Effect of the Nature of Oxide Nanofillers on Changes in the Mechanical Properties of Epoxy Coatings under Thermal Cycling

The paper demonstrates the applicability of micro indentation as a sensitive method for detecting the effect of the nature of oxides as fillers on the properties of epoxy coatings in comparison with conventional physicochemical methods of infrared spectroscopy (IR) and thermogravimetry (TGA). This applicability was discovered when studying the surface mechanical properties (hardness, elastic modulus, and creep) of epoxy coatings filled with nanoscale oxides TiO2, SiO2, and ZnO. The behavior of the mechanical characteristics of the materials under thermal cycling at temperatures ranging from −40 to +60 °С was evaluated by instrumented indentation with the use of a Fischerscope HM system after 5 and 10 cycles. It is shown that the 10% addition of TiO2 oxide increases the values of hardness and the elastic modulus by 5 and 15%, respectively, while the addition of SiO2 and ZnO decreases them by 7 and 5%. The micromechanical properties of the studied materials depend on the time of the increase in mechanical loading. All the compositions exhibit viscous properties consisting of hardness decrease with the decreasing rate of loading. Thermal cycling decreases the hardness and elastic modulus of the unfilled epoxy coating and those containing SiO2 and ZnO by 12 and 18%, respectively, and it ensures the self-restoration of the hardness of the TiO2-filled coating. All the additives decrease the creep index. Thermal cycling increases the creep index for all the materials under study.