Hybrid Multifunctional Biomimetic Composites via Thermal Spray

Natural materials, such as nacre and bone, are known for their exemplary mechanical properties. Over millions of years, nacre has evolved to a level of optimization that the materials science community is working to engineer in synthetic composites. Nacre, a natural composite that has been of interest for years, is formed from an assembly of alternating layers of calcium carbonate with a biologically evolved organic matrix. Atmospheric plasma sprayed ceramic coatings show a similar microstructure to that of nacre. This natural material is described as having a brick and mortar structure, while plasma sprayed ceramic coatings have a brick wall structure. It is known that these coatings can be manipulated to produce varying levels of porosity. By infiltrating the pores of a plasma sprayed coating with polymer, it is possible to mimic these natural materials. Compared to the base ceramic constituent of nacre (aragonite), the fracture toughness of a nacreous assembly is approximately 3000 times greater. Therefore, hybrid multifunctional biomimetic composites via thermal spray are being investigated by using porous ceramic templates such as alumina with polymeric media introduced into the defects. Three-point-bend tests showed an increase in strength over four times that of an as sprayed alumina coating. The fracture toughness of infiltrated ceramics measured by a novel double torsion technique exhibited an increase in fracture toughness by a factor of two. The combination of higher strength as well as fracture toughness can be utilized to produce synthetic composites that behave similarly to natural composites.