On the cyclic hot corrosion behaviour of atmospheric plasma sprayed Lanthanum Zirconate based coatings in contact with a mixture of sodium sulphate and vanadate salts: A comparison with the traditional Ysz duplex and NiCrAlY coated samples

摘要

Thermal barrier coatings (TBCs) have been extensively developed for aero gas turbines operating in clean environments to improve engine efficiency and component life. In gas turbines or diesel engines, hot corrosion resistance over extended exposures in 'contaminated' fuel is a key durability issue. There is a need, therefore, for the development of new design strategies or new materials for TBCs in order to operate under hot corrosion environments. The present study focuses on the comparison of cyclic hot corrosion behaviour of the Base Metal Inconel 738 (BM), the NiCrAlY Bond Coat (BC), the duplex Yttria Stabilised Zirconia (YSZ/BC), the duplex Lanthanum Zirconate (LZ/BC) and a five layered coated specimen with LZ as top layer (LZ/LZ + 50 wt.% YSZ/YSZ/YSZ + 50 wt.% BC/BC). The hot corrosion was conducted in a cyclic manner from 1000 C to room temperature with Na_2SO_4 + 60 wt. % V_2O _5 salt mixture and weight gains of the coated specimens were measured at regular intervals. A highest weight gain of 36 mg/cm~2 was recorded in the case of the BM. A cumulative weight gain of 16, 7, 10 and 4 mg/cm~2 were recorded in the case of the BC, YSZ, LZ and the five layered coated specimens, respectively. The parabolic corrosion rate of the BM was 15 g~2 cm~(-4) s~(-1) and the BC, YSZ, LZ and the five layered coatings were recorded with the parabolic corrosion rates of 2.5, 0.44, 0.98 and 0.15 g~2 cm~(-4) s~(-1), respectively. The reasons for the better cyclic hot corrosion resistance of the five layer coated specimen compared to other considered specimens has been studied using SEM, EDS, Elemental mapping and XRD characterization techniques.