Porous APS YSZ TBC Manufactured at High Powder Feed Rate (100 g/min) and Deposition Efficiency (70%): Microstructure, Bond Strength and Thermal Gradients

There is a strong driving force to improve the production efficiency of thermal barrier coatings (TBCs) manufactured via air plasma spray (APS). To address this need, the high-enthalpy APS torch Axial III Plus was employed to successfully manufacture TBCs by spraying a commercial YSZ feedstock at powder feed rate of 100 g/ min using an optimized set of N-2/H-2 spray parameters; which yielded an impressive YSZ deposition efficiency (DE) value of 70%. This exact same set of optimized spray parameters was used to manufacture the same identical YSZ TBC (over similar to 160 mu m-thick bond-coated substrates) but at two distinct YSZ thickness levels: (i) similar to 420 mu m- thick and (ii) similar to 930 mu m-thick. In spite of the high YSZ feed rate and DE levels, the YSZ TBC revealed a similar to 14% porous (conventional looking) microstructure, without segmented cracking or horizontal delamination at both thickness levels. The bond strength values measured via the ASTM C633 standard for the similar to 420 mu m-thick and similar to 930 mu m-thick YSZ TBCs were similar to 13.0 and similar to 11.6 MPa (respectively); which are among at the upper end values reported in the literature. After the first objective was attained, the second key objective of this work was to evaluate the thermal insulating effectiveness of these two as-sprayed YSZ TBCs. To achieve this objective, a thermal gradient laser-rig was employed to generate a temperature reduction (Delta T) along the TBC-coated coupons under different laser power levels. These distinct laser power levels generated YSZ TBC surface temperatures varying for 1100 to 1500 degrees C, for the similar to 420 mu m-thick YSZ TBC, and from 1100 to 1680 degrees C YSZ TBC similar to 930 mu m-thick YSZ TBC. The respective Delta T values for both TBCs are reported. The results of this engineering paper are promising regarding the possibility of improving considerably the manufacturing efficiency of industrial quality conventional-looking porous YSZ TBCs, by using a high-enthalpy N-2-based APS torch. This is the first paper published in the open literature showing R&D results of coatings manufactured via the Axial III Plus APS torch.

Automated summary

This paper demonstrates the successful manufacturing of thermal barrier coatings using a high-enthalpy APS torch. The results show that by optimizing the spray parameters, the manufacturing efficiency of the coatings can be significantly improved, while maintaining high bond strength and thermal insulation effectiveness.