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1

The influence of silver addition on the microstructure and oxidation behaviour of gamma-TiAl based alloys

Gil A., Niewolak L., Czyrska-Filemonowicz A., Penkalla H.J., Shemet V., Singheiser L., Quadakkers W.J.

Inżynieria Materiałowa

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2001

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R. XXII, nr 4

341-344

EN

The aim of this study was to investigate how the beneficial effect of silver addition on the oxidation behaviour of TiAl alloys is correlated with changes in the alloys microstructure. For this purpose the microstructures of the following alloys were compared: Ti-50Al (full lamellar), Ti-50Al (duplex), Ti-48Al-2Cr and Ti-48Al-2Ag. The results showed that silver addition stabilises the gamma-TiAl phase formation at the expense of alpha2-Ti3Al phase.

PL

Celem pracy było zbadanie, czy korzystny wpływ dodatku srebra na wysokotemperaturowe utlenianie stopów TiAl jest wywołany zmianami w mikrostrukturze tych materiałów. W tym celu porównano mikrostrukturę następujących stopów: Ti-50Al, Ti-50Al-2Cr i Ti-50Al-2Cr. Potwierdzono, że dodatek srebra stabilizuje fazę gamma-TiAl i eliminuje fazę alfa2-Ti3Al.

2

Development of alumina forming coatings for titanium aluminides.

Singheiser L., Niewolak L., Shemet V., Gil A., Quadakkers W.J.

Inżynieria Materiałowa

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2001

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R. XXII, nr 5

829-833

EN

One important hindrance for the use of gamma-TiAl alloys at high temperatures is their relatively poor oxidation resistance and the sensitivity against environmentally induced embrittlement. The latter effect is also of major concern during elevated temperature application of Ti-based alloys. These problems can principally be avoided by the application of oxidation resistant, alumina forming coatings. In the present paper the possibility of using a Ag-containing TiAl alloy as a coating material for Ti and high-strength gamma-TiAl-alloys is being studied. First, oxidation tests in different environments were carried out, to compare the isothermal and cyclic oxidation resitance of a selected Ag containing coating alloy with that of two, new generation, high strength gamma-titanium aluminides. Subsequently, magnetron sputtering was used to apply the TiAl-Ag coating to a gamma-TiAl alloy (Ti-45Al-8Nb-0.2C) and to pure titanium. The coated materials were tested at 800 degrees centigrade in case of the gamma-TiAl substrate, and at 600 degrees centigrade in case of the Ti substrate. The results illustrate, that the coatings in all studied cases formed a protective alumina surface scale even up to the longest studied test times of 1000 hours. The interdiffusion processes between coating and base material, which eventually determine the coating life, were studied by SEM/EDX investigation after different exposure times.

3

Protective coatings for high temperature applications.

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

Inżynieria Materiałowa

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1998

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R. XIX, nr 4

955-962

EN

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.

4

Microstructure and phase distribution of MCrAlY coatings.

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

Inżynieria Materiałowa

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1998

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R. XIX, nr 4

982-985

EN

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.

5

Microstructural investigations of the PM superalloy N18 in deformed and undeformed state.

Neves S., Penkalla H.J., Schubert F., Singheiser L.

Inżynieria Materiałowa

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1998

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R. XIX, nr 3

459-462

EN

In the present work microstructural investigations by means of transmission electron microscopy (TEM) were carried out on the powder metallurgy (PM), nickel-base superalloy N18. The material was characterized in the as-received, hot extruded state as well as after complete heat treatment. Especially the gamma-distribution and the presence of further precipitates were considered. The elemental distribution was characterized with the assistance of energy dispersive X-ray analysis (EDX) and energy filtering (TEM) (EFTEM). Additionally strain rate controlled tensile tests with different strain rates were carried out at 700 degrees centigrade in laboratory air. The microstructure of the deformed material was mainly investigated on dislocation distribution and deformation inhomogeneities.