Thermal barrier coatings (TBCs) are widely used in gas turbine engines because they allow higher operating temperatures due to their thermal insulation effect. The aim of this paper is to explain the effect of the substrate (base metal) on the performance of TBCs applied to various nickel‐based superalloys and stainless steels.
Specimens were prepared by applying atmospheric plasma spraying (APS). Six TBC‐coated samples were prepared. Three of the substrates were stainless steel and the rest were nickel‐based superalloys. Characterization effort included thermal exposure, microhardness testing, optical metallography and image analysis.
Microhardness test results showed that extended periods in high‐temperature environments affected the coating morphology, which was measured by changes in the microhardness values. At the end of the long periods in the furnace, microhardness values increased, which might be a sign that modulus of the coating increased. These changes in the microhardness might be due to the sintering effect and morphological changes that occurred in the coating. Effects of thermal exposure to the coatings were also visible in the micrographs in the form of fully open cracks. Development of larger cracks was life‐threatening for the ceramic coating.
It was shown for the first time that, in the above‐mentioned crack growth and spallation stages, stainless steel and superalloy substrates showed considerably different performances. Microhardness test results of coatings on different substrates were considerably dissimilar, which was a sign that the coating morphology was affected during thermal exposure.
