Fretting fatigue properties of Zr-based bulk amorphous alloy in phosphate-buffered saline solution

A fretting fatigue test was carried out with commercially available Zr-based amorphous alloy (7.6Ni-12.3Cu-3.5A1-76.6Zr in mass%) in air and in a pseudo-body fluid, PBS(-). The fracture behaviors were investigated. The fretting fatigue test was performed under load control using a sinusoidal wave with a stress ratio of 0.1, a frequency of 20 Hz in air or 2 Hz in PBS(-) and a fretting contact pressure of 30 MPa. The 10⁷-cycle fretting fatigue strength in air was one-third the 10⁷-cycle plain fatigue strength. On the other hand, the 2 × 10⁶-cycle fretting fatigue strength in PBS(-) was approximately two times the fretting fatigue strength in air. However, there was little difference between the friction coefficients in air and PBS(-). SEM observations showed that the actual contact area damaged by fretting in air due to the roughness of the surfaces became smaller than that in PBS(-). Thus, it can be considered that the fretting fatigue strength was decreased since in air the actual contact pressure caused by the roughness became higher than the apparent contact pressure. Also, based on the observation that film-forming elements in PBS(-) were different from those in air, it is believed that the surface film can affect the frictional wear characteristics and contribute to the suppression of fretting fatigue crack initiation.