Study of the tribologically transformed structure created during fretting tests

In fretting, without a lubricant, structures fail through wear involving de bris. Various metallographic assessments show that this debris creation der ives from a special structure, hereafter called the "tribologically transfo rmed structure" (TTS). The latter is nucleated at the very beginning of a c ontact's life, and eventually masks the initial material's tribological beh aviour. This TTS is very hard and brittle, and is quickly destroyed, which explains why TTS is rather difficult to observe. This study focuses on init iation mechanisms which, up to now, are still highly controversial. Large a mounts of TTS are observed after fretting tests, which is the reason why th ey were chosen as the means of investigation. In this paper, the various po ssible creation mechanisms for TTS will be analysed. From this overview, tw o nucleation models are chosen: one is based on "mechanical alloying" consi derations, and the other is linked to high-strain-recrystallisation phenome na. Transmission electron microscopy (TEM) investigations are used to check these assumptions. (C) 2000 Elsevier Science Ltd. All rights reserved.