Surface morphology and microstructure of the hole sidewall during drilling of Polyether-Ether-Ketone(PEEK) via single-pulse laser

Abstract

Polyether-ether-ketone (PEEK), as one kind of thermoplastic polymers, exhibits a great deal of remarkable properties and plays an important role in aerospace, electronics, automotive and medicine. An investigation of single-pulse laser drilling on Polyether-ether-ketone (PEEK) was reported to show the influence of irradiation energy on the hole sidewall. In-situ evolution of drilling process was observed by the high-speed camera. The surface morphology and microstructural characteristics of the hole sidewall were evaluated by different characterization techniques. The hole sidewall was divided into three parts: expanded zone at the entrance, linear zone in the middle, and U-shaped zone at the bottom. It was found that the quality of inner sidewall could be obviously improved under high single-pulse energy (>1 J), in terms of the surface morphology with small heat-affected zone (HAZ) thickness and surface roughness, as well as the least adhesion. Besides, chemical and structural characteristics of the hole sidewall changed a lot under high energy. The C content of three parts increased as the energy increased. The crystallinity of the hole sidewall decreased from 35 % to 25 % after laser-energy irradiation, but there was little change under different single-pulse energy. New diffraction peaks appeared in X-ray diffraction images and the intensity of the relative peaks in Raman spectra decreased when the energy was over 1 J. It was proven that some chemical bonds (phenyl ring (1597 cm−1) and C–O–C (1148 cm−1)) would break under high energy, contributing to mass removal of the keyhole. Moreover, the HAZ thickness of the hole sidewall was calculated based on a viscous flow model, which showed a good consistency with experimental results. These results reveal material-removal mechanism accompanying the appearance of direct decomposition of the material and breaking of chemical bonds under high energy. It can provide references for understanding mechanisms of HAZ formation and material-removal and improving surface quality for laser drilling of polymers.