Fretting properties of SUS304 stainless steel in a vacuum environment

In this paper the effect of the ambient pressure on the friction and wear of SUS304 stainless steel during fretting at room temperature is described.

The ambient pressure was varied from 10⁻³ to 10⁵ Pa. The experiment was carried out under the following conditions: normal load, 14 N; slip amplitudes, 35 and 110 μm; frequency, 8.3 Hz; number of fretting cycles, 6 × 10⁴.

The relationship between the frictional behaviour and the number of cycles is affected by the pressure. The coefficient of friction at steady state increases with a decrease in the pressure to below 10 Pa. From the point of view of the wear mechanism, the transition is determined as that from oxidative wear at the higher pressure to adhesive wear at the lower pressure. The transition pressure depends on the slip amplitude, i.e.it is 2.7 Pa at 35 μm and 10⁻¹ Pa at 110 μm. The wear volume is greater in the oxidative wear regime than in the adhesive wear regime. Oxide wear debris is removed easily from the interface in the former regime. In contrast, metallic wear debris is retained at the interface and adhesive transfer occurs from one surface to the opposing surface in the latter regime. The characteristic feature of the wear damage at 10⁻³ Pa and at 35 μm is the formation of a vertical crack at the boundary between the fretted and the unfretted areas.