Nanoindentation of Porous Bulk and Thin Films of LSCF

TL;DR

This study demonstrates reliable nanoindentation techniques to measure the mechanical properties of porous LSCF ceramics and films, revealing how porosity affects elastic modulus and hardness, with validation through microstructural analysis and modeling.

Contribution

It introduces a method for accurate nanoindentation of porous ceramic films and bulk materials, including data extrapolation and microstructural validation, advancing characterization techniques.

Findings

Elastic modulus increases as porosity decreases.

Residual porosity affects elastic modulus measurements.

Microstructure modeling agrees with experimental data.

Abstract

In this paper we show how reliable measurements on porous ceramic films can be made by appropriate nanoindentation experiments and analysis. Room-temperature mechanical properties of the mixed-conducting perovskite material LSCF6428 were investigated by nanoindentation of porous bulk samples and porous films sintered at temperatures from 900-1200C. A spherical indenter was used so that the contact area was much greater than the scale of the porous microstructure. The elastic modulus of the bulk samples was found to increase from 33.8-174.3 GPa and hardness from 0.64-5.32 GPa as the porosity decreased from 45-5% after sintering at 900-1200C. Densification under the indenter was found to have little influence on the measured elastic modulus. The residual porosity in the dense sample was found to account for the discrepancy between the elastic moduli measured by indentation and by impulse excitation. Crack-free LSCF6428 films of acceptable surface roughness for indentation were also prepared by sintering at 900-1200C. Reliable measurements of the true properties of the films were obtained by data extrapolation provided that the ratio of indentation depth to film thickness was in the range 0.1 to 0.2. The elastic moduli of the films and bulk materials were approximately equal for a given porosity. The 3D microstructures of films before and after indentation were characterized using FIB-SEM tomography. Finite element modelling of the elastic deformation of the actual microstructures showed excellent agreement with the nanoindentation results.