a CORNET research project
The threat to en-route aircraft from airborne volcanic ash is widely recognized, with more than 100 encounters occurring since 1973. Solid aerosols suspended in air can enter aircraft engines leading to fatal damages. In particular, volcanic ash represents a high danger. Glassy volcanic ash softens at temperatures that are considerably lower than typical aeroengine operating temperatures exceeding 1,400 °C. The resulting sticky droplets hit and deposit on components inside the turbines.
Turbine blades are protected against heat by porous thermal barrier coatings (TBCs) made of yttrium stabilized zirconia dioxide (YSZ), which lowers the heat input into the component. Molten volcanic ash deposits damage these coatings at high temperatures by infiltration into the porous structure and chemical reaction minimizing the coating’s stability against thermal cycling and resulting in premature failing of the component.
Alternative systems using rare earth zirconates like gadolinium zirconate (GZO) base on a fast chemical reaction of the coating surface with the volcanic ash, building up a barrier layer that stops further penetration of the molten deposits. Generally, these investigations are lead with synthetic, less complex compositions of calcium, magnesium, aluminum, and silica (CMAS).
The project VAsCo focused on the damaging mechanism of TBCs by ashes from real volcanoes with specific chemical composition and physical and thermal properties and the development of resistant TBCs. Therefore, classic YSZ as reference and innovative GZO was deposited via electron-beam physical vapor deposition (EB-PVD) and thermal spray – two coating technologies that are estimated to significantly grow in the next few years.
Since most of the companies engaged in the aeronautic sector are SMEs as subcontractors of major players, the results of this project specifically address their needs and offer them the enlargement of their competence and maintaining their competitiveness on the market. The consortium conducted ash deposition experiments on the developed TBCs and analyzed the damages. Findings were used for the optimization of the coatings. In addition to that, a feasibility study was lead in order to create a model synthetic volcanic ash for standard tests in aviation industry.
This work was funded by the public service of Poland and by the German Ministry for Economics and Energy based on a decision of the German Bundestag via the AiF-IGF Program, as part of a transnational CORNET project (IGF no. 189 EN). The support of all industrial project partners is gratefully acknowledged.