Effects of Heat Treatment on Microstructures and Physical Properties of Segmented Thermal Barrier Coatings

Abstract

Highly segmented thermal barrier coatings (TBCs) were produced by ''hot'' plasma spraying. The effects of heat treatment on the microstructures, mechanical and thermophysical properties were studied. The segmented coatings are denser than traditionally plasma-sprayed TBCs due to its good insplat bonding at high substrate temperature. The segmentation cracks and associating branching cracks hardly propagated or closed during sintering process, indicative of a good stability of crack network. Due to its low porosity, the segmented coatings compromised the property of thermal insulation of TBCs. For the coatings after 24 h heat treatment at 1523 K, the thermal conductivity was improved by around 35%. The segmentation cracks had a strong impact on decreasing the Young's modulus. Heat treatment could not effectively promote the increase of the Young's modulus, especially for the case of highly segmented coatings.

Microstructure and thermo-physical properties of yttria stabilized zirconia coatings with CMAS deposits

“…The small pore sizes are mainly attributed to microcracks and intersplat gaps within the coating. [26][27][28][29] When the YSZ coating was held at 1250 • C, the glassy CMAS penetrated into the coating quickly and filled most of the open porosities which led to the significant reduction in porosity.…”

Sintering‐induced delamination of thermal barrier coatings by gradient thermal cyclic test

“…As a multilayer system with BC, TGO, and top coat stacking sequentially on substrate, the delamination‐resistance of TBCs is highly relevant to the performance of all constituent parts. It is believed that the inducements of TBC failure are as follows: (1) the thickening of TGO; (2) the phase transformation induced volume expansion of top coat; (3) the sintering of top coat . All these three types of failure mechanisms can be attributed to the large strain and stress resulting from the meta‐stable phases and microstructures mentioned above.…”

“…This has a detrimental effect on the strain tolerance of top coat . In addition, the sintering of top coat also leads to an increase in thermal conductivity, resulting in distinct degradation on the thermal barrier performance …”

Low‐temperature stiffening of air plasma‐sprayed 7 wt% Y2O3‐stabilized ZrO2

“…It has thus been of interest to examine the change in microstructure, stiffness, and thermal properties of the APS YSZ system subjected to continuous and cyclic thermal exposures. A large portfolio of scientific literature exists for both such attributes with exposure of free‐standing sprayed bodies to various temperatures and times . Specifically, a number of studies have reported the variation in the elastic modulus with sintering and attempted correlation with the variation in elastic modulus and microstructure evolution with sintering, but most of these studies have been carried out beyond 1000°C.…”