Mechanical characterization of nano-reinforced silica based sol–gel hybrid coatings on AISI 316L stainless steel using nanoindentation techniques

One way to enhance the surface properties of metals used as surgical implants such as wear or protective behaviour is to use hybrid organic–inorganic sol–gel coatings. The addition of SiO2 colloidal particles to some hybrid formulation is thought to give films with bigger thickness than the coatings without particles, acting as mechanical reinforcement and to make an adequate surface to resist the extreme surgical procedures taking place in orthopaedic replacements.Coatings made by sol–gel with tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) with the addition of silica nanoparticles were applied onto surgical grade stainless steel. One of the most recent techniques used to study the mechanical properties of thin films is the instrumented indentation, known as nanoindentation, was used to evaluate elastic modulus, hardness and friction coefficient. This is a superficial technique used to measure quasi-statically the penetration of an indenter at increasing loads applied to very little volumes of material.The mechanical properties values found for the TEOS–MTES–10%SiO2 coating are smaller than for the 30% filled coating, and higher that the coating without nanoparticles. In the scratch test of the TEOS–MTES–SiO2 30 wt.% coating it can be seen that in this case the failure takes place at higher applied load than for the less silica reinforced one, indicating a much better adhesion than the system with 10% of SiO2 nanoparticles.