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National Repository of Grey Literature 3 records found  Search took 0.01 seconds. 
Interaction between TiAl melt and coated oxide refractories
 Dočekalová, Kateřina ; Dlouhý, Antonín ; Zemčík, L. ; Fiala, J.
The present study focuses on reactions between ceramic crucibles and molten TiAl intermetallics. Coating strategies are investigated that exhibit a potential in slowing down the decomposition of the crucible wall. Uncoated crucibles (system TiAl melt - Al2O3 crucible) and crucibles with the coat (system TiAl melt - CaO coat - Al2O3 crucible) were used in melting and casting experiments. The reference state of the coated crucible before the melting trial was also investigated. Results of the SEM, EDAX and X-ray diffraction analysis contributed to the identification of the reaction zone and its chemical composition. The melt contamination with oxide inclusions results from the erosion process in which individual components of the melt diffuse along grain boundaries of the refractory and activate chemical reactions that decompose the crucible wall. Assessment of thermodynamic parameters associated with the chemical reactions helped in identifying the nature of the erosion process.
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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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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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