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Vakuová metalurgie intermetalik TiAl
Zemčík, L. ; Dlouhý, Antonín ; Król, S. ; Pražmowski, M.
To be able to melt successfully type gamma TiAl alloys it is absolutely necessary to solve the fundamental metallurgical problems associated with the reactions between the melt and the refractories of crucibles and ceramic moulds, with the reactions between the melt and residual gases in the furnace chamber, and with the evaporation of aluminium from the melt. The paper deals with the physico - chemical analyses of the above processes and gives their evaluation based on the results of experimental melts of the type of Ti48Al2Cr2Nb1B (at.%) obtained in vacuum induction furnace. The work also gives the results of oxidation tests for the Ti48Al2Cr2Nb1B(at.%) alloy.
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Metallurgy of gamma TiAl based alloys
Zemčík, L. ; Dlouhý, Antonín
The present paper deals with the basic metallurgical processes associated with the investment casting of intermetallic alloys based on gamma TiAl. The analysis focuses on the evaporation of the aluminium from the melt, chemical reactions between the molten intermetallic, the ceramic mould and crucible and also on the reactions between the melt and the residual gases present in the atmosphere of the vacuum furnace. Results of the thermodynamic models are applied to the experimental melts of the Ti-48Al-2Cr-2Nb-1B intermetallic alloy in the vacuum induction furnace.
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Metallography of gamma TiAl intermetallic casts
Dlouhý, Antonín ; Válek, Robert ; Svoboda, Milan ; Zemčík, L.
A quantitative metallographic study was performed which focussed on the cast versions of advanced intermetallic alloys based on gamma TiAl phase. Specimens cut out of cast rods and turbine blades exhibited two pronounced microstructural characteristics: (i) a preferential orientation of lamellae in columnar grains below the cast surface and (ii) increasing fraction of equiaxed grains towards the central part of the casts. The relation between the particular microstrucrure and creep strength has been documented.
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Investment casting of gamma TiAl intermetallics
Zemčík, L. ; Dlouhý, Antonín
The paper deals with the physical and chemical analyses of the above processes and gives their evaluation based on the results of experimental melts of the type of Ti48Al2Cr2Nb1B (at.%) obtained in vacuum induction furnace. In present study introduces a 1D model of heat flow in the system composed of a TiAl intermetallic casting, a ceramic shell mould and the vacuum furnace environment. Furthermore, a coupled 1D model of thermal strain evolves in the casting ů mould system during cooling to room temperature is also presented. The parametric study aimed at the minimization of thermal stresses provided optimum process parameters used later in investment casting of TiAl turbocharger wheels. The semi-optimized initial mould temperatures and cooling kinetics resulted in macroscopically sound castings that were free of misruns, macrocracks and internal porosity.
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Study of transition layers in a gamma TiAl - CaO - Al2O3 SYSTEM
Dočekalová, Kateřina ; Dlouhý, Antonín ; Zemčík, L. ; Fiala, J.
The main attention in the present study focuses on the reactions between a ceramic crucible and the molten intermetallic alloy. The qualitative and quantitative metallographic analysis investigates the transition layers which are built during the melting process on the CaO-coated surface of the Al2O3 crucible. Preliminary results suggest that relevant chemical reactions are limited to a boundary layer with a characteristic thickness of 200 mm. In this layer, the high-temperature diffusion contributes to the nucleation and growth of complex phases the origin of which could result in an enrichment of the melt by oxygen.
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