2002 Volume 20 Issue 2 Pages 287-294
A new method to evaluate the debonding behavior of thermal sprayed coatings is proposed. Type 304 stainless steel substrates were coated with 8% Y2O3-ZrO2 and 80Ni-20Cr by plasma spray. Then, GTA was applied as a moving thermal input to the substrate surface of a specimen while the surface strain of the coating was measured continuously by a non-contacting technique called the laser speckle strain meter. Strain curves were also recorded without thermal sprayed coatings and GTA current was varied from 40 to 120A. By comparing the strain behavior of the coating with that of a bare substrate, it was possible to determine the onset of debonding of the coatings. It was found that while 80Ni-20Cr coatings did not debond under the range of conditions tested, 8% Y2O3-ZrO2 coatings debonded when heat input was above a certain limit. With our method, it was possible to detect debonding beneath the coating surface, even when the debonding was not apparent on the coating surface, which was verified by mechanical testing afterwards.
