TRIBOSCOPY - A NEW QUANTITATIVE TOOL FOR MICROTRIBOLOGY

Knowledge of the degradation of a sliding interface under friction is a major goal in tribology. This study can be stated at different length scales. In microtribology, it is natural to explore the micron and submicron scale. In this paper we present a new experimental technique and describe a way of extracting significant information from the data. Starting from the basic idea that wear is time dependent and occurs at a microscopic scale, a new approach has been developed, named triboscopy. This technique results from the coupling of a reciprocating tribometer and a numerical imager. During the N successive sliding cycles, the friction force F(t) and the electrical contact resistance R(c) are measured and stored. Therefore, we can build two numerical images F(t)(x,N) and R(c)(x,N), giving the evolution of the physical measurement as a function of both position x and number N of cycles. This technique provides the unique possibility of locating microscopic events and studying their evolution during the test. A triboscopic image contains qualitative and quantitative information. The two images produced in one test are complementary and must be interpreted simultaneously. In a first application, we present the degradation of a polymeric layer deposited on a grooved substrate. We show how to recognize the emergence of substrate asperities and the circulation of debris at the interface. In a second application, we give the results obtained on a diamond-like carbon hard coating deposited on an aluminium alloy substrate. We provide evidence for the presence of initial defects in the layer, and describe in detail their spatial evolution during the test.