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Abstract

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′.
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Abstract

The paper presents the results of studies on the development of correlation of solidification parameters and chemical composition of nickel superalloy IN-713C, which is used i.a. on aircraft engine turbine blades. Previous test results indicate significant differences in solidification parameters of the alloy, especially the temperatures Tliq and Tsol for each batch of ingots supplied by the manufacturer. Knowledge of such a relationship has important practical significance, because of the ability to asses and correct the temperatures of casting and heat treatment of casts on the basis of chemical composition. Using the statistical analysis it was found that the temperature of the solidification beginning Tliq is mostly influenced by the addition of carbon (similar to iron alloys). The additions of Al and Nb have smaller but still significant impact. Other alloying components do not have significant effect on Tliq. The temperature Teut is mostly affected by Ni, Ti and Nb. The temperature Tsol is not in any direct correlation with the chemical composition, which is consistent with previous research. The temperature Tsol depends primarily on the presence of non-metallic inclusions present in feed materials and introduced during the melting and casting processes.
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