Silica-based oxide layers were deposited in-situ on turbine blades made from Inconel 713 during the operation of a 13 kgf-class gas turbine, and their effect on the ex-situ oxidation behavior of the blades at 1050°C was examined. The two turbines were driven by burning liquid petroleum gas (LPG), one turbine at a rotation speed of 35,000 rpm for 4 h (TB04), and the other at 42,000 rpm for 8 h (TB08). For deposition, tetraethylorthosilicate (TEOS) was sprayed into the fuel line immediately ahead of the combustion chamber. The TEOS-to-LPG ratio for TB04 and TB08 was maintained at 5.4 wt.% and 2.3 wt.%, respectively. Directly after operation, the turbine blades were coated with silica layers to a thickness of ~10 µm, independent of the operating conditions. These oxide layers on the blades provided excellent protection against oxidation during both operation and the ex-situ isothermal oxidation test.

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The long-term stability of silica layers deposited in situ on the IN713 turbine blades was investigated by surveying an ex situ thermally cycled oxidation test in air at 1050°C. Two types of in situ coatings were prepared by burning tetraethylorthosilicate with fuel during a 100-min operation of a 13 kgf-class gas turbine. The degradation of the blades upon the oxidation test was evaluated by monitoring the weight change and by analyzing the microscopic evolution of surface oxides. One coating, characterized by a uniform and relatively thick porous coating on the pressure side, was chipped off in the early stages of the test. The other coating was ~4 µm thick at the region near the root, but was too thin (and transparent) at the other parts of the blade to be rendered as protective one. However, this coating was found to be more stable towards chipping than the other coating during the oxidation test. The stability of the coatings was examined in terms of the interaction between the deposited layer and the underlying thermally grown oxide or substrate during the operation of the gas turbine.