Fretting Fatigue Behavior of Cu-Al-Coated Ti-6Al-4V

Abstract

Fretting fatigue of a Cu-Al coating deposited on an alumina-gritted Ti-6Al-4V substrate was investigated. Two types of tests were conducted: one series involved fretting fatigue tests at different bulk stress amplitudes under a constant contact load and the second series was run at different contact loads under a constant bulk stress amplitude. The coefficient of friction (COF) was lower on the coated substrate than on the bare substrate before fretting. However, COFs of the coated and the bare (i.e., uncoated) substrates were identical after the exposure to fretting fatigue cycles since fretting fatigue caused wear of the coating. The coating thickness as a function of fretting fatigue cycles was monitored. The coating damage increased as the applied bulk stress amplitude increased. At lower bulk stress amplitudes, the coating damage was gradual and it survived over one million cycles. However, the coating delaminated from the gritted surface and/or caused premature specimen failure at higher stress amplitudes. At the lowest contact load used in the present study, the contact condition was gross slip and the life of the coating was the shortest due to fretting wear. On the other hand, the higher contact loads induced a partial slip contact condition that caused less coating damage, and the coating life increased with increasing contact load. *The views expressed in this article are those of the authors and do not reflect the official policy or position of the United State Air Force, Department of Defense, or the U.S. government