A multi-technique and multi-scale analysis of the thermal degradation of PEEK in laser heating
Dimitrios Gaitanelis, Angeliki Chanteli, Chris Worrall, Paul M. Weaver, Mihalis Kazilas
Abstract
In the present work, the thermal degradation of laser-heated poly-ether-ether-ketone (PEEK) is studied as the heating duration increases. The damage morphology, chemical composition, crystallinity content, and mechanical properties are examined with optical microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, differential scanning calorimetry, Raman spectroscopy, and continuous stiffness measurement nanoindentation. The applicability of those methods in detecting the thermal degradation of laser-heated PEEK and assessing the induced thermal damage is highlighted. Results show that short-time laser heating acts as an annealing process that improves the crystallinity and hardness on the affected surface of PEEK by up to 5.1% and 10.8% respectively. With a further increase in the heating duration, surface carbonisation occurs and a char layer is formed. Surface carbonisation is associated with the thermal limits of PEEK in laser heating decreasing by up to 50% its hardness and by 45% its indentation modulus. The char layer is found to act as a shielding mechanism that protects the bulk PEEK from the applied thermal load, resulting in mostly superficial thermally induced damage.