| Thermal barrier coatings (TBCs) consist of three parts:1) the bond-coat (BC),2) the thermally grown oxide (TGO), and 3) the ceramic top-coat (TC). The TGO does not appear until the TBC system encounters elevated temperature. At the beginning of TGO growth, the TGO layer functions as an oxidation barrier coating which suppresses the formation of other detrimental oxides during extended thermal exposure. The TGO then thickens during TBC use, eventually contributing to TBC spallation. TGO is the dominate cause of the final failure.Several different methods have been proposed in recent years to enhance the oxidation resistance and lifetime of TBCs. Some of them suggested depositing an Al2O3 film as an oxygen barrier material to exploit the very small oxygen diffusion coefficient of Al2O3 (?I0-12 cm2/s at 1400?). Many other researchers have also studied similar application in TBC systems and found that oxidation resistance can indeed be improved this way to some extent, but the inherently porous Al2O3 layer or Al2O3/YSZ layer fabricated by air plasma spray (APS) decreases ceramic coating oxidation resistance.Self-healing materials including ceramics, polymers, metals, and their composites, as the name suggests, can restore their own original properties when damaged through thermal, mechanical, ballistic, or other means. There has been relatively little research regarding the application of self-healing material in TBCs, but some reports on its application in anticorrosion coatings. Self-healing material may represent a solution to the unwanted porous structure of sprayed ceramic coatings through its ability to seal the fast-diffusion paths for oxygen transportation, improving oxidation resistance. In one relevant study, the NASA researchers tested lightweight, self-healing ceramic composites for application in hot sections of high-temperature aircraft engines to find that that SiC and its oxides had sufficient plasticity to reduce crack propagation and that the self-healing materials filled surface-connected cracks to prevent oxygen ingress. Our previous work also proved that TiC also had a good self-healing capacity and its application in tritium permeation barriers was successful.In the present study, Ti-self-healing coatings, SiC-self-healing coatings and other oxidation barriers coatings were prepared by APS. The oxidation resistance, spallation resistance, thermal cycles resistance and hot corrosion resistance of the composite TBCs, which contain all the oxidation barrier coatings mentioned above, are discussed in this paper. The main achievements are summarized as follow:(1) TAZ20, which involved 20 wt% TiC,40 wt% Al2O3 and 40 wt% YSZ in the self-healing coating, was supposed to be the best TiC-self-healing coatings. The inherent porosity in the as-sprayed TAZ20 coating was 9.96%, and it can be dropped into 3.28% after self-healing heat treatment. The TAZ20 TBC system showed the best 1000? oxidation resistance among all the TiC-self-healing TBC. The TGO area percentage was 6.67%, which was 50.11% than that of conventional TBC. The lifetime of TAZ20 TBC, which came from the 1000? thermal cycles test, was almost twice than that of conventional TBC.(2) The most feasible thickness of the TAZ20 coating in the TiC-self-healing TBC was approximate 10 urn, as the thicker TAZ20 coating would induce unnecessary volume expansion and strain which could result in cracks nucleation and propagation in the coatings. The type of triple-ceramic-layer (TAZ20/YSZ/TAZ20) TiC-self-healing TBC perform best during the 1100? oxidation test and 1100? thermal cycles test. The oxidation mass gain, mass loss and lifetime were 64.77%,48.91% and 188.24% than that of conventional TBCs. And the 75 wt% Na2SO4+25 wt% NaCl hot corrosion at 900? had little effect on this kind of TiC-self-healing TBC.(3) SAZ10, which involved 10 vol% SiC,45 vol% Al2O3 and 45 vol% YSZ in the self-healing coating, was supposed to be the best SiC-self-healing coatings. The inherent porosity in the as-sprayed SAZ10 coating was 9.39%, and it can be dropped into 1.94% after self-healing heat treatment. The SAZ10 TBC system showed the best 1100? oxidation resistance among all the SiC-self-healing TBC. The TGO area percentage was 33.11%, which was 57.90% than that of conventional TBC. The lifetime of the SAZ10 TBC, which came from the 1100? thermal cycles test, was 128.57% than that of conventional TBC. (4) The most feasible thickness of the SAZ10 coating in the SiC-self-healing TBC was approximate 10 um, as the thicker SAZ10 coating would induce unnecessary volume expansion and strain which could result in cracks nucleation and propagation in the coatings. The type of triple-ceramic-layer (SAZ10/YSZ/SAZ10) SiC-self-healing TBC perform best during the 1100? oxidation test and 1100? thermal cycles test. The oxidation mass gain, mass loss and lifetime were 61.38%,38.87% and 171.43% than that of conventional TBCs. And the 75 wt% Na2SO4+25 wt% NaCl hot corrosion at 900? had little effect on this kind of SiC-self-healing TBC.(5) A innovational nitriding TBC was designed. The BCs were nitriding before the YSZ coatings were sprayed. The results revealed that the mass gain and mass loss of the nitriding TBCs were 85.90% and 56.11% than that of the conventional TBC in the 1100? oxidation test. And it could resist 123.33% thermal cycles at 1100'C than that of the conventional TBC.(6) A innovational Cr2O3-Al2O3 TBC was designed. The Cr2O3-Al2O3 coatings were supposed to be low porosity as the researchers had studied, which meant less oxygen diffusion paths in the Cr2O3-Al2O3 coatings. What was more, the good oxidation resistance of Al2O3 could impress the TGO growth. The results revealed that the mass gain and mass loss of the Cr2O3-Al2O3 TBCs were 68.99% and 63.92% than that of the conventional TBC in the 1100? oxidation test. And it could resist 123.08% thermal cycles at 1100? than that of the conventional TBC. |
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