Microstructure characterization of bioinspired multilayer coatings on advanced polymer
PEEK
type materials as well as on Carbon Fiber Composites (
CFC
)
Authors: Major Lukasz , Lackner Juergen M. , Janusz Marta , Kot Marcin , Major Boguslaw 
Published: December 2016

The ultimate goal for a materials engineer is to learn from the lessons of nature and to apply this knowledge to new materials and design. In nature materials are often optimized to manage any damage that could occur. The occurrence of damage is expected and accepted as a fact of life. Natural materials can cope with damage due to in‐ built healing abilities. The ability to heal damage is one of the remarkable properties of biological systems and living organisms. One recurring goal of material development was to emulate the materials of nature. In the frame of the presented research, the coatings design was inspired by nature. The first part of the paper deals with the microstructure characterization of a natural shell. The coatings design was based on the nacre structure. The design of materials and structures inspired by nature involves special challenges not encountered before. Traditional design has followed disciplinary lines. Bioinspired design required mulitidisciplinary teams of engineers (design and materials), and scientists (biology, molecular biology, tribology, and micro‐/nano‐ structure characterization). Given the widespread interest in the structure and mechanical properties of abalone shell, there have been some attempts to fabricate nacre like multilayered structure. Advanced hard coating concepts like multilayer coatings, multicomponent solution hardened layer materials, new metastable layer materials, nanocrystalline layer materials or superlattice films became increasingly important for wear protection under extreme and complex loads. Among these advanced coatings, the multilayer concepts seems to be the most versatile and promising with respect to properties and performance in almost all the fields of application. The main objective of the research was to improve the bio‐ activity and tribological properties of advanced polymer PEEK type materials (Polyetherethkethone) as well as Carbon fiber Composites (CFC). It was performed through the development of biomimetic, self‐ healing polymeric and ceramic multilayer coatings. Bio‐ engineering tests considered cell material interaction. In the initial analysis, associated with cytotoxic effect, fibroblasts were applied. The selected materials were undertaken the hemocompatibility. The analysis were executed based on the rules described in ISO 10993‐4, dynamic blood‐material interaction. The final analysis were focused on induced stem cells. Coatings were also subjected to complex mechanical tests based on indentation, ball‐ on disc wear and scratch adhesion tests. The wear test revealed the friction coefficient in the range of 0.3 up to 0.4 under 5N and 2500 cycles.Before and after bio‐ tribological tests the detailed microstructure/ nanostructure analysis of the coatings was performed in order to determine the tribological behavior of the coatings under the influence of a mechanical load and under biological conditions. Microstructural diagnosis was carried out using a high resolution transmission microscopy technique (HRTEM). It showed that cracking was initiated at the coating/substrate interface and the energy of brittle cracking was reduced due to the plastic deformation at each Cr interlayer interface (Fig. 1).