A plasma-sprayed thermal barrier coating consisting of a NiCoCrAlY bond coat and Ce-stabilized zirconia ceramic coating was heat-treated at 400 degrees C for 1000 h, Microhardness measurements were used to evaluate microstructural variations throughout the coating, One hundred and twenty measurements were performed at both the bond coat and ceramic coating positions within the thermal barrier coating system, Both data sets were analyzed to assess whether they could be described as Gaussian (i,e,, 'normal') or Weibull distributions, The influence of the sample size, i.e., the number of microhardness tests for a group, on the mean hardness value was also evaluated by a Monte Carlo simulation procedure. The mean value, the standard deviation, the coefficient of variation, and the Weibull modulus for the subsets of data were calculated to assess these effects, The confidence for the mean value was also considered, The results indicated that the reliability of the microhardness test improved as the sample size increased, At least 20 measurements were needed to distinguish differences in microhardness between the bond coat and the ceramic coating at a 95% confidence level.
Journal of the American Ceramic Society,
Vol. 78, no. 5 (May 1995), pp. 1406-1410