the good quality of the obtained diamond films. Hardness results deduced from classical indentation tests have been analyzed by means of models allowing the separation of the substrate influence on the hardness measurement. In these conditions the hardness of the diamond films was found close to 40 GPa thus confirming their excellent mechanical properties.