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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

Rola mikrostruktury w procesie wysokotemperaturowego utleniania stopów TiAl.

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

Inżynieria Materiałowa

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2001

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R. XXII, nr 1

41-46

PL

W pracy przedstawiono wyniki badań mikrostruktury stopów Ti-50Al, Ti-48Al-2Cr i Ti-48Al-2Ag. Potwierdzono, że tworzenie ochronnej zgorzeliny Al2O3 na dwufazowych stopach TiAl zachodzi tym łatwiej, im większy jest stopień dyspersji faz alfa2-TiAl i gamma-TiAl. Metodami analitycznej transmisyjnej mikroskopii elektronowej wykazano, że dodatek srebra do stopów TiAl stabilizuje w nich fazę gamma-TiAl eliminując zarazem fazę alfa2-Ti3Al odpowiedzialną za tworzenie nieochronnego tlenku TiO2.

EN

The results of the microstructural studies of the alloys Ti-50Al, Ti-48Al-2Cr, Ti-48Al2Ag are presented. It was confirmed that the formation of the protective alumina scale on the two-phased TiAl alloys occurs more easier if the alpha2-Ti3Al phase is finely dispersed in the gamma-TiAl matrix. It has been shown using the analytical transmission electron microscopy that silver additions cause stabilisation of the gamma-TiAl phase and elimination from the alloy of the alpha2-Ti3Al phase, which is responsible for the formation of the non-protective TiO2-type scale.

3

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.