Structure–property differences between supersonic and conventional atmospheric plasma sprayed zirconia thermal barrier coatings

Yttria-stabilized zirconia (YSZ) based thermal barrier coatings (TBCs) were deposited by high efficiency supersonic atmospheric plasma spraying (SAPS) system. The microstructure and thermal shock resistance of the SAPS-TBCs were investigated. As compared to conventional atmospheric plasma sprayed TBCs (APS-TBCs) with the same composition, the microstructure of SAPS-TBCs was much finer. It was found that the thickness of lamellar structure consisted of columnar crystals in the SAPS- and APS-coatings was in the range of 1–4 μm and 2–8 μm, respectively. Besides, the statistical results revealed that the average thickness of the lamellar structure in SAPS-coating was 2.5 ± 0.6 μm, while that of APS-coating was 5.3 ± 0.9 μm. The desirable structure was attributed to higher impact velocity of in-flight particles during SAPS process, which resulted in the improvement of flattening degree of molten particles after impinging on the target. The well-adhered fine lamellar structures, fine micro-cracks and lower growth rate of thermally grown oxide (TGO) appeared to be responsible for greatly improved thermal cycling lives of SAPS-TBCs as compared to their conventional plasma sprayed counterparts. The results of water-quenching test from 1100 °C into room temperature showed that SAPS-TBCs presented high thermal shock resistance, only 10% coating area spalled after 265 thermal cycles, about 90% higher than that of APS-TBCs. The SAPS method, which offered some unique advantages over the conventional plasma spraying process, is expected to be potentially used to deposit high-performance TBCs at lower cost.