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.