Synthesis and characterization of Halar® polymer coating deposited on titanium substrate by electrophoretic deposition process

Abstract

Halar®, an ethylene chlorotrifluoroethylene (ECTFE) thermoplastic polymer, can be considered as an ideal protection coating material for medical application, because of its high purity and unique combination of the mechanical and chemical properties. In this study, Halar® polymer powder particles are deposited onto titanium substrate by the means of electrophoretic deposition (EPD). Differential scanning calorimetry was used to measure thermal characteristics of the raw Halar® powders including glass transition temperature (Tg), melting temperature (Tm) and melting enthalpy (∆Hm). A high crystallinity value was determined for the raw polymer powders by differential scanning calorimetry analysis. Additionally, the effect of heat treatment on Tg, Tm and crystallinity of the polymer are evaluated at different heating temperatures. It was found that heat-treatment of the Halar® powder at the temperature of 260 °C (above its melting temperature) results in increasing of Tg, Tm and crystallinity of this thermoplastic polymer. Thus, after deposition thermal treatment temperature was performed at 260 °C for 15 min which may improve the adhesion of the coating to the substrate and its mechanical properties. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to assess the quality and surface morphology of Ti coated with Halar® polymer. The deposited coating showed a high quality, smooth and homogenous microstructure without any cracks or holes. Nanomechanical properties (hardness and elastic modulus) of the deposited polymer coating were also determined using the nanoindentation technique. Moreover, a comparison is drawn between the fatigue behavior of uncoated and polymer coated Ti specimens by a three-point bend test. The results indicated a blunt crack tip and a higher fatigue strength of Halar® polymer coated Ti.