Paper presents the results of ATD and DSC analysis of two superalloys used in casting of aircraft engine parts. The main aim of the
research was to obtain the solidification parameters, especially Tsol and Tliq, knowledge of which is important for proper selection of
casting and heat treatment parameters. Assessment of the metallurgical quality (presence of impurities) of the feed ingots is also a very
important step in production of castings. It was found that some of the feed ingots delivered by the superalloy producers are contaminated
by oxides located in shrinkage defects. The ATD analysis allows for quite precise interpretation of first stages of solidification at which
solid phases with low values of latent heat of solidification are formed from the liquid. Using DSC analysis it is possible to measure
precisely the heat values accompanying the phase changes during cooling and heating which, with knowledge of phase composition,
permits to calculate the enthalpy of formation of specific phases like γ or γ′.
Tests concerning EN AC 48000 (AlSi12CuNiMg) alloy phase transition covered (ATD) thermal analysis and (DSC) differential scanning
calorimetry specifying characteristic temperatures and enthalpy of transformations. ATD thermal analysis shows that during cooling there
exist: pre-eutectic crystallization effect of Al9Fe2Si phase, double eutectic and crystallization α(Al)+β(Si) and multi-component eutectic
crystallization. During heating, DSC curve showed endothermic effect connected with melting of the eutectic α(Al)+β(Si) and phases:
Al2Cu, Al3Ni, Mg2Si and Al9Fe2Si being its components. The enthalpy of this transformation constitutes approx. +392 J g-1
. During
freezing of the alloy, DSC curve showed two exothermal reactions. One is most likely connected with crystallization of Al9Fe2Si phase
and the second one comes from freezing of the eutectic α(Al)+β(Si). The enthalpy of this transformation constitutes approx. –340 J g-1
.
Calorimetric test was accompanied by structural test (SEM) conducted with the use of optical microscope Reichert and scanning
microscope Hitachi S-4200. There occurred solution's dendrites α(Al), eutectic silicon crystal (β) and two types of eutectic solution: double
eutectic α(Al)+β(Si) and multi-component eutectic α+AlSiCuNiMg+β.