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2 1998

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Protective coatings for high temperature applications.

Singheiser L., Quadakkers W.J., Clemens D., Steinbrech R.W.

Inżynieria Materiałowa

1998

R. XIX, nr 4

955-962

The improvement of efficiencies of land based gas turbines requires a significant increase of gas inlet temperature. This results in an increased service temperature of the blading materials and consequently to an enhanced oxidation attack of the blade coatings, which are usually of the NiCoCrAlY type. These coatings can act as protection against oxidation/corrosion and as bond coats for zirconia based thermal barrier systems. In both applications slow growth rates and optimum adherence of the alumina scales forming on the NiCoCrAlY coating during high temperature service are of crucial importance for component life. The mentioned technologically relevant properties of the alumina scales not only strongly depend on the coatings base composition but also on the presence of minor and trace elements. In the present paper this will be illustrated by showing as examples the effect of minor changes in yttrium and titanium content on MCrAlY oxidation properties. The coatings were tested by cyclic oxidation in the temperature range 950 degrees centigrade - 1100 degrees centigrade. The effect of the composition variation was studied by characterisation of the bulk coating and the corrosion products using light and electron optical microscopy as well as dilatometry.

Microstructure and phase distribution of MCrAlY coatings.

Penkalla H.J., Wosik J., Clemens D., Quadakkers W.J., Singheiser L.

Inżynieria Materiałowa

1998

R. XIX, nr 4

982-985

For the protection of turbine blade materials against oxidation, coatings of the MCrAlY type are applied. The oxidation resistance of these multiphase coatings relies on protective alumina scales which are formed on the coating surface at high service temperatures of about 900 degrees centigrade, and is strongly affected by the phase distribution and composition. In the present study the coating material MCrAlY is investigated by means of transmission electron microscopy (TEM) whereby the chemical composition of the elements Ni, Co, Cr, Al, Re and Y was analysed systematically by EDX elemental mapping. In order to describe the phase distribution and composition in a single image a special method for the evaluation of the EDX elemental maps by statistical methods combined with image analysis were applied and described in this paper.