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

An instrumented depth-sensitive microindentation technique was applied to e valuate mechanical properties of thin corroded layers of some ceramics whic h were immersed in boiling, highly condensed sulfuric acid up to 1000 h. In dentation load-depth curves were analyzed using a finite element model to s ystematically investigate the effect on the ceramics of film or corroded la yer. The mechanical properties of both the oxide films and the corroded lay ers were evaluated through the combination between analytical and experimen tal results on the indentation curves. It was found that the relationship b etween thickness T of oxide films or corroded layers and the depth d determ ined by the slope change on the indentation load/depth-depth curve is descr ibed as T approximate to 10d. The bending strengths of Si3N4 and Al2O3 afte r immersion were evaluated using the d associated with the corroded layer t hickness and the K-IC obtained before immersion. It was confirmed that the strength degradation of Si3N4 and Al2O3 due to the boiling sulfuric acid co rrosion can be estimated using K-IC and d-value. (C) 2000 Elsevier Science Ltd. All rights reserved.