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Tribological conditions in bulk metal forming processes are characterized by high contact pressures and large relative movements at high velocities between the tool and the workpiece. In addition, significant surface enlargements and elevated temperatures can occur. It is very challenging to reproduce such contact conditions on pin-on-disc tribometers. In this study, a method for simulating the contact conditions of a metal forming process on a pin-on disc tribometer is presented. Special test samples have been designed in order to achieve high contact pressures and surface enlargements with a homogeneous distribution of these quantities within the contact zone. It is shown that the test method delivers reproducible results and enables the detection of small changes of the contact conditions. Furthermore, microstructural changes of the real contact surface can also be simulated, which was verified by SEM imaging. [ABSTRACT FROM AUTHOR]

It is generally known that gaseous atmospheres can significantly affect the friction and wear behaviour of non-lubricated contacts; however there still exists a lack of knowledge on the subject, since the tribological behaviour and the tribochemistry of the gas-lubricated systems are highly sensitive to the selection of the operating parameters, and the results from available literature are often scattered and sometimes even contradictable. This study was focused on the identification of the friction and wear mechanisms of technical gases used at atmospheric gas-pressure in non-lubricated DIN 100Cr6 (AISI 52100) bearing steel contacts at severe operating conditions (high-frequency oscillation at high contact pressure). Argon (Ar), nitrogen (N 2 ) and carbon dioxide (CO 2 ) were used as gas atmospheres and air atmosphere was used as a reference. The gases are analysed in terms of their chemical reactivity with the steel surfaces and a correlation between the properties of different tribochemical products and the observed friction and wear mechanisms is made. In N 2 and CO 2 atmospheres, wear was significantly lower than in air atmosphere, with a wear reduction comparable to the effect of using a liquid lubricant. In N 2 atmosphere, a slightly higher friction was measured than in air atmosphere, while in CO 2 atmosphere, friction was 60% lower than in air atmosphere. In Ar atmosphere, both friction and wear were slightly higher than in air atmosphere. With X-ray photoelectron spectroscopy (XPS) of the wear particles, it was observed that the concentrations of different tribochemical products and their mutual ratios critically determine the friction and wear behaviour of the non-lubricated steel contact. [ABSTRACT FROM AUTHOR]