INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
MECHANICAL PROPERTIES OF HYBRID STIFF COATINGS DEPOSITED ONTO A POLYMERIC COMPLIANT/SOFT SUBSTRATE BY NANOINDENTATION
Autor/es:
L. A. FASCE; R. SELTZER; P. M. FRONTINI
Reunión:
Congreso; XX International Materials Research Congress IMRC 2011; 2011
Resumen:
Thin hybrid organic-inorganic coatings deposited on polymeric substrates systems are widely used for optical, packaging, biomedical and microelectronics applications. Their functionality and reliability strongly depend on their mechanical performance, which is mainly controlled by the intrinsic properties of the hybrid coating and the adhesion characteristics with the polymeric substrate. Nanoindentation appears as the most suitable technique to evaluate the mechanical properties of thin coatings due to its capability of deforming materials locally on a very small scale. As a consequence of the complex deformation processes involved during indentation, a standard method to extract elastic coating-only properties from indentation tests does not exist. Experiments have shown that indentation response is strongly influenced by the coating thickness, the intrinsic mechanical properties of both coating and substrate and the tip geometry. This is because the stress generated by the indenter propagates far beyond the indentation depth, and the distribution of the stress depends on all these factors. The defining mechanical characteristics of the analyzed hybrid organic-inorganic coatings (PEO/SiO2) deposited onto a polymeric substrate (PVC) are: i) the compliance mismatch between the polymer and the hybrid and ii) the low plastic flow resistance of the polymeric substrate. Elastic modulus values determined from experimental load-depth curves by applying the Oliver-Pharr approach display a decreasing trend with increasing maximum applied load, and do not exhibit a plateau value at cero depth. Hence, coating-only elastic properties can not be inferred directly from experimental results. Finite element indentation simulations were performed on model systems comprising elastic films onto elastic-plastic substrate with varying elastic mismatch. Effective elastic modulus values of the coating/substrate systems were extracted from load-depth curves simulated up to different maximum applied loads using also the Oliver-Pharr method. FE results were used to analyze the effect of compliance mismatch and substrate plasticity on the effective elastic modulus values. Several fitting functions and literature models such as the Doerner and Nix empirical one were applied in order to recover de intrinsic elastic modulus of the coating without complete success. Further FE simulations were performed considering elastic coating/elastic substrate. Results from elastic mismatch varying from 25 to 1.8 indicate that the influence of substrate yielding on effective modulus increases with increasing elastic mismatch. However, for depth to thickness ratios lower than 0.10 the influence of substrate plastic deformation can be neglected. A calibration curve based on effective values at h/t=0.1 was proposed and used to evaluate intrinsic elastic modulus of several PEO/SiO2 hybrid coatings on PVC with reliability.