Microindentation Test for Determining Mechanical Properties of Corroded Layers of Ceramics

Microindentation tests on ceramics (Si-SiC, SiC, Al2O3 and Si3N4) immersed in boiling 95 wt% sulfuric acid for 100 or 1000 hours were performed to evaluate the mechanical properties of their corroded layers. The thickness (T) of corroded layer on ceramics was evaluated in terms of characteristic depth (d) which was determined from the point of inflection on the Depth-Load/Depth curve by the microindentation test. The relationship between T and d was found to be given as T ≒ 10d. Finite element analyses were performed to validate the relationship and to clarify the effects of mechanical properties of corroded layer and the indenter tip radius on the relationship as well. The mechanical properties [Young's modulus (Ef) and yield stress (σyf)] of corroded layers of Al2O3 and Si3N4 were identified by fitting the predicted Depth-Load/Depth curve to the experimental data.