Mechanical properties, microstructure, and tribological performance of coated polyether-ketone-ketone (PEKK) polymer

This study investigates the mechanical properties, microstructure, and tribological performance of CrN and CrAlN coatings. The coatings were deposited by low power DC reactive magnetron sputtering (PVD) on semicrystalline polyether-ketone-ketone (PEKK) substrates. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed PEKK's thermal stability, with a glass transition temperature of 158.0 °C and a melting point of 309.1 °C, ensuring compatibility with low-temperature coating processes. Microstructural analysis revealed dense, columnar coatings, with CrAlN exhibiting finer grains but minor interfacial voids/cracks that unaffected its adhesion. Tribological tests against stainless steel balls (SS) showed that CrN outperformed CrAlN, reducing the coefficient of friction (COF) by 39 % and specific wear volume by 78 % compared to uncoated PEKK, owing to its higher hardness and the formation of a protective Cr-oxides tribolayer. These results establish CrN as the superior coating for enhancing PEKK's durability and tribological performance, highlighting its potential for applications demanding high durability and wear resistance. • CrN and CrAlN coatings deposited on PEKK using low-power DC magnetron sputtering. • PEKK showed high thermal stability, enabling low-temperature PVD coating. • CrN coating achieved superior tribological performance than CrAlN coating. • CrN reduced friction by 39 % and wear by 78 % compared to uncoated PEKK.