Fretting wear of multilayered (Ti,Al)N/TiN coatings in air of different relative humidity

Physical vapour deposited multilayered (Ti,Al)N/TiN coatings of different s ublayer thicknesses were investigated and compared with monolayered (TI,AI) N and TiN coatings. Mechanical characterisation was done using a depth sens ing nanoindenter. Hardness and elastic modulus of multilayered coatings are higher than those of monolayer (Ti,AI)N coatings and sometimes comparable to TiN coatings. The mechanical properties of multilayered coatings depend upon the ratio of the thickness of (Ti,Al)N and TiN sublayers. Friction and wear were investigated in unlubricated fretting tests performed in air of different relative humidity. Multilayered (Ti,Al)N/TiN coatings show an imp roved fretting wear resistance compared to monolayer (Ti,Al)N coatings and at some fretting conditions the wear is comparable to TiN coatings or even better. A linear relationship between wear volume and dissipated energy was noticed for (TI,AI)N and multilayered (Ti,AI)N/TiN coatings, but a large d ependency upon the relative humidity was observed in contrast to TiN coatin gs. An explanation is put forward based on an evolving tribochemical intera ction between the debris formation and the surrounding atmosphere. (C) 1999 Elsevier Science S.A. All rights reserved.