SIMULATION OF HARDNESS TESTING ON PLASMA-SPRAYED COATINGS

A plasma-sprayed thermal barrier coating consisting of a NiCoCrAlY bon d coat and Ce-stabilized zirconia ceramic coating was heat-treated at 400 degrees C for 1000 h, Microhardness measurements were used to eval uate microstructural variations throughout the coating, One hundred an d twenty measurements were performed at both the bond coat and ceramic coating positions within the thermal barrier coating system, Both dat a sets were analyzed to assess whether they could be described as Gaus sian (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 calcu lated to assess these effects, The confidence for the mean value was a lso considered, The results indicated that the reliability of the micr ohardness test improved as the sample size increased, At least 20 meas urements were needed to distinguish differences in microhardness betwe en the bond coat and the ceramic coating at a 95% confidence level.