In-situ deposition of silica layers during the operation of a micro-gas turbine and their effect on the oxidation of superalloy blades

Abstract

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.

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

“…The blades were cut after coating from the wheel, so the cut face was not coated (~5 % to the total area). The changes in weight due to the oxidation of this face were taken into account and corrected [5]. The data designated as TB04 and "uncoated" were adopted for this figure from our previous study [5].…”

“…The changes in weight due to the oxidation of this face were taken into account and corrected [5]. The data designated as TB04 and "uncoated" were adopted for this figure from our previous study [5]. For TB04, the precursor TEOS was fed together with LPG at 0.37 mol.% of silicon for a relatively long operation time (240 min), yielding silica layers to a thickness of 15 µm all around the blade [5].…”

“…The data designated as TB04 and "uncoated" were adopted for this figure from our previous study [5]. For TB04, the precursor TEOS was fed together with LPG at 0.37 mol.% of silicon for a relatively long operation time (240 min), yielding silica layers to a thickness of 15 µm all around the blade [5]. The data for "uncoated" correspond to the results tested on a new and uncoated blade.…”

“…As the oxygen amount did not follow the trend of Si, other forms of thermally grown oxide was expected to come into existence, such as Cr2O3 and NiO, etc. [5]. SEM images in Fig.…”

“…The turbine inlet temperature (TIT) is hence limited to ~900°C [3], for which the thermal efficiency is relatively low compared to land-based industrial gas turbines. As an alternative way of building up thermally protective coatings on the metallic hot gas components, an in situ deposition method was proposed and examined [4,5] based on the hypothesis that the operation conditions of most gas turbine systems provide a good milieu for combustion chemical vapor deposition (CCVD). Though this method was proven to be a very effective way of delivering coating precursors onto the metallic components during service, it also delivered nano-sized oxide particles in the air during the process, which may have caused environmental problems.…”