The size effect on the hardness value of coatings with Vickers indenter

摘要

This work relates to the characterization with indentation of the hard chromium coatings, carried out by electrolytic way on a steel substrate. Steel thus covered is used for the construction of the jacks of industrial machines. We studied in this work the effect of size which can be due to the preparation of surfaces and which it is necessary to dissociate from a real effect of size related to the movements of dislocations for the vicinity of the free face. The effect of size of the print or the effect of load on the value of hardness with the indenter Vickers is thus studied for various preparations of surfaces, on samples polished by various processes and with or without lubrication. It was shown that pleating mainly masks the phenomenon of the effect of load and hardness and that the presence of an oil film enters the indenter and the material to be tested, led to a significant reduction in hardness. When the test of indentation is carried out with the interface of a coating and its substrate, it is possible to obtain a characteristic value of adherence starting from the cracking which generally develops in the plan of the interface. The number of hardness obtained by the test of Vickers indentation depends on the amplitude of the load applied lubrication and polishing before chromium plating.