Elastic response behavior of four different plasma-sprayed deposits has bee
n investigated using depth-sensing micro-indentation technique. Due to the
high degree of porosity and inhomogeneity of the coatings, the characterist
ic elastic moduli were found to be in the range of 20-75% of that of the de
nse bulk material (200 GPa). Considering the wide variation of properties,
150 data points were generated with five different indentation loads for ea
ch coating, and statistical tools were employed to represent the scatter of
the data. The characteristic elastic moduli of all the coatings were obser
ved to be almost doubled when the magnitude of indentation load was reduced
from the highest (1000 mN) to the lowest (30 mN). The coatings were subseq
uently heat treated at 1100 degrees C, the operational temperature of a gas
turbine, for 2, 25, and 100 h, and in all the coating grades the correspon
ding elastic moduli increased significantly. However, the stiffening effect
was not uniform in two grades and was more pronounced for the smaller inde
ntation loads. The increase in elastic modulus is attributed to elimination
of fine porosity and sintering neck formation, an assumption also supporte
d by the results of mercury porosimetry.