Abstract
In this thesis, the LZ7C3 ceramic was doped by Sm, Gd and Yb, according to R -O(R=rare earth atoms) bond with R ion radius and the atomic number of the relationship.
The LaxA1-xZ7C3(A= Sm 、Gd、Yb) ceramics for TBCs were synthesized by solid -state reaction at 1 400 ℃ for 12 ho urs. The phase composition, microstructure and thermophysical properties of these novel co -dope dzirconate ceramics were studied .In order to meet the needs of air plasma spraying , the hollow spherical powders of these prepared ceramics were prepared by spray drying, and the effect of spray dr ying processing parameters on LaxA1-x Z7C3 performace were analyzed. Double - cermaic-layer (DCL) coatings of 8YSZ and LaxA1-x Z7C3 were prepared by APS. The thermal shock properties and failure mechanism were studied .
The results showed that, the co -doped zirconate LaxA1-xZ7C3 ceramics were synthesized successful. The La xA1-x Z7C3 ceramics consist of pyrochlore structure and fluorite structure. The optimized process parameters w ere determined: solid content was 55%, PVA content was 1wt. %, inlet temperature was 250 ℃, and speed of sprinklers was 9,000 rpm . the flow time of 50g powder was 45-48 seconds,apparent density was 1.45~1.65g/ml, which could the needs of plasma spraying .
The Sm, Gd and Yb doped LZ7C3 ceramics Lax A1-xZ7C3 had lower thermal conductivity than the undoped LZ7C3. Especially the doping of Gd can effectively reduced the thermal conductivity and improved the thermal expansion coefficient of LZ7C3. The spallation of top coatings led to the failure of 8YSZ/LaxA1-xZ7C3 double-ceramic-layer thermal barrier coatings due to the mismatch of thermal expansion of Lax A1-xZ7C3 coating and 8YSZ coating . The La0.25Gd0.75 Z7C3 ha d the best thermophysical properties and thermal shock lifetime, which had 50 cycles , and was much more 25% than 8YSZ/LZ7C3. So the 8YSZ/LaxA1-xZ7C3 double-ceramic-layer thermal barrier coating s had lower thermal conductivity and longer thermal shock lifetime may be widely used in the next generation of aerospace engine .
Key Words：TBCs, Solid stata Synthesis, Plasma spraying, First-principles
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