Ex situ oxidation of IN713 turbine blades in situ deposited with silica layers during operation of a micro-gas turbine

Abstract

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.