Effect of heat treatment on elastic properties of separated thermal barrier coatings

摘要

Elastic response behavior of four different plasma-sprayed deposits has been investigated using depth-sensing micro-indentation technique. Due to the high degree of porosity andinhomogeneity of the coatings, the characteristic elastic moduliwere found to be in the range of 20-percent of that of the densebulk material (200 GPa). Considering the wide variation ofproperties, 150 data points were generated with five differentindentation loads for each coating, and statistical tools wereemployed to represent the scatter of the data. The characteristicelastic moduli of all the coatings were observed to be almostdoubled when the magnitude of indentation load was reduced fromthe highest (1000 mN) to the lowest (30 mN. The coatings weresubsequently heat treated at 1100 beg C, the operationaltemperature of a gas turbine, for 2, 25, and 100 h, and in all thecoating grades the corresponding elastic moduli increasedsignificantly. However, the stiffening effect was not uniform intwo grades and was more pronounced for the smaller indentationloads. The increase in elastic modulus is attributed to eliminationof fine porosity and sintering neck formation, an assumption alsosupported by the results of mercury porosimetry.