Mechanical-property evaluation of thin corroded surface layers of ceramic materials by the microindentation technique

An instrumented depth-sensitive microindentation technique was applied to evaluate mechanical properties of thin corroded layers of some ceramics which were immersed in boiling, highly condensed sulfuric acid up to 1000 h. Indentation load–depth curves were analyzed using a finite element model to systematically investigate the effect on the ceramics of film or corroded layer. The mechanical properties of both the oxide films and the corroded layers were evaluated through the combination between analytical and experimental results on the indentation curves. It was found that the relationship between thickness T of oxide films or corroded layers and the depth d determined by the slope change on the indentation load/depth–depth curve is described as T≈10d. The bending strengths of Si3N4 and Al2O3 after immersion were evaluated using the d associated with the corroded layer thickness and the KIC obtained before immersion. It was confirmed that the strength degradation of Si3N4 and Al2O3 due to the boiling sulfuric acid corrosion can be estimated using KIC and d-value.