Influence of gamma irradiation-induced surface oxidation on tribological property of polyetheretherketone (PEEK)

Abstract

In this paper, the semicrystalline PEEK was irradiated in the atmosphere by gamma rays with a dose up to 20 MGy. The influence of the surface degradation and the internal structural changes on the tribological behavior of PEEK was investigated. X-ray photoelectron spectroscopy analysis shows an increase in the percentage of C=O and O–C=O functional groups on the surface of irradiated PEEK samples. It reveals that irradiation-induced oxidation is the primary form of degradation on the PEEK surface. Scanning electron microscopy results indicate that the surface morphology defects such as micropores and microcracks appear when the irradiation dose exceeds 10 MGy. The friction experiments show that the static friction coefficient of the irradiated PEEK surface increases due to the existence of the surface oxide layer, and the appearance of a shorter run-in period attributes to the formation of uniform and stable transfer film in the initial stage of friction. In addition, when the dose is more than 1 MGy, the steady-state dynamic friction coefficient of the irradiated PEEK surface gradually decreases. The surface oxidation products play a rolling effect of three bodies, resulting in the fall of the dynamic friction coefficient. However, the corresponding wear rate increases by one order of magnitude compared to that of the unirradiated sample. The surface microdefects proliferation and the abrasive wear caused by oxidized clusters during the friction process lead to wear deterioration of the irradiated PEEK at high doses.