The influence of substrate material and hardness on the fretting behaviourof TiN

TiN is used industrially as a coating resistant to sliding wear. However, i ts importance as an anti-fretting wear coating is less certain. In this pap er, we report on the fretting wear behaviour of a TIN coating and the effec t substrate properties have on it. The substrate materials used were three ferrous alloys (188 to 674 HV), a titanium alloy (Ti6Al4V) and an aluminium alloy (ASCM20). A TiN coating, thickness 1.6 mu m, was applied using the a re-ion plating process. Crossed-cylinder fretting tests were carried out on both coated and uncoated specimens, without external lubrication, at a fre quency of 10 Hz. Relative strokes from 15 to 138 mu m and normal forces fro m 1.4 to 22.7 N, that is, initial Hertzian contact stresses from 301 to 116 0 MPa, were used. Each test involved a single substrate material. Substrate hardness had a marked effect on the number of cycles at which breakdown of the TiN coating occurred, breakdown occurring earlier on the lower hardnes s substrates. More unexpectedly, the effect of the coating, after breakdown , was also substrate dependent. For the ferrous substrates, the coating had almost no effect on post-breakdown wear, and neither did the substrate har dness. In contrast, for both the titanium and aluminium alloy substrates, t he coating affected beneficially post-breakdown fretting wear. This behavio ur is interpreted qualitatively in terms of the stresses in the TiN coating and substrate, and from EPMA analysis of the wear scars. (C) 1999 Elsevier Science S.A. All rights reserved.