Ridha Mnif

Analysis of friction, wear and oxidation behaviour of X40CrMoV5/Fe360B steel couple in an open-sliding contact

In hot-forming processes, the interface tool/product is important for the quality of the finished product surfaces. Consequently, it is important to better understand the phenomena, namely, oxidation, which occurs at the interface between tool and sheet in this kind of process. It is in this context that an experimental program was conducted to analyse friction, wear and oxidation behaviours on the tribological performance of the combination of tool and sheet. A high-temperature pin-on-disc tribometer, with an original open-sliding contact, was used. Pins, representing tools are X40CrMoV5 high-alloyed steel, and discs, representing drawing products, are Fe360B steel plates (EN 10025–S235JRG2). The friction and wear study of the combination was carried out at temperatures ranging from ambient (room temperature) to 800℃ and within a normal load range of 35–140 N. Regarding oxidation effect and wear mechanisms, they are examined and characterized by scanning electron microscope and energy-dispersive X-ray spectrometer. As for the experimental results, they showed that the increase in temperature involves the decrease in the friction coefficient due to the oxide scales for all the tests. Pre-oxidized discs are also tested. It was found that the wear process is characterized by an adhesive wear with a transfer of oxides on the pins.

Tribological failure analysis of ball valve seals

The ball valve seals are exposed during their use to thermal gradients (alternating the flow of cold and hot water), static loading (clamping force) and cyclic loading (alternating opening and closing) which can be sources of valve failures. The ball valves usually fail as a result of different failure modes such as wear, plastic deformation and corrosion. In order to describe these modes a failed ball valve which was belonged to a sanitary installation is investigated. The investigation of the failure was carried out by using several experimental tests including optical microscopy and Scanning Electron Microscopy (SEM). Tests were performed on a specific reciprocating tribometer for ball valve seals application. Experimental results revealed that the friction behaviour of polymeric seal depends strongly on the clamping load of seal and the manipulation frequency of counterface ball. Optical microscope observation of the worn surface showed that strong adhesion of the polymeric transfer layer to the counterface ball.