Effect of variable normal force and frequency on fretting wear response of Ti–6Al–4V contact

Fretting wear damage is one of the major problems in turbojet compressors. In conventional fretting test investigations, the normal force is usually imposed constant whereas contact displacement oscillates. The real blade-disk contact is in fact much more complex: both normal force and relative sliding vary during the cycle. Hence, a new fretting wear system has been developed where the relative sliding evolution can be controlled and the normal force varied, and which includes a contact opening stage during the loading cycle. The wear processes and wear kinetics under constant and variable normal conditions have been investigated. We demonstrate that variation in the normal force and the contact opening sequence significantly modify the wear process. Another result of the normal force variation is that the dissipated energy decreases. In addition to the complex influence of the variable loading spectrum, the influence of frequency is investigated. It is shown that the formation of a titanium nitride layer previously observed in a constant normal force contact, which is related to limited oxygen diffusion inside the contact, no longer takes place in a contact opening situation where the fretting wear damage process is mainly controlled by an oxidation process.